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Spring 1999
Paleoclimatic significance of insoluble microparticle records from Canadian Arctic and Greenland ice cores
Christian Michel Zdanowicz University of New Hampshire, Durham
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Recommended Citation Zdanowicz, Christian Michel, "Paleoclimatic significance of insoluble microparticle records from Canadian Arctic and Greenland ice cores" (1999). Doctoral Dissertations. 2088. https://scholars.unh.edu/dissertation/2088
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PALEOCLIMATTC SIGNIFICANCE OF INSOLUBLE MICROPARTICLE RECORDS FROM CANADIAN ARCTIC AND GREENLAND ICE CORES
BY
CHRISTIAN MICHEL ZDANOWICZ
B.Sc., Universite de Montreal, 1991 M.Sc., Carleton University, 1994
DISSERTATION
Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy in Earth Sciences
May, 1999
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Copyright 1999 by Zdanowicz, Christian Michel
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DissertationDirector, Dr. Gregory A. Zielinski Research Associate Professor of Earth Sciences and EOS, University of New Hampshire
Dr. Paul A. Mayewskt Professor of Earth Sciences and EOS, University of New Hampshire
Dr.r. CaiperonCameron P.P. WakeWal Research Assistant Professor of Earth Sciences and EOS, Universi few Hampshire
Dr. Loren D.'Meeker Professor of Mathematics and EOS, University of New Hampshire
Dr. Roy M. Kberaer Senior Research Scientist,Terrain Sciences Division, Geological Survey of Canada
/? y ^ / Date
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I first wish to thank my dissertation director Dr. Gregory Zielinski who guided me with endless patience and sound advice through my years of doctoral research. I also benefited from the precious tutoring of my other committee members at the Climate Change Research Center Dr Paul Mayewski, Dr. Cameron Wake and Dr. L. David Meeker. To all of them I am deeply indebted. I am especially grateful to my external advisor Dr. Roy Koemer (Geological Survey of Canada) who introduced me to this field of research and whose experienced judgment, facetious criticism, and friendship I greatly value. I also extend my sincere thanks to Dr. Wayne Pollard who acted as my advisor during an instructive preparatory year spent at McGill University. His unrelenting enthusiasm and supportive attitude motivated me to pursue this research. Next, I wish to acknowledge the co-authors and colleagues who made valuable contributions to this dissertation: Dr. David Fisher (Geological Survey of Canada), Dr. David Robinson (Rutgers University) and Dr. Mark Germani (Micromaterials Research, Inc.). In preparing this dissertation and related publications I also benefited from help, comments and reviews by several people, including Dr. Iqbal Pittalwala (University of New Hampshire), Dr. Charles Mandeville (American Museum of Natural History), Dr. C. Bacon (United States Geological Survey) and Dr. Arthur Dyke (Geological Survey of Canada). My field work on Baffin Island was conducted with logistical and technical support from the Geological Survey of Canada, the Polar Continental Shelf Project, Parks Canada and the people of the communities of Iqaluit and Pangnirtung. In the field I received additional assistance from my fellow student Nancy Grumet and from Eric Blake and Mike Gerasimoff of Icefield Instruments Inc. In performing microparticle analyses I was ably assisted by Michelle Day and Mike Leo. Major ions in the P95 ice core were analyzed by Sallie Whitlow and Nancy Grumet. All aspects of field work, sample processing and analysis were supported by grants from the National Science Foundation (Office of Polar Programs) to Dr. Gregory Zielinski. I also benefited from a grant by the Association of Canadian Universities for Northern Studies to Dr. Wayne Pollard, and from awards by the Department of Earth Sciences and Sigma Xi Scientific Research Society of the University of New Hampshire.
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ACKNOWLEDGMENTS ...... v TABLE OF CONTENTS ...... vi LIST OF TABLES...... vii LIST OF FIGURES...... ix ABSTRACT...... xi
CHAPTER PAGE
I INTRODUCTION...... 1
H. CHARACTERISTICS OF MODERN ATMOSPHERIC DUST DEPOSITION IN SNOW ON THE PENNY ICE CAP, BAFFIN ISLAND, CANADIAN ARCTIC...... 11 m . PALEOENVIRONMENTAL SIGNIFICANCE OF A HOLOCENE RECORD OF EOLIAN DUST DEPOSITION FROM THE PENNY ICE CAP, BAFFIN ISLAND, CANADIAN ARCTIC...... 35
IV. EFFECTS OF ATMOSPHERIC CIRCULATION AND SNOW COVER VARIABILITY ON EOLIAN DUST DEPOSITION IN THE EASTERN CANADIAN ARCTIC...... 55
V. RELATIONSHIP BETWEEN SOLUBLE AND INSOLUBLE ARCTIC AEROSOLS IN CONTRASTING CLIMATE REGIMES AS REVEALED IN ICE CORES...... 75
VI. THE MOUNT MAZAMA ERUPTION: AGE VERIFICATION AND ATMOSPHERIC IMPACT ASSESSMENT FROM THE GISP2 ICE CORE RECORD...... 92
VH. CONCLUSIONS...... 107
REFERENCES...... 115 APPENDICES...... 135
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES
TABLE PAGE
1.1A Characteristics of selected long Arctic ice core records: Canadian A rctic 8
I.1B Characteristics of selected long Arctic ice core records: G reenland ...... 9
II. 1A Atmospheric dust concentration and flux in snow and ice: Greenland and Canadian Arctic sites ...... 24
II. 1B Atmospheric dust concentration and flux in snow and ice: Other Northern Hemisphere sites ...... 25
n.2 Microparticle concentration and size distribution in Penny Ice Cap snowpit samples based on stratigraphy and inferred timing of deposition 26
11.3 Size distribution of microparticles and mineral aerosols at various Northern Hemisphere sites ...... 27
HI. 1 Time scale, resolution and dating methods for the P95 (Penny Ice Cap) and GISP2 (Greenland) ice co res ...... 49
m .2 Mean microparticle concentration (N,M), nssCa2+ and 5180 for selected periods in the P95 ice core record ...... 50
111.3 Microparticle mass (M) and mode(s) for selected time periods in the P95 and GISP2 ice core records ...... 51
IV. 1 Principal EOF modes of interannual variability in the P95 ice core dust record and dominant high and low sea level pressure centers during the Northern Hemisphere winter for the period AD 1899-1995 ...... 69
IV.2 Correlation (R) between dust concentration in the P95 ice core and seasonal snow cover extent in 10 regions of the Northern Hemisphere for the period 1971 to 1995 ...... 70
V. 1 Principal modes of covariance among microparticles and major ions in the GISP2 record of glacial conditions (25,000-15,000 yr ago) ...... 89
V.2 Principal modes of covariance among microparticles and major ions in the GISP2 record of interglacial conditions (8000-3350 yr ago) ...... 90
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. V.3 Principal modes of covariance among microparticles and major ions in the P95 record of interglacial conditions (8000-3350 yr ago) ...... 91
VI. 1 Mean major oxide composition of GISP2 volcanic glass and Mount Mazama tephra ...... 102
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FIGURE PAGE
1.1 Location map, eastern Canadian Arctic and Greenland, for ice core sites and other geographical features discussed in the te x t ...... 10
n .l Location map of the Penny Ice Cap, Baffin Island ...... 28
n.2 Field study area on the Penny Ice Cap, Baffin Island ...... 29
H.3 Example of a log-normal curve fitted to microparticle size distribution data... 30
n.4 Stratigraphy, microparticle number (N) and Na+ in Penny Ice Cap snowpits .. 31
IL5 Microparticle size distributions in Penny Ice Cap snowpits based on stratigraphy and input tim ing ...... 32
n.6 Stratigraphy and profiles of 8180, microparticle number (N) and mean diameter (NMD), P and Na+ in snowpit 94-1 ...... 33
n.7 Fourier power spectrum of microparticle number (N) as a function of depth in the P95 ice c o re ...... 34
HI. 1 (a) Dust (N, M), nssCa2+ and 8180 in the bottom 10 m of the P95 ice core. (b) Holocene time series of N, M, nssCa2+ and 8180 in the P95 and P96 ice cores...... 52
111.2 Mean size distribution of microparticles in the P95 and GISP2 ice cores for late glacial and Holocene time periods ...... 53
111.3 Comparison between 100-yr averaged Holocene time series of dust mass (M) and nssCa2+ from the P95 and GISP2 ice cores ...... 54
IV. 1 Comparison of annual and 5-yr averaged time series of dust concentration in the P95 core with mean sea-level pressure of the winter Siberian High, 1900-1995 ...... 71
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with permission of the copyright owner. Further reproduction prohibited without permission. IV.2 (a) Geographical boundaries of the Azores High (AH), Siberian High (SH), North American High (NAH), Aleutian Low (AL) and Icelandic Low (IL) used in this study, (b) and (c) Composite maps o f Northern Hemisphere winter sea level pressure anomalies associated with years of extreme high and low dust concentration in the P95 ice co re...... 72 IV.3 Seasonal mean snow cover extent in the Northern Hemisphere, 1971-1995 . . . 73
IV.4 Comparison of annual and 3-yr averaged time series of dust concentration in the P95 ice core and spring snow cover extent in four regions of the Northern Hemisphere for 1971-1995 ...... 74
VI. 1. Time series of SO42', Cl' and microparticle concentration (N) in the GISP2 ice core, showing the peaks assigned to Mount Mazama eruption fallout 103
VI.2. Electron photomicrograph of typical glass shard collected from the GISP2 ice core and associated with Mount Mazama eruption fallout ...... 104
VI.3. Comparison of the major oxide composition of volcanic glass filtered from the GISP2 ice core with rhyodacitic pumice from Crater lake, Oregon (a) CaO-KiO-FeO* ternary plot, (b) and (c) Ti 0 2 ~, Na2 0 -Si0 2 covariation plots ...... 105
VI.4. Comparison between the Mount Mazama eruption signal in the GISP2 ice core SO 42* record and the GRIP ice core 8180 record ...... 106
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT
The past and present variability of climate in the Arctic region is investigated using ice core records of atmospheric dust (microparticles) and volcanic aerosols developed from the Canadian Arctic and Greenland. As part of this study, a high-resolution, 104*year long proxy record of atmospheric dust deposition is developed from an ice core (P95) drilled through the Penny Ice Cap, Baffin Island. Snowpit studies indicate that dust deposited on the Penny Ice Cap are representative of background mineral aerosol, and demonstrate that the variability of dust fallout is preserved in the P95 core at multi-annual to longer time scales. The P95 dust record reveals a significant increase in dust deposition on the Penny Ice Cap that occurred between ca 7500-5000 yr ago. This increase was driven by early to mid-/late Holocene transformations in the Northern Hemisphere landscape (ice cover retreat, postglacial land emergence) and climate (transition to colder, drier conditions) that led to an expansion of sources and enhanced eolian activity. Comparison between dust records in the P95 and GISP2 (Greenland) ice cores shows an increasing divergence between the two records beginning ca 7500 years ago. The diverging trends suggest that as climate evolved during the Holocene, the transport and deposition of atmospheric dust in the Canadian Arctic and Greenland gradually came to be controlled by regionally-specific environmental factors (i.e., meteorological or other). The effects of Northern Hemisphere atmospheric circulation and snow cover extent on atmospheric dust deposition in the Arctic are evaluated by comparing the P95 dust record with observational data documenting variability in these parameters. Changes in dust deposition on the Penny Ice Cap are strongly linked to, and possibly controlled by, modes of the Northern Hemisphere winter circulation with centers of action over Eurasia, the North Pacific Ocean, and western North America. Most prominently, an inverse relationship between the P95 dust record and the intensity of the winter Siberian High accounts for over 50 % of the interannual variance of these two parameters over the period 1899-1995. It is speculated that weakening of the winter Siberian High enhances the long- range export of dust from Eurasian source regions by hastening the spring retreat of seasonal snow cover while increasing the frequency of dust storms in the arid continental interior. On inter- to multi-annual time scales, the P95 dust record is significantly anricorrelated with variations in spring, and to a lesser extent fall, snow cover extent in the mid-latitude interior regions of Eurasia and North America. These relationships account for
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. an estimated 10 to 20 % of variance in the P95 dust record, and are attributed to the limiting effect of snow cover on the potential for eolian dust deflation. Findings from this study raise the possibility of using ice core dust records to document changes in Northern Hemisphere atmospheric circulation patterns or snow cover extent before the period of satellite and weather station observations. An empirical orthogonal function (EOF) analysis is used to investigate patterns of temporal covariance among insoluble microparticles and major ions deposited in the GISP2 and P95 ice cores under both glacial and interglacial climatic conditions. Dust and major ions covary strongly in the GISP2 late glacial record when the polar atmosphere was well- mixed, but are uncorrelated in both the GISP2 and P95 Holocene records due to a regionalization of climate and atmospheric circulation patterns after the retreat of the large continental ice sheets. As a result of this regionalization, soluble and insoluble aerosols were transported and deposited in the Arctic by different atmospheric circulation systems and associated air masses. Companion EOF analyses of the GISP2 and P95 Holocene records identify distinctive covariance patterns among microparticles and/or major ions that are associated with certain aerosols types (e.g., gas-derived SO 42', N0 3 - and NHt+), or with source-specific air masses reaching the Arctic (e.g., K+ and NRf*" in forest fire emissions). These patterns differ in the GISP2 and P95 cores, providing further evidence of increased regional-scale climatic and atmospheric variability over the last - 12,000 years. The atmospheric and climatic impact of the early Holocene eruption of Mount Mazama (Crater Lake, Oregon) is evaluated from the GISP2 ice core record of volcanically-derived sulfate and ash particles. The calendrical age of the eruption is determined to be 7627 ± 150 cal yr B.P. (5677 ± 150 BC), thus providing a more accurate early Holocene stratigraphic timeline than previously available. The GISP2 sulfate record suggests a total stratospheric aerosol loading between 88 and 224 Mt spread over a ~ 6-year period following the eruption. From these figures, the Mount Mazama eruption is estimated to have depressed temperature by -0.6 to 0.7°C at mid- to high northern latitudes, thereby ranking it as one of the most climatically significant Holocene volcanic events in the Northern Hemisphere. Scientific findings presented in the dissertation demonstrate the wide scope of paleoenviromental information obtainable from ice core records of particulate atmospheric impurities. Additional and comparable records to be developed from circum-Arctic ice caps will assist in expanding our knowledge of climatic and atmospheric variability at northern high latitudes on annual to millennial time scales.
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INTRODUCTION
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CHAPTER 1
INTRODUCTION
In recent decades, growing concerns about the potential impact of human activity on the Earth's climate have stressed our need to understand natural climatic variability on seasonal to millennial time scales (Houghton et al., 1990). In particular, climate observations and simulations suggest that environmental changes in the Arctic caused by rising atmospheric C02 levels (e.g., the accelerated melting of ice caps) could severely impact the climate of temperate regions by perturbing the oceanic and atmospheric energy exchange between high and low latitudes (Maxwell and Barrie, 1989). Accordingly, there is a need to investigate the nature of, and responses to, past climatic changes at high northern latitudes. Ice cores document past fluctuations in climatic parameters such as temperature, precipitation, and windiness, as well as changes in the gaseous, soluble and insoluble aerosol composition of the atmosphere (Hammer, 1982; Oeschger and Langway, 1989; Mayewski et al., 1992; Boutron, 1995). Climate records developed from ice cores have greatly expanded our understanding of the global climate system, its variability, and the forcings that drive climatic change over annual to millennial time scales. In particular, the lO^-yr. long multivariate records developed from the Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice Core Project (GRIP) ice cores have provided a perspective on paleoclimate unprecedented in temporal resolution and level of detail (e.g., Dansgaard et al., 1993; Mayewski etal., 1997; O'Brien etal., 1995; Stuiver et al., 1995). Among other findings, the new Greenland ice cores have revealed the existence of abrupt climatic changes of regional to hemispheric extent punctuating the last glacial period, some of which persisted with subdued amplitude during the Holocene (Johnsen et al., 1993; Taylor et al., 1993; O'Brien etal., 1995; Mayewski etal., 1997). These rapid climate change events demonstrate a greater degree of structure and variability in the Earth's climate than was previously suspected. Prior to GISP2 and GRIP, several other deep ice cores (> 100 m) were obtained from Greenland and the smaller Arctic ice caps of the Canadian Arctic Archipelago (Fig. 1.1). Climate records developed from these ice cores provide valuable information on decadal- to millennial climatic variability in the Arctic, and also document the impact of anthropogenic industrial emissions on the remote polar atmosphere (e.g., Paterson et al., 1977; Fisher and Koemer, 1981; Dansgaard et al., 1984; Barrie et al., 1985; Hansson, 1994). However ice
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cores from these sites were often measured continuously for a few parameters only (Table 1.1), therefore limiting the possibilities for comparison with the new and more detailed multivariate Greenland ice core records. In order to extrapolate findings from the GISP2 and GRIP cores to larger spatial scales and to expand the geographical coverage of existing paleoclimatic data, new ice core records of past climate change are needed that may be directly compared to the Greenland records, in terms of temporal resolution and parameters measured. This objective is now being addressed by a multi-institutional collaborative effort initiated in 1995, the Ice-core Circum-Arctic Paleoclimatic Program (ICAPP), which aims at reconstructing late Quaternary climatic and atmospheric changes in the northern circumpolar region using ice core records as the main database. As part of ICAPP, a new 334-m long ice core (P95) was drilled in the spring of 1995 from the summit of the Penny Ice Cap, Baffin Island. The P95 ice core was sampled and analyzed for oxygen isotopes, insoluble microparticles and major ionic species using techniques comparable or identical to those employed on the GISP2 ice core, thereby making it the first ice core record developed from the Canadian Arctic to offer such a wide array of proxy climatic parameters for interpretation.
OVERVIEW OF DISSERTATION RESEARCH
The unifying theme of the research presented in this dissertation is the analysis and interpretation of long (> 103 years) records of insoluble particulate impurities deposited in Arctic snow and ice. More specifically, two main types of particulates are considered which together comprise the majority of insoluble impurities present in polar ice: atmospheric dust (microparticles) and volcanic ash.
Ice Core Microparticle Records
Atmospheric dust deposited in polar snow consists primarily of mineral particles mobilized by eolian deflation of soils and sediments (Briat et al., 1982; Gaudichet et al., 1986; Maggi, 1997). During transport to polar latitudes, mixing of air masses and particle removal by gravity and precipitation contribute to homogenize dust aerosols (Schuetz, 1989). Consequently, atmospheric dust deposited in polar snow may be considered as representative of the crustal background aerosol on a regional to hemispheric scale (Ram and Gayley, 1994; Hinkley et al., 1997). As such, long records of microparticle deposition (up to lO^yr. long) developed from polar ice cores can help document past changes in the
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atmospheric dust load and the dynamics of airborne dust entrainment, transport and deposition (Petit et al., 1981; Thompson and Mosley-Thompson, 1981; Hammer et al., 1985; Hansson, 1994; Steffensen, 1997; Zielinski and Mershon, 1997). In addition, ice core microparticles provide valuable information on the size distribution of insoluble aerosols in the Arctic atmosphere and their spatial and temporal variability. Such knowledge is needed for accurate modeling of the climatic effects of Arctic pollutants, the radiation-absorbing component of which may be composed of up to 25 % crustal dust and carbonaceous particles (Rahn and McCaffrey, 1980). A core component of the research reported here is the analysis and interpretation of long (104 to lO^yr.), high-resolution records of atmospheric dust deposition developed from two separate ice cores: the 334-m long P95 ice core drilled in 1995 from the Penny Ice Cap in the eastern Canadian Arctic, and the 3053-m long GISP2 core drilled through the Greenland Ice Sheet between 1989 and 1993 (Fig. 1.1). The analysis of these records is focused on temporal variations in the physical characteristics of microparticles measured in the ice cores, namely their concentration and size distribution. These data are used to infer past environmental changes that affected the sources, transport pathways, and dynamics of atmospheric circulation controlling the deposition of dust aerosols in the Canadian Arctic and central Greenland over the last -12,000 years. Results from this research are presented under Chapters II to V of the dissertation, as outlined below. In Chapter n, the characteristics of modem atmospheric dust deposition on the Penny Ice Cap are evaluated from the concentration and size distribution of microparticles in a series of snowpits excavated in the summit region of the ice cap. These data are used to define the seasonality, spatial and temporal variability, and relative transport distance (i.e., source remoteness) of eolian dust presently deposited on the Penny Ice Cap so as to establish a basis of comparison with microparticle data from the P95 ice core record. In addition, the post-depositional effects of meltwater percolation on dust distribution in the snowpack are evaluated in order to define the optimal resolution attainable from the P95 ice core microparticle record. Chapter III presents a first-order interpretation of the P95 ice core record of eolian dust deposition over the last -12,000 years. This interpretation draws upon findings from snowpit studies, from a detailed analysis of microparticle populations deposited on the Penny Ice Cap during different time periods, and from knowledge on the nature of processes controlling the long-range transport of atmospheric dust to high latitudes. The analysis of the P95 dust record also takes into consideration existing proxy evidence documenting past changes in dust source availability, continental aridity, windiness and other environmental factors that may have affected the transport and deposition of
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atmospheric dust on the Penny Ice Cap in the last 12,000 years. Comparisons are made between time series of insoluble microparticles and non-sea salt calcium (a continental dust indicator) developed from the P95 and GISP2 ice cores. Findings from these comparisons help define the spatial and temporal variability of atmospheric circulation over the eastern Canadian Arctic and Greenland during the Holocene. In Chapter IV, The effects of atmospheric circulation and snow cover variability on dust deposition in the P95 ice core are investigated through comparisons with various historical, instrumental and satellite data documenting changes in these climatic parameters over recent last decades to the last century. Using a combination of techniques (cross correlation, multivariate statistics and composite anomaly analysis), significant physical linkages are identified between centers of action in the Northern Hemisphere winter circulation, continental snow cover and long-range dust transport to the eastern Canadian Arctic. This study is the first attempt made to calibrate an ice core record of atmospheric dust deposition against observational records of climatic variables such as sea level pressure and snow cover extent. Results of this work will assist in a more quantitative interpretation of ice core records so that they may be used to infer (for example) past changes in continental snow cover beyond the time period covered by available instrumental and historical records. In Chapter V, an empirical orthogonal function (EOF) analysis is used to explore temporal changes in the relationship between insoluble (eolian dust) and soluble (major ions) impurities deposited in the GISP2 and P95 ice cores under late glacial and Holocene climatic conditions. Results of the EOF analysis reveal distinctive patterns of temporal covariance among microparticles and major ions in the GISP2 late glacial record and in the GISP2 and P95 Holocene records. These covariance patterns document changes that affected the sources and transport pathways of air masses and associated aerosols reaching the Arctic atmosphere, or changes in environmental factors that control the deposition of certain soluble and insoluble atmospheric impurities in snow. Findings from this study will serve to further define the evolution of climate and atmospheric composition at high latitudes from glacial to interglacial conditions.
Ice Core Paleovolcanic Records
Polar ice cores can provide detailed proxy records of past volcanism by preserving atmospheric fallout from past eruptions (Gow and Williamson, 1971; Hammer, 1984; Delmas et al., 1985). Ice core paleovolcanic records are exceptional in two critical respects: they are longer, more continuous and more highly-resolved than most other geological
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records (terrestrial, lacustrine or marine), and they preserve both the climatic-forcing sulfuric aerosol (H 2SO4) and particulate silica (tephra) components of volcanic eruptions. Volcanic deposits in ice cores can therefore be used to estimate the atmospheric and climatic impact of past eruptions. The primary record of paleovolcanism in the GISP2 ice core was developed by isolating the volcanically-derived component of the S 0 4 2- record using statistical methods. This allowed for a well-dated chronology of explosive volcanism over the past 110,000 years to be established (Zielinski et al., 1996a). Chapter VI of this dissertation reports on the identification and analysis in the GISP2 ice core of SO 42- and volcanic glass (tephra) representing atmospheric fallout from the early Holocene climactic eruption of Mount Mazama (Crater Lake, Oregon). The geochemical composition of tephra associated with the Mount Mazama SO 42- signal in the GISP2 ice core is compared with that of pumice collected near the Crater Lake caldera in order to verify the source of the eruption. The positive identification of Mount Mazama tephra in the GISP2 core provides a new estimate for the calendrical age of this eruption. The atmospheric and climatic-forcing impact of the Mount Mazama eruption are evaluated from the GISP2 SO 42* record following the methodology developed by Zielinski (1995). Results from this study will contribute to the ongoing development of a detailed tephrochronological record of late Pleistocene-early Holocene volcanism from the GISP2 ice core. The GISP2 paleovolcanic record will allow for the relationship between volcanism and climate to be studied under the strongly contrasted climatic and environmental conditions of the late glacial and present interglacial (Holocene) periods. In addition, the tephrochronological database developed as part of this study will provide new opportunities to match volcanic time markers between different paleoenvironmental records, thus providing precisely dated timelines for accurate correlation of these records (e.g., Gronvold et al., 1995; Zielinski et al., 1997). Analyses of tephra composition will also assist in resolving correlation ambiguities that may arise when the dating uncertainties on a geologically documented eruption are such that its assigned age range spans a portion of the ice core record in which several volcanic sulfate peaks are present.
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THESIS ORGANIZATION AND PUBLICATIONS
The individual chapters of this dissertation were written for publication in peer- reviewed scientific journals, and are formatted accordingly. Chapter II ("Characteristics of Modem Atmospheric Dust Deposition in Snow on the Penny Ice Cap, Baffin Island, Canadian Arctic") was published in Tellus, vol. 50B (1998), pp. 506-520. Chapter HI ("Paleoenvironmental Significance of a Holocene Record of Eolian Dust Deposition from the Penny Ice Cap, Canadian Arctic") is currently under review for publication in Quaternary Research. Chapter VI ("The Mount Mazama Eruption: Age Verification and Atmospheric Impact Assessment from the GISP2 Ice Core Record”) is in press and will appear in an upcoming issue of Geology. Chapter TV ("Effects of Atmospheric Circulation and Snow Cover Variability on Eolian Dust Deposition in the Eastern Canadian Arctic") and Chapter V ("Relationship between Soluble and Insoluble Arctic Aerosols under Contrasting Climate Regimes as Revealed in Ice Cores") will be submitted to Journal of Climate and Journal o f Geophysical, respectively. Preliminary results from the study presented in Chapter IV were reported at the Interdisciplinary Conference on Dust Aerosols, Loess Soils and Global Change held in Seattle, Washington, October 11-13, 1998 (Zdanowicz et al., 1998b). Chapters HI, IV and VI were written with external collaborators whose names and institutional affiliations appear on the cover page of the appropriate chapters. Contributions made by these collaborators are duly acknowledged in the opening pages of the dissertation. The closing chapter of the manuscript (Chapter VII; Conclusions) summarizes the major scientific findings of this work and emphasizes their contribution and significance to our understanding of high-latitude climatic variability at annual to millennial time scales. Recommendations for related future research are also provided. References from individual chapters are assembled and indexed in a dedicated section following Chapter VII. The last section of the manuscript consists in two appendices. Appendix A provides microparticle concentrations (number and mass), mean diameter and parameters measured in snowpits excavated on the Penny Ice Cap in 1994-1995. These data are discussed in Chapter n. Appendix B gives the concentration of microparticles (number and mass) measured along the full length of the P95 ice core. Ages are given to about 11,500 years before present (326.54 m) based on the depth-age scale of the P95 core developed by Fisher et al. (1998). These data are discussed in Chapters EH, IV and V. The P95 ice core microparticle data will also be made publicly available through the National Snow and Ice Data Center at the University of Colorado, Boulder, CO.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 0 , ECM, IL 8 lsO, ECM 8I80, ions, ECM, part Parameters measured Parameters 8 k k k 8l80, ECM, IL k 8I80 k 8,80 , part k 8> k 8I80, ECM, ion, part 1 2 12 12 1 2 12 1 2 12 < 4 k 8I80, DL, Xtal > > > > length Recordd 121 (m) 340 300300 > > 334 Depth 1995,1998; Grumet, Koerner, Koemer 1977; 1997; 1965 1998 1977 1979 137 1995 Year drilled 1972-73 et al., et 0 15 100 (%) < 15 1984-87 127 > Melt 1977. Footnotes on Table 1977. I.1B. 10 12 22 34 50 1996 176 11.5 etal., Accum.b Accum.b y(cm r 1) -23 -23 -16 (°Q MAST® 1700 1800 1710 1810 1980 Elev. Elev. (m asl) (m Site characteristics Core characteristics °W Long 82°W 66 1985; Fisher, and FisherFisher Koerner, 1981; 1979; 1985; Lat 77°N et al., et Sources: Sources: Barrie Meighen Ice Cap Ice Meighen 80°NCap Ice Devon 100°W 268 -17 9.5 and Fisher, and Paterson, Koerner 1982; Paterson 1974; Canadian Arctic Table I.1A. Characteristics of selected long (> 100 m) Arctic ice core records: Canadian Arctic. Site locations are shown on Fig. 1.1. 1.1. onFig. are shown locations Site Arctic. Canadian core records: ice Arctic m) (> long selected of 100 Characteristics Table I.1A. Agassiz Ice Cap Ice Agassiz 82°N 74°W 1715 Penny Ice Cap Ice Penny 67°N
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. v© 6 8180 8I80 8180, ions, ECM, part measured Parameters *1 k k k 5I80, ions, ECM, part k 5I80, k ions, ECM, part years. 3 120 120 120 120 -1 2 0 > > Core characteristics 1997. (m) (m) length Depth Depth Record et al., et 1966 1390 > 1993 3053 > 1981 2038 drilled 1994; Meese 1994; 15 1992 3029 (%) £ 15 £ 15 £ 15 £ 15 1988 324 Melt? Year et al., et 38 23 Accum.h 8 ice, based on ice core stratigraphic measurements. measurements. stratigraphic core on ice based ice, -24 -31 24 -18 50 % 1992; Mayewski 1992; et al., et 1883 3208 3240 -32 2479 -18 56 2340 (masl) (°Q (cmyr1) Site characteristics 61°W 38°W 26°W 1982; Johnsen 1982; Lat Lat Long Elev. MAST et al., et 77°N 71°N The figures give the approximate limit of reliable dating for cores. The actual records may extend well beyond these limits. limits. these beyond well extend may records actual The cores. for dating reliable of limit approximate the give The figures 8,80 = oxygen isotopes; ECM = solid electrical conductivity; LC = liquid conductivity; pH or H+ = acidity; = acidity; H+ or pH conductivity; conductivity; electrical liquid = = solid ECM LC 8,80 isotopes; oxygen = layer; dirt = visible DL = layers; ice IL microparticles; = insoluble part. cations); + (anions species ionic = major ions cristallography. = Xtal ice Mean annual surface temperature from weather station data or 10 m borehole measurements. measurements. borehole m or data station 10 weather from temperature surface annual Mean e Parameters that were measured continuously (or nearly so) along the full length of the cores. of the length full the so) along nearly (or continuously measured were that Parameters e Sources: Dansgaard Sources: Dansgaard d Estimated time period covered by the ice core record, based on the adopted depth-age scale. 1 = ka scale. depth-age 10 1 coreadopted on the based record, the by ice covered period time Estimated d b Modem annual accumulation rate (recent years or decades) expressed in cm of water equivalent. equivalent. water ofcm in expressed decades) or years (recent rate accumulation Modem annual b weight in expressed rate melting annual Mean c 8 Table I. IB. Characteristics of selected long (> 100 m) Arctic ice core records: Greenland. Site locations are shown on Fig. 1.1. on1.1. Fig. shown are Greenland. locations Site core records: m) ice Arctic (> of selected long 100 Characteristics IB. Table I. Camp Century Camp Dye 3 Dye 65°N 43°W Greenland Summit(GISP2) 72°N Summit (GRIP) 72°N 38°W Renland
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A Queen Elizabeth Islands 120°W
Devon • Camp Century
GREENLAND Summit* ReniancH '70°N 20°W
Ungava Pen.
Cumberland Pen.
60°W
Fig. 1.1. Location map, eastern Canadian Arctic and Greenland, for ice core sites (bold dots) and other geographical features discussed in the text.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER H
CHARACTERISTICS OF MODERN ATMOSPHERIC DUST DEPOSITION IN SNOW ON THE PENNY ICE CAP, BAFFIN ISLAND, CANADIAN ARCTIC
C.M. Zdanowicz, G.A. Zielinski and C.P. Wake Climate Change Research Center, University of New Hampshire, Durham, NH 03824 USA
Published in Tellus, vol. 50B (1998), pp. 506-520
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CHAPTER H
CHARACTERISTICS OF MODERN ATMOSPHERIC DUST DEPOSITION IN SNOW ON THE PENNY ICE CAP, BAFFIN ISLAND, CANADIAN ARCTIC
ABSTRACT
We evaluated the concentration, size and distribution of insoluble dust microparticles in snowpits on the Penny Ice Cap, Baffin Island, to define 1) the characteristics of modem atmospheric dust deposition at the site, 2 ) the relative contributions of proximal and distal dust sources, and 3) the effects of summer melting on depositional signals in snow. The mean concentration (143 pg kg'1), flux (4.8 pg cm 2 y r 1) and diameter (2.3 pm) of dust deposited on the Penny Ice Cap are similar to those observed in remote Arctic sites such as central Greenland, implying that dust is primarily supplied through long-range transport from far-removed source regions (at least HP-IO 3 km distant). There is evidence for two seasonal maxima of dust deposition, one in late winter-early spring and one in late summer-early fall, although seasonal signals can not always be resolved in the snowpack due to some post-depositional particle migration with summer melt. However, ice layers appear to limit the mobility of particles, thereby preserving valuable paleoclimatic information in the P95 ice core dust record at a multi-annual to decadal temporal resolution.
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INTRODUCTION
Insoluble mineral microparticles deposited in polar snow originate primarily from wind deflation of soils and sediments over continental source regions (Kumai, 1977; Briat et al., 1982; Gaudichet et al., 1986). Because atmospheric dust deposition on glaciers frequently follows a seasonal cycle, microparticles can be used to identify annual layering in ice cores, provided the depositional sequence is preserved in the stratigraphy (e.g., Hamilton and Langway, 1967; Hammer et al., 1978). Changes in the concentration and size distribution of ice core dust particles are also used to document past changes in the atmospheric dust load or the dynamics of airborne dust transport and deposition (e.g., Thompson and Mosley-Thompson, 1981; Petit etal., 1981,1990; Zielinski andMershon, 1997; Hansson, 1995). Accurate interpretation of ice core dust records requires an understanding of the various physical factors that affect the measured concentration, variability, and size distribution of dust in ice. Here we present results of an investigation on the deposition and post- depositional modification of dust microparticles in snow on the Penny Ice Cap (67° N; 65° W), southern Baffin Island, Arctic Canada (Fig. n. 1). This study will assist in the interpretation of a continuous Holocene record of dust deposition currently being developed from a 334 m surface-to-bedrock ice core (P95) drilled in 1995 from the summit region of the Penny Ice Cap. The specific objectives of this investigation are to: 1) define the modem characteristics of dust deposition in snow on the Penny Ice Cap (flux, size distribution, input timing) in order to establish a basis for interpreting the ice core dust record, 2 ) evaluate the relative contribution of proximal and distal sources to dust deposition on the Penny Ice Cap, and 3) evaluate the effects of summer melting on the preservation of dust depositional signals in the ice. Previous investigations showed the potential for long-range eolian transport of mineral dust to the Arctic, including possible dominant source regions and transport pathways. The transport of Eurasian dust plumes over Alaska was extensively discussed by Rahn and co- workers (e.g., Shaw, 1980; Rahn et al., 1981). Welch et al. (1991) described a major dust fallout event over the Keewatin region which they attributed to an Asian source on the basis of composition and air-mass trajectories. Mullen et al. (1972), Darby et al. (1974) and Rahn et al. (1979) presented various estimates of the atmospheric dust flux to the Arctic Ocean. Studies pertaining to the transport and deposition of dust to Greenland may be found in (among others) special journal issues on the Dye 3 Aerosol and Gas Sampling Program {Atmos. Env. 27A, No2 17/18,1993) and the Greenland deep ice cores (/. Geophys. Res. 102, No C l2, 1997). However to the best of our knowledge, the only
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study of dust deposition to the Canadian ice caps previously published is that of Koemer (1977), who examined the distribution of microparticles > 1 pm in snowpits and ice cores from the Devon Island Ice Cap. We later compare his findings with ours.
METHODS
In April-May 1994 and 1995, a total of six snowpits, ranging in depth from 1.70 to 5.15 m, were excavated within a 10 km 2 area on the summit region of the Penny Ice Cap (-1980 m asl; Fig. H.2) as part of a survey of snow stratigraphy and chemistry. Surface snow samples were also collected on a daily basis during the 1995 field season. Snowpits 94-1 and 95-4 were dug near a permanent automatic weather station (AWS) maintained by Canada's Atmospheric Environment Service, thus allowing us to compare snowpit stratigraphy with snow depth soundings and daily temperature readings (e.g., Grumet et al., 1998). Snowpit walls were sampled at 3 to 5 cm resolution by personnel wearing non- particulating clean suits, masks and gloves and using pre-cleaned polyethylene tools and containers. Although the mean annual surface temperature at the summit of the Penny Ice Cap is about -16°C, the study area is affected by summer melting and refreezing, leading to the formation of ice layers in the snowpack. Based on visual analysis of ice core stratigraphy, the average annual percentage of melt was estimated at about 50 % (mass) for the last 100 years (R.M. Koemer, pers. comm.). Average accumulation rate for the period 1963-1995 was estimated to be 0.38 m ice or 0.34 m water equivalent (w.e.) using the beta-radioactive 1963 bomb fallout reference horizon in the ice core. All snowpit and surface snow samples were shipped frozen from the Penny Ice Cap and stored at -15°C until prior to analysis. Samples were then melted and aliquots were collected for microparticle and chemical analyses. Microparticle concentrations and size distributions were measured on an Elzone 280PC particle counter equipped with a 30 pm orifice. Measurements were performed under class 100 conditions on sample aliquots diluted with a pre-filtered NaCl solution to give a 2 % vol. electrolyte concentration. The particle counter was calibrated with monodisperse latex spheres with diameters of 1 and 5 pm. The data were acquired for a size range of 0.65 to 12 pm equivalent spherical diameter id) in 64 logarithmically-distributed size channels. Routine analysis of filtered de-ionized water blanks showed background counts to be on average 10 times lower than in samples. Consequently background counts were not substracted from the sample data. All samples were analyzed in random order and in triplicate. Results were then averaged for individual samples, yielding an estimated error of 10 % or less on particle concentrations. Because some dust fraction composed of soluble mineral phases such as CaCC >3 and CaSC >4 may be
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lost to solution during analysis, some discrepancy may exist between the actual dust concentration in the snow and the measured concentrations. Microparticle concentrations for 0.65
dN In - % =-Blnd + lnC d(lnd) H
fitted to particles with d <5 pm (Junge, 1963). The coefficient {3 is inversely related to the coarseness of the microparticle population and can therefore be used to characterize it (Steffensen, 1985). For example, a higher value of f3 may imply relatively more fine particles and/or fewer coarse particles in the size distribution, and inversely for low f3 values. In addition to microparticles, the concentration of eight major ions (Na+, NH 4+ K+, Mg2+, Ca2+, Cl*, NO 3- and SO 42-) were measured at trace levels on a Dionex 4000i ion chromatograph using the procedure described in Buck et al. (1992). Duplicate analyses on 10 % of all samples yielded a precision of 8 % for K+ and less than 5 % for all other species. In addition to microparticles and ionic chemistry, sample aliquots from snowpit 94-1 were analyzed for oxygen isotopes at the Department of Geophysics of the University of Copenhagen. Results are expressed as 8180 (in %o) normalized to SMOW.
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RESULTS AND DISCUSSION
Dust Concentration and Flux
To determine how representative dust deposition on the Penny Ice Cap is of regional to hemispheric atmospheric dust fallout, we compared the mean dust concentration and flux in snow on the Penny Ice Cap with similar measurements from remote polar and non-polar sites (Table 0.1). The mean concentration of microparticles with 0.65 (im < d < \2 pm in the Penny Ice Cap snowpack is 31.6 (±19.4) x 10 3 mb 1 with a mass concentration of 143 (±84) jig kg-1. For particles with d > 1 pm, the mean concentration is of 13.7 (±8.5) x 10 3 m l'1, which is comparable to that measured on the Devon and Agassiz ice caps and in central Greenland. Based on the estimated accumulation rate of 0.38 m ice y r 1, we derived an average value for the modem eolian dust flux to the Penny Ice Cap of 4.8 pg cnr 2 y r 1 for particles with 0.65 pm
Size Distribution of Dust and Source Proximity
In order to assess further the relative contribution of proximal and distal sources to the Penny Ice Cap snowpack, we determined the microparticle size distribution characteristics of our snowpit samples. For this, we applied a least squares regression to fit the measured particle volume distributions with a log-normal curve of the form
dV V [ In \ d / d v) = - — -exp —:—— dlnd Vainer 21n2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 17 where V is the total particle volume over the size interval considered, dv is the mode of the distribution and <7, the standard deviation. This type of distribution was previously found to provide a convenient representation of soil-derived aerosols and ice core microparticles (e.g., Patterson and Gillette, 1977; Wagenbach and Geiss, 1989; Steffensen, 1997). Because of the larger scatter of data at the upper and lower ends of the measured size range, we restricted the log-normal fit to a diameter interval of 0.8 to 5 fim. An example of microparticle size distribution fitted with a log-normal curve is shown on Fig. H.3. Goodness of fit estimates for the log-normal model were obtained by the x2 method (Table n.2). Consistently low (< 1) values of x2 indicate that the log-normal model is a satisfactory approximation of the particle size distribution over the diameter range 0.8 to 5 Jim . Based on all snowpit samples (n = 452), we found the average volume size distribution of dust particles in the Penny Ice Cap snowpack to be centered around a mode of 2.3 ± 2.1 pm. This value also represents the modal mass diameter dm, since the volume and mass size distributions are linearly related by M (d) = pV(d) where p is the particle density. Other modes may exist for d < 0.65 pm, but there probably are none for d > 12 pm since particles of that size are rare. When compared to measurements from other polar and non polar sites (Table n.3), the size mode of dust deposited on the Penny Ice Cap is found to be similar to that at Summit, central Greenland (1.7 ± 2.0 pm). In view of the remoteness of Summit from continental dust sources, this suggests that atmospheric dust is delivered to the Penny Ice Cap by long-range transport from source regions distant by hundreds to thousands of km. Because coarse airborne particles settle out rapidly, the size distribution of dust aerosols shifts to an increasingly finer mode during long-range transport, such that beyond distances of several thousands of km the modal diameter approaches 1 pm (Radke et al, 1980; Schuetz et al, 1981). A far-removed origin for the Penny Ice Cap dust is also supported by comparison with the mid-latitude, high elevation sites listed in Table H.3. Mustagh Ata and the Chongce Ice Cap are located near the Taklamakan desert of central Asia and are characterized by rates of dust deposition in excess of 200 pg cm *2 y r 1 (Wake et al, 1994), which accounts for the coarser mode of dust measured in snow at these sites (3.7 pm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18 Saharan dust fallout episodes shows a modal size (dv = 2.5 ± 1.9 pm) closer to that measured on the Penny Ice Cap and at Summit, Greenland. To estimate the probable transport distance of atmospheric dust deposited on the Penny Ice Cap, we also compared the particle size distribution of our snowpit samples with those of soil-derived aerosol populations collected proximally and distally from known source regions (Table n.3). Aerosol measurements from Texas and the Saharan region were made under conditions of moderate atmospheric dust loading. The Cape Verde, Barbados and Bermuda aerosols represent Saharan dust transported over the tropical Atlantic Ocean, while the Enewetak dust aerosol originated from the arid regions of central Asia. The Barrow data represent the mineral aerosol component of late winter Arctic haze layers sampled by aircraft over Alaska. Each of these aerosol populations is described by the log normal mode and standard deviation of its volume or mass size distribution. However, because the aerosol data were gathered using different techniques (including nephelometers and cascade impactors), caution must be observed in drawing direct comparisons with ice core microparticle measurements. In particular, estimates of the size mode of aerosols based on cascade impactors measurements may entail considerable error due to particle bounce effects (Walsh et al., 1978) or to uncertainties inherent in the log-normal curve fitting procedure (e.g., Dzubay and Hasan, 1990). Keeping these limitations in mind, a comparison of values in Table n.3 indicates that the size mode of microparticles deposited on the Penny Ice Cap is finer than that of soil-derived aerosols measured in arid, dust- producing regions such as northwest Africa, but closely resembles that of desert dust aerosols sampled thousands of km away from their sources. It is also noteworthy that the modal size of dust on the Penny Ice Cap approaches that of mineral aerosol transported over Barrow (Alaska) and attributed by Rahn et al. (1981) to long-range transport from the Gobi desert and/or Loess Plateau of China. Weekly aerosol observations at Alert (Ellesmere Island; 82.5°N) between 1980 and 1990 reveal that the spring peak concentration of soil-derived Al coincides with the maximum seasonal occurrence of dust storms in China (Barrie, 1995), thereby suggesting a long-range Asian source. A central Asian source has also been inferred for dust aerosols sampled in Keewatin, in the mainland Canadian Arctic (Welch et al., 1991). This does not rule out possible contributions from other remote sources (e.g. continental North America) or from more proximal dust sources near the Penny Ice Cap; however, this comparison further supports our conclusion that dust deposited in modem snow on the Penny Ice Cap is representative of the atmospheric dust fallout on a spatial scale of 103 km2 or more. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19 Timing and Variability of Dust Deposition A comparison of dust concentration profiles from the 1994 and 1995 Penny Ice Cap snowpits (Fig. n.4) reveals considerable variability between and within individual snowpits, making it difficult to identify correlative features among snowpit dust profiles. A two-factor analysis of variance of the 1995 snowpits revealed that for 1 to 2 years of snow accumulation, the variance of dust distribution within one snowpit is comparable to that among snowpits. Furthermore, the mean dust concentration does not differ significantly among snowpits, suggesting a relatively uniform dust fallout over a spatial scale of < 10 km2. Grumet (1997) reported similar findings for the distribution of major ions in Penny Ice Cap snow. Together, these results indicate that a record of dust or major ion deposition from a single snowpit site may be considered representative of deposition on the summit area of the Penny Ice Cap, at least when averaging over a period of a few years. To define the seasonal timing of dust deposition on the Penny Ice Cap, we examined the distribution of microparticles in snowpits in relation to snowpack stratigraphy, 8 180 and major ion chemistry. For convenience, we chose to represent the distribution of major ions in the snowpack by profiles of Na+ concentration (Fig. n.4). Most of the other major ionic species measured (Cl-, Ca2+, Mg2+, S 0 4 2- and NO 3') show very similar profiles (Grumet et al., 1998). Individual accumulation years were delineated in the snowpits by placing the end of the ablation season at the top of the icy fim and/or thick ice layers (e.g., Alt and Bourgeois, 1995). This interpretation is supported by the frequent occurrence above the ablation surface of depth hoar layers which generally form in late summer or fall when the air-snow temperature gradient is conducive to fimification (Alley et al., 1990; Paterson, 1993; R.M. Koemer. pers. comm.). The presence of refrozen meltwater percolations and ice lenses in winter or fall fim layers indicates that summer meltwater can percolate and refreeze well below the ablation surface and into accumulation from previous years. Comparison of the Penny Ice Cap snowpit profiles reveals the presence of two distinct dust concentration peaks in the upper part of all but one snowpit (i.e. pit 94-2). Based on our stratigraphic interpretation, we can assign the upper and lower peaks to late winter- spring and late summer-fall accumulation, respectively. The dust peaks also correlate approximately with distinct Na+ enhancements attributed by Grumet et a l (1998) to spring and fall depositional signals partly altered by meltwater redistribution during summer melt These findings suggest that the Penny Ice Cap may experience two seasonal maxima of dust deposition. The lack of clear dust signals in the lower parts of most snowpits is attributed to post-depositional particle mobilization, as discussed later. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 An explanation for the apparent bi-seasonal character of dust deposition on the Penny Ice Cap may be found by considering data from other polar sites. In the interior regions of Greenland and on the Devon Ice Cap, atmospheric dust deposition typically reaches a maximum in late winter or spring, although a second maxima in summer is not uncommon (Hamilton and Langway, 1967; Koemer, 1977; Hammer etal., 1978; Steffensen, 1985, 1988). Some Arctic coastal sites surrounded by seasonally snow-free terrain also experience dust deposition in snow in late summer and/or early fall (Barrie and Barrie, 1990; Heidam et al, 1997). Thus, the seasonal doublet of dust concentration observed in the Penny Ice Cap snowpits may be accounted for by contributions from both distal and possibly proximal (primarily in the fall and/or summer) sources. Furthermore, spring and fall are the dominant seasons of storm activity in the eastern Canadian Arctic, with the bulk of precipitation over southern Baffin Island supplied by cyclonic systems in the Baffin Bay-Davis Strait sector (Barry et al, 1973; Bradley and England, 1979; Keen, 1980). Thus, enhanced meridional flow and increased precipitation scavenging of atmospheric dust associated with spring and fall storm activity could contribute to an enhanced dust flux into snow in those seasons. However, some of the dust peaks seen in our Penny Ice Cap snowpit profiles may result from the concentration of dust by meltwater loss during melt episodes, as was observed on the Devon Ice Cap (Koemer, 1977) and at Dye 3, Greenland (Steffensen, 1985). To better characterize dust deposited on the Penny Ice Cap under different meteorological regimes, we compared the size distribution of microparticles based on snowpit stratigraphy and on the inferred season of deposition. The mean particle size distributions for snow, fim, hoar and ice samples and for three seasonal intervals (fall, winter and spring + summer) were calculated by stacking the volume distribution data from individual samples. A weighted log-normal curve fit was then applied to the stacked distributions. We defined the seasonal intervals based on our stradgraphic interpretation of the 1995 snowpits, as discussed above. Because meltwater from summer abladon may cause displacement of particles below the uppermost melt layers, our calculations were restricted to the 1993-94 accumulation period for the 1994 snowpits, and to the 1994-95 period for the 1995 pits. Results of these comparisons (Table n.2 and Fig. n.5) indicate that on average, the concentration and modal size idv) of dust in fall accumulation are greater than for winter or spring+summer accumulation, although the size differences are within the error range. The coarser size of dust deposited with fall accumulation suggests a more important contribution from proximal dust sources at a time when snow cover extent is minimal. However the lack of very coarse particles and the overall fine mode of particles deposited in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 21 Penny Ice Cap snow indicate that such proximal sources are still relatively far from the study site. By comparison, winter and spring+summer accumulation are nearly equal both in terms of dust concentration (M =144 pg kg*1) and modal size (dv =2 pm). This lack of difference suggests that the apparent late winter-spring deposition signal observed in our snowpit dust profiles primarily reflects the deposition of finer (submicron) particles transported from more distant sources. Our interpretation is in agreement with Steffensen's (1988) suggestion that microparticles deposited in Arctic spring snowfall may largely represent dust from distant sources that has accumulated in the Arctic troposphere during the winter season, when the extensive snow cover and southerly position of the polar front cut off more proximal dust sources. The data in Table II.2 and Fig. n.5 also show that the concentration of dust in hoar layers is significantly lower than in snow, fim or ice layers. This implies that maximum dust deposition in late summer-fall probably precedes the timing of depth hoar formation, as is suggested by the snowpit dust profiles. Post-depositional Redistribution of Dust in the Snowpack Below the first summer melt layers, identification of seasonal dust signals in the Penny Ice Cap snowpits is ambiguous, with discrete peaks often lacking from the expected sequence. We attribute this primarily to post-depositional particle migration resulting from meltwater percolation during the ablation season. To investigate these post-depositional effects, we examined detailed depth profiles of microparticle parameters (N, NMD, fi) and major ion chemistry (represented by Na+) in snowpit 94-1, which spans the longest period of accumulation (> 5 years) of all our pits (Fig. II. 6). Our stratigraphic interpretation of pit 94-1 was found to be in overall good agreement with seasonal 8I80 excursions. However, we failed to identify any consistent relationship between dust concentration or size distribution, and ionic chemistry or snowpack stratigraphy. While some dust peaks are found to be associated with ice layers or Na+ enhancements, others are not Similarly, variations of NMD and fi can not be systematically correlated to stratigraphic features of the snowpack. This lack of consistency indicates that microparticles are remobilized by meltwater in such a way that seasonal (and stratigraphic) differences are obscured. At Dye 3, south Greenland, Steffensen (1985) observed that melt layers in a snowpit profile were generally correlated with low b values, suggesting preferential wash-out of the finer particles from the snow layers affected by melting. We observed no such relationship in snowpit 94-1, indicating that meltwater percolation in Penny Ice Cap snow affects both fine and coarse particles. However if meltwater was completely remobilizing dust particles in the snowpack, one would expect the resulting vertical distribution profiles to be flat. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 22 Instead, our snowpit dust profiles still display considerable structure and variability, as shown by baseline concentration variations of up to 104 ml-1 and by the presence of well- defined peaks. Factors that may preserve this variability are interannual variations of snow accumulation or summer m elt Another is the presence of numerous ice layers acting as physical obstacles against particle migration in snow, a scenario previously suggested by Grumet et al. (1998) for the translocation of major ions. While we lack data to quantify the post-depositional migration of particles, we consider it unlikely that such migration would exceed a depth of 2-3 m in view of the frequency of ice layers in the snowpack. At the current rate of snow accumulation (~ 1 m y r 1), a depth of 2-3 m would correspond to about 3 years of accumulation, which puts an approximate upper limit on the temporal resolution of our dust deposition record under present conditions. A higher resolution may be attainable in the ice core record during climatic periods that were characterized by lower summer melt percentages than at present. To evaluate the preservation of dust variability over a longer interval of deposition, we performed a Fourier analysis on dust concentration against ice equivalent depth for the upper 20 m of the P95 core. Sampling resolution for this portion of the core was of 5 cm, which should be sufficient to resolve sub-annual variability of depositional signals if the latter are preserved. Results of our analysis reveal strong spectral power concentrated between 0.4 and 0.7 m ice eq., with a maximum (well above the 99.9% confidence level) at 0.41 m ice eq., remarkably close to our estimated modem annual accumulation rate of 0.38 m ice eq. (Fig. n.7). These results do not imply that the original stratigraphic sequence of dust deposition is intact, but do support our contention that annual to multi-annual variability is still preserved downcore, as was previously shown for major ions (Grumet et al., 1998). Thus, valuable paleoclimatic information may still be obtained by considering multi-annual to decadal averages of the P95 ice core microparticle record. CONCLUSIONS Our analysis of dust distribution in snowpits on the Penny Ice Cap brings forth three main conclusions: 1) The average concentration (143 pg kg-1), flux (4.8 pg cm 2 y r 1) and size mode (2.3 pm) of dust deposited in modem Penny Ice Cap snow are essentially similar to those observed in other remote Arctic sites such as central Greenland. Furthermore, the modal size of Penny Ice Cap dust (dv = 2.3 pm) resembles that of desert dust aerosols transported over distances in excess of 1000 km. These similarities suggest that the bulk of dust Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 23 deposited on the Penny Ice Cap originates from an atmospheric reservoir supplied through long-range transport of dust emitted from far-removed regions (i.e., 10 2 tolO 3 km distant). 2) The variability of dust deposition in the Penny Ice Cap snowpack appears to be equal on a spatial scale of at least 10 km 2 and a temporal scale of 1-2 years. There is some evidence for two seasonal maxima of atmospheric dust deposition, one in late winter spring, one in late summer-fall, which correlate approximately with seasonal enhancements in major ion chemistry (Grumet et al., 1998). The slightly coarser mode (-3.0 pm) of dust deposited with late summer-fall accumulation suggests some influence from more proximal (albeit still distant) dust sources, possibly as a result of dust emissions from snow-free terrain in this time of the year. In contrast, the late winter-spring dust peak may primarily reflect the deposition of finer, far-traveled dust originating from sources such as continental North America or central Eurasia. 3) Because of post-depositional particle migration, seasonal dust signals can not always be unambiguously resolved in the Penny Ice Cap snowpack. However the formation of ice layers limits the mobility of particles, such that redistribution is likely to be minimal beyond the depth equivalent of 3 years of snow accumulation. This is supported by the presence of strong yearly spectral component in the distribution of dust in the P95 ice core. These findings imply that while the Holocene dust record from the P95 core may not resolve interannual differences, it may still provide valuable paleoclimatic information at a multi annual to decadal resolution. ACKNOWLEDGMENTS Support in the field was provided by the Polar Continental Shelf Project, our colleagues of the Geological Survey of Canada, Parks Canada, the Northern Science Training Program and the communities of Iqaluit and Pangnirtung. AWS data were used with permission from Canada's Atmospheric Environment Service. Thanks are due to N. Grumet and S. Whitlow for performing the chemical analyses. Discussions with R. Koemer, D. Fisher, J. Bourgeois, P. Mayewski as well as comments by two anonymous reviewers greatly improved earlier drafts of the manuscript. The lead author (CMZ) also thanks Dr. Wayne Pollard at McGill University for guidance and support in the early stages of the program. This research project was supported by the Office of Polar Programs, National Science Foundation. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1985 1972 1974 1979 efal. etal. etal. et al. et Kumai Kumai 1977 Hammer 1977 Hammer Steffensen Steffensen 1997 1969 Murozumi Rahn Rahn Koemer and and Koemer Koemer 1981 Fisher 1982 Fisher 1982 and Fisher Reference This This work i 1.0 n/a n/a n/a n/a 2.5 Hammer 4.2 4.4 4.8 Fluxc 1.4 to 1.4 13.3 Darby 8.5 8.5 to 21.0 Mullen (pgcm-2yr') n/an/a n/a n/a n/a n/a n/a n/a 129 143 235 n/a 35 1.4 n/a 50 n/a 46 n/a n/a 3.1 14.0 18.2 18.3 18.3 13.7 13.7 20.0 8.30 31.6 Number Number Mass (103 ml-') (103 (pg kg-1) >1 n/a n/a >1 n/a >1 >1 >1 1-12 1-12 0.2-4 0.2-4 0.2-4 9.4 0.2-4 n/a 74 2.5 Steffensen 1988 (fim) 0.65 0.65 -12 Size range range Size CC EM 0.02-8 CC CC CC CC LLS LLS LLS LLS FLTR CHEM n/a n/a 35 1.4 CHEM method** Analytical 1978-1983 1780-1951 1753-1965 1891-19101940-1950 LLS 1950-1977 1950-1977 1988-1994 Recent snow Recent CC 0.5-12 Last years 104 Recent snow Recent snow Recent Last 7000 years 7000 Last Recent snow Recent Last 5000 years 5000 Last (Years AD) (Years 1885 1800 1980 1600 3207 2479 3070 (m asl) (m sea sea level snow Recent FLTR n/a n/a sea sea level Elevation Elevation Site Period9 Dust concentration and flux 38°W 39°W 43°W 61°W 82°W 72°W sea level 73°W 65°W 150°W LONG LAT 84°N 65°N 77°N 70°N 75°N 81°N 77°N 67°N Dye 3 Dye Summit 72°N Canada Basin Canada Agassiz Ice Cap Ice Agassiz Cap Ice Devon Arctic Ocean Greenland (avg) sites Inland >2400 Canada Basin Canada Century Camp (avg) D and A Sites Arctic Ocean Arctic Penny Ice Cap Cap Ice Penny Canadian Arctic IB. II. Table in Footnotes sites. Arctic Canadian and Greenland ice: and snow in flux and concentration dust Atmospheric A. 11.1 Table Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1994 1994 1994 etal. et al. et et al. et Gaudichet 1991 Gaudichet Wake Wake Windom 1969 Windom 1969 Windom Wagenbach and Wagenbach Wake Wake Wake Hinkley Hinkley 1994 27 n/a 247 607 16.0 32.0 20.0 Geiss 1989 21.0 to 35.0 De Angelis and and 21.0 to Angelis 35.0 De n/a n/a n/a n/an/a n/a 300 379 8220 6780 n/a n/a n/a n/a n/a 37.0 18.17 CC 1-22 276.4 FLTR n/a CHEM n/a 1955-1985 CHEM n/a 1989-19901980-1987 CC CC 1-13 1-22 616.0 1936-1982 CC 0.63-16 1990-1992 Recent snow Recent Recent snowRecent snowRecent CHEM FLTR n/a n/a 2000 2500 5700 6327 4270 5910 (m asl) asl) (m method*5 (Hm) m (103 l1) ([igkg*1) (jigcm ^yr1) 7°E 4450 81°W 86°W 123°W 139°W 2600 Site Period8 Dust concentration and flux LAT LAT LONG Elevation AD) (Years range Size Analytical Number Mass p|uxc 35°N 38°N 75°W 63°N 151°W 47°N 60°N 28°N 45°N 6°E 46°N IB. Atmospheric dust concentration and flux in snow and ice: Other Northern Hemisphere sites. sites. Hemisphere Northern Other and ice: snow in flux and concentration dust Atmospheric IB. EL (USA) (USA) (USA) (China) electron microscope; FLTR, based on dry filter weights; LLS, laser light scattering. light laser LLS, weights; filter dry on based FLTR, microscope; electron (France) (Switzerland) (China) (Nepal) Mount Olympus Olympus Mount Blanc Mont Alaska Range Range Alaska Range St-Elias b Analytical methods: CC, Coulter counter or equivalent method; CHEM, calculated from chemical data (typically [Al], [Ca] or [Si]); EM, EM, or[Si]); [Ca] [Al], (typically data chemical from calculated CHEM, method; equivalent or counter Coulter CC, methods: Analytical b Colie Gnifetti Gnifetti Colie Ata Mustagh Glacier Ngozumpa a Period of snow accumulation represented by the data. the by represented accumulation snow of Period a Chongce Ice Cap Cap Ice Chongce Other sites Reference Table Table cFlux values were taken from the literature or calculated from mass concentrations using published estimates of snow accumulation rates. accumulation snow of estimates published using concentrations mass from calculated or literature the from taken were values cFlux Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 X 0.07 0.32 0.18 0.57 0.16 0.03 of fi 0.98 0.98 0.42 Goodness ) 0.99 6 . 1 and x2) for n-4 of degrees for x2) and 2 (pm) (± ae 2.1 2.1 (±1.4) 2.1 (±1.4) 0.99 0.99 0.06 2.4 2.4 (±2.2) 2.1 2.1 (±1.3)2.1 0.99 ) 2.3 (±2.5) 0.90 ) 0 0 . . 1 1 (± and standard deviation ( Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and standard standard and 1997 1990 1997 (dv) 1994 1994 1980 etal. et al. et etal. et al. et et al. et et al. et Savoie and Prospero and Savoie 1980 Arimoto Patterson and Gillette Gillette and 1977 Patterson Arimoto Arimoto Gomes Wake Wake Reference transport distance Asia; > 5000 km 5000 > Asia; era/. Rahn 1981 LocalLocal 1983 ShUtz and d'Almeida Local N. Africa; > 1000 km > Africa; N. 1000 Geiss and Wagenbach 1989 Central Asia; > 100 km> 100 Asia; Central Wake Background + local Background This work km > Asia; 100 Central Background Steffensen 1997 2.1 2.4km > 500 N. Africa; 2.1 2.1 2.2 2 .0 2 .0 (pm) oe (pm) dv 2 ~ 8 Range (pm) Range Size distribution parameters Dust source(s) and 0.01 0.01 to 100 0.1 to 20 ~3 ~3 0.025 0.025 to 0.98 0.98 to 22 5.7 0.63 0.63 to 16 2.5 1.9+local Background 0.8 0.8 to 5 2.3 were calculated by fitting log-normal curves to size distribution data. All aerosol data are from surface measurements, measurements, surface from data are aerosol All data. distribution size to curves log-normal by fitting calculated were (cg) Sal Island, Cape VerdeCape Island, Sal 0.71 to 5.8 5.1 Barrow, Alaska Barrow, Plains, TexasPlains, 0.3 to 20 4.6 Sahara (Algeria) Sahara Sahara (Nigeria) Sahara Tudor Hill, Bermuda Tudor Hill, BarbadosRagged Point, 0.52 to >16.8 0.52 to >16.8 2.4 2.3 3.4 3.1km 5000 > Africa; N. Africa; N. km > 5000 Mineral aerosols Atoll Enewetak 0.2 to >7 to 2.0 1.4 km 5000 > Asia; Duce Microparticles (modern snow) Canada Ice Cap, Penny Mustagh Ata, China Ata, Mustagh Chongce Ice Cap, China Cap, Ice Chongce 0.98 to 22 3.7 Summit, Greenland Summit, SwitzerlandGnifetti, Colle 0.63 to 16 0.4 to 2 4.5 1.7 deviation deviation except for the Barrow aerosol, collected at ~2 km asl. Some desert dust aerosols have a coarse mode > 20 pm,coarse > mode here. 20 shown a not have dust aerosols desert Some kmasl. at ~2 collected aerosol, Barrow the except for Table D.3. Size distribution of microparticles and mineral aerosols at various Northern Hemisphere sites. The mode The mode sites. Hemisphere Northern at various aerosols and mineral microparticles of distribution Size Table D.3. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28 68°00'W 63°40’W 68°00'N 5 5 $ % Study Are * * WJVJ 66°30'N retife Clrel». °Pangnirtung 66°00,N 68°00'W Fig. n .l. Location map of the Penny Ice Cap, Baffin Island. Contour lines in meters. The location of the P95 ice core site and automatic weather station (AWS) are shown. The field study area (outlined) is enlarged on Fig. H.2. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. «a0Z N.9LSloZ9 N«0a00oZ9 65°15'15"W I 1 1 n 1 V •vP95 95-1 j \ ' \ 94-2 D AWS AWS 1^95-4 \ ' I ‘ " 1 1 A T ' Ice Ice-free terrain ® Snowpit site KEY TO SYMBOLS KEY 66°30'15"W 66°30'15"W | = K = ] L = d 65°15'15"W location of snowpits, the P95 ofsnowpits, the P95 and P96 weatherice core the automatic sites location and (AWS) station are shown. are Fig. study Field area II.2. on Contour the Cap, Baffin Penny Ice The Fig. Island. lines in meters. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. without prohibited reproduction Further owner. copyright the of permission with Reproduced dV/dln d (|im3) 0.5 standard deviation (crg) of the modeled distribution are (crg)shown. deviation distribution theof modeled standard samples. The interval of curve fitting, and the mode mode the and curve fitting, of interval The samples. snowpit 30 of average stacked a histogram is The data. distribution Fig. Fig. n.3. Example of log-normal curve fitted to microparticle size size microparticle to fitted log-normal curve of Example 1 curve fitting curve Interval of of Interval Diameter d (pm) ± a, ± 30 0 15 10 5 (dj and opyo op op iy i o i s 7,5190 5.0 0 20 40 50 0 20 0 4 50 N (103 part, (103 N m b) Na+ (ppb) N (103 part, (103 ml-')N Na+ (ppb) Pit 95-1 Pit 95-1 part, (103 N ml-') Na+ (ppb) Pit 95-3 Pit 94-2 •x-x*x-x*x .V.V.V.V.W April 17,1995April May May 11,1995 May 10,1994 04- 0 40 SO 120 0 SO 100150 N (103 part, (103 N ml-i) Na+ (ppb) alto) Pit 95-4Pit PH 95-2 PH April 20 April |’>4.||| I I’l'lYl I |’>4.||| W3888 (AWS (AWS May 12,1995 part, (103 N ml-') Na+ (ppb) & May 2,1995 May & os - — — — — teatana Qradualcontact Shupcontact *wp*w teatayar Icy fim Icy o eo ioo iso o 50 100 150 Depth hoar Coarse fim Surfacesnow KEY TO SYMBOLS TO SYMBOLS KEY PH 94-1 PH AWS site) AWS Arrowsindicate the inferred input timing ofmicroparticles and Na+ peaks (S= Spring; F= Fall). x*x«x-:-x<: Fig. II.4. Stratigraphy, microparticle number (N) and in PennyNa+ Ice Cap snowpits. May 6-9,1994May part, (103 ml-') N Na+ (ppb) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A\__ — Fall Fall (28) (pm) d Winter Winter (24) Diameter Diameter Summer & Spring (42) 1 10 Ice (45) Ice shown in parentheses. n Snow (117) d(\im) _ _ _ Hoar (39) Hoar samples, with Diameter Diameter Fim Fim (251) n Microparticle size distributions in Penny Ice Cap snowpits based on stratigraphy (left) and input timing (right). 11.5. Fig. represents an average of The size distributions were fitted with log-normal curves, the parameters ofwhich are given in Table II.2. Each curve CO Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Depth (m) 3.5 2.5 4.0 5.0 0.5 2.0 0.0 1.0 1.5 3.0 4.5 -I. NMD (pm) (pm) NMD Beta /) (ppb) |s|a+ 0.9 1.15 1.4 1.5 . 2.5 . 3,5 0 50 1Q0 150 40 40 80 120 N(103 mh)N(103 5"0 (%o) -34 -34 -30 -26 -22 -18 1988 1988 r 1989 1989 1993 1992 1993 1231 I I'M 'A W V sW 1 ' Stratigraphic symbols as on Fig. II.4. Shading in profiles of 8i«0, NMD and j3 highlights departures from the mean. the from departures highlights j3 and 8i«0, NMD of profiles in Shading II.4. Fig. on as symbols Stratigraphic Fig. II.6. Stratigraphy and profiles of 8i*0, microparticle number (N) and mean diameter (NMD), /Jand Na+ in snowpit 94 94 snowpit in Na+ /Jand (NMD), diameter mean and (N) number 8i*0, ofmicroparticle profiles and Stratigraphy II.6. Fig. (Key on 3) (Key Fig. - 0 . 0.0 1 0.5 2.0 3.5 1.5 3.0- Qb a> 5= 5= 2.5 O Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. z = 0.41 0.41 = z m Ice equivalent depth z(m) depth equivalent Ice 0 0.2 0.4 0.6 0.8 1 0 03 0.1 0.2 0.6 0.8 0.7 0.5 in the P95 ice core. Spectral power is shown for z = 0.08-1 0.08-1 only. = are core. the uppermost Data thez m Spectral powerfrom 20 of in P95 m ice shown is for core. lines 99.9 the P95 to bottom) top Dashed 99%95%(from the identify confidence%, ice and limits. Fig. II.7. Fourier power spectrum of microparticle number (N) as a function of depth (z; spectrumequivalent) Fig. power as ofnumberice depth (N) aofmicroparticle II.7. Fourier (z; function 2 0.4 % o Q. 3 £ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER H I PALEOENVIRONMENTAL SIGNIFICANCE OF A HOLOCENE RECORD OF EOLIAN DUST DEPOSITION FROM THE PENNY ICE CAP, BAFFIN ISLAND, CANADIAN ARCTIC C. M. Zdanowicz, G. A. Zielinski and C. P. Wake Climate Change Research Center, University of New Hampshire, Durham, NH 03824 USA D. A. Fisher and R. M. Koemer Terrain Sciences, Geological Survey of Canada, 601 Booth Street, Ottawa, ON. KIA OE8, Canada Submitted for publication in Quaternary Research, January, 1999. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36 CHAPTER HI PALEOENVIRONMENTAL SIGNIFICANCE OF A HOLOCENE RECORD OF EOLIAN DUST DEPOSITION FROM THE PENNY ICE CAP, CANADIAN ARCTIC ABSTRACT Insoluble microparticle (dust) records developed from ice cores can help define climatic variability in the circumpolar north by documenting past changes in atmospheric loading, transport and deposition of eolian dust. We developed an -12,000 yr-long record of atmospheric dust deposition from a core (P95) drilled through the Penny Ice Cap on Baffin Island, Arctic Canada. Dust deposition on the Penny Ice Cap peaked in late glacial time, then declined in the early Holocene and remained comparatively low until ca. 7500 yr ago. The concentration and mean dust grain size increased markedly thereafter, partly due to recession and thinning of the Penny Ice Cap that facilitated the advection of wind-blown dust from nearby sources onto the ice. We postulate that a concurrent regional to pan-Arctic climatic deterioration led to more severe, winter-like conditions in the eastern Canadian Arctic and enhanced eolian deflation of dust sources. Dust levels in the P95 and GISP2 (central Greenland) ice cores were comparable in the early Holocene but diverged after ca. 7500 yr ago. We suggest that this divergence stems from a regionalization of Holocene climate accompanying the recession of continental ice sheets, thereby allowing for regional atmospheric circulation patterns in the Baffin Island region to dominate dust transport to and deposition on the Penny Ice Cap. Our findings further demonstrate how valuable records of regional-scale paleoenvironmental change can be developed from small circum- Arctic ice caps. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37 INTRODUCTION Proxy-climatic records developed from ice caps in the Canadian, Norwegian and Russian Arctic have been used to document regional-scale climatic variability in the circumpolar north (e.g., Koemer and Fisher, 1990; Kotlyakov et al., 1991). The insoluble microparticle (dust) record in ice cores documents past changes in the atmospheric dust load and the dynamics of airborne dust transport and deposition (e.g.. Petit etaL, 1981; Thompson and Mosley-Thompson, 1981; Hammer etaL, 1985; Hansson, 1994; Steffensen, 1997; Zielinski and Mershon, 1997). In addition to providing valuable paleoclimatic information, ice core microparticle data can help assess the climate-forcing radiative impact resulting from changes in atmospheric dust loading (e.g., Tegen et al., 1996). Studies of dust from polar ice cores have thus far been largely restricted to Greenland and Antarctica. A notable exception is the work of Koemer (1977), who analyzed the concentration of microparticles > 1 pm in a core from the Devon Ice Cap. Here we report on a new Holocene record of eolian dust deposition developed from an ice core drilled through the Penny Ice Cap on southern Baffin Island (Fig. n. 1). Ours is the first such record developed from the Canadian Arctic to include high-resolution measurements of microparticle number, mass and grain-size distribution. This approach may allow discrimination between time-varying environmental factors such as dust source strength, regulating the dust flux to the atmosphere, or relative transport distance, affecting the mean grain size of eolian dust (e.g., Zielinski and Mershon, 1997). We discuss the paleoenvironmental significance of the Penny Ice Cap dust record in relation to the glacial and environmental history of the Canadian Arctic region. Comparisons are also made with the Greenland Ice Sheet Project 2 (GISP2) ice core record and with documented Holocene changes in Northern Hemisphere climatic and environmental conditions that may have affected eolian dust transport and deposition in the northern polar region. METHODS The Penny Ice Cap (P95) Ice Core The 334-m P95 ice core was drilled in April-May 1995 from a site along the main ice divide of the Penny Ice Cap (Fig. n.2; 67° 14N, 65°43*W; elevation 1980 m asl). Radar soundings indicate that the drill penetrated to within a few tens of cm from the bed. The core was measured for solid electrical conductivity (ECM) and sampled continuously for 5lsO, major ion chemistry and microparticles. The core was stringently sampled by clean Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38 techniques to prevent contamination, as described in Grumet et aL (1998). All samples remained frozen until prior to analysis. The concentration and size distribution of microparticles between 0.8 and 12 (jm diameter were determined on an Elzone™ 280PC particle counter following procedures described in Zdanowicz et al. (1998a). Major ions (Na+, NH4+, K+, Mg2+, Ca2+, Cl*, NO 3* and SC> 42*) were measured at trace levels on a ■PW Dionex 4000i ion chromatograph (Buck et al., 1992) with a precision of 8 % for K+ and < 5 % for all other species. Oxygen isotope measurements were performed at the Department of Geophysics of the University of Copenhagen. Results are expressed as 8180 (in %a) normalized to SMOW (Fisher et al., 1998). A modem accumulation rate of 0.37 m y r 1 (ice equivalent) was calculated for the Penny Ice Cap (Grumet et aL, 1998), while the annual melt percentage was estimated to average 50 % (mass) for the last 100 years. Despite this substantial melt, residual glaciochemical and microparticle signals were found to be preserved in the P95 core, allowing for valuable paleoclimatic records to be developed at multi-annual or lower (decadal to centennial) resolution (Grumet et al., 1998; Zdanowicz et al., 1998a). The P95 core was dated back to 7900 yr ago (319 m) based on spectral analysis of the high-resolution ECM record which tracks seasonal variations in bulk chemistry of the ice (Fisher et al. 1998; Grumet et al., 1998). Time control was provided by ECM and S 0 4 2" peaks related to the Laki (A.D. 1783), Katmai (A.D. 1912), A.D. 1259 and 50 B.C. volcanic eruptions. Age estimates for these peaks fell within ±15% of expected values. Beyond 7900 yr ago, the depth-age curve was adjusted smoothly to the end of the Holocene-Younger Dryas transition (326 m) dated at 11,550 ± 70 yr ago in high-resolution Greenland ice core records (Johnsen et al., 1992; Alley et al., 1993). A summary of dating techniques, sampling and temporal resolution, and age error estimates for the P95 and GISP2 ice core records is given in Table HI. 1. Comparison of the P95 core 8180 record with that of another core (P96) 16 km away (Fig. n.2) showed evidence of stratigraphic disturbance due to ice flow discontinuities below -326 m. Although microparticle measurements were performed on the entire P95 core, we primarily discuss the dust record of the period -11,600 yr ago to present over which the core is believed undisturbed and the depth-age scale constrained. The Greenland Ice Sheet Project 2 (GISP2) Ice Core The GISP2 ice core was drilled between 1990 and 1993 from the summit of the Greenland Ice Sheet (72°35’N, 38°28'W) at an elevation of 3208 m asl. Details on core processing techniques are reported elsewhere (Mayewski etaL, 1987,1990). The GISP2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 39 core was dated back to ~ 110,000 years ago by identifying and counting individual annual layers using multiple physical and chemical parameters including visual stratigraphy, ECM, laser light scattering (LLS), 5I80, and major ion chemistry (Table ELI; Meese et aL, 1997). Dating control was provided by volcanic time markers and by comparisons with other, independently-dated paleoclimate records such as the GRIP ice core and North Atlantic sediment cores. Absolute and relative error estimates for the GISP2 depth-age scale indicate that dating is accurate to within 1-5% of assigned ages for most of the Holocene, and to within 5-10 % for the remainder of the record (Alley et al., 1993; Meese et al., 1997). The core was sampled and analyzed for 8 lsO, insoluble microparticles and major ion chemistry (Na+, Ca2+, Mg2+, K+, Cl- SO 42, NO3- and NH 4+) at a resolution of 0.6-2.5 years through the Holocene, a mean of 3.48 years for the deglaciation, and 3 to >100 years over the remainder of the record (Meese et al., 1997). Sampling and analytical techniques were essentially the same as previously described for the PIC core. Definition of Dust Parameters To optimize the paleoclimatic information available from the P95 and GISP2 dust records, we calculated several parameters from the raw microparticle data. Dust particles are detected in the Elzone counter by their volume and assigned to specific size bins assuming a spherical shape of diameter d. The number concentration (N) of dust particles is reported here in units of 10 3 ml*1 (H2O). The dust mass concentration (M) was calculated from the total volume V following M = pV and using a mean particle density p = 2.6 g cnr 3, close to that of average crustal material. To compensate for the decreasing sampling resolution in the P95 core with depth and to improve on the statistical significance of our data, time series of N and M are were averaged over discrete 100-yr intervals from 11,600 yr ago to the present. For comparative purposes, we also analyzed the size distribution (by volume) of microparticles in the P95 and GISP2 ice cores for selected pre-Holocene and Holocene time periods. These periods are defined in Table m .3 and identified by capital letters (A to F) on Figures EQ.I and IH.2. Each size distribution was produced by stacking data from multiple samples over the time intervals considered. We found that in most cases, the stacked distributions could be conveniently, if not accurately, characterized by fitting them with one or more log-normal curves of the form dV V f In 2(d /d v) dlnd V 2 /rlncr,eXP 21n 2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40 where V Is the total dust volume (the area under the curve), dv the mode and crg the standard deviation. This type of distribution is commonly used in the representation of soil- derived aerosol or ice core microparticle populations (e.g., Patterson and Gillette, 1977; Steffensen, 1997). Parameters (dv, crg) defining the log-normal curves used in our comparisons are given in Table EH.3. THE P95 ICE CORE DUST RECORD The Late Pleistocene-Holocene Transition The contact between Holocene and pre-Holocene ice in the P95 core occurs between 326 and 327 m, and is identified by abrupt increases in microparticle concentrations (AN = 125 X 103 ml-1) and soluble Ca (ACa = 250 |i.g kg*1) coincident with a 12.5 %o decline in 8180 (Fig. in. la; Fisher et al., 1998). From comparisons with 8180 and microparticle records in Canadian High Arctic and Greenland ice cores (Fisher and Koemer, 1981; Ram and Koenig, 1997), we infer that the maximum particle concentrations (165 X 103 ml-1) found between 326.6 to 327.2 m in the P95 core (Fig. El. la) are associated with ice of late glacial age formed between 12,000 and 25,000 yr ago. However, given our lack of dating control prior to 11,600 yr ago, it is possible that the timing of late glacial maximum dust deposition on the Penny Ice Cap was not synchronous, hence non-correlative, with that in central Greenland. Nevertheless, the elevated microparticle concentrations found in late glacial age ice of the P95 core suggest a generally higher than present atmospheric dust load over the eastern Canadian Arctic at that time. Similar findings were made in Greenland and Antarctic ice cores (e.g., Thompson and Mosley-Thompson, 1981), and presumably reflect generally enhanced aridity conditions in the glacial climate, leading to expansion of continental dust sources and to an increase in eolian dust production (Samthein, 1978; Wells, 1983). Microparticles deposited in Greenland and Antarctica during the late glacial age were also noticeably coarser than those deposited in the Holocene, suggesting a more vigorous atmospheric circulation that allowed for relatively coarser dust particles to be transported over longer distances (Petit etal., 1981; De Angelis etaL, 1984; Steffensen, 1997). In comparison, the mean concentration and grain size of dust particles deposited on the Penny Ice Cap in the late glacial age were considerably less than for dust deposited in central Greenland during the same approximate time period (Table HL2 and Fig. IIL2-A). Likewise, microparticles in pre-Holocene ice from the Devon Ice Cap were found to be predominantly smaller than 2 pm diameter, thus smaller than in late glacial age ice from Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41 Greenland (Koemer, 1977). These differences may imply that the transit time of wind blown dust transported to the Canadian Arctic during this period was longer than for Greenland, thus allowing for greater settling and removal of coarse (> 2 pm) particles while in transit. Longer trajectories from dust source regions could have resulted from the expanded size of the Canadian Arctic ice caps during late Wisconsinan glaciation. Moreover, pre-Holocene in the P95 core may have originated from a higher and more remote accumulation area than in the Holocene, as postulated by Fisher et aL (1998) using isotopic ( 8 I80 ) evidence, thereby further increasing the distance and orographic lifting of airborne dust to the site of deposition. Another possibility is that atmospheric dust deposited on the Canadian Arctic ice caps in the late glacial age originated from soil and/or sediment source(s) distinct from those supplying Greenland and characterized by a comparatively finer particle size range. Some support for this hypothesis comes from recent climate model simulations suggesting that dust deposited in Greenland during the last glacial maximum (LGM; ca 23,000 to 25,000 yr ago) came primarily from source regions north of 47°N, whereas dust advected over the Baffin Bay region may have originated from more distant, lower latitude sources (Andersen et aL, 1998). Hence, although this remains to be verified, distinct physical characteristics of soils and sediments between these regions could conceivably account, in part, for differences in the size distribution of dust deposited in the Canadian Arctic and Greenland during the LGM. The Holocene The microparticle record in the P95 ice core shows that dust concentrations remained relatively low from the end of the Pleistocene-Holocene transition (ca. 11,600 yr ago) to about 7500 yr ago (Fig. HI. lb). The number (N) and mass (M) of microparticles deposited in the ice then gradually increased to attain their Holocene maxima between 5000 and 4500 yr ago. Dust concentrations varied considerably thereafter, but remained on average significantly above early Holocene levels (Table in.2) before declining slightly towards present values after ca. 2000 yr ago. For the purpose of the ensuing discussion, the P95 Holocene dust record can be divided into an early Holocene interval (ca. 11,600-7500 yr ago), with consistently low dust concentrations followed by a ~1500-yr long transitional period leading to a mid- to late Holocene interval (ca. 5000 yr ago to present) with markedly higher and more variable dust levels. Lower concentrations of dust in the P95 core prior to ca 7500 yr ago could conceivably reflect losses of ice (and microparticles) due to intense summer ablation and runoff in the early Holocene (e.g., Koemer and Fisher, 1990). However, the ECM signal in early Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 42 Holocene ice of the Penny Ice Cap shows no indications of ice de-acidification, as would be expected to result from high melt rates (Fisher et aL, 1998). Another possibility is that higher than present snow accumulation rates during the early Holocene effectively diluted the concentration of dust deposited in snow on the Penny Ice Cap at that time. Yet ice core records from the Canadian Arctic and Greenland suggest only limited changes in snow accumulation rates in these regions for the last -6500 to 9000 years (Paterson and Waddington, 1984; Meese et cd., 1994). Hence, we consider that the mid- to late Holocene dust increase in the P95 record must be accounted for by other factors, such as changes in dominant dust source or source strength, increased eolian activity leading to greater atmospheric dust loading, or more efficient wind-blown dust transport to the Penny Ice Cap. To investigate how possible changes in dominant dust sources during the Holocene may have contributed to the trends observed in the P95 dust record, we analyzed time series of crus tally-derived Ca* a common element in soils and terrestrial or marine sediments. We first apportioned the total Ca2+ measured in the P95 core into sea-salt and non-sea salt (nss) components using an iterative procedure described by O'Brien et al. (1995). Our calculations revealed that non-sea salt sources, presumably crustal, accounted, on average, for 88 % of total Ca2+ deposited in snow on the Penny Ice Cap during the Holocene. We also found that nssCa2+ in the P95 core declined markedly from maximum late glacial levels to ca. 10,000 yr ago, but remained essentially constant thereafter through most of the Holocene (Fig. HI. lb). Our findings suggest that (1) the dominant mineralogical type of dust deposited on the Penny Ice Cap did not change during the Holocene; and (2) that microparticles accounting for the early to mid-Holocene dust increase in the P95 record were not associated with Ca-rich soluble phases (for e.g., CaCOs) such as those found in marine or glaciomarine sediments (e.g., De Angelis et al., 1992). Alternatively, they may have been deflated from till, alluvial and/or glaciofluvial sediments derived from crystalline rocks that comprise most of the substrate on southeastern Baffin Island (Dyke et al., 1982). To further characterize eolian dusts deposited on the Penny Ice Cap at different times during the Holocene, we analyzed and compared the mean size distribution of microparticles for discrete intervals in the P95 core representing Preboreal (B), early Holocene (C), mid-Holocene (D), late Holocene (E) and recent conditions (F) (Table m.3; Figures HI. lb and m.2). In order to identify spatial as well as temporal differences in atmospheric dust deposition over the Arctic region, we also compared the size distributions of microparticles in the P95 core with those measured in the GISP2 ice core for approximately the same time periods during the Holocene. Results of our comparisons Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 43 revealed that dust particles (0.8-12 pm) deposited on the Penny Ice Cap in the Preboreal and early Holocene (Fig. IH2-B and -Q are predominantly characterized by a single log normal mode centered at 2 to 3 pm, similar to what is observed in modem ice and snow (Fig. IU.2-F and Zdanowicz et aL, 1998a). In contrast, dust deposited during the mid- to late Holocene (Fig. IH.2-D and -E) appear to have a second, coarser mode centered around 6 to 8 pm. Because the mass of dust increases geometrically with particle size (i.e., M a cfi), it follows that this coarse mode probably is mostly responsible for the early to mid- Holocene increase in dust mass concentration documented in the P95 record (Fig. HI. lb). The lack of a comparable coarse dust mode in Holocene ice from the GISP2 core (Fig. m.2 ) suggests that these large particles must have originated from dust sources relatively proximal to the Penny Ice Cap. We postulate that the increasing supply of relatively coarse dust to the Penny Ice Cap from the early to mid-/late Holocene resulted from environmental changes that affected the sources and transport dynamics of wind-blown dust to the Penny Ice Cap. One contributing factor may have been a strengthening of surface winds blowing over exposed (unglaciated) terrain surrounding the Penny Ice Cap. Indeed, it has been shown (e.g., Patterson and Gillette, 1977) that soil-derived aerosols (0.1-10 pm) produced by intense surface winds are commonly characterized by a bimodal size distribution not unlike that of dust deposited on the Penny Ice Cap during the mid- to late Holocene. Moreover, a thick succession of eolian sand began accumulating on Cumberland Peninsula (Fig. m .l), southeast of the Penny Ice Cap, around 5000 yr ago (4500 14C yr B.P.; Dyke et al., 1 9 8 2 ) , indicating a transition to drier and/or windier conditions at the time. Expansion of an eolian dust source or multiple sources in the eastern sector of the Canadian Arctic may have also contributed to an increase in the flux of coarse dust transported to the Penny Ice Cap. This expansion could have resulted from accelerating rates of postglacial emergence along the Baffin Bay and Hudson Strait coastlines after ca 7 8 0 0 yr ago (Gray et al., 1993), although our time series of nssCa2+ show no evidence of increased calcareous dust deposition on the Penny Ice Cap. Concurrently, a general recession of snow and ice cover was occurring throughout the Canadian Arctic (Dyke and Prest, 1 9 8 7 ) . Indeed, oxygen isotope evidence suggests that the Penny Ice Cap started t h i n n i n g substantially ca 8 0 0 0 yr ago as it gradually separated from the former Laurentide Ice Sheet Foxe Dome (Fisher et al., 1 9 9 8 ) . Moreover, geological evidence indicates that the northern and southern margins of the Penny Ice Cap retreated to or behind their present positions by about 7 8 0 0 yr ago ( 7 0 0 0 I4C yr B.P.), although final separation from the Laurentide Ice Sheet probably postdated 5 0 0 0 yr ago ( 4 5 0 0 I4C yr B.P.; Dyke et al., 1 9 8 2 ) . Based on these data, we infer that the greater concentration and coarsening of microparticles deposited on the Penny Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 44 Ice Cap from the early to mid-/late Holocene resulted, at least partly, from increasing deflation of relatively proximal, glacially-derived dust sources. This change was apparently coincident with a phase of substantial recession and thinning of the Penny Ice Cap that facilitated the advection of wind-blown dust on its surface. The climatological conditions that led to increased enhanced eolian dust deflation were presumably linked to a regional- scale climatic deterioration in the eastern Canadian Arctic from the early to late Holocene, as discussed in the next section. The late Holocene portion of the P95 dust record shows fairly consistent values of N, M and nssCa2+ (Fig. m .lb). Although considerable centennial-scale variability is observed, the range of variations for each parameter remained constant, suggesting that the sources, transport pathways and/or rates of atmospheric dust deposition to the eastern Canadian Arctic were essentially unchanged over the last 2000 years. Several paleoenvironmental proxy records indicate that during this period, century-scale climatic fluctuations affected the hydrological balance in mid-latitude regions of the USA (Smiley, 1961; Bradbury et al., 1993; Fritz et al., 1994), China (Zhang, 1984), western Europe (Pfister et al., 1994) and former Soviet Eurasia (Gumilev, 1966). In some instances, for example in China from the 12th to mid- 13th centuries AD., these climatic variations affected eolian dust production and probably modified the regional to hemispheric atmospheric dust load (Zhang, 1984). The P95 dust record of the last 2000 years suggests that such perturbations did not significantly affect the transport and deposition of atmospheric dust to the eastern Canadian Arctic, at least not on a centennial time scale. This may indicate that microparticles deposited on the Penny Ice Cap during this period originated primarily from relatively proximal high-latitude sources, as previously discussed. Yet, ongoing studies suggest that on decadal or shorter time scales, the P95 dust record is sensitive to environmental factors such as changes in continental snow coverage, that can limit seasonal eolian dust production (e.g., Zdanowicz et al., 1998b), or the interannual variability of Northern Hemisphere atmospheric circulation, that controls the long-range transport of wind-blown dust from distant source regions to the Arctic. These relationships will be explored further in a separate, upcoming publication. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45 COMPARISON OF THE P95 AND GISP2 ICE CORE DUST RECORDS In order to establish how our record of eolian dust deposition from the Penny Ice Cap relates to Holocene climatic variability in the Arctic on a larger spatial scale, we compared time series of dust concentration (M) and nssCa2+ developed from the P95 and GISP2 ice cores using identical methods (Fig. m.3). Because central Greenland is isolated from proximal dust sources (hence from local influences), the microparticle record in the GISP2 core is assumed to reflect environmental changes that affected the atmospheric dust load on a broad, possibly hemispheric scale (Zielinski and Mershon, 1997). Time series of M and nssCa2+ in the GISP2 core were first averaged over 100-year intervals to make them comparable to the lower-resolution P95 record. Microparticle data between 1330-3350 and 8060-9430 yr ago in the GISP2 core were found to be inconsistent with the remainder of the record due to sampling problems and therefore were excluded from our analysis. Nevertheless, comparison of the GISP2 and P95 records reveals interesting differences. Whereas levels and trends of dust and nssCa2+ in both cores were comparable during the early Holocene, they began to diverge markedly ca 7000 to 6000 yr ago as dust levels in the P95 core rose and nssCa2+ in the GISP2 core declined. The declining nssCa2+ trend in the GISP2 record was interpreted as reflecting a decrease in the area of exposed continental shelves accompanying global sea level rise during the Holocene (O’Brien et a l, 1995). The lack of a comparable trend in the P95 nssCa2+ record suggests that terrigeneous Ca-bearing aerosols deposited on the Penny Ice Cap in the Holocene were not derived from continental shelf sediment sources, and were therefore unaffected by eustatic sea level rise. The departure of the P95 and GISP2 dust (M) records from the early to mid-/late Holocene reflects the trend towards increasing dust deposition on the Penny Ice Cap. This trend probably resulted in part from changes in the size and thickness of the ice cap itself, as discussed earlier. In addition, we postulate that eolian deflation around the Penny Ice Cap increased starting ca 7500 yr ago due to a transition towards more severe winter or winter-like climatic conditions (colder, drier and/or windier) in the eastern C a n a d i a n Arctic. Our inference is founded on modem field observations indicating that eolian activity in the Arctic periglacial environment is greatest in the fall and winter, when the absence of surface water flow, combined with gusty winds, facilitates deflation of soils and sediments (e.g., Lewkowicz and Young, 1991; McKenna-Neumann, 1993). The postulated gradual climatic deterioration in the eastern Canadian Arctic may have been driven in part by decreasing summer insolation during the Holocene (Fig. in.3). This is supported by 8I80 and melt % records from Greenland, Canadian and Siberian Arctic ice cores indicating that summer Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46 temperatures in the circum-Arctic declined from the early Holocene (ca. 8000 to 7000 yr ago) until ca. 400 to 100 yr ago (Koemer and Fisher, 1990; Kotlyakov et a l, 1991; Alley and Anandakrishnan, 1995; Johnsen etal., 1995). We suggest that a gradual pan-Holocene cooling at high northern latitudes led to the strengthening and eastward shift in the mean position of the upper level (700 mb) low pressure trough above the eastern Canadian Arctic, thereby promoting more frequent advection of northern cold, dry air m a s s e s over the Baffin Island region (Keen, 1980). This climatic change would have been favored by the gradual weakening of the large anticyclonic system stationed above the waning Laurentide Ice Sheet, allowing for a strengthening of more regional atmospheric circulation patterns. Our inference supports the view that following the final retreat of major continental ice sheets between 8000 and 6000 years ago, Holocene climatic conditions evolved towards increasing regional controls (O'Brien et al., 1995). The onset of the early to mid-/late Holocene divergence between the P95 and GISP2 dust (M) also coincides (within dating uncertainties) with proxy indications of a widespread, inter-hemispheric reorganization of atmospheric circulation patterns ca 8000 yr ago that presumably accompanied the retreat of continental ice sheets and ensuing stabilization of global sea levels (Stager and Mayewski, 1997). From the mid-Holocene to ca. 500 yr ago, nssCa2+ and dust levels in the P95 and GISP2 records fluctuated about their average without showing any significant trends (Fig. m.3). However in the last -600 years, nssCa2+ and dust concentrations in the GISP2 core increased markedly while levels in the P95 record remained comparatively stable. Increasing deposition of dust and sea salts in the last 600 years has also been documented in Antarctic ice cores (Mosley-Thompson and Thompson, 1982; Kreutz et al., 1997). Some of these features have been interpreted as reflecting a bipolar cooling and/or intensified atmospheric circulation during the Little Ice Age climatic interval (Kreutz et al., 1997). In the Canadian High Arctic, a variety of proxy climate records indicate that summer temperatures declined to their Holocene m i n i m a some 400 to 100 years ago, in phase with the approximate timing of latest Neoglacial glacier advances (Bradley, 1990; Overpeck et al., 1997). Decreased deposition of sea salts in the P95 core over the last -600 years, presumably reflecting an expansion of Baffin Bay-Labrador Sea ice cover, also provide some evidence for a cold interval beginning ca. AD 1400 (Grumet, 1997). By comparison, dust and nssCa2+ levels show no significant departures from late Holocene averages in the last 600 years, even when analyzed at decadal or higher resolution. Moreover, the size distribution of dust deposited on the Penny Ice Cap during the last 1000 years (not shown here) remained close to that observed in recent snow and ice. These findings may imply that late Holocene cooling in the eastern Canadian Arctic did not affect eolian activity Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 47 supplying dust to the Penny Ice Cap, or that some other factor(s), such as increased snow coverage, maintained the flux of dust to the Penny Ice Cap near its late Holocene mean. Indeed, large areas of lichen-free or sparsely vegetated upland terrain have been mapped on Baffin and Melville Islands, that presumably attest to increased snow accumulation and coverage during the coldest phase of the Little Ice Age, some 400-500 years ago (e.g., Locke and Locke, 1977; Edlund, 1985; Koemer 1980). CONCLUSIONS We developed and analyzed an -12,000 yr-long record of eolian dust deposition from an ice core drilled through the Penny Ice Cap, Baffin Island. Maximum dust levels are found in late glacial age ice, and were presumably deposited sometime between 12,000 to 25,000 yr ago. Lack of dating control beyond 11,600 yr ago in the P95 core does not allow a more precise timing estimation. The predominantly fine (d < 2 pm) size of particles in late glacial age ice suggests that they originated from sources further from the ice cap than at present The elevated concentration of these particles also indicate that they were emitted and transported from their sources by a more vigorous atmospheric circulation than at present. Dust concentration in the P95 core declined after the Pleistocene-Holocene transition (ca 11,600 yr ago) and remained comparatively low until ca 7500 yr ago. There followed a gradual increase leading to a mid- to late Holocene interval (from ca 5000 to present) with markedly higher dust levels. The early to mid-/late Holocene dust increase in the P95 core apparently resulted from a greater supply of relatively coarse dust (d>2 pm) to the Penny Ice Cap, as indicated by the distincdy bimodal size distribution of micro particles deposited during the mid- to late Holocene. Factors that contributed to this increase may include ( 1) a possible expansion of dust sources from postglacial land emergence in the Hudson Strait area; (2) recession and thinning of the Penny Ice Cap, thereby facilitating the advection of wind-blown dust onto the ice; and (3) a regional and possibly pan-Arctic climatic deterioration leading to colder, drier and windier conditions that promoted increased eolian dust deflation around the Penny Ice Cap. While dust and nssCa2+ levels in the P95 and GISP2 ice cores were comparable during the early Holocene, they began to diverge markedly after ca. 7500 yr ago as dust levels in the P95 core increased while nssCa2+ in the GISP2 core declined. We suggest that this divergence stems from a regionalization of Holocene climate accompanying the recession of continental ice sheets, thereby allowing for regional atmospheric circulation patterns in the Baffin Island region to dominate dust transport to and deposition on the Penny Ice Cap. Microparticle concentrations in the GISP2 core increased in the last 600 years, presumably Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48 reflecting intensified atmospheric circulation and enhanced dust transport to Greenland during the Little Ice Age. Dust levels in the P95 remained comparatively stable over the same period, suggesting that other factors (e.g., snow cover) contributed to keep dust deflation around and deposition on the Penny Ice Cap unchanged. Our f i n d i n g s further demonstrate how valuable records of regional-scale paleoenvironmental changes can be developed from the small circum-Arctic ice caps. Development of additional records will contribute to a better understanding of the spatio-temporal variability of paleoclimate in the Arctic which is needed to assess the sensitivity of high latitude regions to future climatic change. ACKNOWLEDGMENTS Support in the field was provided by the Polar Continental Shelf Project, Parks Canada and the communities of Iqaluit and Pangnirtung. M. Day and M. Leo helped with microparticle measurements, and S. Whitlow and N. Grumet performed the major ion analyses. This research was supported by the Office of Polar Programs, National Science Foundation. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. years) years) 8 2000 1997. years) and correlation correlation and years) et al,et 2000 Dating methods with Vostok ice core record. core ice Vostok with markers (last (last markers Annual layer counting by 8I80, Annual layer VS, time by volcanic control Age LLS. ECM, volcanic time markers (last (last markers time volcanic transition. Pleistocene-Holocene and Depth-age modeling based on spectral spectral on based modeling Depth-age by control age record; ECM of analysis yr ago. ago. yr 1998; GISP2 ice core: Meese core: GISP2 ice 1998; 1000 et al., et Resolution annual to 6000 yr ago. yr ago. 6000 annual to decadal yrto decadal ago. 11,550 biannual yrbiannual ago. to 11,300 subannual-annual to subannual-annual ~decadal (15-year) to 25,000 yrtoago. 25,000 (15-year) ~decadal 50 ., 1998; Grumet 1997; Grumet Grumet Grumet ., 1997; 1998; 3289 8021 2210 9374 11,550 et al et 25,000 Time scale Depth (m) (m) Depth (yr ago) Age 1510-2010 1371-1510 GISP2 ice core 0-719 719-1371 290-326 P95 ice core 0-40 40-290 aVS = visual stratigraphy; 8,80 = oxygen isotopes, ECM = electrical conductivity; LLS = laser light scattering (dust). scattering light =laser LLS conductivity; electrical 8,80 = ECM stratigraphy; isotopes, oxygen = = visual aVS Age in years before AD 2000 (yr ago) The depth-age relationship in the P95 ice core is undefined below 326 m (11,550 (11,550 m 326 below undefined is core the ice P95 in relationship depth-age The ago) (yr 2000 AD before years in Age P95 ice core: Fisher core: ice P95 Table III. 1. Time scale, resolution and dating methods for the P95 (Penny Ice Cap) and GISP2 (Greenland) ice cores. cores. ice (Greenland) GISP2 and Cap) (Penny Ice the P95 for methods dating and resolution Time scale, 1. Table III. Sources: the text. in discussed present agoyr to 25,000 interval the for described only is scale time GISP2 The yrago). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ) 6 . 1 (± 6.7 6.7 (±9.1) 19.5 19.5 (±2.6) 12.2 41.3 41.3 (±9.1) -24.1 -24.1 (±1.4) 6.7 (±6.1) 12.6 12.6 (±4.2) -24.0 (±1.1) 42.4 (±18.8) 272.7 (±151.2) 329.2 (±71.6) (7.5 (7.5 to kyrago) 1 present) to ago yr (50 7.3 7.3 (±7.5) 8.7 8.7 (±4.7) 20.2 (±6.7) 5.5 5.5 (±1.4) 18.1 18.1 (±9.2) -24.1 -24.1 (±1.2) 53.6 (±61.6) 73.5 73.5 (±66.7) 319.0 (±162.5) 374.1 (±79.8) Early Holocene Mid/Late Holocene Modern snow (11.6 (11.6 to 7.5 kyr ago) ) 2 . 11 (±1.7) 1.1 (±3.0) 3.4 (±1.5) 3.4 (±0.8) (± (±20.9) to kyr ago) 7.9 (±9.7) 2.0 (±1.3) 4.1 (±2.3) 3.7 (±0.8) 7.8 7.8 (±9.6) 2.1 (±1.4) 4.2 (±1.5) 3.9 (±0.5) -31.8 (±1.6) 12.2 39.4 (±30.1) 45.9 (±39.3) 11.6 Pre>Holocene 120.1 120.1 (±167.1) 167.4 167.4 (±176.5) 1 12 21.8 12 1 12 12 1.8 2 2 to to to to to to to to to 1 1 2 0.8 2 Size range (pm) range Size (> 0.8 0.8 0.8 yr. The pre-Holocene period corresponds the interval 326.3-330.8 m in the P95 ice core (Fig. III. 1). P95 core m correspondsthe Thein the interval 326.3-330.8 period ice III. yr. pre-Holocene (Fig. 3 ml*1) (%o) 3 6 ' 8 0 nssCa2+ (ppb) nssCa2+ N N (10 M (jig kg'1) M Parameter 1 = kyr 10 1 Table III.2. Mean microparticle concentration (N,M), nssCa2+ and 8180 for selected time periods in the P95 ice core record. record. core P95 ice the periods in time selected 8180 and for nssCa2+ (N,M), concentration microparticle Mean III.2. Table Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 X n/d n/d 0.25 0.8 6 0.12 0.23 0.09 yr. yr. 3 ) ) 8 . 1 Og n/a n/a (± (Um) (± 1.8 1.9 1.9 (±0.6) dy 2.3 2.3 (±2.1) 2.9 2.9 (±2.4) core n/d n/d n/a (Um) Range 0.8-4.5 0.8-4.5 0.8-4.5 0.8-4.5 2.8 (±1.9) M 59.1 62.3 153.7 0.8-4.5 4016.9 (Ug kg’1) (Ug = 0.01) for the log-normal curves are shown, curves shown, are the log-normal 0.01) = for n 28 12.5 82 n/a n/a 101 n/d n/d n/d n/d n/d n/d (%2' ) 8 . of dust for each time period were estimated by fitting log-normal log-normal by fitting estimated were period time each of dust for 1 (Jg) (ag) (± ( i (Um) dv 2.6 (±1.9) 6.7 6.7 (±1.8) 5.5 5.5 (±1.6) 2.5 (±1.9) 2.2 for selected time periods in the P95 and GISP2 ice core records. 1 = kyr core records. ice and GISP2 P95 in the time 10 periods 1 selected for 8-2 8-2 . . 2-12 2-12 P95 ice core GISP2 ice (Um) 0 0 (dv) Size range Size and standard deviation deviation standard and M 34.268.4 0.8-4.5 0.8-4.5 2.7 (±2.0) 165.1 0.8-4.5 1.0 (±1.5) (Ug kg'1) (Ug (dv) n 11 11 11 30 179.6 0.8-4.5 3.3 (±2.3) 36 147.6 yr.) 103 kyr = (1 to 7.5 kyrago 50 yr ago to present to ago yr 50 5.5 toago kyr5.5 5 8 E agoto kyr2.5 3 41 165.1 F P95 and GISP2 cores. The mode(s) The mode(s) cores. GISP2 and P95 Table III.3. Microparticle mass (M) and mode(s) and (M) mass Microparticle Table III.3. D the in concentration dust maximum of interval glacial late estimated the A is Interval 1. III. Figure on defined as are F) to (A Time periods AB to 25 12 C ago kyr kyrto ago 10.5 10 curves to the size distribution data (Fig. III.2). of criteria Chi-square goodness fit III.2). (Fig. data distribution size the curves to n/d = no data; n/a = not applicable. not = n/a data; =no n/d Period Duration Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 328 330 Depth (m) 6 0 - M9 kg- 5 6 7 103 yrago Fig. H U . (a) Dust (N, M), nssCa2+ and 8180 in the bottom 10 m of the P95 ice core, (b) Holocene time series of N, M, nssCa2+ and 8180 in the P95 and P96 (5180 only) ice cores. Dating error bars (top; ± la ) after Fisher et a l (1998). Shaded areas define time periods (A-F) analyzed on Fig. m.2. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 53 10 '- • 10* B 10 6 - co n o 5 E 1 1 0 5. p Poo °o ° - f i p h o 4 (euir1)pu|p//\p 104-J <5° o o \ o P95 . GISP2 1 0 * M "I I I'I t I If i 1111 i i i i i 11 ii i| i i i 111111* ■■ 10 1 0 6p m - 105- E a. p 5 . o p 1 0 4 -J 10 ' 11111 i i i i 11111 10 10 1 10 Diameter (pm) Fig. m.2. Mean size distribution of microparticles in the P95 and GISP2 ice cores for late glacial (A) and Holocene (B to F) time periods defined on Fig. m .l. Note different ordinate scale for period A. There are no GISP2 data for period E. The size distributions were fitted with log-normal curves, the parameters (dv, og) of which are given in Table m.3. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. without prohibited reproduction Further owner. copyright the of permission with Reproduced insolation curve (June-August) for the Northern Hemisphere from Berger (1979). Berger from Hemisphere Northern the for (June-August) curve insolation summer the mean is shown Also ELI. Fig. on as (top) bars error Dating records. dust lCX)-yrof series time between Holocene Comparison averaged .3. m Fig. were plotted on a log-scaled y-axis to facilitate comparison of the two ice core core ice two the of comparison facilitate to y-axis log-scaled a on plotted were M of series time The cores. ice GISP2 and nssCa2+P95 the and from (M) mass Wm-2 M9 kg' 10 950- - GISP2 nssCa2+ GISP2 GISP2 logMGISP2 P95 logM P95 ■—i—■—r — t 6 7 6 5 54 0 yrago 103 NH summer insolationNHsummer -10 _ _ 5 _ _15 _20 0 9 kg' M9 CHAPTER IV EFFECTS OF ATMOSPHERIC CIRCULATION AND SNOW COVER VARIABILITY ON EOLIAN DUST DEPOSITION IN THE EASTERN CANADIAN ARCTIC C.M. Zdanowicz, G.A. Zielinski, L.D. Meeker and C.P. Wake Climate Change Research Center, University of New Hampshire, Durham, NH 03824 USA D.A. Robinson Department of Geography, Rutgers University, Piscataway, NJ 08854 USA To be submitted for publication in Journal o f Climate. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 56 CHAPTER IV EFFECTS OF ATMOSPHERIC CIRCULATION AND SNOW COVER VARIABILITY ON EOLIAN DUST DEPOSITION IN THE EASTERN CANADIAN ARCTIC ABSTRACT We analyzed relationships between surface atmospheric circulation, snow cover variability and dust deposition in the Arctic as documented in an ice core (P95) from the Penny Ice Cap, Baffin Island. We found that interannual changes in the P95 dust record are strongly linked to modes of the Northern Hemisphere winter circulation with centers of action over Eurasia, the North Pacific Ocean, and western North America. Most prominently, over 50 % of the variance in the P95 dust record is explained by an inverse relationship with the intensity of the winter Siberian High. We speculate that this relationship has its origin in the interplay between the large scale Northern Hemisphere winter circulation and Eurasian surface air temperatures and snow cover. Specifically, weakening of the winter Siberian High may enhance the long-range export of dust from Eurasian source regions by hastening the spring retreat of seasonal snow cover and increasing the frequency of dust storms in the arid continental interior. In support of this hypothesis, we found that interannual changes in the P95 core are anticonelated (R= -0.38 to -0.46) with variations of spring and fall snow cover in Europe, central Eurasia, eastern China and western North America, reflecting snow cover control on the availability of dust for long-range eolian transport. These relationships account for an estimated 10-20 % of variance in the P95 dust record. Our findings demonstrate the potential for calibrating ice core proxy climate records with instrumental and historical data, and raise the possibility of using such records to document Northern Hemisphere winter circulation and snow cover variability beyond the period of satellite and weather station observations. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57 INTRODUCTION Atmospheric dust deposited in polar snow mainly consists of mineral particles emitted to the troposphere by eolian deflation of soils and sediments (Kumai, 1977; Briat et al., 1982; Gaudichet et al., 1986 Maggi, 1997). During transport to polar latitudes, mixing of air masses and particle removal by gravity and precipitation contribute to homogenize dust aerosols (Schiietz, 1989). Consequently, atmospheric dust deposited in polar snow may be considered as representative of the crustal background aerosol on a regional to hemispheric scale (Ram and Gayley, 1994; Hinkley et al., 1997). As such, long records (i.e. KP-years) of eolian dust deposition developed from polar ice cores can help document past changes in the atmospheric dust load and the dynamics of airborne dust emission, transport and deposition (Petit et al., 1981; Thompson and Mosley-Thompson, 1981; Hammer et al., 1985; Hansson, 1996; Steffensen, 1997; Zielinski and Mershon, 1997). The paleoclimatic interpretation of ice core dust records is complicated by the numerous factors that determine the concentration of dust measured in the ice. From any given source region, the flux of dust into the atmosphere depends on the relative aridity, the characteristics of land cover (vegetadon, snow and ice) and on climadc and meteorological factors that control the frequency and intensity of dust storms (Gillette, 1981; Goudie, 1983; Middleton et al., 1986; Littman, 1991). In remote polar areas, the atmospheric dust load is determined by the transit time of dust from source regions and its residence time aloft, the latter being controlled by wet/dry removal processes during transport (Hansson, 1996). These same processes also affect the relationship between measured ice core dust levels and airborne concentrations (e.g., Alley et al., 1995). As all the aforementioned factors may vary under different climatic regimes, proper interpretation of ice core dust records requires that the relative influence of these factors be evaluated. This may be accomplished by comparing dust records developed from high resolution ice cores against instrumental or historical records documenting changes in variables such as precipitation, atmospheric circulation or the frequency of wind storms in dust source regions. Here we investigate environmental controls on an ice core record of atmospheric dust deposition from the Penny Ice Cap, Arctic Canada. More specifically, we evaluate the influence of Northern Hemisphere winter circulation and snow cover variability on dust deposition on the Penny Ice Cap. Using multivariate statistical techniques, we identify specific relationships between time series of atmospheric dust fallout developed from the Penny Ice Cap ice core and Northern Hemisphere hydro-meteorological conditions as documented in observational and instrumental records. Ours is the first attempt at Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58 calibrating an ice core dust record against observational data. Thus, our results should guide further research efforts to improve the interpretation of such records. THE P95 ICE CORE DUST RECORD The proxy record of eolian dust deposition presented in this paper was developed from a 334-m long ice core (P95) drilled in 1995 through the Penny Ice Cap on Baffin Island, Arctic Canada (67°14’N, 65°43rW; 1980 m asl; Fig. 1.1). The P95 core was analyzed for electrical conductivity (ECM), melt %, oxygen isotopes (8180), insoluble microparticles and major glaciochemical species. The number concentration (N) of microparticles > 0.85 pm (equivalent spherical diameter) in the ice core was measured with an Elzone multichannel particle counter equipped with a 30 pm orifice (Zdanowicz et al., 1998a) and is reported here in units of particles ml *1 H2O. The depth-age scale for the P95 ice core was developed from a detailed analysis of the ECM record of seasonal glaciochemical variations (Fisher et al. 1998; Grumet et al., 1998). In the Holocene, independent age control was provided by the 1963 bomb test radioactivity peak and by volcanic SO 42' reference horizons of known age (e.g., the Icelandic eruption of Laki, AD 1783). Based on this time scale, the sampling resolution for the latest 100 years of the P95 dust record presented here- ranges from sub-annual (in the last few decades) to annual, with an estimated mean dating error of ± 2-3 years. For the purpose of our investigation, time series of N were uniformly resampled at a yearly resolution using the depth-age relationship developed for the P95 core. The resulting annually-resolved time series are hereafter designated by P95N. Detailed studies of microparticle distribution in snowpits suggest that, at least under modem conditions, the bulk of atmospheric dust in snow on the Penny Ice Cap is deposited during late winter/early spring and late summer/fall (Zdanowicz et al., 1998a). The predominantly fine microparticles (mean diameter = 2 pm) deposited during late winter/early spring are believed to represent dust from distant sources transported to the Arctic troposphere when winter snow cover and the polar front cut off more proximal sources (Heidam, 1984; Steffensen, 1988). In contrast, the slightly coarser microparticles (mean diameter = 3 pm) deposited in late summer/fall may represent dust from more proximal dust sources entrained over the Penny Ice Cap when the surrounding snow cover is at its minimal extent The bi-seasonal timing of dust deposition on the Penny Ice Cap may also reflect increased precipitation scavenging of airborne dust associated with frequent storm activity in the Baffin Bay region during the spring and fall months (Barry et al., 1973; Bradley and England, 1979; Grumet et al., 1998; Zdanowicz et al., 1998a). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 59 On interannuai to longer time scales, changes in dry or wet deposition rates may account for much of the variance of dust in polar ice cores (Hansson, 1996). The scarcity of long precipitation or accumulation records in the Canadian Arctic limits our ability to account for the possible effects of such changes on the P95 dust record. In this study, we are making the assumption that variations in the mean annual dust concentration measured in the P95 ice core are primarily a function of the atmospheric dust load above the Penny Ice Cap. To account for the spatial heterogeneity of dust fallout and the effects of post- depositional processes (e.g., meltwater percolation; Zdanowicz et al., 1998a), we applied different averaging methods to the P95 dust record. These methods are discussed in greater detail in the following sections. RELATIONSHIP TO NORTHERN HEMISPHERE ATMOSPHERIC CIRCULATION VARIABILITY In the first part of our study, we investigated how seasonal to interannuai changes in the large-scale surface atmospheric circulation of the Northern Hemisphere may affect dust deposition on the Penny Ice Cap. To do so, we first analyzed patterns of temporal covariance between the P95N record and Northern Hemisphere sea level pressure (SLP) over the last -100 years using an empirical orthogonal function (EOF) decomposition. In this method the combined time series are factored in a series of uncorrelated principal components, each representing a different mode of the temporal variability in the data set (e.g., Mayewski et al., 1993; Meeker etal., 1995). Eigenmodes that account for a large percentage of the total and factored variance in the time series are likely to represent some underlying physical linkage(s) among these variates. The SLP data set used in this analysis was prepared and made available by the National Center for Atmospheric Research (NCAR) and consists of mean monthly grid-point SLP values at every 5° of latitude and longitude from 20°N to the pole, beginning in 1899. These data were assembled from various sources (e.g., historical map series and Navy shipboard observations) and consequently contain some internal inconsistencies, as reviewed in detail by Trenberth and Paolino (1980). Using the NCAR data set, seasonally-averaged time series of SLP were developed that document variability in the main centers of action governing the mid- to high latitude Northern Hemisphere circulation, namely the Siberian, North American and Azores Highs, and the Icelandic and Aleutian Lows (Barry and Chorley, 1992). The SLP time series were prepared by averaging the mean monthly grid- point SLP data over the geographical areas defined in Table IV. 1. Because the Siberian Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60 High, Aleutian Low and North American High are solely or more strongly defined during the winter (DJF) months, we confined our EOF analysis to this season. Results reveal that together, the first four EOF eigenmodes account for over 85 % of the variance in the P95 dust record, as well as for all combined variables (Table IV. 1). Accordingly, we focus the ensuing discussion on these four modes of variability. The dominant eigenmode (EOF1) is characterized by a strong anticorrelation between the Icelandic Low and Azores High that accounts for over 60 % of the interannuai variance in the strength of these SLP centers. This result suggests that EOF1 is related to the North Atlantic Oscillation (NAO; Lamb and Peppier, 1987), which is the dominant mode of winter climatic variability in the Northern Hemisphere (Wallace and Gutzler, 1981). Changes in moisture transport over the North Atlantic region driven by the NAO are known to influence the composition of Arctic precipitation as revealed in Greenland ice cores (e.g., Barlow et al., 1993). However, the low percentage of variance in the time series of P95N (2 %) associated with our EOF1 indicates that the NAO exerts relatively little influence on interannuai changes in atmospheric dust transport to the Penny Ice Cap. In contrast, over 50 % of the variance in the time series of P95N is explained by the third EOF eigenmode, which is characterized by a strong inverse relationship between P95N and the strength of the winter Siberian High (Table IV.2). This anticorrelation also accounts for more than 50 % of the interannuai variance in the Siberian High. The strength of this relationship may be somewhat positively or negatively biased due to uncertainties in high-latitude SLP data over the Siberian region for the early part of the century. Although these effects are greatest at 80°N, they are also present at 70°N and further south in the Siberian sector (Trenberth and Paolino, 1980). However, a comparison of interannuai trends in P95N and the mean Siberian High SLP shows that the time series are anticorrelated over the entire period 1899- 1995 (Fig. IV. 1). Our EOF analysis also reveals anticorrelations between the P95 dust record and interannuai changes in the Aleutian Low (EOF4; 19 % of P95N variance explained) and North American High (EOF2; 16 % of P95N variance explained) (Table IV. 1). Together, these findings suggest that changes in atmospheric dust deposition on the Penny Ice Cap are strongly related, and possibly controlled, by modes of the Northern Hemisphere winter circulation with primary SLP centers of action in Eurasia, the North Pacific Ocean, and western North America. The dominant mode of winter circulation in the North Atlantic-western European sector, the NAO, appears to exert a comparatively benign influence on dust fallout in the eastern Canadian Arctic. To further define modes of the Northern Hemisphere winter circulation that may influence atmospheric dust transport to or deposition on, the Penny Ice Cap, we examined winter SLP anomalies associated with years of highest and lowest mean dust concentration Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 61 in the P95 record of the last-100 years. More specifically, we considered the composite (mean) pattern of seasonal SLP anomalies for 11 years representing the upper and lower 15th percentiles in the frequency distribution of P95N over the period AD 1899-1995. High and low SLP anomalies were defined as positive or negative pressure departures from the 100-year median value at each of the grid cell in the NCAR SLP data set. An advantage of this approach is that by considering multi-annual composite SLP anomalies, we compensate, to some extent, for the dating uncertainty in the annual layering in the P95 ice core record. Results show that for years of both highest and lowest dust levels in the P95 record, some of the strongest positive and negative winter SLP anomalies were geographically centered near the approximate mean position of the Siberian and North American Highs, and the Aleutian and Icelandic Lows (Fig. IV.2). A readily apparent feature of these SLP anomaly patterns is that years of highest dust concentration in the P95 record were characterized by an abnormally deep Aleutian Low and by relatively weak Siberian and North American Highs, whereas an opposite situation (weak Aleutian Low, strong Siberian and North American Highs) prevailed in years of lowest dust concentration. These opposing patterns are in agreement with findings from our EOF analysis, and therefore appear to support the existence of physical linkages between atmospheric dust transport to the eastern Canadian Arctic and interannual fluctuations in the strength of the Aleutian Low, Siberian High and North American High. We speculate that these linkages find their origin in the interplay between the large scale Northern Hemisphere winter circulation, surface air temperatures and continental snow cover. We expand on this hypothesis below. RELATIONSHIP TO NORTHERN HEMISPHERE SNOW COVER VARIABILITY In this second part of our study, we investigated the potential influence of snow cover variations on atmospheric dust loading in the Canadian Arctic by comparing the P95 ice core record of dust concentration with observational (satellite) data on interannual Northern Hemisphere snow cover variability over the last -30 years. Our approach is based on the hypothesis that in any given year, the relative areal extent and/or duration of seasonal snow coverage in dust source regions of the Northern Hemisphere may exert a limiting control on atmospheric dust export from these regions, i.e. greater snow cover can inhibit eolian dust production. Consequently, interannual to decadal changes in high-latitude atmospheric dust loading recorded in ice cores may be, in part, related to variations in snow coverage in dust source regions. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 62 To document Northern Hemisphere snow cover variability, we used a snow cover extent data set based on visible-band satellite imagery produced by the National Oceanic and Atmospheric Administration (NOAA) and standardized at Rutgers University (Robinson 1993; Robinson et al. 1993). These data consist of weekly charts of Northern Hemisphere snow cover extent for the period January 1971 to present, digitized on a gridded polar stereographic map with individual cells of 16,000-42,000 km2. From the geographical distribution of dust sources in the Northern Hemisphere (Goudie, 1983; Pye, 1987), we defined 10 regions within the latitudinal range of seasonal snow cover variation (Fig. IV.3). We then used the NOAA/Rutgers snow cover data set to produce seasonally averaged time series of winter (DJF), spring (MAM) and fall (SON) snow cover for these 10 regions over the period January 1971 through August 1995. Finally, cross-correlation analyses were performed between the P95N record and seasonal snow cover variations in each of the 10 Northern Hemisphere continental regions. To assess how the dating uncertainty of the P95 dust record may affect our results, we performed all correlation analyses at lags of zero and ± 1 year on the annually-resolved P95N and regional snow cover records, and on 3-yr smoothed time series (3-year running mean). We tested the significance of results by correlating each of the regional snow cover records with randomly-generated time series of microparticle concentrations (N) of equal size, mean and standard deviation as the actual P95N series. This procedure was repeated 1000 times and the mean (absolute) 95th percentile coefficient (IR0.95I = 0.30) was chosen as a critical value. Thus, correlations between the P95N and regional snow cover time series were considered significant only if the associated coefficients exceeded ±0.30. Results (Table IV.2 and Fig. IV.4) revealed that for the period 1971-1995, interannual changes in dust deposition on the Penny Ice Cap (as inferred from the P95N record) were significantly anticorrelated (R = -0.36 to -0.46) with spring snow cover variations in mid latitude Eurasia (regions 8 through 10) and central North America (region 3). Marginally significant anti-correlations (R = -0.31 to -0.36) were also found with fall snow cover in Europe (region 10) and central North America (region 3). For all other regions and seasons, correlation coefficients were generally weak (R ^ ±0.20) and did not exceed Ro.95 - Some anticorrelation coefficients increased when the analyses were repeated with 3- yr smoothed time series (results not shown here), but the correlation pattern between different regions or seasons remained unchanged, indicating that these results are robust on interannual time scales. All anticorrelation coefficients were found to increase markedly when the P95N time series lagged snow cover variations by a year (Table IV.2). However because the residence time of dust in the atmosphere rarely exceeds a few weeks (Jaenicke, 1980), we believe this result reflects the error in dating of the P95 record relative to Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 63 regional snow cover time series, rather than an actual time lag between snow cover and dust fallout fluctuations. Although these analyses were based on a relatively short period of record (24 years), results support our premise that snow cover variability may exert an important control on atmospheric dust loading in the Northern Hemisphere, at least on an interannual time scale. The similarity of relationships found with North America and Eurasia snow cover probably reflects the coherent interannual variability of snow cover over both continents, which is especially pronounced in the winter and spring (Gutzler and Rosen, 1992; Robinson et al., 1995). Interestingly, the strongest anticorrelation in Eurasia (R = -0.46) was obtained for region 9, which defines a broad area between 40° and 60° N encompassing the arid sectors of Mongolia and western China, as well as large parts of the Turkestan and Kazakhstan steppes. All of these areas are subject to Sequent dust storms (Zhirkov, 1964; Goudie, 1983; Middleton et al., 1986) and are within the latitudinal range of interannual snowline migration, implying that they are likely to experience important year-to-year seasonal changes in snow cover extent (Robinson et aL, 1995). In addition, the anticorrelation observed in region 10 (Europe) suggests that there may be some significant control of springtime snow coverage on eolian dust production in the agricultural sectors of the eastern European plain, and/or in the arid region between the Aral and Caspian seas. The fact that almost all significant anticorrelations were observed for the spring likely reflects the large interannual snow cover variability in the Northern Hemisphere during this season. For example, in the Great Plains of the western USA snow cover variability is most pronounced in the late winter and early spring months (Robinson et al., 1995). This may account for the anticorrelation found between the P95 dust record and winter snow cover in region 3 (central North America). The seasonality of dust outbreaks in the Northern Hemisphere may also contribute to the apparent relationship found between the P95 dust record and spring snow cover variations. In mid-continental North America and central Eurasia, the frequency of dust storms tends to peak in March-April as a result of relatively dry conditions, strong surface heating, the plowing of soils, the presence of an upper-level jet stream at mid-latitudes, and the frequent passage of frontal disturbances in the westerlies, which commonly trigger dust storms (Orgill and Sehmel, 1976; Goudie, 1983; Middleton etal., 1986; Pye, 1987; Littman, 1991). Dust outbreaks in the fall season, although not as frequent, are also common in the midwestem USA, central Eurasia and in China, often as a result of late summer plowing on cultivated soils. However, our findings suggest it is during the spring months (MAM) that snow cover exerts the greatest control on eolian dust emissions from mid-latitude continental regions. The timing of retreat of spring snow cover relative to seasonal meteorological conditions, for example the passage Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 64 of frontal depressions, may be particularly determinant on the frequency of dust storm occurrences, as it is in the dry lands of Kazakhstan and southwestern Siberia (Zhirkov, 1964). Moreover, aerosol measurements over the North Pacific Ocean, Alaska and the Canadian High Arctic indicate that the late winter-early spring peak of atmospheric dust loading coincides with the seasonal frequency maximum of dust outbreaks in central Eurasia and western China (Parrington et al'., 1983; Li and Winchester, 1989; Merrill et al., 1989; Barrie, 1995). These facts suggest that late winter-early spring is a favorable period for the long-range transport of Asian dust to the eastern Canadian Arctic. Although results from our analyses are supportive of a link between snow cover variability and atmospheric dust loading, we are aware that they are based on a time period when human activities may have considerably affected the global dust cycle. In the southern Great Plains of the USA for example, overplowing and mismanagement of soils by pioneer agriculturists, combined with a succession of drought years, led to a dramatic increase in dust storm frequency during the 1930s Dust Bowl era (Middleton et al., 1986). A similar increase in dust storm occurrence was also experienced in the south-central former Soviet Union as a result of large-scale deforestation and agricultural development during the 1950s (Klimenko and Moscaleva, 1979). Evidence for such human-induced perturbations during the 19th and 20th centuries were found in Greenland ice core dust records (Holdsworth et al., 1996), indicating that they affected atmospheric dust loading at high northern latitudes. However, we believe that the snow cover-atmospheric dustiness relationships inferred by our analysis are largely independent of these perturbations because they are the result of naturally-occurring hydrological and meteorological conditions. More specifically, they may find their origin in a natural linkage with the Northern Hemisphere winter atmospheric circulation, continental surface temperatures and snow cover, as discussed hereafter. DISCUSSION The extent and duration of seasonal snow cover affects the planetary albedo and diabatic heat exchange between the surface and atmosphere, thereby influencing tropospheric temperatures, pressure fields and atmospheric circulation patterns (Foster et al., 1983; Karl etal., 1993; Groisman etal., 1994; Barnett etal., 1988; Gutzler and Rosen, 1992; Cohen and Entekhabi, 1999). Since the late 1980s, the Northern Hemisphere continents are experiencing the longest period of below-average snow coverage of the last 30 years (Robinson etal., 1995). This snow cover deficit was most pronounced in spring and may have contributed largely, through land-atmosphere albedo feedbacks, to the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65 observed rise in continental spring surface air temperatures in the past 20 years (Groisman et al., 1994; Robinson et al., 1995). The period from the late 1980s to the present also witnessed a general decline in intensity of the Siberian High associated with more frequent, warmer than average winters in north-central Eurasia (e.g., Brown, 1993; Rogers and Mosley-Thompson, 1995). It is speculated that opposing trends in Northern Hemisphere snow cover and Eurasian winter surface air temperatures over the last two decades may be parallel manifestations of an anomalous tropospheric planetary-wave pattern that developed in response to a general strengthening in the polar vortex (Thompson and Wallace, 1998). A suspected consequence was to increase the frequency of intrusion of Atlantic cyclones and the advection of relatively mild maritime air into the interior of the Eurasian continent, thereby leading to warmer than average winters, a weaker Siberian anticyclone and an early retreat of spring snow cover extent (Rogers and Mosley-Thompson, 1995; Thompson and Wallace, 1998). This combination of circumstances may have contributed in several ways to an apparent recent increase in atmospheric dust fallout in the Canadian Arctic region, beginning ca. 1990, seen in the P95 dust record (Fig. IV. 1). Firstly, a weakened Siberian High would lead to a more frequent passage of cyclonic waves and frontal disturbances over Eurasia, a leading meteorological factor for initiating dust storms in the arid continental interior (Goudie, 1983; Middleton et al., 1986). In particular, the formation of steep baroclinic gradients between cold, dry air to the north and warm, moist air masses advected from the south with the Asian monsoon was observed to trigger vigorous dust storms (e.g., Rahn et al., 1981). A weakened Siberian High might also lead to greater convective air motion in the lower troposphere over dark (low albedo) snow-free terrain, thereby carrying dust above the planetary boundary layer. Secondly, early retreat of the seasonal snow cover would increase the potential for eolian dust mobilization in late winter and spring. Together, these factors could have increased the atmospheric export of dust from Eurasian sources, and, with a more vigorous upper-level polar vortex, its long-range transport to the Arctic region. The circumstances described above suggest plausible physical linkages that could account for the apparent relationships, revealed in our analyses, between large-scale anomalies in the Northern Hemisphere winter SLP field, Eurasian continental snow cover, and the interannual variability of atmospheric dust fallout over the eastern Canadian Arctic. Declining trends in the strength of the winter Siberian High (Brown, 1993) and in Eurasian snow cover (Robinson et al., 1995) suggest that winter and spring conditions favoring enhanced long-range transport of Eurasian dust to the Arctic may have become more prominent in recent decades. This may account, to some extent, for the anticorrelation found between our P95 dust record and Northern Hemisphere spring snow cover Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 66 variations over the period 1971-1995. However, our analyses of SLP data were based on a considerably longer period of record (1899-1995). Relationships between Northern Hemisphere winter circulation and atmospheric dust fallout in the Arctic inferred from these analyses are therefore less likely to be biased by recent decadal trends, and are probably robust over longer time scales. It is comparatively more difficult to speculate about the control exerted by the winter atmospheric circulation and snow cover on atmospheric dust export from North American source regions. Results from our EOF analysis and examination of composite winter SLP anomaly patterns indicate that years of abnormally high dust deposition in the P95 ice core record for 1899-1995 were typically associated with a deeper (stronger) than normal Aleutian Low and weaker than normal North American High. An opposite situation prevailed in years of low dust deposition, with a shallower (weaker) Aleutian Low and stronger North American High. Either of these situations would weaken the meridional flow over western North America and, conversely, strengthen the zonal westerlies, thereby increasing the advection of moist air from the Pacific Ocean over the continental interior. However, the most arid regions in North America are located in the southwestern United States, and eolian dust emissions from these regions are generally controlled by meteorological conditions prevailing in the subtropical eastern Pacific and Gulf of Mexico (Orgill and Sehmel, 1976; Middleton et al., 1986). As yet, we can not propose a simple explanation on how the contrasting modes and patterns of winter Northern Hemisphere circulation identified in our analyses may affect atmospheric dust transport from North American sources to the eastern Canadian Arctic region. CONCLUSIONS We evaluated the influence of Northern Hemisphere atmospheric circulation and snow cover variability on an ice core record of atmospheric dust deposition from the Penny Ice Cap, Baffin Island. Multivariate (EOF) analysis of the P95 dust record and 100-year time series of seasonal sea level pressure (SLP) variations reveals strong linkages among some of the dominant SLP centers of action of the Northern Hemisphere winter circulation and dust deposition on the Penny Ice Cap. Most prominently, over 50 % of the variance in the P95 dust record is explained by an inverse relationship with the strength of the winter Siberian High. Together, changes in the North American High and Aleutian Low account for an additional 35 % of variance in the record. Our findings suggest that interannual changes in atmospheric dust transport to the eastern Canadian Arctic are controlled by modes of the Northern Hemisphere winter circulation with centers of action over Eurasia, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 67 the North Pacific Ocean, and western North America. This is supported by the pattern of seasonal SLP anomalies associated with years of abnormally high and low dust levels in the P95 ice core. We speculate that the apparent relationship between the P95 dust record and the Siberian High finds its origin in the interplay between the large scale Northern Hemisphere winter circulation and Eurasian surface air temperatures and snow cover. Specifically, weakening of the winter Siberian High may allow for an early retreat of spring snow cover and to a more frequent passage of cyclonic waves and frontal disturbances over Eurasia. Together, these factors would lead to more frequent dust outbreaks in the arid, interior continental regions, thereby increasing the flux of dust to the troposphere that may be transported in the westerlies to the Arctic. However we cannot as yet propose a comparable explanation for dust transport from North American sources. On inter-annual to multi-annual time scales, changes in the amount of dust deposited in the P95 core are also significantly anticorrelated with variations in spring, and to a lesser extent fall, snow cover extent in the mid-latitude interior regions of Eurasia and North America. These findings are attributed to the high frequency of dust outbreaks in arid interior regions of the Northern Hemisphere during spring and autumn, and the limiting effect of snow cover on eolian dust deflation during these seasons (primarily in the spring). We estimate that changes in Northern Hemisphere snow cover extent may account for 10 to 20 % of the variability of dust deposition on the Penny Ice Cap at interannual to multi annual time scales. Results of our investigation demonstrate the potential for calibrating ice core proxy climate records through comparison with instrumental and historical records of specific environmental and climatic variables. To verify and progress beyond our preliminary findings, future efforts should be directed at developing additional, more highly-resolved Northern Hemisphere ice core dust records from other circum-Arctic sites and calibrating them against available instrumental climatological data sets. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 68 ACKNOWLEDGMENTS We thank our colleagues at the Geological Survey of Canada, Eric Blake and Mike Gerasimoff of Icefield Instruments Inc. (Whitehorse, Y.T.), the Polar Continental Shelf Project, Parks Canada and the communities of Iqaluit and Pangnirtung for support in the field operations. Thanks are due to M. Day and M. Leo (University of New Hampshire) for help with the microparticle analyses. I. Pittalwala (University of New Hampshire) prepared the SLP time series, and R. Cermak (Rutgers University) assisted in the preparation of the satellite snow cover data. The manuscript benefited from reviews by P. Mayewski and R. Koemer. This research was supported by the National Science Foundation through grants OPP-9322045 to G. Zielinski, ATM-9314721 and SBR- 930786 to D. Robinson, and by the National Space and Aeronautics Administration through grant NAGW-3586 to D. Robinson. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 69 EOF mode Percent total variance explained 31 21 19 13 Factored variance ______Total P95N 2 (+) 16 (-) 52 (-) 19 (+) 89 Azores H [25-40°N; 0-40°W] 63 (-) 12 (-) 1 (+) 6 (-) 82 N. American H [40-70°N; 90-120°W] 4 (-) 66 (+) 3 (-) 2 (-) 75 Siberian H [35-50°N; 75-125°W] 12 (+) 3 (-) 55 (+) 12 (+) 82 Aleutian L [35-65°N; 140°W-150°E] 31 (-) 22 (+) 1 (+) 41 (-) 95 Icelandic L [60-75°N; 0-40°W] 76 (+) 10 (+) 1 (-) 0 (-) 87 Table IV. 1. Principal EOF modes of interannual variability in the P95 ice core dust record (P95N) and dominant high (H) and low (L) sea level pressure centers during the Northern Hemisphere winter for the period AD 1899-1995. Signs in parentheses indicate if any pair of factors covary together (identical signs) or in opposition (opposite signs). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 70 Season Lag Region 1 2 3 4 5 6 7 8 9 10 Winter 1 0.24 ao6 024 007 003 013 0.16 O il 0.18 0.19 (DJF) 0 -0.21 -ao7 0.25 -0.06 -0.06 003 o o t -0.17 0.06 0.23 -1 -0.07 -0.07 0.05 -0.07 -0.05 -006 -0.05 -013 0.12 0.18 Spring 1 0.11 -aos - a n -0.04 -0.03 -0.10 -009 -0.16 -0.26 -0.25 (MAM) 0 -aoi -a 13 -0.36 -0.14 -Oil -0.20 -020 -028 •0.38 -0.30 -1 -a 17 -a 19 -0.38 -0.20 -0.17 -025 -025 -0.39 -0.46 -0.46 Fall 1 -0.07 -ao 2 -006 -0.02 -0.01 -0.06 -007 -0.12 -030 -028 (SON) 0 -0.19 -a 12 0.06 -0.12 -O10 -0.15 -016 -0.20 -0.04 -009 -1 -0.26 -a is -0.36 -0.19 -0.16 -0.22 -022 -0.15 0.20 -0.31 Table IV.2. Correlation (R) between dust concentration in the P95 ice core and seasonal snow cover extent in 10 regions of the Northern Hemisphere for the period 1971 to 1995. Correlation coefficients in bold exceed the critical value IR 0 .95 I = 30. Lag is defined with respect to the snow cover time series. Regions are as defined on Fig. IV.3. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 71 -1034 .1030 m m in ii in in u in ii in u iii mu in mu uni ii in in ii in mil ii itmi n iii n in n iii hi ii hi 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year AD Fig. IV. 1. Comparison of annual and 5-year averaged (bold line) time series of dust concentration in the P95 ice core (P95N; top) with mean sea-level pressure of the winter Siberian High (SH; middle), 1900-1995. Also shown are time series of the third principal mode of covariance of P95N and Northern Hemisphere winter sea-level pressure (EOF3; bottom). Note inverted ordinate scale of P95N to facilitate comparisons. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and and (c) Composite maps 90?E Low Dust Low (b) (b) 0° 180' 90.°E High Dust High °-j 180 ° 0 Approximate geographical boundaries of boundaries geographical Approximate the Azores High North (SH), (AH), Siberian High 90°W 90°W 90°W 90°W (a) ah 21 A of Northern Hemisphere winter sea level pressure anomalies associated with years ofextreme high (b) and low (c) American American High (NAH), Aleutian Low (AL) and Icelandic Low (IL) used in this study, dust concentration in the P95 anomalies concentration dust the core. P95 at right. in in scale barmb, Pressure ice Fig. IV.2. IV.2. Fig. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73 WINTER 90°E SPRING 90°E (DJF) (MAM) I80a 0 ° I80c SUMMER AUTUMN (JJA) (SON) 180°- 0°I80- 90 W 90bW Fig. IV.3. Seasonal mean snow cover extent in the Northern Hemisphere (shaded areas) for 1971-1995. Based on data from NOAA/Rutgers University (Robinson 1993). Also shown are the boundaries defining continental regions (labeled 1 to 10) used to analyze snow cover variability, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 4 P95N ® 35 Q-25 NH spring snow cover variations h-2 • - A -1 _ - 0 . 1 v ^ I -2 (1) western North America: R = -0.38 3CO -1 o £ o 0 - o < 1 © 2 tw 3 (K\ Pastam nhina- R — -f) 30 © o> -1 I 0 0 + 1 1 m -2 (9) Central Eurasia: R = -0.46 . 2 -1 - 0 1 + 2 3 (10) Europe: R = -0.46 1970 1975 1985 1990 19951980 Year AD Fig. IV.4. Comparison between annual and 3-year averaged (bold) time series of (a) dust concentration in the P95 ice core (P95N) and (b) spring (MAM) snow cover extent in four regions of the Northern Hemisphere for 1971-1995. Snow cover regions (numbers in parentheses) are as defined on Fig. IV.3. The snow cover time series were normalized to make inter-comparisons easier. Also note inverted ordinate scale to facilitate comparison with the P95 dust record. Correlation coefficients with the P95 record (R; lag = -1 year) are shown. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER V RELATIONSHIP BETWEEN SOLUBLE AND INSOLUBLE ARCTIC AEROSOLS IN CONTRASTING CLIMATE REGIMES AS REVEALED IN ICE CORES C.M. Zdanowicz, P.A. Mayewski, G.A. Zielinski and C.P. Wake Climate Change Research Center, University of New Hampshire, Durham, NH 03824 To be submitted fo r publication in Journal of Geophysical Research. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 76 CHAPTER V RELATIONSHIP BETWEEN SOLUBLE AND INSOLUBLE ARCTIC AEROSOLS IN CONTRASTING CLIMATIC REGIMES AS REVEALED IN ICE CORES ABSTRACT We use an empirical orthogonal function (EOF) analysis to investigate patterns of temporal covariance among insoluble microparticles (dust) and major ions deposited in ice cores from Greenland (GISP2) and the eastern Canadian Arctic (P95) under glacial and interglacial climatic conditions. Dust and major ions covaried strongly in the GISP2 core during the late glacial period when the polar atmosphere was well-mixed, but were uncorrelated in both the GISP2 and P95 cores during the Holocene due to a regionalization of climate and atmospheric circulation patterns. As a result of this regionalization, changes in the composition of the aerosol composition above Greenland and the eastern Canadian Arctic became increasingly controlled by distinct sources or regional environmental factors (i.e., meteorological or other). Our EOF analysis also identifies distinctive associations among microparticles and/or major ions in the GISP2 and P95 ice cores representing covariance patterns associated with certain aerosols types (e.g., gas-derived SO 42*, N 0 3 " and NH 4+), or with source-specific air masses transported in the Arctic (e.g., K+ and NH4+ from forest fire emissions). These patterns differ in the GISP2 and P95 Holocene records, providing further evidence of increased regional-scale climatic and atmospheric variability during interglacial periods. Our work shows that EOF analysis applied to multivariate ice core records can reveal time-varying physical relationships among insoluble and soluble aerosols that characterize different states (glacial / interglacial) of the climate. Applied to circum-Arctic ice cores, this investigative method can lead to a better understanding of atmospheric and climate dynamics at high northern latitudes needed to assess the sensitivity of the Arctic region to human-driven climatic change. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 77 INTRODUCTION Climate observations and simulations suggest that environmental changes in the Arctic driven by rising atmospheric CO, levels (e.g., the accelerated melting of ice caps) may severely impact the climate of temperate regions through perturbations in the oceanic and atmospheric energy exchange between high and low latitudes. Accordingly, there is a need to investigate the nature of, and responses to, past climatic changes at high northern latitudes. This can be accomplished through the study of polar ice cores which document past changes in climatic parameters (e.g., temperature, atmospheric circulation), as well as in the gaseous, soluble and insoluble aerosol composition of the atmosphere (Hammer, 1982; Oeschger and Langway, 1989; Mayewski et al., 1992; Boutron, 1995). Two commonly measured parameters in ice cores are insoluble microparticles and major ionic species. Ice core microparticles can be used to evaluate past changes in the atmospheric dust load and the dynamics of airborne dust transport and deposition (Petit et al., 1981; Thompson and Mosley-Thompson, 1981; Hammer etal., 1985; Hansson, 1994; Steffensen, 1997; Zielinski and Mershon, 1997). They can also provide valuable information on the radiative forcing potential of mineral dust aerosols (e.g., Tegen et al., 1996). The aerosols and gases which contribute to the ionic burden in polar ice originate from multiple sources that include crustal dust (Al24*, Ca+, K+, Mg2+, Mn2+), sea spray (Cl~, K+, Mg2+, Na+, S042-), biogenic and biomass burning emissions (MSA, K+, NH4+ N 03', S042-) volcanic emissions (Cl“, F", S042-), and upper atmosphere photochemical reactions (N 03~) (Mayewski et al., 1992; Legrand and Mayewski, 1997). Long (up to lC^-year) ice core records of these species are used to document past changes in components of the climate system such as atmospheric circulation, biogeochemical cycles, or paleovolcanism that affected their concentration in the atmosphere and deposition in snow (e.g., Mayewski et al., 1994; Zielinski et al., 1996a; Meeker et al., 1997). Recently, specially-adapted statistical techniques have been developed to assist in the interpretation of ice core paleoclimate records (Meeker et al., 1995). In particular, an empirical orthogonal function (EOF) analysis allows for multivariate time series (e.g., major ions in ice cores) to be factored into a series of independent linear approximations or eigenmodes, each describing some portion of the temporal variance in the data (Peixoto and Oort, 1992). Eigenmodes that account for a large percentage of total variance are likely to represent some underlying physical relationship among the variables. In previous studies, EOF analysis was used to define temporal relationships among glaciochemical species (e.g., Mayewski et al., 1993) or to identify spatial patterns of covariance among climate proxies such as 5180 measured in multiple ice cores (e.g., Fisher et al., 1996). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 8 Here we use an EOF analysis to investigate the relationship between soluble and insoluble aerosols deposited in the Arctic under glacial (late Pleistocene) and interglacial (Holocene) climatic conditions. We apply our analysis to combined time series of major ions and size-resolved insoluble microparticles measured in two ice cores, one drilled from Greenland (Greenland Ice Sheet Project Two (GISP2) core) and the other from the Penny Ice Cap, Baffin Island, in the eastern Canadian Arctic (P95 core) (Fig. 1.1). Ours is the first attempt made to link these two commonly measured ice-core parameters to obtain a more complete understanding of past atmospheric and climate dynamics. Because our approach focuses on the covariance of microparticles and major ions rather than on their separate variance, it may expand significantly on the level of paleoclimatic interpretation obtainable from ice cores. Also, the GISP2 and P95 ice core records register changes in climate and atmospheric composition on hemispheric and regional scales, respectively (Mayewski et al., 1994; Grumet, 1997). Hence, comparison between these records can improve our knowledge of both the spatial and temporal variability of climate in the Arctic. METHODS The GISP2 core was drilled between 1989 and 1993 at Summit, Greenland (72°N; 38°W; 3208 m asl), and the P95 core drilled in 1995 from the Penny Ice Cap, Baffin Island, eastern Canadian Arctic (67°N; 65°W; 1980 m asl) (Fig. 1.1). Both cores were sampled at high resolution using clean techniques to prevent contamination (Mayewski et al. 1990; Grumet, 1997). All samples were analyzed for insoluble microparticles and major ion chemistry (Na+, Ca2+, Mg2+, K+, Cl* SC> 42' , NO3- and NH 4+) using comparable techniques. The concentration of microparticles was determined for the size range 0.65-12 pm on an Elzone 280PC multichannel particle counter with a precision of < 10 % following procedures described in Zielinski and Mershon (1997) and Zdanowicz et al. (1998a). Major ions in the GISP2 and P95 ice cores were measured on a Dionex 4000i ion chromatograph with an average precision of 8 % for K+ and < 5 % for other species (Buck et al., 1992). The GISP2 core was annually dated back to ~110,000 years ago (y.a., with respect to AD 2000) by identifying and counting annual layers using multiple physical and chemical parameters including visual stratigraphy, electrical conductivity (ECM), laser light scattering of dust, and SlsO (Meese et al, 1997). Dating control was provided by volcanic time markers for the most recent 2 0 0 0 years, and by comparison with the independently- dated Vostok ice core from East Antarctica (Bender et al., 1994; Zielinski, 1995). Error estimates are within 1-5% of assigned ages for most of the Holocene, and within 5-10 % for the remainder of the record (Meese et al., 1997). The P95 core was dated by spectral Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 79 analysis of the ECM record which tracks seasonal variations in ice chemistry (Fisher et al. 1998; Grumet et al., 1998). Time control was based on volcanic time markers (e.g., Laki; A.D. 1783) and the Holocene-Younger Dryas transition (326 m) dated at 11,550 ± 70 y.a. in Greenland ice core records (Johnsen et al., 1992; Alley et al, 1993). Age estimates for the volcanic timelines gave errors < 15 % over the last -2000 years, but dating uncertainties may be greater (10-20 %) in the early to mid-Holocene. We applied our EOF analysis to combined microparticle and major ion time series representing late glacial and interglacial conditions in the GISP2 core, and interglacial conditions in the GISP2 and P95 ice cores. The interval 25,000-15,000 y.a. was used as an example of glacial conditions in the GISP2 core. On the basis of various proxies, this interval corresponds to the most climatically severe period (i.e., coldest, driest and windiest) of the last glacial cycle (e.g., Johnsen eta l, 1992; Petit et al, 1981; Mayewski et a l, 1994). Interglacial conditions were considered to begin ca 8000 y.a., when climatic boundary conditions (ice cover, sea level) reached near-present values (Kutzbach and Ruddiman, 1993). The younger limit of the Holocene interval was set at 3350 y.a. because of a gap in the GISP2 microparticle record between 1328 and 3350 y.a. However on the basis of other proxy climatic indicators in the GISP2 ice core, we regard the period 8000- 3350 y.a. as adequately representative of mean Holocene conditions (Meese et al., 1994; O'Brien et a l, 1995; Stuiver et al, 1995). To ensure comparability, time series of microparticles and major ions from both the GISP2 and P95 cores were resampled at a constant 10-year resolution before applying the EOF analysis. The GISP2 and P95 microparticle data were originally acquired in 64 individual channels over the size range 0.65-12 pm. On the basis of comparisons between time series for different microparticle sizes, we found that we could conveniently summarize these data by summing microparticle concentrations in six size groups, as defined in Table V.l. Na+, C1-, Ca2+, Mg2+, K+ and SO 42* in the GISP2 and P95 core were apportioned into sea-salt (ss) and non-sea salt (= excess; ex) fractions using the average sea water ratio of these elements (Holland, 1978). Estimated contributions from marine source species showed that most Na+ measured in the GISP2 ice core is derived from sea salt (Mayewski et al, 1994; O’Brien et al., 1995). Likewise, we found Na+ to be the most limiting species (in 70 % of cases) for sea-salt calculations in the P95 ice core. Accordingly, ssNa+ was used to represent all other sea-salt derived ionic species in both the GISP2 and P95 cores. The variables in our EOF analyses included microparticle concentrations for the six size groups defined in Table V.l, and ssNa+, exCa2+, exK+, exMg2+, exCl*, exS 0 4 2, total NO 3- and NH4+. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80 RESULTS AND DISCUSSION Results of our EOF analyses of the GISP2 and P95 ice core records are summarized in Tables V. 1-V.3 . Only those eigenmodes that account for > 10 % of variance in at least one variable (microparticles or major ion species) are shown. Together, these modes account for most of the variance in the GISP2 late glacial record (94 %) and in the GISP2 and P95 interglacial records (> 80 %). The variance explained by other modes is < 2 % in both cases. In any single eigenmode, two parameters covary together if their respective signs are identical, and the strength of their covariance is proportional to the variance explained for each one. A strong covariance among ionic species and microparticles implies that they were deposited at the ice core site from the same air mass, or that their source emissions varied in response to the same controlling environmental factors). Conversely, opposite signs would indicate that these same impurities were delivered by competing atmospheric circulation patterns, or that their respective source emissions varied under opposing environmental conditions. Also, an eigenmode that accounts for a large amount of variance of two particular ions and/or microparticle size groups may identify an important physical linkage between these parameters, even if this mode only represents a small portion of overall variance in the data. Late Glacial Conditions: 25,000 to 15,000 y.a. 78 % of total variance in the GISP2 late glacial record is explained by EOF #1 (Table V.l). In this mode all microparticles and major ions covary together, suggesting transport to Greenland in the same atmospheric circulation system and deposition from the same well-mixed air mass. Using EOF analysis, Mayewski et al. (1993, 1994) found a strong covariance among major ions in the GISP2 glacial record. They attributed this to an expansion and intensification of the polar vortex, thereby enhancing the transport and mixing of marine and continental aerosols above Greenland. Our EOF analysis provides further support for this interpretation, and indicates that changes in the atmospheric concentration of insoluble and soluble Arctic aerosols were closely coupled under glacial climatic conditions. The remarkably high percentage of variance for all microparticle sizes (81-90 %) explained by EOF #1 denotes a strong covariance among these particles which we attribute to the vigor of the Northern Hemisphere atmospheric circulation during the glacial period. Strong surface winds blowing over continental regions mobilized large amounts of both fine and coarse dust particles, and the intensified upper level circulation ensured rapid Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81 transport of this dust to the polar regions, thereby limiting gravitational settling and precipitation scavenging during transit (Petit et al., 1981; Zielinski and Mershon, 1997). As a result, the flux of atmospheric dust in Greenland was increased over a broad spectrum of sizes, thereby accounting for their covariance in the GISP2 late glacial record (Alley et aL, 1995). In addition to microparticles, EOF #1 also identifies a strong covariance among ssNa+, exCa2+, exMg2+, exSO^-and N0 3 -. Excess Ca2+ and Mg2+ in the GISP2 core are primarily of crustal origin (Mayewski et al, 1992, 1994; O’Brien et a l, 1995). NO 3' and exS0 4 2-, on the other hand, have several potential sources. Sources of exS 0 4 2- include volcanic eruptions, marine or continental biogenic emissions, whereas N 0 3 ~ may originate from biomass burning, soil exhalations and upper atmosphere photochemical reactions. (Herron, 1982; Legrand and Kirchner, 1990; Mayewski et al., 1990; Yang et al., 1995). The covariance of exS 0 4 2- and NOV with continental dust and sea salts suggests that they were deposited in Greenland snow by scavenging on dust or sea salt particles or in the form of salts (e.g., CaS 0 4 ) formed by heterogeneous phase reactions with these particles (Busenberg and Langway, 1979; Wolff, 1984; Dibb e ta l, 1994; Sequeira, 1993). The lower percentage variance for NH 4+ (54 %) and exCl* (53 %) explained by EOF #1 indicate that other, distinct sources or air masses contributed to the presence of these species in the GISP2 core, such that their temporal variation was uncorrelated with that of the primary aerosols (sea salt and dust-related species). The second EOF mode in the GISP2 record identifies a correlation between exS 0 4 2- and NH 4* that explains 13 and 18 % of the variance in these species, respectively. In contrast to EOF #1, this mode only accounts for a marginal portion of the variance (< 10 %) of microparticles. Much of the NH 4+and exS 0 4 2- aerosols deposited in Greenland prior to this century were from terrestrial and marine biogenic emissions (Mayewski et al., 1997; Meeker e ta l, 1997). In the late glacial period, the main sources of NH 4+were probably in the mid- to low latitudes where most of the terrestrial biota was concentrated and the climate more temperate. Biogenic exS 0 4 2-could have been emitted at both low and high latitudes, but its association with NH 4+ in EOF #2 indicates that both species were transported to Greenland together, possibly in the form of salts such as (NH 4)2S0 4 (Dibb et al., 1994). These considerations suggest that the GISP2 EOF #2 describes temporal changes in the meridional transport of air masses carrying NH 4+ (and associated exS 0 4 2-) from mid- to low latitude source regions to Greenland. Furthermore, the low variance for microparticles explained by EOF #2 suggests that the terrestrial regions that contributed the NH4+ and/or exS 0 4 2- in this mode were not strong dust sources, hence they were probably experiencing a moist climate during the late glacial period. Our interpretation is comparable Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 82 to that proposed by Mayewski etal., (1997) for the second principal EOF component in the GISP2 glaciochemical record of the last 1 10,000 years. The remaining EOF modes in Table V.l identify variability in the time series of individual glaciochemical species in the GISP2 ice core, namely NH 4+ (EOF #3), exCl" (EOF #4) and exMg2+ (EOF #5). None of these modes show any significant amount of covariance among major ions or microparticles. It is likely that some of these eigenmodes are mathematical constructions of the EOF analysis that compensate for the variance in the GISP2 glaciochemical time series of individual species that is unaccounted for by EOF #1 and 2. Hence, some these EOFs may have no real physical meaning while others may identify patterns of temporal variability that are specific to a particular major ion species. However at present, we cannot identify these patterns. Interglacial Conditions: 8000-3350 y.a. GISP2 ice core. The principal modes of covariance in the GISP2 Holocene record differ markedly from those of glacial conditions (Table V.2). Most prominently, the variance of microparticles is almost entirely accounted for in EOF #1, while that of major ions is distributed among several eigenmodes. This suggests that changes in the aerosol composition above Greenland during the Holocene resulted from the interaction of compositionally distinct air masses. We point out that the EOF eigenmodes are defined so as to maximize the amount of total variance in the data accounted by each one. An EOF analysis may therefore exaggerate, to some degree, differences between groups of variables that have distinct patterns of covariance. Hence, our EOF analysis of the GISP2 Holocene record may somewhat accentuate the division of variance between microparticles and major ions. Nevertheless, our findings demonstrate that the emission patterns and the dynamics of transport and deposition of aerosols to Greenland were considerably more complex in the interglacial than in the glacial climate. The GISP2 Holocene EOF #1 also shows a weaker covariance among microparticles than was apparent in the principal EOF mode for late glacial conditions (Table V. 1). This is most evident in the lower percentage of variance explained for microparticles > 5 fim in the Holocene (49 %) than in the late glacial period (90 %). These contrasting results can be explained by glacial-interglacial differences in atmospheric dynamics. With the recession of continental ice sheets in the Holocene, the vigor of the Northern Hemisphere atmospheric circulation gradually decreased while atmospheric moisture (hence, precipitation) increased (Kutzbach and Ruddiman, 1993). Concurrently, eolian dust mobilization declined over the continents while the transit time of airborne dust particles to Greenland, and amount of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83 precipitation scavenging en route, increased (Petit et al., 1981; Royer et al., 1983; Zielinski and Mershon, 1997). As a result, atmospheric dust deposited in Greenland snow during the Holocene had a lesser proportion of large microparticles than those deposited under glacial conditions (Steffensen, 1997). The balance of unexplained variance in the GISP2 Holocene microparticle record is accounted for by EOF # 6 . Coarse (> 4 pm) and fine (< 1 pm) particles are uncorrelated in this mode, suggesting that they were delivered in Greenland by different modes of atmospheric transport. Submicron-size dust particles could be associated with well-aged air masses from which most coarser particles settled or were precipitated during long-range transport. In contrast, coarse particles could be deposited during episodes of rapid, vigorous atmospheric dust transport from desert regions, for example in eastern Asia (e.g., Rahn et al., 1981, Welch et al., 1991) or North Africa (e.g., Franz€n et al., 1994). Interestingly, EOF # 6 shows weak correlations with all major ions except for NO 3-, which covaries with the coarser particles (> 4 pm). Atmospheric NO 3- is deposited in Greenland snow primarily as nitric acid (HNO 3) that is readily scavenged by coarse dust aerosols (Wolff, 1984; Dibb et aL, 1994). This could account for the relationship between these two types of ice core impurities revealed in EOF # 6 . The glaciochemical species in the GISP2 Holocene record show a more complex factorization of variance among the different eigenmodes than did microparticles. Nevertheless some interesting relationships among major ions are apparent, notably those represented by EOFs #2,3 and 4. We focus the ensuing discussion on those three modes of variability for which we can offer some plausible interpretation. Other eigenmodes may also be physically meaningful, but the environmental conditions they represent are as yet undefined. EOF2 identifies a pattern of covariance among crustal-source cations (exCa2+, exK+ and exMg2+), exS0 4 2- and NO 3". The Ca-Mg-K association and the poor correlation of these species with microparticles suggests that EOF #2 describes variability in the atmospheric deposition of soluble mineral dust phases such as CaC 0 3 , CaMg(S0 4 )2 or KC1. The covariance of exS 0 4 2- and N 0 3 " with the major cations suggests simultaneous deposition of these species, possibly as salts (e.g., CaS 0 4 ) formed via the neutralization of alkaline dust by sulfuric aerosols during long-range transport (Wolff, 1984; Sequeira, 1993). Because it is only weakly correlated with insoluble microparticles, the glaciochemical association in EOF #2 may identify a specific source for soluble dust deposited in Greenland during the Holocene. The exCa 2+:exMg2+ ratio in snow at Summit suggests that the dominant Holocene dust sources to Greenland were located in eastern Asia or inland North America (O'Brien et al., 1995). A possible source for Ca-, K- and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 84 Mg-rich soluble dust aerosols could be the widespread evaporites that occur in the Qaidam Basin of eastern China (Lowenstein et al., 1989). Indeed, eolian sediments derived from these deposits account for high levels of Ca2+ and K+ in surface snow of nearby mountainous areas (Wake et al., 1993; Yao et al, 1995). EOF #3 is characterized by the covariance of exS 0 4 2* and exCl", and an inverse relationship between these two species and ssNa+, exCa2+ and exK+. Both exS 0 4 2- and exCl" may originate from a marine source, exS 0 4 2- by the oxidation o f planktonic sulfur emissions and exCl" from HC1 released by the reaction o f sea salt aerosols with sulfuric aerosols in the marine boundary layer (Legrand and Delmas, 1988; Legrand et a l, 1988). Marine air masses reaching the interior regions o f the Greenland ice sheet may carry high levels of exS 0 4 2' and exCl" relative to sea level concentrations as a result o f sea-salt fractionation processes during transport (Gjessing, 1989; Mulvaney et al., 1993). Also, as a result of Na:Cl fractionation, the estimated concentration of exCa2+ and exK+ in aged marine air may be overestimated, such that these species would appear to covary with ssNa+, as observed in EOF #3. This EOF mode could therefore describe changes in the frequency of transport of relatively aged marine air masses to central Greenland, or changes in ocean boundary layer conditions that affects the aerosol composition o f marine air (e.g., surface winds or sea surface temperature). The covarying ionic species in EOF #4, exSC> 4 2', NO3 ' and NH 4 +, have this in common that they are derived, at least in part, from gaseous precursors. In addition to episodic volcanic contributions, exS 0 4 2’ aerosol may be formed by the oxidation of SO 2 and other reduced sulfur gases released from biogenic sources (e.g., phytoplankton). N(V is derived from various N gases produced by terrestrial biota, lightning, or photochemical reactions in the stratosphere (Parker and Zeller, 1979; Legrand and Kirchner, 1990; Dibb et al., 1994). NH4 + is mostly deposited as ammonium salts (e.g., (NH 4 )2 SC>4 ) formed by the reaction of ammonia gas (NH 3 ) and acidic aerosols such as H 2 SO4 (Busenberg and Langway, 1979; Dibb et al., 1994). Hence, EOF #4 appears to describe variability in the trace gas composition (primarily SOx, NOx and NH 3 ) o f the atmosphere above Greenland during the Holocene. Because EOF #4 is uncorrelated with other eigenmodes, we infer that the climatological factors that controlled the deposition o f gas-derived ionic species in Greenland snow differed from those of other soluble and insoluble aerosols. The identification of these climatological factors, however, remains to be defined. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 85 P95 ice core. Our EOF analysis of the P95 Holocene record reveals some important similarities with the GISP2 Holocene record. As in the GISP2 record, most of the microparticle variance in the P95 record is explained by EOF #1, and is uncorrelated with that of major ions (Table V.3). Also, the balance of unexplained microparticle variance is accounted for in a separate eigenmode (EOF #4) that shows an opposing relationship between fine (< 1 pm) and coarse (> 4 pm) microparticles. As previously discussed, the EOF analysis may exaggerate the apparent decoupling between microparticles and major ions in the P95 Holocene record. Nevertheless, the similarities between the GISP2 and P95 Holocene records revealed by our analysis suggest that distinct patterns of covariance for insoluble and soluble aerosols are a characteristic feature of the interglacial climate at northern high latitudes on a broad spatial scale (regional to hemispheric). The first EOF mode in the P95 Holocene record (Table V.2) accounts for a larger percentage of variance of coarse microparticles, and particularly those > 5 pm, than the first EOF in the GISP2 core (Table V.l). These differences imply that continental dust deposited on the Penny Ice Cap during the Holocene consisted of a greater proportion of coarse particles than those deposited at Summit, Greenland. We attribute the coarser size of dusts deposited in the P95 core during the Holocene to the relative proximity of, hence shorter transport distance from, soil and sediment sources around the Penny Ice Cap (Zdanowicz et al., in review). These sources may have been periglacial loess or glacigenic sediments exposed by the receding snow and ice cover (e.g., Wells, 1983). Most of the covariance among major ions in the P95 core is accounted for by EOF #2, while the other EOF components represent patterns of variance between pairs of individual species (Table V.3). EOF #2 shows a high degree of covariance among all major ion species with the exception of exCl- and NH 4+. Patterns of variability for these two species are described by separate eigenmodes, as further discussed below. In view of the large proportion of total variance in the P95 record explained by EOF #2 (24 %), we infer that this mode describes changes in the dominant pattern of atmospheric circulation that delivered primary aerosols (sea salt, dust) to the Penny Ice Cap during the Holocene. On decadal or longer time scales, climatic variability in the eastern Canadian Arctic may be controlled, to a large extent, by changes in the strength and mean position of the upper air pressure trough (700 mb) above Baffin Island (Keen, 1980; Maxwell, 1981; Agnew and Silis, 1995). These changes affect the frequency of southerly air flow over southern Baffin Island which, under present conditions, accounts for much of the variability of major ion deposition in snow on the Penny Ice Cap (Grumet, 1997; Grumet et al., 1998; Zdanowicz et al., 1998a). Hence, the P95 EOF #2 could be documenting changes in atmospheric circulation over the eastern Canadian Arctic related to variability in the Baffin Bay upper air Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 86 trough. The effects of such changes on the composition of ice on the Penny Ice Cap are investigated in separate publications (Grumet et ai; Zielinski et al., in preparation). The 49 % of variance in the P95 time series of ssNa+ that is unexplained by EOF #2 is distributed between two separate eigenmodes characterized by opposing relationships between ssNa+ and exCl' (EOF #3), and by ssNa+ and exMg2+ (EOF # 6 ) (Table V.3). The exact physical significance of these modes is unclear, but they appear to represent different patterns of sea salt ion transport to and deposition to the Penny Ice Cap. These ions are probably derived, to a large extent, from the seasonally open marine areas that surround southern Baffin Island (Baffin Bay, Davis Strait, Labrador Sea; Grumet, 1997). The relationships among ssNa+, exCl- and exMg2+ described in EOF #3 and 6 could be related to fractionation processes affecting the ratio of these elements in sea salt aerosols during transport For example, a loss of Na+ relative to Cl* can result in an overestimation of the calculated exCl* in ice, such that Na+ and exCl* may appear to covary, as in EOF #3. A similar effect could account for the apparent inverse relationship between Na+ and exMg2+ in EOF #6 . Another interesting glaciochemical association in the P95 Holocene record is identified by EOF #5. This mode describes a correlation between exK+ and NH 4+ accounting for 17 and 20 % variance of these species, respectively. An important source for exK+ and NH 4+ aerosols at high northern latitudes may be biomass burning emissions from forest fires, particularly from Canada or Siberia (Radke et al., 1991; Talbot et a i, 1994). Hence, the distinctive association of exK+ and NfLi* in the P95 ice core identified by EOF #5 may represent air masses impacted by forest fire emissions from the boreal regions of North America or Eurasia. Biomass burning signatures from boreal and subarctic regions were identified in the GISP2 core (Whitlow et a i, 1994; Holdsworth et a i, 1996; Taylor et al., 1996). However, our EOF analysis of the GISP2 Holocene record does not reveal a specific mode of glaciochemical variance associated with these events. Hence, the Penny Ice Cap may be more strongly impacted than Greenland by biomass burning aerosols, or at least by those from northern Canadian source regions. If this inference can be verified, for example by comparison of the EOF #5 time series with independent records of forest fire activity (historical or other), long proxy records of past biomass burning activity could be developed from the P95 ice core or from other cores recovered from the eastern Canadian Arctic. The remaining EOF modes in Table V.3 describe relationships between ssNa+ and exMg2+ (EOF #6 ) and between exK+ and NH 4+ (EOF #7). Neither of these two modes show any covariance between ions and microparticles. At present, we can not offer a satisfactory interpretation of these eigenmodes. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 87 CONCLUSIONS Our EOF analysis of the GISP2 and P95 multivariate ice core records revealed important differences in the behavior of insoluble and soluble Arctic aerosols in contrasting glacial and interglacial climates. Most prominently, we found that microparticles and major ions covaried strongly in Greenland under glacial conditions, but were largely uncorrelated in both Greenland and the eastern Canadian Arctic during the Holocene. We attribute the former covariance among particles and ions to the highly dynamic character of the late glacial polar atmosphere in which most aerosol species and types were well mixed. Conversely, the decoupling of microparticles and major ions in the Holocene climate is interpreted as reflecting the competing effects of regional atmospheric circulation systems and associated air masses carrying aerosols from different source(s) and source region(s) to Greenland and the Penny Ice Cap. Furthermore, the principal modes of covariance among major ions in the GISP2 and P95 Holocene records are different, implying that the aerosol sources or circulation systems that affected the composition of Arctic snow differed between Greenland and the eastern Canadian Arctic. Our findings therefore support a gradual regionalization of the Northern Hemisphere climate from the late glacial period through the Holocene, as was previously postulated from the GISP2 glaciochemical record (O’Brien et al., 1995). We suggest that as a result of this trend, changes in aerosol transport and deposition in Greenland and Arctic Canada during the Holocene became increasingly controlled by regional environmental factors (i.e., meteorological or other). EOF analyses of the GISP2 and P95 records revealed distinctive associations among microparticles and major ionic species that may represent the source-specific signature of transporting air masses, or particular environmental factors that control the deposition of these impurities in snow. As an example, the second EOF mode (EOF #2) in the GISP2 record of glacial conditions identifies a pattern of covariance among ionic species derived from gaseous precursors (exS 0 4 2*, N 0 3 " and NH 4+ ). Because it is independent from other modes, we infer that EOF #2 describes changes in the trace gas composition in the glacial atmosphere above Greenland, or changes in the physical processes (as yet undefined) that controlled the deposition of gas-derived ionic species in snow. Another example is EOF #5 in the P95 Holocene record, which identifies the covariance of exK+ and NH 4+, exclusively. Because these species share a common biomass burning source, we postulate that EOF #5 describes variability in forest fire emissions from boreal regions in the Northern Hemisphere, and particularly from Canada. If this hypothesis is verified, time series of the P95 EOF #5 may provide a useful proxy documenting changes in forest fire activity in northern Canada during the Holocene. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 8 Results of this study demonstrate how EOF analysis applied to combined ice core time series of microparticles and major ions can reveal important physical relationships among these impurities that may not be apparent when examining their separate behavior. Future efforts should be dedicated to applying this technique to a larger number of circum-Arctic ice core records in order to further define patterns of Northern Hemisphere climatic and atmospheric variability at different spatial (regional to hemispheric) and temporal (annual to millennial) scales. ACKNOWLEDGMENTS We extend our thanks to all those who participated in the development of the multivariate ice core records used in this study. Drilling of the GISP2 ice core was made possible with the support of the Polar Ice Coring Office (University of Alaska), the GISP2 Science Management Office (University of New Hampshire) and the 109th Air National guard (Schenectady, New York). The P95 ice core was recovered with field support from the Geological Survey of Canada, the Polar Continental Shelf Project (Ottawa) and Icefield Instruments Inc .(Whitehorse, Yukon). Special thanks are due to S. Whitlow and N. Grumet for conducting major ion analyses on the GISP2 and P95 ice cores, and to G. Mershon, M. Leo and M. Day who helped with the microparticle analyses. This research was supported by the Office of Polar Programs, National Science Foundation. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 89 EOF mode 1 2 3 3 5 % total variance 78 7 4 3 2 Factored variance Total Microparticle size (fim) 0.65-1 81 (+) 8 (+) 3 (-) 1 (+) 0 (-) 94 1-2 87 (+) 7 (+) 4 (-) 1 (+) 0 (-) 98 2-3 91 (+) 2 (+) 4 (-) 0 (+) 0 (-) 98 3-4 94 (+) 0 (+) 3 (-) 0 (+) 0 (-) 97 4-5 93 (+) 1 (-) 1 (-) 0 (-) 0 (-) 95 5-12 90 (+) 3 (-) 0 (-) 1 (-) 0 (-) 94 Major ions ssNa* 87 (+) 3 (-) 0 (-) 1 (-) o (-) 92 exCa2* & 2 (+) 6 (-) 0 (+) 1 (-) o (+) 89 exK* 64(+) 8 (-) 2 (+) 3 (-) 6 (-) 84 exMg2* 70 (+) 9 (-) 0 (+) 2 (-) 10 (+) 91 exCl 5 3 (+) 11 (-) 7 (+) 28 (+) 0 (-) 1 0 0 exSQ»2' 67 (+) 13 (+) 4 (+) 0 (-) 4 (-) 89 NOj 78 (+) 4 (+) 0 (+) 1 (+) 7 (+) 90 NH f 54 (+) 18 (+) 21 (+) 2 (-) 1 (+) 95 Table V .l. Principal modes of covariance among insoluble microparticles and major ions in the GISP2 record of late glacial conditions (25,000 to 15,000 y.a.; n = 665). Figures in bold exceed 10 % variance. Signs indicate if any two given parameters covary together (identical signs) or in opposition (opposite signs). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 88 89 84 90 83 88 84 90 96 90 98 95 85 Total (+) (-) (+) 97 <+) 8 (-) (-) 1 (+) 1 1 1 2 7 7 0(+) O(-) 4 0(+) 0(+) 0 0 (+) 10(-) 12 12 (-) 27 27 (+) (+) (-) (+) (-) (+) 5 4 (-) 1 1 1 0 O(-) 4 (-) 0 O(-) 0<+) O(-) 15 15 24 24 25 25 (+) (-) (+) (-) (+) (+) (■) (-) 6 (-) (+) 6 7 1 1 1 5 5 8 0 0 9 (-) O(-) 4 (-) 16 16 10 (+) 10 18(+) 1 0 (+) (+) (+) 4 (-) (-) (+) (-) (+) 5 1 1 1 3(+) 8 3 3 (+) 9 (+) 4 4 (-) 6 10(-) 27 27 (+) 21 21 (+) (+) (+) (-) (-) 9 7 (+) 4 (+) 1 (-) 1 1 (-) 1 1 1 5 5 (-) 3 (-) 0 9 (-) 7 O(-) 0 4 (+) 11 (+) 11 27 27 55 55 (-) (-) (-) (-) (+) (-) (-) (+) (-) 3 (+) 10 1 1 1 5 5 (+) 6 0 2 0(-) 0 = 450). See Table V. 1 caption details. for 1 Table 450). V. = See 19 19 24 24 23 23 (+) 46 46 (+) 38 38 n (+) (+) (+) (+) (+) (+) (-) 2 15 8 0 9 (-) 2 9 (-) 0 0 18 18 13 (-) 13 1©(+) 20 20 (+) 51 51 (+) 47 47 (+) (+) (+) 1 3 3 (+) 3(+) 5 5 (+) 7 (+) 6 7 7 (+) 7(+) 2 0 68 68 (+) 49 49 (+) 76(+) 79 79 (+) 79(+) 62 (+) 1-2 Major ions Major ssNa* NO, 3-4 5-12 exSQ,1- NH<+ 2-3 Microparticle size (pm) size Microparticle exCa1* Factored variance Factored 4-5 exCl’ exMg* % total variancetotal % 32 exK* EOF mode EOF 0.65-1 interglacial conditions (8000 to 3350 y.a.; y.a.; 3350 to (8000 conditions interglacial Table V.2. Principal modes of covariance among insoluble microparticles and major ions in the GISP2 record of record GISP2 the in ions and major microparticles insoluble among covariance of modes Principal V.2. Table Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 87 88 96 96 86 98 93 98 91 93 97 99 95 97 Total (+) (-) 4 (+) (-) 7 1 1 3 3 (+) O(-) 2 4 (+) O(-) 0 O(-) O(-) 13 (-) 19 (+) (+) (+) (+) (-) O(-) (-) (-) O(-) (+) (+) (+) (-) (-) 6 6 2 O(-) 0 0 0 0 0 0 0 0 0 29 (+) 2 2 (-) (+) 3 (-) (+) (-) (+) (+) (-) 7 (-) (+) 5 1 2 8 9 (-) 2 3 3 (-) 2 4 (-) 4 (-) 0 0 2 17 (+) 2 0 (-) (-) (-) (-) (+) (+) 8 (-) (+) (-) 1 1 1 0 0 0 0 4 (-) 0 1 0 13 (-) 14 (+) 27 (+) = 450). See Table V. 1 details. caption for 1 Table V. 450). See = n (+) (+) (+) (+) (+) (+) (-) (-) 5(+) (-) (+) 3 4 1 1 2 4<+) 2 0 0 0 0 0 0 14 14 (+) 79 (+) 27 (-) (+) (-) (-) (+) (-) (-) (-) 1 1 1 2 0 0 0 51 51 (+) 78 (+) 57 (+) 73 (+) 80 (+) 49 (+) 40 (+ ) (-) (+) (+) (-) (+) (+) (+) (+) 1 2 1 1 0 0 0 2 0 0 91 (+) 87 (+) 81 (+) 6 7 (+ ) 42 total variance total 31 24 9 1-2 NH4‘ NO, 3-4 exCl exS0 5-12 75 (+) exMg2* Major ions Major 2-34-5 93(+ ) ssNa+ exCa2* exK+ Microparticle size (pm) size Microparticle % 0.65-1 Factored variance* Factored EOF mode EOF record of interglacial conditions (8000-3350 y.a.; y.a.; conditions (8000-3350 interglacial of record Table V.3. Principal modes of covariance among insoluble microparticles and major ions in the P95 P95 the in ions and major microparticles insoluble among covariance of modes Principal V.3. Table Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER VI THE MOUNT MAZAMA ERUPTION: AGE VERIFICATION AND ATMOSPHERIC IMPACT ASSESSMENT FROM THE GISP2 ICE CORE RECORD C.M. Zdanowicz and G.A. Zielinski Climate Change Research Center, University of New Hampshire, Durham, NH 03824 M.S. Germani Micromaterials Research Inc., Suite 200, 136 Shore Drive, Burr Ridge, IL 60521 In press, Geology, April, 1999. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 93 CHAPTER VI THE MOUNT MAZAMA ERUPTION: AGE VERIFICATION AND ATMOSPHERIC IMPACT ASSESSMENT FROM THE GISP2 ICE CORE RECORD ABSTRACT Geochemical identification of Mount Mazama ash in the GISP2 (Greenland) ice core gives a calendrical age of 7627 ± 150 cal yr B.P. (5677 ± 150 B.C.) for the eruption, thus providing a more accurate early Holocene stratigraphic time line than previously available. The GISP2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 8 8 and 224 Mt spread over an ~ 6 -yr period following the eruption of Mount Mazama. Taking into account the likelihood of some tropospheric aerosol transport to Greenland, realistic estimates of the resulting atmospheric optical depth range from 0.6 to 1.5. These values may have produced a temperature depression of -0.6 to 0.7 °C at mid- to high northern latitudes for 1-3 yr after the eruption. These results indicate that the 5677 B.C. eruption of Mount Mazama was one of the most climatically significant volcanic events of the Holocene in the Northern Hemisphere. We also calculate a maximum stratospheric Cl' release of 8 .1 Mt from the eruption, which may have led to substantial stratospheric ozone depletion. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 94 INTRODUCTION The magnitude and duration of the radiative forcing associated with explosive volcanic eruptions is largely determined by the volume, spatial distribution and residence time of the H2SO4 aerosol emitted to the atmosphere (Rampino and Self, 1984, Rampino et al., 1988; Sigurdsson, 1990). A critical factor is the proportion of H 2SO4 aerosol injected above the tropopause, as the stratospheric residence time of sulfuric aerosols may extend to several years (Sear et a l, 1987). Polar ice cores provide detailed proxy records of past voicanism by preserving atmospheric fallout from past eruptions (e.g., Gow and Williamson, 1971; Hammer, 1984; Delmas et al., 1985; Zielinski et al., 1997). The potential atmospheric and climatic impact of paleo-eruptions can therefore be evaluated from ice core measurements by estimating the amount of ash, volatiles (Cl, F) and particularly of climate-forcing H 2SO4 aerosol released in the atmosphere from those eruptions, and the resulting changes in optical depth, (e.g., Fiacco etal., 1994; Yang etal., 1996; Zielinski etal., 1996a). Long (> 10 3 years) proxy records of paleovolcanism have been developed from ice cores by continuous measurements of the acidity or electrical conductivity of the ice, which is primarily, but not exclusively, related to soluble volcanic aerosols (H 2SO4 + HC1 + HF) (e.g., Legrand and Delmas, 1987; Clausen etal., 1995; Moore etal., 1991; Zielinski etal., 1994,1996b). Continuous measurements of SO 42" in ice cores provide a more direct estimate of atmospheric H 2SO4 loading, although other sources such as marine and continental salts and biogenic emissions may also contribute to the measured sulfate levels (Legrand and Delmas, 1987; Legrand and Mayewski, 1997). In addition, the geochemical characterization of volcanic glass particles associated with ice core volcanic signals can allow for source volcanoes to be unambiguously identified, provided the tephra composition in ice cores can be matched with that of terrestrial or marine ash deposits (e.g., Palais et al., 1991; Fiacco et al., 1994; Gronvold et al., 1995; Zielinski et al., 1995). Here we report on the identification and analysis of atmospheric fallout (volcanic glass and soluble aerosols) from the early Holocene climactic eruption of Mount Mazama (Crater Lake, Oregon, 43°N; 122°W) in the Greenland Ice Sheet Project Two (GISP2) ice core. The geochemical matching of volcanic glass from the GISP2 ice core with pumice from Crater Lake allowed us to assign a new calendrical age to the eruption, thereby improving on previous radiometric ( 14C) age estimates. We used the GISP2 record of volcanically- derived SO42' to derive a range of estimates of the stratospheric loading of H 2SO4 aerosol resulting from the Mount Mazama eruption, and evaluated its potential climatic impact using empirical aerosol-optical depth relationships. In addition, we also provide estimates of stratospheric aerosol Cl" loading from the eruption. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 95 THE CLIMACTIC ERUPTION OF MOUNT MAZAMA The early Holocene plinian eruption of Mount Mazama ejected nearly 50 km 3 (dense rock equivalent) of rhyodacitic magma into the atmosphere and deposited ash over an area of about 1.7 x 10 6 km2, making it the most widespread late Quaternary tephra layer in the United States and southwestern Canada (Sama-Wojcicki et ai, 1983). The eruption, initially dated ca 6845 ± 50 14C yr B.P. (Bacon, 1983), was assigned a volcanic explosivity index (VEI) of 7 (Simkin and Siebert, 1994), ranking it among the largest eruptions of the late Quaternary. The eruption sequence began with a single-vent Plinian phase that ejected an estimated 30 to 38 km 3 of rhyodacitic pumice of which -13 km 3 were deposited as pyroclastic flows (Bacon, 1983; Bacon and Druitt, 1988). The single-vent phase ended when the caldera collapsed and was followed by a ring-vent phase that emplaced compositionally-zoned pyroclastic flow deposits ranging from juvenile rhyodacitic pumice (> 80% volume) to dominantly mafic scoriae and partially fused granitoid rocks derived from the walls of the magma chamber (Bacon, 1983). Ashfall and flow deposits associated with the single-vent phase of the eruption were shown to be compositionally homogeneous and rhyodacitic, averaging 70.4 ± 0.3 % SiQ2, with rare silicic andesite scoriae (Bacon and Druitt, 1988). On the basis of pollen evidence, Mehringer et al. (1977) inferred an upper limit of 3 years for the period of ash fall associated with the climactic eruption, although its duration may have been considerably shorter (Bacon, 1983). Because it occurred in a mid-latitude area near modem population centers, improved knowledge of the environmental effects of the Mount Mazama eruption are needed to help assess potential volcanic hazards in the Pacific Northwest region. Here we use the volcanic record in the Greenland Ice Sheet Project Two (GISP2) ice core to provide such information. Hammer et al. (1980) and Zielinski et al. (1994) previously estimated the atmospheric SO 42* loading from the Mount Mazama eruption on the basis of tentative identification of the eruption signal (acidity and SC> 42’ peaks) in Greenland ice cores. However, their assignment was based on questionable matching of ice core-based calendrical ages with uncalibrated 14C dates bracketing the Mount Mazama ash in geological records, and was unsupported by direct tephrochronological evidence linking ice core signals to an eruptive source. Identification of volcanic glass from Mount Mazama in the GISP2 ice core allows us to provide an accurate calendrical age and reliable quantitative assessment of the atmospheric impact of the eruption. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 96 METHODS The GISP2 ice core was drilled to a depth of 3053 m from the summit region of the Greenland Ice Sheet (72.6°N, 38.5°W, 3200 m asl; Fig. LI). The depth-age scale was determined by multi-parameter counting of annual signals. Time control was provided in part by the identification of volcanic horizons (acidic aerosols and/or tephra) from documented eruptions (Meese et al., 1997). Conservative dating error estimates for the GISP2 Holocene record range from ± 1 % back to 3300 years ago, to ±2 % at 12,000 years before present. Major ionic species in the GISP2 ice core (including SO 42' and Cl") were analyzed by ion chromatography (Mayewski et al., 1997) and the concentration (N) of insoluble microparticles with diameters between 0.65 and 12 pm was determined with an Elzone™ particle counter equipped with a 30 pm orifice (Zielinski and Mershon, 1997). The volcanic record used in this study was developed from the GISP2 time series of SO 42* (Zielinski et al., 1994). In order to locate the Mount Mazama signal in the GISP2 record, we converted Bacon's (1983) widely accepted eruption age of 6845 ± 50 14C yr B JP. to calendrical years using the radiocarbon calibration program of Stuiver and Reimer (1993). Age calibration was performed by the intercept method using the composite tree-ring/marine coral data set and a lab error multiplier of 1 (Stuiver and Reimer, 1993). The resulting calendrical age range (2a) was 7545 to 7711 cal yr B.P. As observed by Southon and Brown (1995), the corresponding interval in the GISP2 core includes, at 1325.9 m, one of the highest SO 42* peaks (654 pg kg *1 above background values) of the record for the past 9000 years. The signal is also coincident with strong peaks in excess Cl" (total Cl" minus estimated sea-salt contribution) and microparticles (Fig. V.l). To help determine the source of the signal, we sampled the GISP2 core for volcanic ash between 1317-1336 m. Samples were melted and filtered on 0 .2 pm pore-diameter polycarbonate membranes, which were then carbon- coated and examined using a Hitachi S-570 scanning electron microscope (SEM) equipped with an energy-dispersive X-ray (EDX) microanalyzer (Germani and Buseck, 1991). Volcanic glass shards ranging in size from < 1 to 20 pm (average diameter) were identified on four filters between 1325.11 to 1326.15 m (Fig. V.2). Ten glass shards > 10 pm from one filter (1325.89 to 1326.15 m) were analyzed for major oxide composition. Analyses on filters between 1325.11 and 1325.89 m interval (not reported here) showed identical compositions, thus a single eruptive source for the glass is assumed. For direct comparison with the ice core tephra, we analyzed glass from 2 samples (79C-109 and 81C- 631) of Mount Mazama rhyodacitic pumice collected in the vicinity of the Crater Lake caldera. Sample 79C-109 was obtained from -3.5 m above the base of the climactic plinian Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 97 deposit at Pumice Point on the caldera rim, while sample 81C-631 is from silicic ignimbrite 33 m up a 65 m thick section along the Rogue River (Bruggman et al., 1987, and C. Bacon, pers. comm.). The pumice samples were ground in a mortar, dispersed in hexane and filtered through a 0.4 (im pore-diameter membrane which was then carbon-coated for X-ray microanalysis. All scanning electron microscope (SEM) analyses were performed under the same operating conditions and with an identical set of standards. Mount Mazama glass samples of the same size and shape as the GISP2 sample were analyzed to ensure consistency in the procedure and to limit potential bias in the results from size fractionation of tephra during transport and/or deposition. RESULTS AND DISCUSSION Identification and Age Verification of the Mount Mazama Eruption Signal The scanning electron microscope (SEM) analyses reveal that the major oxide composition of the GISP2 tephra is identical within analytical uncertainties to that of Mount Mazama pumice samples 79C-109 and 81C-631, thus verifying it as the source eruption for the 654 ppb SC> 42' signal (Table V. 1 and Fig. V.3). Differences in the wt. % of FeO* (total iron as FeO) between Mount Mazama pumice 79C-109 and 81C-631 may be due to the presence of late-erupted andesitic to mafic material indistinguishable from glass in either of these samples (C. Bacon, pers. comm.). For most major oxides, our GISP2 tephra falls in the compositional range reported for other Mount Mazama ash samples analyzed by comparable methods (e.g., Sama-Wojcicki etal., 1983; Bruggman etal., 1987; Bacon and Druitt, 1988). However, we note that the wt. % of Na 2 0 measured in our GISP2 and Mount Mazama tephra samples (6.6-7.8 wt. %) are higher than those of electron microprobe or X-ray fluorescence analyses reported in these publications (3.9-5.1 wt. %). This is presumably because our major oxide data are from energy-dispersive, rather than wavelength-specific, analyses, and because these analyses were performed on individual glass particles rather than flat polished samples. We stress that these differences in our Na2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 98 confident that Mount Mazama is indeed the source of the 654 ppb SO 42' signal identified in the GISP2 ice core. Our identification of Mount Mazama ash in the GISP2 ice core provides a new calendrical age of 7627 ± 150 cal yr Bi*. (5677 ± 150 BQ for the climactic eruption. We stress that this error estimate is very conservative and note that our ice-core age for the Mount Mazama eruption agrees closely with the recently produced weighted mean I4C age of 6730 ± 40 (2a) yr Bi>. (7640-7620 cal yr B.P.; Hallet et al., 1997). The lack of detectable tephra or high microparticle concentrations in ice immediately before the SO 42- peak suggests that fallout of Mount Mazama ash and SO 42* over Greenland began simultaneously, implying rapid initial transport to the ice sheet, probably in the troposphere. Whereas deposition of Mount Mazama SO 42- and Cl* aerosol in Greenland lasted as many as 6 years, ash fallout (indicated by high microparticle concentrations) was mostly limited to a period of < 3 years (Fig. V.l), in agreement with an estimated 2-3 years of ash fall in the northwestern USA inferred from lake sediment records (Mehringer et al., 1977). Atmospheric and Climatic Impact of the Mount Mazama Eruption We postulated the potential climatic impact of the Mount Mazama eruption by estimating the resulting stratospheric mass loading (Mp) of H 2SO4 aerosol and atmospheric optical depth (r). The Mo was derived from the GISP2 SC> 42' record using the method of Hammer et al. (1980), which assumes that stratospheric dispersion and fallout of volcanic aerosol follow the same pattern as that observed for radioactive products of nuclear bomb tests. From this premise, Clausen and Hammer (1988) derived latitude-dependent multipliers to convert the amount of volcanic fallout products (total H+ or SO 42') deposited in Greenland ice into estimates of Mo for some historical volcanic eruptions. Using the relationship of Carey and Sigurdsson (1989), the height of the Mount Mazama eruptive column was estimated from the total mass o f erupted material (M ~ 50 km3 DRE; Bacon and Druitt, 1988) at 40 km (±10-20 %). The eruptive column was therefore high enough to penetrate above the mid-latitude tropopause, and likely resulted in widespread stratospheric aerosol dispersion. To estimate M o, we multiplied the amount (flux) of volcanic SO 42' deposited in Greenland ice over the ~ 6 year period of the Mount Mazama SO 42- signal by a mid latitude scaling factor of 1.8 x 10 9 (Zielinski, 1995) to derive a value of M o equal to 440 Mt H2SO4. However this figure should be regarded as an upper limit since some volcanic SO42- deposition in Greenland may have occurred through tropospheric rather than stratospheric transport on the basis of simultaneous fallout of glass and SO 42*. Also, gas- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 99 to-particle conversion of sulfur dioxide and scavenging of SO 42' aerosol may have been enhanced by adsorption onto ash particles in the volcanic cloud (Rose, 1977). Moreover, Zielinski (1995) found that aerosols from mid- to high-latitude eruptions are more likely to have some tropospheric transport toward Greenland, resulting in enhanced SO 42' signals in the ice. This was probably the case for the Mount Manama eruption, which is inferred from pollen data to have occurred in autumn (Mehringer et a/., 1977), a time when migration of the polar front enhances cyclogenesis and meridional flow in the westerlies. The dispersal pattern of Mazama ash (Sama-Wojcicki et al., 1983) also suggests predominant east- northeasterly upper winds at the time of the eruption which would have favored rapid transport of ash and SO 42* towards Greenland. We used our estimate of M o and the methods of Stothers (1984) and Zielinski (1995) to determine a possible range of atmospheric optical depths (T) resulting from the Mount Mazama eruption. Our calculations yielded values of r between 0.6 and 2.9. However, M o may be overestimated because of some tropospheric aerosol. Therefore, a minimum to intermediate r range of 0.6 to 1.5, corresponding to stratospheric mass loadings of 8 8 to 224 Mt H2SO4, is probably more realistic. This lower range figure is in good agreement with a new petrological estimate of 92.9 Mt (minimum) for total SO 42- degassing during the Mount Mazama eruption (Mandeville et al., 1998). On the basis of the work of Palais and Sigurdsson (1989), the averaged Northern Hemisphere temperature decrease (AT) associated with our estimated range for Mo would be 1.2 to 1.5°C in the 1-3 years following the eruption. Given that Palais and Sigurdsson’s relationship tends to overestimate AT for mid-latitude eruptions by factors of 1 to 3 (based on data from historical eruptions), the mean Northern Hemisphere temperature depression following the Mount Mazama eruption may have been closer to about 0.6-0.7°C. This estimate of AT is considerably larger than that for the AD 1912 eruption (VEI = 6 ) of Katmai (58°N; Kelly and Sear, 1984), and is comparable that of Tambora, Indonesia (AD 1815; VEI = 7), the largest and deadliest eruption in recorded history (Stothers, 1984). Therefore, even if the impact of the Mount Mazama eruption may have been primarily felt at mid- to high northern latitudes, our estimates of M o, f and AT still rank it among the most climatically significant volcanic events of the Holocene in the Northern Hemisphere. Using the same technique as for SO 42*, we calculated a maximum stratospheric mass loading of 8 .1 Mt Cl- produced by the Mount Mazama eruption. This is two orders of magnitude lower than the 100 Mt Cl- release calculated by Bacon et aL (1992) from petrological analyses of melt inclusions in Mount Mazama tephra. This discrepancy probably reflects the efficient removal of degassed Cl- by rainout or adsorption onto tephra particles near the eruption source (Rose, 1977), thus limiting long-distance transport Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 Nevertheless, our estimated Cl~ release from Mount Mazama exceeds that for most major historical eruptions (Palais and Sigurdsson, 1989) and may have been of a magnitude that would lead to substantial stratospheric ozone depletion after the eruption. Eruptions that cause atmospheric cooling at high latitudes may leave a detectable signature in the oxygen isotope ( 8 lsO) composition of polar ice that forms in the months or years following these eruptions (e.g., Stuiver et a i, 1995). To verify if the 7627 B.P. eruption of Mount Mazama left a similar signature in Greenland ice, we examined a section of the high resolution 8 isO record from the Greenland Ice Core Project (GRIP) ice core (Grootes et a/., 1993) ice core representing the period 7650-7600 cal. yr B.P. bracketing the eruption (Fig. VI.4). The GRIP ice core 8 lsO record shows a 0.5 %o decline to isotopically lighter values in the ~ 6 -year period that followed the eruption relative to the preceding 10-year mean. However, this 8180 departure falls within the intra- and inter- decadal variability of the GRIP isotopic record for the period 7650-7600 cal. yr B.P. and may therefore not be a direct response to temperature forcing by the Mount Mazama eruption. The apparent lack of a clear 8180 signature for the Mount Mazama eruption in the GRIP ice core may be due to factors other than temperature affecting the oxygen isotope composition of polar ice (e.g., moisture source; Charles et al., 1994), or from the uncertain correlation between the Holocene portion of the GISP2 and GRIP ice core records (Grootes et al., 1993). Consequently, it does not invalidate our assessment of the climatic impact of the Mount Mazama eruption on the basis of the GISP2 ice core SO 42' record. CONCLUSIONS By verifying the calendrical age of the Mount Mazama eruption, we have improved the possibility for correlation among paleoclimate records developed from terrestrial and lacustrine sediments over a large portion of western North America, records that may now be better linked to ice core and marine records. Furthermore, the significant climatic-forcing potential and possible impact on Northern Hemisphere ozone levels from other mid-latitude eruptions of the magnitude of Mount Mazama should be duly noted by individuals concerned with the widespread impact on society associated with future volcanic eruptions. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 101 ACKNOWLEDGMENTS The Mount Mazama pumice samples were provided by C. Mandeville (American Museum of Natural History) with kind permission by C. Bacon (United States Geological Survey). Insightful comments from these individuals as well as from an anonymous reviewer improved an earlier draft of the manuscript. This research was supported by a grant to G.A.Z. from the Office of Polar Programs, U.S. National Science Foundation. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 102 GISP2 glass______79C-109 ______81C-631 n 10 10 11 S 1O2 69.9 (±0.6) 70.3 (±0.8) 69.0 (±1.1) Ti0 2 0 .6 (±0 . 1) 0 .6 (±0 .1) 0 .6 (±0 .1) AI2O3 14.8 (±0.3) 15.1 (±0.4) 15.3 (±0.6) FeO* 2.7 (±0.4) 1.0 (±0.4) 2.5 (±0.3) CaO 2 .1 (±0 .2 ) 1.9 (±0.2) 2.0 (±0.3) Na20 6 .6 (±0.7) 7.8 (±1.1) 7.4 (±1.3) K20 3.3 (±0.3) 3.3 (±0.2) 3.1 (±0.2) Table VI. 1. Mean major oxide composition (weight %) of GISP2 volcanic glass and Mount Mazama tephra. FeO* = Total Fe reported as FeO. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103 7621 cal yr B.P 7627 cal yr B.P. 8 0 0 - MHi g E ++ ++++ ++++++ ++ + S 0 42- 600 - 654.5 4 0 0 - M9 kg’ I ■» T 1 I | I I I I I 1324 1325 1326 1327 1328 Depth (m) Fig. VI. 1. Time series of SO,*2-* Cl" and microparticle concentration (N) in the GISP2 ice core, showing the peaks assigned to Mount Mazama eruption fallout. Horizontal dotted lines denote average background levels of S 0 4 2*> C l' and N for the last 9000 years. Crosses delineate yearly increments as determined by annual signal counting (Meese et al., 1997). The maximum duration of the Mount Mazama eruption signal is outlined. Shaded area indicates the interval from which volcanic glass was analyzed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 104 Fig. VI.2. Electron photomicrograph of typical glass shard collected from the GISP2 ice core and associated with Mt. Mazama eruption fallout. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 105 (a) 60 40 60 O GISP2 tephra 20 □ Pumice 81C-631 80 A Pumice 79C-109 80 60 <■ CaO 0. 8 - □ o o m a CM0.6 - □ AA/SZD O □ □ □ QA OD A A P 0.4- 0.2- 1 0 - 6 - 4 - 65 66 67 68 69 70 71 72 73 74 75 Si02 Fig. VI.3. Comparison of the major oxide composition (weight %) of volcanic glass filtered from the GISP2 ice core with rhyodacitic pumice from Crater lake, Oregon (samples 79C-109 and 81C-631). (a) CaO-K^O-FeO* ternary plot. (b) and (c) Ti 0 2 -, Na2 0 -Si0 2 covariation plots. FeO* = Total Fe as FeO. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. without prohibited reproduction Further owner. copyright the of permission with Reproduced M9 kg 0 0 2 40Q.- - 0 0 6 800 7600 i the GISP2 SO GISP2 the SO Mazama Mount 5[gO record (bottom). The shaded area delineates the period of period the delineates area shaded The (bottom). record 5[gO in the GISP2 ice core SO core ice GISP2 the in signal eruption Mazama Mount the between Comparison IA V Fig. - IP > O S GISP2 6072 7630 7620 7610 4 2*record. 4 2 - aerosol fallout in Greenland, as inferred from from inferred as Greenland, in 2- fallout aerosol 4 2* record (top) and the GRIP ice core GRIP the 2*and (top) record cal. years B.P. years cal. 106 7640 7650 --34 --33 -36 -35 CHAPTER VH CONCLUSIONS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 108 CHAPTER VH CONCLUSIONS The main scientific contribution of this dissertation is the development and analysis of a Holocene record of high-ladtude atmospheric dust deposition from the Penny Ice Cap, Baffin Island. By its high resolution (multi-annual to decadal) and by the number of parameters measured or calculated (dust concentration, mass, size distribution), this record (P95) is the first of its kind developed from an Arctic ice cap outside of Greenland. It is also unique in terms of its location, the Penny Ice Cap being the southernmost ( 6 6 °N) of the smaller circum-Arctic ice caps from which a surface-to-bed ice core was ever recovered. Consequently, the records of aerosol composition and climatic parameters developed from the P95 ice core offer an unprecedented opportunity to investigate past changes in the atmospheric environment in the North Atlantic sector of the Arctic at interannual to longer time scales (Fisher et al., 1998; Grumet et al., 1998; Zdanowicz et al., 1998a, 1998b). As such, this research represents a valuable contribution to the new Ice-core Circum-Arctic Paleoclimate Program (ICAPP) program, as well to other programs investigating past and present high-latitude climatic variability. SUMMARY OF MAJOR FINDINGS Snowpit investigations on the Penny Ice Cap (Chapter II) demonstrate that high resolution (multi-annual or longer), useful paleoclimatic data can be obtained from ice core microparticle records obtained at polar sites that are affected by considerable amounts of summer melt (up to 50 %) and meltwater percolation. These findings are encouraging with respect to the potential development of other multivariate ice core records from small Canadian or Eurasian Arctic ice caps. Results from the snowpit studies also show that atmospheric dust deposited on the Penny Ice Cap originates, in part, from far-distant sources possibly as remote from the eastern Canadian Arctic as central Asia. Hence, changes in atmospheric dust deposition recorded in the P95 ice core record reflect, in part, the effects of environmental controls acting on a regional to hemispheric scale. On the basis of these initial findings, a first-order paleoenvironmental interpretation of the P95 ice core dust record is proposed (Chapter HI). Atmospheric dust deposition on the Penny Ice Cap decreased markedly during the transition from the late Pleistocene to the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 109 present interglacial period (Holocene). It is speculated that this decrease occurred in response to a hemispheric-scale weakening of the atmospheric circulation and transition to generally moister climatic conditions (hence, reduced continental aridity) in the Northern Hemisphere during and after deglaciation. A gradual increase in dust deposition in the P9S core began ca 7500 years ago due to enhanced dust export from sources relatively proximal to the Penny Ice Cap. Factors that may have promoted this increase include an expansion of dust sources from postglacial land emergence in the Hudson Strait area, recession and thinning of the Penny Ice Cap, thereby facilitating the upslope transport of wind-blown dust onto the ice, and a regional and possibly pan-Arctic climatic deterioration leading to colder, drier and windier conditions in the southern Baffin Island region. Comparison of trends in dust and non-sea salt calcium (a glaciochemical dust tracer) in the P95 and GISP2 (Greenland) ice cores reveals an increasing divergence between the two records beginning ca 7500 years ago. The diverging trends suggest that as climate evolved during the Holocene, transport and deposition of atmospheric dust in the Canadian Arctic and Greenland gradually came to be controlled by regionally-specific environmental factors. The P95 dust record documents regional-scale changes in geographical (e.g., snow and ice cover extent) and climatic factors (e.g., wind strength) that affected the sources, transport and deposition of eolian dust in the eastern Canadian Arctic during the Holocene. As such, it provides a new perspective on Arctic paleoenvironmental change that will complement proxy records previously developed from other ice cores, lake sediments, tree- rings and other media (e.g., Fisher and Koemer, 1981; Bradley, 1990; Overpeck et al., 1997). The P95 dust record is all the more valuable as it was obtained from a region of the Arctic (the southern Baffin Island region) where sources of high-resolution paleo environmental data are scarce. The comparison between the P95 and GISP2 Holocene records also provides a good example of how geographically separate, yet comparable, ice core records can assist in defining the spatio-temporal variability of paleoclimate in the Arctic region, a founding premise of the ICAPP program. An important requirement for progress in ice core paleoclimate research is that the various proxy climatic indicators (e.g., 5180, major ions, dust) measured in ice cores be calibrated against independently-derived records of temperature, precipitation, atmospheric circulation or other climatic variables. As part of this dissertation, the effects of Northern Hemisphere circulation and snow cover variability on the P95 dust record were evaluated by comparing it with observational and satellite data documenting seasonal to decadal-scale variability in these parameters (Chapter IV). An empirical orthogonal function (EOF) analysis of the P95 dust record and seasonal sea level pressure variations reveals that changes in dust deposition on the Penny Ice Cap are strongly linked to, and possibly Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 110 controlled by, modes of the Northern Hemisphere winter circulation with centers of action over Eurasia, the North Pacific Ocean, and western North America. These findings are supported by seasonal SLP anomaly patterns for years of extreme high and low dust levels in the P95 ice core. Most prominently, an inverse relationship between the P95 dust record and the intensity of the winter Siberian High accounts for over 50 % of the interannual variance in time series of these parameters over the period 1899-1995. This relationship may find its origin in the interplay between the large scale Northern Hemisphere winter circulation and Eurasian surface air temperatures and snow cover. Specifically, weakening of the winter Siberian High could enhance the long-range export of dust from Eurasian source regions by hastening the spring retreat of seasonal snow cover while increasing the frequency of dust storms in the arid continental interior. Support for this hypothesis comes from a correlation analysis of the P95 dust record with time series of Northern Hemisphere regional snow cover extent On inter- to multi-annual time scales, changes in dust deposition in the P95 ice core are significantly anticorrelated (R= -0.38 to -0.46) with variations in spring, and to a lesser extent fall, snow cover extent in the mid-latitude interior regions of Eurasia and North America. These relationships account for an estimated 10 to 20 % of variance in the P95 dust record, and are attributed to the limiting effect of snow cover on the potential for eolian dust deflation, particularly during the spring season. Findings from this investigation raise the possibility of using ice core microparticle records to document changes in Northern Hemisphere atmospheric circulation patterns or snow cover extent before the period of satellite and weather station observations. Lengthy records of snow cover variability are particularly needed to improve our understanding of snow cover-climate relationships and to integrate their effects in climate simulations. In Chapter V, an EOF analysis was used to investigate patterns of covariance between insoluble (dust) and soluble (major ions) aerosols deposited in the P95 and GISP2 ice cores under glacial and interglacial climatic conditions. Results show that microparticles and major ions deposited in Greenland covaried strongly in the late glacial period, but were uncorrelated during the Holocene. The covariance among particles and major ions in the glacial climate was a consequence of the highly dynamic and well-mixed composition of the polar atmosphere during this time (Mayewski etal., 1993,1994). The apparent decoupling between microparticles and major ions in the Holocene c limate is attributed to the effects of competing, regional-scale atmospheric circulation systems transporting aerosols from different source(s) to Greenland and the eastern Canadian Arctic. These findings support a gradual regionalization of the Northern Hemisphere climate from the late glacial period through the Holocene, as was previously postulated from the GISP2 glaciochemical record (O’Brien et al., 1995). Companion EOF analyses of the GISP2 and P95 records also reveal Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ill distinctive relationships among microparticles and major ions that document changes affecting the sources, transport and/or deposition of particular aerosols or aerosol types. For example, EOF #2 in the GISP2 late glacial record describes the covariance of ionic species derived from gaseous precursors (exS 0 4 2-, NC>3" and NH 4+ ). Another example is EOF #5 in the P95 Holocene record, which identifies variability in the time series of exK+ and NH 4+ attributed to changes in biomass burning emissions from boreal regions of North America or Eurasia. This study demonstrates how EOF analysis applied to combined ice core time series of insoluble and soluble impurities can reveal important physical relationships among these aerosols, and thus increase the scope of paleoenvironmental information that can be obtained from such records. In addition to the findings described above, the P95 microparticle record will provide valuable data to researchers concerned with estimating the radiative effects of aerosols in the Arctic atmosphere. These effects may be very significant to the Arctic heat budget as the length of the polar day-night cycle prevents damping of the radiative perturbation (Shaw and Stamnes, 1980). Because radiation-absorbing polar aerosols are primarily concentrated in particles > 1 pm (Rahn and McCaffrey, 1980), accurate modeling of the radiative effects of these aerosols requires a proper knowledge of their number density, mass and volume size distribution in the Arctic atmosphere and precipitation (e.g., Blanchet and List, 1987). The P95 core microparticle record can provide useful estimates of these parameters and of their temporal variability at the time scale of instrumental records for use by atmospheric radiation modelers. In the final part of this dissertation, the atmospheric and climatic impact of the early Holocene eruption of Mount Mazama (Crater Lake, Oregon) was evaluated from the GISP2 ice core record of volcanically-derived sulfate and ash particles (Chapter VI). To this end, calibrated radiocarbon ages from the widespread Mount Mazama ash were used to circum scribe a systematic search for volcanic glass particles from the eruption in the GISP2 core. The geochemical matching of ice core tephra with Mount Mazama pumice samples provides a positive identification of the eruption signal in the GISP2 record, and allows for a new estimate of it calendrical age at 7627 ± 150 cal yr B P. (5677 ± 150 BC). The atmospheric and climatic impact of the Mount Mazama eruption was evaluated by calculating the stratospheric loading of H 2SO4 aerosol produced by the eruption (88 to 224 Mt), and the resulting range of atmospheric optical depths (0.6 to 1.5). Based on these estimates, the Mount Mazama eruption is estimated to have resulted in a temperature depression of -0.6 to 0.7°C at mid- to high northern latitudes, thereby ranking it as one of the most climatically significant volcanic events of the Holocene in the Northern Hemisphere. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 112 This study provides a good example of the type of paleoclimatic information that can be obtained from the volcanic component of particulate impurities in ice cores. The estimated climatic impact of the Mount Mazama eruption will contribute to expand our knowledge of the potential environmental effects of large explosive eruptions under different climatic regimes. Findings from this study will be of particularly relevance for preventive planning against volcanic hazards in the densely populated and volcanically active Pacific Northwest region. The newly verified calendrical age for the Mount Mazama eruption will also assist in correlating paieoclimate records developed from terrestrial and lacustrine sediments in western North America, records that may now be better linked to ice core and marine records. Finally, the tephrochronological data obtained as part of this investigation will contribute to the ongoing development of the tephrochronological record of the GISP2 ice core, as recommended by the International Geosphere-Biosphere Program (IGBP) and International Quaternary Association (INQUA) Commission on Tephrochronology. RECOMMENDATIONS FOR FUTURE WORK This scientific findings presented in the dissertation demonstrate the wide scope of paleoenviromental information that can be obtained from ice core records of particulate atmospheric impurities. To verify and progress beyond these results, additional ice core microparticle records should be developed from other circum-Arctic sites, that may be compared with the P95 and GISP2 records. Much of the paleoenvironmental interpretation presented in this dissertation rests on the fundamental assumption that changes in ice core microparticle concentrations reflect, at least in relative terms, changes in the atmospheric dust load above the site of deposition. There are, however, many other factors that can affect the amount of dust deposited in polar ice, such as changes in snow accumulation rates or changes in the relative efficiency of wet and dry dust deposition in different years or seasons (Hansson, 1995). While considerable efforts have gone into evaluating the influence of these factors on glaciochemical records (e.g., Dibb et aL, 1992; Davidson et al., 1996), comparatively little has been done for microparticles. There is also a scarcity of data on the spatial variability of dust deposition in polar snow, and on post-depositional effects that may affect the preservation of seasonal to annual dust signals in ice cores (Steffensen et a l, 1996). These factors need to be addressed in future studies in order to support an accurate interpretation of ice core microparticle records. In addition to the physical properties of ice core microparticles (concentration, size distribution), valuable paleoenvironmental information can be obtained by analyzing their composition. In particular, the mineralogical and geochemical characterization of individual Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 113 dust particles can allow for discrimination between different potential source regions (e.g., Gaudichet et al., 1986; De Angelis et a l., 1992; Biscaye et al., 1997). At present, the identification of ice core dust sources by these methods is limited to a broad regional scale (-103 km2) due to the compositional homogenization of dust during long-range transport (Schuetz, 1989; Shaw, 1989). However, new source identification techniques based on multi-elemental geochemical analysis or on isotopic tracers show promising results in studies of ice core dust (e.g., Grousset and Biscaye, 1989; Basile et al., 1997; Biscaye et al., 1997). Possibilities brought about by these new techniques will increase as additional data on the composition of polar aerosols and ice core dust become available. Accordingly, it is recommended that compositional studies of individual ice core particles be integrated into the research agenda of ICAPP or similar programs. Results of comparisons between the P9S dust record and observational and satellite data (Chapter IV) raise the possibility of using ice core microparticle records to document changes in Northern Hemisphere atmospheric circulation patterns or snow cover extent before the period of satellite and weather station observations. Recent observational evidence indicates that the winter Siberian High is strongly coupled with multi-seasonal snow cover and winter-time circulation anomalies at mid- to high northern latitudes (Cohen and Entekhabi, 1999). The P95 ice core dust record, or similar records developed from Arctic ice cores, may allow for an improved understanding of these relationships by providing a long-term perspective on the variability of the Siberian High and of Northern Hemisphere snow cover. Further validation of the results presented in Chapter IV is warranted, and could be accomplished through comparison with other high-resolution Northern Hemisphere ice core dust records such as the one currently being developed from the Devon Ice Cap. Further examination of instrumental and historical archives, for example the historical snow depth records from the former Soviet Union (Barry et al., 1993), may help to verify how snow cover variability in central Asia influences atmospheric dust deposition at high latitudes. However in order to progress in this direction of research, efforts should be dedicated to improve the temporal resolution and reduce dating errors of microparticle records, as poor dating control can be a major source of uncertainty when comparing these records to, or calibrating them against, historical, instrumental or observational data. This is of particular relevance to ice core records developed from the small ice caps of the circum-Arctic, some of which experience considerable melt that may compromise the preservation of microparticle signals (Zdanowicz etal., 1998a). In order to improve the dating control of circum-Arctic ice core records, and to allow for accurate correlation between ice cores drilled at different sites, it is recommended that Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 114 further efforts be invested in the continuing development of a tephrochronological database of potential ice core volcanic markers. The identification of the Mount Mazama eruption signal in the GISP2 ice core (Chapter VI) shows the usefulness of such data to studies of the volcano-climate system, and illustrates how accurately-dated volcanic time markers can allow for intercomparisons between different types of paleoenvironmental records. The identification of volcanic signals in circum-Arctic ice cores may prove more problematic than in Greenland due to the effects of summer melt and meltwater percolation that can alter the sulfate, acidity, or electrical conductivity peaks identifying these events (e.g., Fujii et al., 1990). Eruptions from volcanoes in Iceland, Alaska, Kamtchatka or other high-latitude regions tend to deliver large amounts of tropospheric aerosols to the Arctic and thus are more likely to leave strong signals in circum-Arctic ice caps. Accordingly, special efforts should be made to improve the late Quaternary chronology of these eruptions (particularly in the Holocene) from ice cores and geological deposits, and to assemble a database of tephra composition from source volcanoes that may be compared with glass particles from ice cores (e.g., Gronvold et al. 1995; Braitseva et al., 1997; Zielinski et al., 1997). Reproduced with permission of the copyright owner. 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(1997) Volcanic aerosol records and tephrochronology of the Summit, Greenland, ice cores. J. Geophys. Res. 102, 26,625-26,640. Zielinski, G.A., Pittalawala, I., Wake, C.P., Grumet, N.S., Zdanowicz, C.M., Whitlow, S. and Jacobs, J.D. (in preparation) Relevance of 700 mb synoptic patterns across the circum-Arctic to the paleoclimatic interpretation of snow and ice records from the Penny Ice Cap, Baffin Island. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDICES Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 136 Appendix A. Microparticle number (N), mass (M), mean diameter (NMD) and fi* in Penny Ice Cap snowpits [ 0.85 < d < 12 pm] Depth N MNMD P Depth N M NMD P (m) (103 m l'1) (pg kg'1) (pm) (m) (10* ml*') (P g k g ‘) (pm ) 0.00 92.19 341.52 1.12 2.69 1.44 14.12 57.38 1.15 2.30 0.03 105.60 426.93 1.14 2.85 1.47 21.93 57.63 1.03 2.63 0.06 56.38 221.44 1.14 2 J 5 IJO 26.001 93.46 1.09 2.71 0.09 53.49 146.23 1.04 2.98 1 J4 17.23; 58.76 1.08 2.44 0.12 49.48 239.25 1.08 2.45 U 8 16.00; 50.82 1.11 2.51 0.15 30.76 153.54 1.12 2.66 1.62 16.90’ 50.78 1.07 2.49 0.18 37.86 110.89 1.02 2.88 1.66 21.32 57.38 1.02 2.68 0.21 29.67 74.69 1.00 2.89 1.70 23.11 75.10 1.08 2 J 4 0.24 16.58 64.85 1.13 2.21 1.74 30.03 81.83 1.04 2.82 0.27 46.35 112.21 0.86 2.84 1.77 10.02 22.95 1.01 2.68 0.30 20.80 92.86 1.05 2 J 5 1.80 23.15 78.47 1.06 2.37 0.33 17.38 46.68 1.01 2.47 1.83 36.56 149.58 1.12 2 J 6 0.36 41.87 91.35 0.92 2.96 1.86 21.08 53.31 1.02 2.64 0.39 26.86 63.49 0.96 2.89 1.89 15.74 59.79 1.10 2.42 0.42 14.94 88.87 1.04 2.26 1.92 14 J3 45.38 1.08 2.42 0.45 15.31 58.12 1.08 2.27 1.95 14.25 44.72 1.09 2.29 0.48 9.53 26.94 1.02 2.71 1.98 20.27 79.90 1.14 2.38 0.51 15.00 31.12 0.94 2.82 2.01 22.33 66.88 1.08 2.51 0.54 34.45 69.26 0.96 3.13 2.04 21.13 59.26 1.06 2.62 0.57 17.18 55.46 0.99 2.87 2.07 14.25 51.92 1.10 2.37 0.60 23.05 135.02 1.14 2.46 2.10 32.73 121.14 1.09 2 J 2 0.63 9.25 44.95 1.08 2.22 2.13 21.99 79.32 1.06 2.58 0.66 18.82 77.60 1.06 2.28 2.16 24.02 70.18 1.06 2.83 0.69 27.16 130.49 1.17 2.20 2.19 23.05 97.46 1.16 2.22 0.72 207.37 428.06 0.92 3.26 2.22 31.95 135.54 1.09 2.62 0.75 46.01 189.48 1.19 2.48 2.29 103.37 561.69 1.19 2.38 0.78 66.10 220.95 1.10 2.76 2.32 121.07 344.73 1.04 3.16 0.81 31.07 114.05 1.13 2.68 2.35 48.44 159.68 1.05 2.82 0.84 63.94 163.80 1.01 3.08 2.39 34.65 123.87 1.10 2.55 0.87 35.12 112.49 1.06 2.88 2.42 20.98 72.19 1.10 2.56 0.90 35.38 128.90 1.09 2.71 2.46 31.76 114.27 1.10 2.71 0.93 34.58 105.43 1.07 2.83 2.50 39.37 260.86 1.12 2.62 0.96 29.43 71.08 1.01 2.97 2 J 4 55.15 244.46 1.12 2.55 0.99 32.75 149.23 1.11 2.62 2 J 8 27.85 220.21 1.20 2.17 1.02 42.92 123.47 1.05 2.91 2.62 23.84 84.29 1.07 2.68 1.05 22.55 98.26 1.12 2.54 2.66 26.88 106.34 1.12 2.34 1.08 40.12 133.88 1.08 2.86 2.70 41.98 149.04, 1.06 2.74 l . l l 24.53 91.55 1.10 2.47 2.74; 4433 152.33 1.06 2.78 1.14 25 JO 128.20 1.17 2.34 2.781 46.93 229.98; 1.15 2.49 1.17 44.97 131.00 1.05 2.96 2.82; 34.69 160 J8 1.16 2.44 1.20 55.82 171.13 1.07 2.83 2.82; 47.45 171.67 1.08 2.70 1.23 32.88 129.64 l . l l 2.39 2.91 33.48 168 JO 1.13 2.44 1.26 33.55 125.08 1.15 2.36 2.94 27.94, 73.54 1.01 2.81 1.29 39.17 156.75 1.13 2.54 2.97 35.44 226.45 1.26 2.10 1.32 25.14 99.87 1.15 2.54 3.01 68.64> 329 J 6 1.26 2.65 1.35 17.27 58.78 1.12 2.17 3.05; 32.38 157.21 1.19, 2.31 1.38 14.57 55.62 1.11 2.39 3.09; 32 J3; 146.87! 1.12; 2.56 1.41 11.97 36.22 1.08 2.40 3.12! 25.94! 78.17! 1.031 2.65 *jS calculated fo r d <5 pm only. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 137 Appendix A. (continued) Depth N M NMD P Depth N M NMD P (m) (103 m l'1) (ug kg’1) (pm ) (m) (103ml ‘) (ugkg1) (um ) 3.15 25.12 102.73 1.14 2.40 4.09 2 430 17731 1.18 2.20 3.18 18.50 50.65 1.02 2.76 4.12 18.45 53.97 1.05 258 3.21 33.01 84.40 1.02 2.77 4.15 14.66 39.86 1.06 2.47 3.24 23.89 75.96 1.09 2.62 4.18 21.36 64.17 1.06 2.43 3.27 16.02 6331 1.13 2.28 4.21 17.10 98.74 1.19 2.04 3.30 16.08 59.21 1.10 2.28 4.24 43.85 297.82 1.26 2.08 3.33 27.42 160.11 1.13 253 4.27 39.34 301.19 1.26 1.99 3.36 21.08 171.03 1.20 1.97 432 17.27 110.27 1.10 2.14 3.39 16.75 45.28 1.04 258 4.37 9.29 69.25 1.19 1.87 3.42 53.47 190.32 1.09 2.82 4.42 33.74 306.31 1.17 2.30 3.45 21.04 99.90 1.13 2.30 4.47 32.73 136.01 1.08 2.43 3.55 29.97 145.68 1.17 2.31 452 28.78 12455 1.08 2.46 3.58 50.86 220.41 1.14 254 4.57 28.44 134.70 1.08 255 3.61 60.06 132.04 1.00 3.27 4.62 32.27 178.83 1.15 2.28 3.64 54.54 204.48 1.09 2.77 4.67 2652 122.61 1.11 2.34 3.67 34.73 148.69 1.12 258 4.72 45.04 223.90 1.13 2.36 3.70 47.75 107.77 1.01 3.21 4.75 17.40 126.07 1.26 2.04 3.73 26.84 122.26 1.15 2.42 4.78. 23.93 207.02 1.22 2.04 3.76 42.75 179.98 1.10 2.68 4.81 28.91 209.34 1.15 2.31 3.79 47.71 152.25 1.08 2.83 4.84 26.95 171.87 1.19 2.10 3.82 38.94 125.01 1.07 2.85 4.87 20.80 145.34 1.15 2.21 3.85 42.00 134.67 1.06 2.67 4.90 21.15 124.47 1.14 2.29 3.88 35.87 114.64 1.10 2.69 4.93 18.13 98.46 1.23 1.99 3.91 37.36 123.17 1.08 2.88 4.96 12.96 74.65 1.18 2.02 3.94 45.23 153.77 1.07 2.77 4.99 14.88 61.04 l . l l 2.02 3.97 20.52 80.11 1.09 250 5.02 12.96 54.80 1.12 2.33 4.00 17.05 67.34 l . l l 2.27 5.05 19.83 95.43 1.16 2.25 4.03 18.97 83.13 1.10 2.46 5.08 22.64 106.04 1.17 2.14 4.06 26.28 106.50 1.11 2.29 5.11 41.93 214.67 1.11 2.60 Depth N M NMD P Depth N M NMD P (m) (103 m l1) (UK kg'1) (Um) (m) (103 m l'1) (Ug k g ') (um ) 0.00 53.10 424.47 1.30 2.06 0.39 27.81 68.35 1.02 2.93 0.03 96.39 395.49 1.15 2.77 0.42 18.24 44.16 0.98 2.73 0.06 89.64 376.05 1.15 2.74 0.45 19.08 57.43 1.00 2.84 0.09 62.91 228.22 1.13 2.70 0.48 13.13; 47.18 1.01 2.66 0.12 73.24 225.56 1.09 2.74 0 51 12.20| 36.03 1.02 2 52 0.15 42.19 146.62 1.12 2.72 0.54; 30.03; 82.28 1.05! 2.79 0.18 20.27 10856 1.17 2.21 0 5 7 16.90' 39.74! 1.031 2.64 0.21 33.27 162.73 1.13 2.52 0.60 11.97 37.08 1.02, 2.76 0.24 30.44 125.19 1.13 2 5 0 0.63: 10.05: 39.72 1.06 2.34 0.27 24.73 105.26 1.12 2.38 0.66; 11.62 35.44 1.07 2.33 0.30 23.05 81.60 1.08 2 5 3 0.69 1136 31.94 1.04 2.41 0.33 19.21 7051 1.12 2.25 0.72 8.08: 26.97 0.99 2 53 0.36 20.11 95.06 1.09 2.64 0.76 8.47 25.71 1.07 2.25 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 138 Appendix A. (continued) Depth N M NMD P Depth N M NMD P (m) ( 103 m l'1) (U g k g 1) (Um) (m) (10*ml'1) (ugkg1) (Um) 0.80 38.96 244.53 1.22 2.48 1.25 53.27 313.95 1.19 2.40 0.83 37.99 14538 1.10 2.60 1.28 3634 179.57 1.16 2.40 0.86 3 1 3 0 100.62 1.08 2.71 1.31 21.45 78.07 1.10: 2.45 0.89 26.04 79.15 1.06 2.72 134 4033 16030 1.03 2.87 0.92 14.60 71.14 1.05 2 3 0 1.37 40.14 200.37 1.12 2.42 0.95 20.57 87.65 1.09 2.32 1.40 33.14 189.73 1.11 2.63 0.98 24.86 67.36 1.00 2.66 1.43 21.47 110.90 1.10 2 3 1 1.01 38.89 208.47 1.09 236 1.46 25.76 12836 1.11 2.25 1.04 23.87 67.27 1.01 2.73 1.49 32.68 237.83 1.15 2.43 1.07 18.63 134.34 1.18 2.01 1.52 31.99 212.63 1.22 2 3 0 1.10 32.75 17830 1.09 2.61 135 2934 135.43 1.15 2.10 1.13 32.25 238.15 1.16 2.30 138 18.76 94.57 1.12 2.24 1.16 39.84 121.51 1.05 231 1.61 18.30 86.88 1.11 2.26 1.19 38.66 158.54 1.07 2.46 1.64 20.74 9837 1.14 2.08 1.22 26.73 138.93 1.10 2.31 Depth N M NMD P Depth N M NMD P (m) (10* m l'1) (U g k g ‘) (Um) (m) (103 m l') (U g k g ‘) (Um) 0.00 40.03 137.50 0.97 2 3 9 1.05 20.65 57.58 1.03 2.56 0.05 17.40 72.82 1.11 2.25 1.10 32.86 6736 1.00 3.25 0.10 11.84 141.98 1.20 1.79 1.15 18.41 65.40 1.04 2.60 0.15 15.11 52.18 1.12 2.45 1.20 13.22 34.26 1.04 2.48 0.20 22.57 98.51 1.15 2.27 1.25 20.01 62.79 1.08 2.45 0.25 17.89 103.99 1.15 2 3 0 130 19.81 50.82 1.03 2 3 5 0.30 14.77 135.24 1.14 2.34 1.35 6.94 22.85 1.07 2.17 0.35 15.54 178.33 1.14 2.26 1.40 10.46 48.10 1.08 2.15 0.40 35.83 276.18 1.20 2.16 1.45 13.78 37.24 1.03 2.47 0.45 48.08 308.73 1.15 2.29 130 10.69 41.58 1.12 2.07 0 3 0 19.77 112.52 1.14 2.27 135 7.67 3536 1.09 1.79 0 3 5 14.27 68.63 1.16 2.21 1.60 9.03 87.29 1.28 1.59 0.60 2 4 3 6 180.50 1.23 2.07 1.65 13.73 68.18 1.10 2.28 0.65 18.76 135.28 1.17 2.07 1.70 15.69 86.86 1.07 2.29 0.70 20.50 148.07 1.17 2.26 1.75 37.34 143.06 1.10 2.73 0.75 24.38 158.00 1.18 2.03 1.80 30.20 84.14 1.04 2.94 0.80 18.95 120.18 1.17 2.05 1.85 26.99 77.15 1.04 2.68 0.85 15.57 58.38 1.07 2.33 1.90 14.53 27.72 0.97 2.87 0.90 13.80 44.59 1.09 2.23 1.95 20.44 45.49 1.02 3.03 0.95 16.04 73.67 1.13 2.33 2.00 24.51 52.95 1.01 2.92 1.00 25.44 111.26 1.08 2.61 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 139 Appendix A. (continued) Depth N M NMD P D epth N M NMD P (m) (103 ml'1) (|ig kg ') (um ) (m) (103 m l1) (UR kg ') (Um) 0.00 50.17 194.86 1.14 2 3 7 1.65 29.84 260.86 1.22 2.14 0.05 48.14 159.29 1.11 2.81 1.70 29.90 587.87 1.47 133 0.10 47.26 237.69 1.15 2.31 1.75 41.63 346.17 1.21 2.08 0.15 24.49 125.23 1.16 2.15 1.80 42.17 272.67 1.16 233 0.20 26.69 129.48 1.13 2.47 1.85 13.97 70.94 1.17 2.07 0.25 17.27 87.05 1.15 2.22 1.90 40.90 330.59 139 1.88 0.30 23.80 101.94 1.17 2.24 1.95 46.80 288.78 1.29 2.02 0.35 18.26 86.37 1.15 2.19 2.00 64.18 272.65 1.16 2.66 0.40 3139 260.22 1.20 2.14 2.05 47.99 302.29 1.17 2.15 0.45 55.92 377.61 1.20 236 2.10 3 2 3 8 160.83 1.12 2.43 0.50 35.18 16034 1.13 2.45 2.15 3 038 92.31 1.07 2.80 0.55 37.77 2 5 1 3 0 1.15 238 2.20 3 7 3 0 164.72 1.11 231 0.60 36.09 157.31 1.11 2.46 2.25 55.13 400.47 1.16 2.24 0.65 22.53 14537 1.12 2.28 2.27 19.94 55.93 1.04 2.50 0.70 37.66 272.73 1.28 1.81 2.29 20.93 66.10 1.06 2.53 0.75 47.04 259.10 1.19 2.29 2.32 19.64 95.00 1.16 2.03 0.80 3035 202.12 1.17 2.28 2 3 5 2334 71.34 1.06 2.64 0.85 36.09 234.57 1.18 2.28 2.40 43.40 163.93 1.13 2.63 0.95 35.42 110.98 1.05 2.85 2.44 23.24 64.98 1.07 2.79 1.00 18.17 63.35 1.05 2.62 2.46 50.10 187.36 1.03 2.99 1.05 36.22 158.32 1.08 2.47 2.50 17.89 55.61 1.07 2.63 1.10 52.06 266.53 1.18 2.47 2 3 5 13.84 31.90 1.01 2.70 1.15 16.04 76.62 1.18 1.94 2 .6 0 1 17.72 46.47 1.04 2.56 1.20 51.61 141.02 1.06 2.98 2.64 19.92 72.17 1.05 2 35 1.25 25.14 144.20 1.16 2.34 2.71 8.49 18.99 1.00 2.56 1.30 17.74 92.49 1.14 2.19 2.75 12.16 55.66 1.12 2.22 1.35 21.32 163.80 1.17 2.02 2.80 14.64 6633 1.13 2.13 1.40 20.29 87.55 1.12 232 2.85 22.18 150.33 1.16 2.22 1.45 14.27 32.52 0.99 2.75 2.90 22.44 112.45 1.03 2.61 1.50 14.16 65.68 1.13 2.28 2.95 33.96 50.94 0.86 3.21 1.55 37.32 2 7 3 3 2 1.23 2.17 3.00 12.29 45.90 1.10 2.01 1.60 81.28 611.98 1.17 2.26 3.05 2735 112.98 1.14 2.47 Depth N M NMD P D epth N M NMD P (m) (103 ml') (Ug kg ') (Um) (m) (103 ml"1) (UR kR'1) (Um) 0.00 38.55 173.81 1.09 2.64 0 3 5 2339 61.46 1.00 2.85 0.05 31.61 83.90 1.01 2.87 0.60 23.18 111.95 1.07 2.48 0.10 50.90 160.15 1.06 2.73 0.63 37.15 268.46 1.16 2.26 0.15 35.55 101.50 0.98 2.83 0.64 46.16 389.29 1.20 2.37 0.20 19.62 62.22 1.02 2.60 0.65 35.18 155.53 1.10 2.64 0.25 25.33 109.68 1.07 2.43 0.69 37.73 155.88 1.14; 2 3 2 0.30 28.93 111.20 1.12; 2.46 0.761 25.611 120.921 1.08; 2 3 6 0.35 46.70 182.04 1.11 2 3 7 0.80 i 34.69; 99.23! 1.02' 2.93 0.40 84.62 566.19 1.141 2 3 0 0.85 57.63; 237.77! 1.081 2.79 0.45 79.72 4 3 3 3 2 1.21 2.27 0.90; 24.64^ 49.65 0.95; 2.82 0.50 55.71 268.39 1.12; 2.47 0.95 29.47; 92.70 1.06 2.74 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 140 Appendix A. (continued) Depth N M NMD P Depth N MNMD P (m) (l(r ml ) (tig kg' ) (Min) (m) ( l( r m l ) (u g kg ) (Um) 1.00 17.10 60.67 1.10 2 3 7 1351 9.64 41.151 I.16i 2.05 1.05 35.23 117.73 1.05 2.89 1.601 14.98 57.95 1.08 2.21 1.10 22.27 162.02 1.13 2 3 4 1.65 13.82 83.02 1.08 2.32 1.13 39.52 269.81 1.13 2.43 1.70 15.61 53.05 1.001 2.44 1.15 30.92 114.68 1.06 2.79 1.75 25.27 108.28 1.04 2.56 1.20 39.95 93.26 1.04 3.16 1.80 43.81 243.34 1.18 2.14 1.25 28.11 73.74 1.02 2.90 1.85 52.02 266.80 1.16 2.42 1.30 21.84 61.75 1.03 2.74 1.90 30.89 86.98 1.01 2.73 1.35 81.15 91.73 0.77 2.90 1.95 27.49 70.26 1.00 2.79 1.40 21.15 66.17 0.86 2.29 2.00 38.18 107.23 1.02 2.83 1.42 1634 50.81 1.04 2.61 2.05 28.85 64.45 1.00; 2.99 1.45 12.09 113.08 l . l l 2.16 2.10 38.16 114.30 0.99 2.63 1.50 6.25 18.81 1.04 2.09 Depth N M NMD P Depth N M NMD P (m) (I0 3 m l'1) (Ug k g ‘) (Um) (m) (10* ml*1) (Ug k g ') (Um) 0.00 114.46 3.31 1.97 1.03 1.25 24.06 2.69 2.05 1.01 0.05 74.68 2.99 2.98 1.08 1.30 33.37 2.69 2.13 1.09 0.10 59.98 2.66 2.15 1.14 1.35 50.02 3.02 1.72 1.02 0.15 55.95 2.65 2.15 1.11 1.40 43.96 2.75 3.19 1.08 0.20 66.53 3.28 1.86 1.04 1.42 58.81 2.84 2.04 1.11 0.25 46.09 2.92 1.96 1.02 1.45 69.25 2.90 2.09 1.09 0.30 37.86 231 3.32 1.21 1.50 35.33 2.43 2.07 1.15 0.35 27.40 2.11 2.56 1.17 1.55 40.32 3.03 1.81 1.01 0.41 33.42 2.25 2.98 1.23 1.60 20.89 2.35 2.99 1.13 0.45 26.28 2.73 2.26 1.00 1.65 23.24 2.24 3.07 1.14 0.50 30.53 2.67 2.68 1.06 1.70 21.41 2.36 1.88 1.08 0.55 34.49 2.78 2.25 1.02 1.75 23.22 2.43 2.44 1.14 0.60 24.90 2.64 2.41 1.02 1.80 17.48 2.35 2.72 1.15 0.65 95.79 2.42 3.91 1.17 1.85 37.30 2.38 3.40 1.15 0.70 55.45 2.56 2.76 1.13 1.90 30.94 2.77 2.03 1.04 0.75 26.15 3.08 3.20 0.98 1.95 20.33 2.73 2.92 1.03 0.80 16.19 2.99 1.55 0.94 2.00 28.91 2.72; 2.13 1.05 0.85 20.55 2.51 2.02 1.06 2.05 20.46 2.64 2.35! 1.02 0.90 54.65 2.72 2.94 1.13 2.10 29.23; 2.19 5.16 1.16 0.95 44.61 2.41 2.19 1.18 2.15: I9.30i 2.54 3.23; 1.05 1.00 33.83 2.76 1.81 1.06 2.20 42.32 2.62 2.68 1.10 1.05 48.01 2.49 2.65 1.14 2.25 27.49 2.18 3.56 1.19 1.10 23.91 2.80 1.92 0.99 2.30 27.03 2.69 2.00 1.05 1.15 22.01 3.15 1.72 0.94 2.35 20.74 2.39 2.78 1.07 1.20 36.00 2.86 2.28 0.98 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 141 Appendix B. Microparticle number (N) and mass (M) in the P95 ice core [0.8< d <12 pm ] Depth Age N M Depth Age N M (m ) (yr b2k)* (103 m l'1) (H g k g 1) (m) (vr b2k)* (10* ml*1) (Ug kg’") 0.00 5.01 29.32 158.98 2.48 8.25 21.77 474.28 0.05 5.06 26.43 10536 2 3 3 8 3 2 11.72 42.04 0.10 5.12 25.90 222.18 2 3 8 8.40 13.42 60.01 0.15 5.17 6.93 36.78 2.63 8.48 5 3 9 16.67 0.20 5.22 7.09 3337 2.68 8 3 5 11.23 77.63 0.25 5.27 0.87 137 2.73 8.63 7.81 25.27 0.30 5.33 6.87 29.22 2.78 8.71 6.36 14.13 0.35 5.38 1.46 5.41 2.83 8.79 2.44 137 0.40 5.44 13.29 418.12 2.88 8.87 15.66 79.47 0.45 5.49 37.43 647.00 2.93 8.95 4.67 5.34 0.50 5.55 16.18 128.12 2.98 9.02 24.15 220.81 0.55 5.61 18.43 37037 3.03 9.10 21.27 108.26 0.60 5.67 1534 93.94 3.07 9.17 49.70 472.28 0.65 5.73 3.74 119.48 3.12 9.25 6.35 8.04 0.70 5.79 21.43 326.05 3.17 9 3 6 1.95 8.43 0.75 5.85 2 7 3 8 270.68 3.25 9.46 4.40 8.60 0.80 5.91 12.01 231.55 3 3 0 9 3 4 3.98 23.78 0.85 6.00 17.50 296.45 3.35 9.62 3.67 6.77 0.90 6.05 14.93 34.08 3.40 9.71 n/d n/d 0.95 6.09 1.01 1.04 3.45 9.79 4.68 6.67 1.00 6.16 14.66 70.02 3.50 9.86 5.74 139.32 1.05 6.22 33.73 283.77 3 3 4 9.93 15.37 77.53 1.10 6.29 0.13 3.22 3 3 9 10.02 30.75 50.14 1.15 6.35 29.82 84.56 3.64 10.10 6.39 15.75 1.20 6.42 8.72 98.15 3.69 10.18 7.85 13.91 1.25 6.48 0.54 0.35 3.74 10.26 3.71 4.57 1.30 6.55 3.54 154.24 3.79 10.34 2.98 5.78 1.35 6.62 3.71 8.03 3.84 10.44 0.40 0.48 1.40 6.68 0.50 0.44 3.91 10.58 5.09 14.94 1.45 6.75 n/d n/d 4.00 10.70 2.73 6.41 1.50 6.82 19.65 378.62 4.05 10.78 5.36 16.76 1.55 6.89 55.69 1307.18 4.10 10.87 17.61 167.92 1.60 6.96 12.04 419.69 4.15 10.95 3.06 20.86 1.65 7.03 17.16 1511.22 4.20 11.03 8.18 55.77 1.70 7.10 22.20 628.16 4.25 11.12 n/d n/d 1.75 7.17 22.66 392.64 4.30 11.20 4.16 8.21 1.80 7.24 n/d n/d 4.35 11.28 1.34 3.25 1.85 7.32 28.18 432.94 4.40 11.37 2.79 8.00 1.90 7.39 30.77 280.03 4.45 11.45 11.64 51.49 1.95 7.46 42.69 273.29 4 3 0 1134 20.09 381.04 2.00 7.53 27.14 427.87 4 3 5 11.62 38.24 570.24 2.05 7 3 9 13.39 89.47 4.60 11.70 14.70 391.73 2.08 7.64 22.31 145.82 4.65 11.79 32.47 1307.18 2.13 7.72 21.10 127.77 4.70 11.87 9.00 34.36 2.18 7.79 24.56 65.99 4.75 11.96 10.18 39.22 2.23 7.87 9.39 24.10 4.80 12.04 12.35 139.84 2.28 7.98 20.92 163.52 4.85 12.13 5.92 23.72 2.33 8.04 15.89 145.87 4.90 12.24 5.99 198.17 2.38 8.09 14.04 35.76 4.99 12.36 9.98 37.88 2.43 8.17 13.05 71.84 5.04 12.44 n/d n/d *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 142 Appendix B. (continued) Depth Age N M Depth Age N M (m) (vrb2k>* (10* ml*1) (U g k g 1) (m) fvr b2k)* (10* mT1) (Ug kg'1) 5.09 1233 5.296 13.91 7.74 17.11 8.471 11233 5.14 12.61 30.663 257.62 7.81 17.21 16365 378.60 5.19 12.71 12.335 38.89 7.86 17.29 7389 29.05 5.25 12.80 0.613 0.69 7.91 17.38 4 3 5 5 18.43 5.30 12.88 8.828 317.26 7.96 17.47 8.418 18.38 5.35 12.97 9.061 30333 8.01 1736 0.867 0.93 5.40 13.06 5.817 12.87 8.07 17.66 38.911 17135 5.46 13.16 11357 117.94 8.12 17.74 9.053 19.47 5.51 13.24 7 3 4 23.76 8.17 17.83 12.424 177.16 5.56 13.33 7.88 75.27 8.22 17.91 13.635 169.26 5.61 13.42 6.478 16.67 8.27 18.00 8.213 16.61 5.67 1332 13.88 39.02 8.32 18.09 3 9 3 2 6 505.14 5.72 13.60 14.891 119.61 8.37 18.20 41.483 1187.46 5.77 13.69 11.803 91.98 8.45 18.31 28.116 221.90 5.82 13.78 13.141 61.78 8 3 0 18.40 15.189 137.02 5.87 13.88 7.631 48.78 8 3 5 18.48 5.054 2130 5.94 13.99 3.664 10.23 8.60 1837 5.224 15.20 5.99 14.07 6.107 15.41 8.65 18.66 10.74 83.23 6.04 14.16 5.224 38.10 8.70 18.76 n/d n/d 6.09 14.25 6.317 251.79 8.77 18.87 1.405 1.48 6.14 14.33 12.501 13031 8.82 18.96 3.673 7.19 6.19 14.46 17.408 369.32 8.87 19.04 21.296 161.69 6.24 14.56 1.468 2.74 8.92 19.13 2.613 4.13 6.29 14.65 9.22 115.07 8.97 19.22 1.986 1.75 6.36 14.73 5.215 12.07 9.02 19.30 12.349 41.53 6.41 14.81 7.646 105.66 9.16 19.54 12.945 37.34 6.48 14.92 32.534 122.22 9.21 19.63 5.154 11.73 6.53 15.00 16.577 45.11 9.26 19.72 9.152 51.91 6.58 15.09 4.575 25.29 9.31 19.80 0.526 0.35 6.63 15.18 0.491 0.40 9.36 19.89 7.278 82.65 6.68 15.26 8.645 90.73 9.41 19.98 3.861 15.54 6.73 15.35 7.448 15.24 9.46 20.06 7.06 14.81 6.78 15.43 4.766 6.42 9.51 20.15 10.406 124.67 6.83 15.55 12353 54.36 9.56 20.24 8.912 57.83 6.91 15.67 8.85 47.32 9.62 20.33 13.08 102.86 6.96 15.75 12.928 310.84 9.67 20.42 12.023 46.73 7.01 15.84 11.563 66.50 9.72 20.50 10.69 21.25 7.06 15.92 3.132 3.71 9.77 20 3 9 16.702 406.29 7.11 16.01 9.022 19.94 9.82 20.68 9.767 33.75 7.16 16.10 7.152 17.43 9.87 20.81 11.89 58.41 7.21 16.20 10.346 6232 9.92 20.87 16.804 206.22 7.28 16.30 21.942 349.91 9.97 20.94 14.275 93.63 7.33 16.39 53.247 525.00 10.02 21.02 28.489 698.52 7 3 8 16.48 4.339 71.71 10.07 21.11 18.882 680.79 7.43 16.56 6.887 131.19 10.12 21.20 8.007 38.46 7.48 16.66 4.692 199.76 10.17 21.28 12.791 92.09 7.54 16.75 2.799 9.80 10.22 21.37 9.699 64.09 7 3 9 16.84 19.021 276.29 10.27 21.46 3.039 4.66 7.64 16.92 6.357 124.16 10.32 21 3 7 6.253 240.36 7.69 17.01 14.932 262.09 10.48 21.83 15.119 104.08 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 143 Appendix B. (continued) Depth Age N M Depth Age N M (m) (y r b2k)* (10*m r‘) (Ug k g ') (m) (vr b2k)* CIO3 ml'*) (U g k g 1) 10.53 21.92 8.038 46.01 13.09 26.49 21.161 507.18 1038 22.00 20.567 70433 13.14 2638 15.715 455.06 10.63 22.09 8.038 34.30 13.18 26.66 22.639 295.89 10.68 22.18 19.176 359.12 13.23 26.75 53.594 389.69 10.73 22.27 27335 511.44 13.28 26.85 48.863 6 3 2 3 8 10.78 22.35 21.371 888.60 13.33 26.94 16.739 514.32 10.83 22.44 10.434 319.66 1338 27.03 19397 425.29 10.88 22.53 19.692 138.86 13.43 27.12 10.277 161.66 10.93 22.62 11333 42.37 13.48 27.22 10.91 4 4 2 3 0 10.98 22.71 11.875 112.49 1333 2731 4 3 0 9 4 6 3 2 11.04 22.81 28.644 894.02 1338 27.40 18394 596.89 11.09 22.90 17.673 13430 13.63 27 3 0 12.867 412.48 11.14 22.99 5.828 6239 13.68 2739 18.018 527.94 11.19 23.08 9.418 52.36 13.73 27.69 18.999 597.75 11.24 23.16 13.973 127.89 13.79 27.79 14.683 79.86 11.29 23.27 2.979 4.70 13.84 27.89 25.769 887.66 11.36 23.37 20.804 234.02 13.89 27.98 17.482 366.72 11.41 23.46 12.921 79.03 13.94 28.08 29.227 1494.82 11.46 23.55 30.369 365.93 13.99 28.17 12.416 462.48 11.51 23.64 19.486 64137 14.04 28.26 22384 496.83 11.56 23.73 8.034 109.12 14.09 2836 14.855 588.17 11.61 23.81 7.777 42.36 14.14 28.47 12.255 622.13 11.66 23.90 20.16 22135 14.21 28.57 10.401 561.91 11.71 23.99 2.618 5.72 14.26 28.67 12.4 113.06 11.76 24.08 3369 156.43 14.31 28.76 29.824 243.41 11.81 24.17 0.192 25.75 14.36 28.86 10.204 46.89 11.86 24.26 5.855 53.33 14.41 28.95 29.979 800.14 11.91 24.35 2.497 193.79 14.46 29.05 22.402 325.65 11.96 24.44 12.772 38.76 14.51 29.15 16.776 407.32 12.01 24.53 26.142 167.08 14.56 29.24 12.49 368.95 12.06 24.62 38.196 428.97 14.61 29.34 13.028 181.03 12.11 24.71 15.867 65.62 14.66 29.43 13.144 115.36 12.16 24.80 4.344 17.02 14.71 29.53 11.091 436.48 12.21 24.89 10.578 76.96 14.76 29.63 18.385 183.65 12.26 25.00 n/d n/d 14.81 29.72 3.772 15.81 12.33 25.11 9.236 393.37 14.86 29.82 4.673 65.38 12.38 25.20 3.337 7.71 14.91 29.92 10.489 418.25 12.43 25.29 1.914 19334 14.96 30.02 9.758 247.18 12.48 25.40 4.342 8.15 15.01 30.12 3.171 134.06 12.55 25.51 21.076 78.06 15.06 30.21 3.462 8.76 12.60 25.60 22.346 56.17 15.11 30.31 5.408 17.29 12.65 25.69 5.028 10.92 15.16 30.41 12.731 325.73 12.70 25.77 11.882 160.70 15.21 3031 17.913 466.23 12.74 25.85 20.735 183.78 15.26 30.61 7.043 34.98 12.79 25.94 10.609 232.34 15.31 30.70 34 3 3 7 1075.39 12.84 26.03 28.838 502.41 1536 30.80 15.729 161.17 12.89 26.12 21.186 563.13 15.41 30.90 13.202 492.11 12.94 26.22 16.96 30731 15.46 31.00 1.475 5 2 3 0 12.99 26.31 18364 389.28 15.51 31.10 11.801 842.11 13.04 26.40 10.881 27333 1536 31.20 5.118 147.94 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 144 Appendix B. (continued) Depth Age N M Depth A ge N M (m) (vr b2k>* (10* mT') (H g k g 1) (m) (v r b2k)* (10* mT1) (H g k g 1) 15.61 31.30 5.988 155.43 18.20 36.68 14.956 511.88 15.66 31.40 14.493 802.05 18.25 36.79 3 0 3 8 1086.16 15.71 31.50 13.731 131.95 1830 36.90 16.176 315.65 15.76 31.60 4.197 15.21 1835 37.01 23.228 748.18 15.81 31.70 7.933 88.62 18.40 37.12 60.288 791.21 15.86 31.80 9.795 91.82 18.45 37.23 47.076 593.85 15.92 31.91 12.793 206.47 1830 3 7 3 4 13.291 189.79 15.97 32.01 42.761 1387.83 1835 37.49 24308 225.79 16.02 32.12 11.689 197.74 18.63 37.63 20.855 172.49 16.07 32.22 16379 98.57 18.68 37.74 10.865 6 2 3 9 16.12 3232 23.839 402.42 18.73 37.86 32.339 479.25 16.17 32.42 18305 576.63 18.78 37.97 7.966 60.21 16.22 3232 13.866 314.66 18.83 38.08 24.723 216.09 16.27 32.62 11.628 135.13 18.88 38.19 19331 277.21 16.32 32.72 7.799 74.29 18.93 38.30 18.942 102.10 16.37 32.83 13.993 113.74 18.98 38.41 15.245 154.45 16.42 32.93 21.357 239.03 19.03 3 8 3 2 12.745 401.78 16.47 33.03 22.66 264.74 19.08 38.64 16.231 501.07 16.52 33.13 9.835 150.04 19.13 38.75 12.761 331.43 16.57 33.24 12.831 768.97 19.18 38.86 20.037 926.36 16.62 3334 9.18 328.32 19.23 38.97 15.642 638.70 16.67 33.44 7.529 181.75 19.28 39.09 3.843 100.82 16.72 3334 2.412 51.82 19.33 39.19 2.942 7.76 16.77 33.68 38.911 285.86 19.38 39.30 5.214 65.94 16.85 33.82 7.056 61.65 19.43 39.41 22.554 421.97 16.90 33.93 14.314 288.13 19.48 3 9 3 2 10.372 103.43 16.95 34.03 12.734 407.26 19.53 39.66 6.745 106.21 17.00 34.14 10.024 38.01 19.60 39.79 9.415 21.72 17.05 34.24 17.201 276.52 19.65 39.91 22 3 8 2 306.73 17.10 34.34 14.45 481.92 19.70 40.02 5.205 40.91 17.15 34.45 2.46 47.90 19.75 40.14 0.921 29.27 17.20 34.55 7.439 198.60 19.80 40.25 n/d n/d 17.25 34.66 7.922 66.85 19.85 40.37 2.136 3.17 17.30 34.76 25.915 428.31 19.90 4 0 3 3 1.442 52.51 17.35 34.87 17.739 186.47 19.99 40.69 23.495 536.16 17.40 34.98 31.991 842.40 20.04 40.80 15.033 224.05 17.45 35.08 6.826 370.70 20.09 40.92 28.722 1055.27 17.50 35.19 18.482 964.64 20.14 41.03 23.1 314.21 17.55 35.30 18.14 446.19 20.19 41.15 54.057 773.14 17.60 35.40 13.926 76737 20.24 41.27 17.664 87.34 17.65 3531 1.466 1.78 20.29 41.38 12.416 70.97 17.70 35.61 16.983 187.43 20.34 4 1 3 0 4.787 28.94 17.75 35.71 3.013 10.08 20.39 41.62 3.391 14.45 17.80 35.87 13.191 74.40 20.44 41.75 32.647 698.60 17.90 36.03 27.83 338.64 20.49 41.87 9.773 40.87 17.95 36.14 3.616 10.70 2034 41.98 1938 563.79 18.00 36.25 40.469 1970.27 2039 42.10 4.822 10.36 18.05 36.36 18.243 516.20 20.64 42.22 36.799 352.74 18.10 36.46 33.227 1005.81 20.69 42.34 73.728 260.78 18.15 36.57 23.612 639.26 20.74 42.45 37.496 675.72 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 145 Appendix B. (continued) Depth Age N M Depth Age N M (m) (vr b2k)* (103 ml'1) Itfgfcg1)- A m i__ (vr b2k)* (103 ml'1) M te l> 20.79 42.57 21.399 425.39 2 3 3 2 48.68 6 6 3 7 7 58251 20.84 42.69 39.265 215.22 2 3 3 7 48.81 3 6 3 9 393.56 20.89 42.81 20.261 64.18 23.42 48.93 23.875 398.61 20.94 42.92 15.564 180.23 23.47 49.05 8.256 69.29 20.99 43.04 7.136 91.00 2 3 5 2 49.18 8 5 6 2 2653 21.04 43.16 6.086 14.72 2 3 5 7 4 9 3 0 3.922 43.30 21.09 43.28 21.545 765.46 23.62 49.42 2.279 7.31 21.14 43.40 20.257 208.72 23.67 4 9 5 5 n/d n/d 21.19 43.52 17.188 169.76 23.72 49.71 1.469 154 21.24 43.64 16.111 287.45 23.81 49.87 8.466 15550 21.29 43.77 8^513 17.68 23.86 50.00 47.026 332.63 21.36 43.91 8.355 1959 23.91 50.12 7.443 21.34 21.41 44.03 7.918 43.71 23.96 50.24 6.97 25.97 21.46 44.15 29.288 673.12 24.01 5 0 3 7 7.818 23 5 7 21.51 44.27 11.926 40.14 24.06 50.49 1055 87.08 21.56 44.38 27.871 145.62 24.11 50.62 8.829 134.18 21.61 44.50 17.003 194.16 24.16 50.74 6.18 389.83 21.66 44.62 6.584 28.61 24.21 50.87 7.244 374.26 21.71 44.74 n/d n/d 24.26 50.99 7.47 143.54 21.76 44.86 9.213 112.48 24.31 51.11 15.034 106.31 21.81 44.98 11.793 230.71 24.36 51.24 18.703 277.23 21.86 45.11 6.18 14.35 24.41 51.36 17599 287.89 21.91 45.23 6.42 15.31 24.46 51 5 3 8.732 76.72 21.96 45.35 4.646 9.22 2 4 5 4 51.71 13.333 21352 22.01 45.47 5.196 15.33 24.59 51.83 14.33 89.76 22.06 45.59 4.786 16.15 24.64 51.96 11.772 60751 22.11 45.71 18.593 55955 24.69 52.08 13517 276.26 22.16 45.85 21.025 24456 24.74 52.21 17.39 833.55 22.22 45.98 14.25 239.13 24.79 52.33 20.162 253.87 22.27 46.10 12.618 39.61 24.84 52.46 11.987 137.64 22.32 46.23 18.318 327.34 24.89 52 5 8 7.15 16.39 22.37 46.35 17.121 155.57 24.94 52.71 12.01 80.47 22.42 46.47 9.896 70.16 24.99 52.83 8.766 375.78 22.47 46.59 15.036 284.51 25.09 53.08 11.136 219.00 22.52 46.71 20.314 167.77 25.14 53.21 16.955 161.37 22.57 46.83 24.722 420.88 25.19 53.33 18.708 548.15 22.62 46.96 16.822 952.90 25.24 53.46 22.099 318.49 22.67 47.08 14.263 119.23 25.29 5 3 5 8 0.863 3.15 22.72 47.20 21.753 199.12 25.34 53.72 21.251 143.24 22.77 47.32 7.142 39.83 25.41 53.87 10.995 31550 22.82 47.45 17.432 460.86 25.46 53.99 6.363 16.98 22.87 47.57 11.444 70.86 25.51 54.12 3.403 1856 22.92 47.70 8.802 136.90 2 5 5 6 54.24 n/d n/d 22.97 47.82 3.412 207.05 25.61 54.37 6.242 84.16 23.02 47.94 15.984 515.15 25.66 54.49 7.255 161.86 23.07 48.07 158 5.57 25.71 54.62 9.452 71.29 23.12 48.19 7.646 36.65 25.76 54.74 15.248 79.84 23.17 48.31 27.224 308.36 25.81 54.87 9.604 193.73 23.22 48.44 13563 105.46 25.86 55.00 8.357 79.22 23.27 48.56 0528 0.47 25.91 55.12 10.006 34.72 *yrb2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 146 Appendix B. (continued) Depth Age N M Depth Age N M (m) (vr b2k)* (103 m l') ( n g k g 1) (m> (vr b2k)* CIO3 ml'1) (ngfcg') 25.96 55.25 I.40I 5.26 2831 61.69 16.856 56.88 26.01 55.37 4.43 117.93 2836 61.82 I.039 1.08 26.06 55.55 n/d n/d 28.61 61.95 235 6.15 26.15 55.73 5.302 33.69 28.66 62.07 4.705 17.79 26.20 55.85 2.668 443.20 28.81 62.45 6.845 479.87 26.25 55.98 1.828 1135 28.86 6 2 3 8 6369 216.34 26.30 56.11 5.581 150.19 28.91 62.71 1.862 2.19 26.35 56.23 9.555 121.99 28.96 62.83 4.612 10.07 26.40 56.36 19.569 162.25 29.01 62.96 11.785 129.60 26.45 56.48 6.599 34.49 29.06 63.09 0.036 0.09 26.50 56.62 7.944 50.16 29.11 63.21 8.686 94.85 26.56 56.76 10.877 160.60 29.16 63.34 10.552 75.00 26.61 56.89 II.91 276.06 29.21 63.47 II.52 84.30 26.66 57.01 15.85 99.95 29.26 63.60 14.012 134.39 26.71 57.17 39.623 198.43 2931 63.72 6.851 51.64 26.78 57.29 19.425 274.08 29.36 63.88 4.327 151.10 26.81 57.39 25.06 714.35 29.44 64.04 20.639 771.75 26.86 57.52 10.424 150.67 29.49 64.16 17.954 1601.35 26.91 57.65 7.062 134.96 2934 64.29 24.87 1565.41 26.96 57.77 1.278 148.40 2939 64.42 5.343 309.56 27.01 57.90 8.344 145.70 29.64 64.55 30.704 859.39 27.06 58.02 19.689 159.74 29.69 64.68 46.053 2599.96 27.11 58.15 7.77 305.68 29.74 64.80 15.618 688.15 27.16 58.28 5.1 50.42 29.79 64.93 11.623 360.86 27.21 58.40 14.402 343.27 29.84 65.06 41.711 1809.70 27.26 58.53 18.813 351.06 29.89 65.19 7.173 489.73 27.31 58.65 24.837 202.77 29.94 65.32 5.107 237.76 27.36 58.78 24.363 526.94 29.99 65.42 14.583 651.72 27.41 58.91 13.411 100.34 30.04 65.53 13.52 588.04 27.46 59.03 24.916 261.05 30.09 65.62 8.296 437.63 27.51 59.16 6.766 265.20 30.14 65.67 10.188 129.72 27.56 59.28 3.701 9.52 30.20 65.76 26.614 780.41 27.61 59.41 7.68 499.86 30.25 65.84 34.409 996.58 27.66 59.54 6.423 17.90 30.30 65.92 24.081 574.49 27.71 59.66 3.251 62.51 30.35 66.01 14.567 364.24 27.76 59.79 19.821 339.07 30.40 66.09 4.946 10.28 27.81 59.92 18.587 82.11 30.45 66.17 19.733 342.67 27.86 60.05 7.592 18.73 3030 66.26 14.928 719.15 27.91 60.17 10.654 27.28 3035 66.34 7.799 48.05 27.96 60.30 7.064 10.69 30.60 66.42 45.332 1637.84 28.01 60.43 21.32 783.98 30.65 6 6 3 0 22.633 473.83 28.06 60.55 10.744 61.81 30.70 66.60 11.672 157.40 28.11 60.68 12.874 79.58 30.75 66.74 29.436 863.60 28.16 60.80 20.46 376.70 30.80 66.87 66.228 534.91 28.21 60.93 6.039 18.07 30.85 67.01 16.065 126.71 28.26 61.06 11335 6931 30.90 67.14 9.629 96.35 28.31 61.18 0.187 0.18 30.95 67.30 11.921 86.19 28.36 61.31 3.657 13.88 31.02 67.47 9.624 158.28 28.41 61.44 n/d n/d 31.07 67.60 8.241 58.51 28.46 61.57 1.921 1.79 31.12 67.74 26.151 492.81 *yr b2k years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 147 Appendix B. (continued) Depth Age N M Depth Age N M (m) (yr b2k)* (103 m l1) (Hgfcg1) j E i __ (vr b2k)* (103 ml'1) (Ug kg'1) 31.17 67.88 15.375 396.57 33.76 74.93 12.793 108.83 31.22 68.01 6.333 117.20 33.81 75.06 11.281 66.96 31.27 68.15 23.732 98.83 33.86 1520 30.939 1068.62 31.32 68.28 72.104 578.37 33.91 75.34 41.555 739.26 31.37 68.42 52.255 268.04 33.96 75.48 12.35 83.17 31.42 68.55 15.056 122.14 34.01 75.61 13.22 221.02 31.52 68.82 18.822 380.98 34.06 75.75 36.772 540.12 31.57 68.96 10.301 22.32 34.11 75.89 31.598 371.01 31.62 69.09 10.795 40.82 34.16 76.03 21.587 184.74 31.67 69.23 0.555 18.58 34.22 76.17 45.497 374.30 31.72 69.36 6.213 15.51 34.27 7631 55.568 580.70 31.77 69.52 8.742 91.89 3 4 3 2 76.44 66.251 753.28 31.83 69.67 11.139 179.23 34.37 76.58 70.12 1554.56 31.88 69.81 21.975 387.23 34.42 76.72 13.786 127.41 31.94 69.95 3.846 10.72 34.47 76.86 13.081 758.13 31.99 70.09 8.935 109.41 34.52 76.99 22.734 265.22 32.04 70.23 5.704 22.38 34.62 77.27 39.974 400.96 32.09 70.36 n/d n/d 34.67 77.41 28.258 833.98 32.14 70.50 6.285 135.02 34.72 77.54 15.544 334.54 32.19 70.63 10.992 664.15 34.77 77.72 26.34 330.85 32.24 70.77 11.179 295.42 34.85 77.90 29.46 249.91 32.29 70.90 18.733 154.83 34.90 78.04 25.737 259.62 32.34 71.04 19.995 709.69 34.95 78.18 26.663 202.82 32.39 71.18 52.381 556.08 35.00 78.38 33.171 388.36 32.44 71.31 25.595 284.89 35.09 78.59 36.594 393.98 32.49 71.45 21.444 586.98 35.14 78.73 21.748 138.11 32.54 71.58 12.998 335.63 35.19 78.89 16.557 104.22 32.59 71.71 4.615 20.90 35.26 79.06 45.811 802.11 32.63 71.84 10.167 346.28 35.31 79.19 21.389 70.00 32.68 71.97 13.957 540.20 35.36 79.33 22.833 95.26 32.73 72.11 28.792 173.12 35.41 79.47 13.758 44.69 32.78 72.24 27.176 145.33 35.46 79.61 18.203 479.32 32.83 72.38 15.464 106.67 35.51 79.75 19.301 399.47 32.88 72.52 17.749 79.18 35.57 79.90 32.108 149.07 32.93 72.65 12.163 49.64 35.62 80.04 25.477 803.75 32.98 72.79 8.183 18.80 35.67 80.18 26.027 214.74 33.03 72.93 15.464 176.25 35.72 80.31 20.363 132.10 33.08 73.06 12.244 23952 35.77 80.45 34.402 717.40 33.13 73.20 9.439 50.86 35.82 80.59 46.944 792.20 33.18 73.38 29.843 153.01 35.87 80.73 30.88 157.75 33.26 73.56 14.684 94.05 35.92 80.87 24.976 529.30 33.31 73.70 18.71 74.50 35.97 81.01 24.189 106.22 33.36 73.83 6.449 18.25 36.02 81.14 16.966 247.81 33.41 73.97 4.607 48.48 36.07 81.28 12.092 152.63 33.46 74.11 18.956 122.23 36.12 81.42 21.143 213.67 33.51 74.24 12.649 290.80 36.17 81.56 15.214 41.31 33.56 74.38 7.244 21.11 36.22 81.70 13.009 59.72 33.61 74.52 15.233 58.29 36.27 81.89 30.9 180.22 33.66 74.65 6.689 17.84 36.36 82.09 39.501 242.31 33.71 74.79 14.505 44.03 36.41 82.23 57.05 467.60 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 148 Appendix B. (continued) Depth Age M Depth Age N M (m) (vr b2k)* (lO^mT*) frgfcg1) (m) (vrb2k)* CIO3 m l1) (Hgfcg1) 36.46 82.37 39.403 267.70 39.10 89.74 14.814 199.86 36.51 8251 36.938 232.75 39.16 89.90 20.062 467.42 36.56 82.65 26.986 456.94 39.21 90.04 6 5 5 5 4 408.96 36.61 82.79 33.241 462.60 39.26 90.18 36.737 365.13 36.66 82.92 53.289 571.21 39.31 9052 28.251 223.10 36.71 83.06 19.421 121.33 39.36 90.46 83.149 876.72 36.76 83.20 18.696 92.75 39.41 90.60 2 0 5 6 180.70 36.81 83.36 25.428 158.68 39.46 90.74 22.016 126.47 36.87 83.51 28.121 14653 3951 90.90 15571 180.25 36.92 83.65 25.977 233.34 3 9 5 7 91.06 15.378 264.92 36.97 83.79 19.137 18559 39.62 91.20 13.386 282.87 37.02 83.93 7.779 57.85 39.67 91.34 21.604 185.24 37.07 84.06 22.326 882.40 39.72 91.48 10.924 135.89 37.12 84.19 11.349 58.56 39.77 91.62 6.671 22.01 37.16 84.32 1.308 6.42 39.82 91.76 7.958 38.07 37.21 84.46 11.316 81.49 39.87 91.90 2 2 5 9 746.75 37.26 84.60 12.183 127.36 39.92 92.04 52.421 355.61 37.31 84.74 12.579 127.64 39.97 92.19 112.488 844.14 37.36 84.88 25.494 280.33 40.02 92.33 50.018 555.31 37.41 85.02 7.247 33.77 40.07 92.47 57.47 476.90 37.56 85.44 14.599 231.83 40.12 92.61 43.379 676.34 37.61 85.57 6.949 28154 40.17 92.75 12.076 338.01 37.66 85.71 20.658 367.76 40.22 92.89 30.584 383.23 37.71 85.85 10.538 53.16 40.27 93.03 14.943 82.34 37.76 85.99 19.226 32252 40.32 93.19 34.772 68455 37.81 86.13 10.489 42.35 40.38 93.35 24.041 236.28 37.86 86.27 9.746 51.85 40.43 93.49 18.159 70.86 37.91 86.42 28.959 621.95 40.48 93.63 10.563 37.99 37.97 8 6 5 6 30.662 962.90 4 0 5 3 93.77 8.435 58.20 38.02 86.70 6.737 51.97 40.58 93.92 7.334 16.32 38.07 86.84 2.791 11.74 40.63 94.06 20.425 624.13 38.12 87.02 6.439 104.80 40.68 94.20 13.739 136.04 38.20 87.20 20.129 75.63 40.73 94.34 45.881 665.05 38.25 87.34 7.524 156.13 40.78 94.48 69.626 110955 38.30 87.48 7.515 34.27 40.83 94.62 57.619 1152.67 38.35 87.62 18.059 82.90 40.88 94.76 48.726 1248.82 38.40 87.76 49.956 152.94 40.93 94.91 18.251 53053 38.45 87.90 6.577 13.98 40.98 95.05 18.963 99.40 38.50 88.04 15.419 91.18 41.03 95.19 63.057 1106.00 38.55 88.18 23.787 852.82 41.08 95.32 83.505 621.45 38.60 88.32 15.933 152.56 41.12 95.43 33.74 126.88 38.65 88.46 19.74 146.67 41.16 95.61 24545 137.26 38.70 88.60 45.035 1082.65 41.24 95.82 12.103 47.95 38.75 88.75 19.209 73.73 4151 96.02 11.12 69.22 38.80 88.89 33.437 331.85 41.38 96.22 6.603 17.09 38.85 89.03 18501 785.30 41.45 96.42 4.606 7.87 38.90 89.17 42.664 727.22 4 1 5 2 96.61 5.824 17.87 38.95 89.31 26.17 311.97 4 1 5 9 96.79 16.383 54.89 39.00 89.45 19.232 153.04 41.65 96.99 7.472 30.88 39.05 89.59 11.971 77.94 41.73 97.20 9 5 1 8 77.15 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 149 Appendix B. (continued) Depth Age N M Depth Age N M (m) (yr b2k)* (10* ml'1) (Ug kg'1) (m) (vr b2k)* (103 m l1) (Ug kg') 41.80 97.40 3.172 3.79 47.22 113.06 6.625 3735 41.87 97.64 6.247 18.63 4731 11335 16.141 247.46 41.96 97.87 9.054 60.16 47.42 113.65 19.724 117.81 42.03 98.07 6.95 16.48 4 7 3 2 113.94 5.843 97.34 42.10 98.27 21.354 153.91 47.62 114.28 5.969 39.96 42.17 98.47 13.256 51.60 47.75 114.61 14.131 78.68 42.24 98.67 77.245 4 1 0 3 0 47.85 114.92 6.019 500.95 42.31 98.87 16.144 57.72 47.96 115.23 16.279 229.42 42.38 99.07 15.036 56.71 48.06 11532 19.57 326.82 42.66 99.92 737 34836 48.16 115.77 10363 92.70 42.84 100.38 8.994 27.85 4833 11631 1336 96.69 42.92 100.60 4316 7.03 4833 116.89 35.404 16138 42.99 100.81 4.389 4.47 48.63 117.19 12.724 35.28 43.07 101.03 20.108 60.67 48.73 11730 7.074 21.11 43.14 101.24 9.343 51.18 48.84 117.81 8.334 27.79 43.22 101.45 26.119 468.06 48.94 118.08 11.696 27.62 43.29 101.65 3.689 23.12 49.02 118.36 10306 33331 43.36 101.85 5.318 20.96 49.12 118.65 7.468 58.88 43.43 102.05 13.886 141.64 49.22 118.95 74.338 1158.84 43.50 102.26 6.581 32.01 49.32 119.26 5.395 10.40 43.57 102.49 14.36 849.90 49.43 119.57 8.889 35.55 43.66 102.75 17.611 437.51 4933 119.85 9.021 44.98 43.75 103.00 18.512 332.26 49.63 120.13 15.905 132.32 43.83 103.23 17.564 115.23 49.72 120.40 12.787 94.23 43.91 103.48 10.867 44.65 49.81 120.68 11.716 39.94 44.00 103.72 5.777 16.76 50.00 121.24 12.997 120.05 44.08 103.92 10.357 70.04 50.10 121.55 7.157 73.37 44.22 104.33 11.48 68.34 50.31 122.18 16.745 106.92 44.38 104.81 7.248 21.93 50.72 123.37 13.739 173.35 44.47 105.10 7.115 18.75 50.82 123.68 19.895 52.45 44.58 105.40 6.372 12.11 50.93 123.99 16.822 94.26 44.68 105.69 4.32 5.81 51.12 124.53 14.556 71.92 44.78 105.97 3.334 3.39 51.20 124.78 16.588 63.72 44.97 106.54 6.214 14.79 51.37 125.24 6.713 987.42 45.18 107.15 15.412 50.21 51.43 125.47 6.795 11.13 45.28 107.44 11.784 35.78 51.53 125.77 13.004 32.51 45.38 107.75 18.027 62.44 51.63 126.07 21.742 184.74 45.49 108.03 21.758 306.93 51.73 126.37 40.282 715.01 45.68 108.60 12.567 46.27 51.83 126.69 15.202 65.11 45.78 108.89 14.207 38.12 51.95 127.01 31.559 634.82 45.97 109.44 18.103 275.77 52.04 127.29 57.918 842.55 46.07 109.74 17.345 57.15 52.14 12736 31.022 549.59 46.18 110.13 14.129 44.46 52.22 127.82 11.237 356.10 46.34 110.43 5.732 13.13 52.32 128.32 6.154 14630 46.39 110.66 8.093 30.24 5235 128.85 22.692 417.87 46.70 111.55 12.768 48.19 52.67 129.15 21.18 270.27 46.80 111.86 6.545 12.27 52.75 12939 9.429 10139 46.91 112.18 8.626 21.68 52.83 129.65 20.161 14631 47.02 112.47 10.882 103.20 52.92 129.92 15.793 220.93 47.11 112.76 23.137 198.19 53.01 13036 17.47 100.42 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 150 Appendix B. (continued) Depth Age N M Depth Age N M 0”) (yr b2k)* (IQ3 m l'1) (Ug k g 1) ft” ) (vr b2k)* (10* m l1) kg.‘) 53.22 130.80 17.087 199.41 58.34 146.47 19.719 141.35 5331 131.07 13.947 165.24 58-50 146.91 8.016 36.16 53.40 131.34 5.449 18.22 58.63 147.28 7.876 38.89 53.49 131.61 8.661 77.81 58.74 147.66 15.727 212.46 5 3 3 8 131.89 10.599 91.18 58.88 148.00 61.671 812.01 53.68 132.19 30.489 600.05 58.96 148.25 31.098 596.25 53.78 132.54 19.861 632.61 59.04 148.56 8.035 20.75 53.91 132.90 15.657 292.89 59.16 148.91 15.484 76.19 54.01 133.24 23.544 557.73 59.27 149.29 9.964 32.37 54.13 133.57 13.23 61.40 59.41 149.66 9.024 73.47 54.23 133.86 9.69 39.78 5951 149.97 13.562 287.46 54.32 134.11 9.697 24.57 59.61 150.28 13.696 63.63 54.40 134.25 12.365 88.12 59.71 150.60 9.899 24.93 54.52 134.75 8.882 63.86 59.82 150.93 8.201 22.05 54.62 135.33 24.3 295.59 59.92 151.25 6.729 13.05 54.72 135.63 14.446 54.21 60.03 15158 25.43 100.88 54.91 135.92 6.484 223.49 60.13 151.88 7.868 556.71 55.01 136.22 5.116 11.00 60.33 152.48 4.504 6.42 55.11 136.49 43.157 250.24 60.42 152.78 12.081 61.26 55.19 136.74 13.462 58.84 60.52 153.09 14.244 36.91 55.27 136.98 18.561 98.37 60.62 153.40 4.504 5.31 55.43 137.46 34.504 108.70 60.72 153.72 5.284 16.35 55.51 137.83 7.233 33.01 60.83 154.03 6.741 11.51 55.67 138.23 36.371 1161.34 60.92 154.31 34.522 345.25 55.77 138.53 17.99 61.06 61.01 154.63 28.37 650.68 55.87 138.84 6.391 23.21 61.13 155.02 18.18 223.26 55.97 139.14 32.797 153.57 61.26 155.36 11-532 57.73 56.07 139.48 11.099 60.53 61.35 155.63 17.685 331.00 56.20 139.83 10.015 348.34 61.43 155.92 36.906 413.56 56.30 140.13 15.829 183.73 61.54 156.25 31.937 348.03 56.40 140.43 31.886 242.89 61.64 156.61 24.334 503.53 56.50 140.73 10.164 65.81 61.77 156.96 46.981 908.76 56.60 141.04 24.448 36.87 61.87 157.29 12.355 126.83 56.70 141.34 15.839 82.18 61.98 157.62 10.588 22.26 56.80 141.65 14.669 270.08 62.08 157.93 16.323 114.04 56.90 141.95 21.287 298.24 62.18 158.24 8.028 91.47 57.00 142.26 18.97 161.72 62.28 158.54 31.154 314.20 57.10 142.57 8.429 67.69 62.37 158.84 17.236 140.03 57.21 142.89 16.988 221.11 62.47 159.22 8.119 36.86 57.31 143.20 24.656 106.03 62.61 159.61 10.292 30.46 57.41 143.50 20.029 765.20 62.71 159.89 17.4 66.78 57.51 143.81 25.043 456.49 62.79 160.16 14.292 42.88 57.61 144.14 16.208 328.66 62.88 160.46 13.955 81.54 57.73 144.48 17.736 134.78 62.98 160.77 55.859 1542.01 57.83 144.79 33.426 515_51 63.08 161.27 33.623 354.92 57.93 145.09 19.665 531.37 63.17 161.54 12.323 83.96 58.02 145.39 52.163 1236.36 63.30 161.80 15.945 87.80 58.12 145.70 21.969 398.23 63.42 162.18 106.882 1449.43 58.22 145.98 6.709 92.26 6 3 5 4 162.54 13.998 59.81 5 8 3 0 146.16 9.421 61.93 63.65 162.85 36.394 295.48 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 151 Appendix B. (continued) Age N M Depth Age N s i (yr b2k)* (10* m l'1) (Mg k g'') (m) (vrb2kV* (103 m l'1) J e£ 63. 163.14 9.778 70.64 69.01 179.92 21.046 135. 63. 163.40 20.96 176.07 69.11 180.24 53.676 062. 63. 163.69 103.641 1018.57 69.20 18034 32.47 379. 64. 164.02 20.589 199.71 6 9 3 0 180.98 14.25 88. 64. 164.35 18.056 327.98 69.48 181.43 3 5 3 0 7 313. 64. 164.68 25.484 446.39 6 9 3 8 181.80 6.96 30. 64. 164.96 10.15 64.76 69.71 182.17 32.048 201. 64. 165.24 18.393 127.00 69.81 182.49 29.248 210. 64. 165.56 12.705 122.71 69.91 182.82 27.385 161. 64. 165.87 12.695 90.58 70.01 183.12 20.048 119. 64. 166.18 31.563 524.56 70.10 183.48 4.962 10. 64. 166.48 12.789 73.40 70.23 183.86 10.326 112. 64. 166.84 14.729 149.52 7033 184.21 12.62 54. 65. 167.22 27.04 1058.49 70.45 18437 5.075 53. 65. 167.59 10.791 117.15 7035 184.90 10.926 47. 65. 167.97 7.013 28.88 70.65 185.24 7.085 16. 65. 168.31 18.353 233.29 70.76 18536 12.398 54. 65. 168.66 71.76 714.36 70.85 185.95 12.453 52. 65. 169.01 8.699 58.75 71.00 186.36 5.977 18. 65. 169.39 21.028 187.71 71.10 186.72 19.365 93. 65. 169.82 15.509 191.72 71.22 187.09 6.612 21. 65. 170.17 12.491 62.97 71.33 187.43 10.358 119. 66 . 170.48 8.376 26.99 71.43 187.76 28.754 443. 66 . 170.83 25.541 112.36 71.53 188.08 25.995 413. 66 . 171.17 18.852 143.17 71.63 188.39 18.488 234. 66 . 171.49 25.346 340.56 71.72 188.67 38.588 318. 66 . 171.82 24.112 107.39 71.80 189.02 9.499 110. 66 . 172.14 14.045 107.03 71.93 189.41 11.695 92. 66 . 172.41 7.429 38.73 72.04 189.75 16.508 208. 66. 172.68 7.039 21.74 72.14 190.04 48.44 671. 66 . 172.97 17.969 75.42 72.22 190.34 10.375 48. 66 . 173.29 9.431 162.20 7 2 3 2 190.66 18.631 565. 67. 173.62 7.267 194.70 72.42 190.99 17.725 84. 67. 173.94 4.704 8.65 7 2 3 2 191.32 14.671 171. 67. 174.26 31.948 843.28 72.62 191.65 9.869 115. 67. 174.58 20.625 256.03 72.72 191.99 17.523 53. 67. 174.90 17.396 319.85 72.83 192.34 5.113 18. 67. 175.21 15.512 93.72 72.93 192.66 13357 216. 67. 175.50 10.477 53.78 73.03 192.99 24.325 190. 67. 175.82 16.759 93.42 73.13 193.32 8.422 49. 67. 176.15 10.878 92.24 73.23 193.66 18.06 76. 67. 176.47 24.975 204.58 73.34 193.95 18.516 110. 68 . 176.84 7.496 25.18 73.41 194.23 9.892 110. 68 . 177.23 19.89 233.56 7331 19435 30.726 670. 68 . 177.55 13.869 57.36 73.61 194.88 17.457 204. 68 . 177.82 7.91 42.45 73.71 195.23 54.714 505. 68 . 178.34 6.433 35.21 73.91 195.87 14.423 305. 68 . 178.89 13.208 51.52 74.01 196.22 30.88 500. 68 . 179.20 9.999 33.70 74.12 196.54 12.481 343. 68 . 179.55 8.569 85.86 74.20 196.84 16317 733. *yr b2k = years before AD 2000; n/d = no data copyright owner. Further reproduction prohibited without permission. 152 Appendix B. (continued) Depth Age N M Depth Age N M (yr b2k)* (103 ml*) (i^g kg‘) (m) (vr b2k)* (103 m l1) (Ug kg'1) 74.30 197.34 36.427 518.67 7 9 3 8 214.10 18.679 690.54 74.40 197.59 23.975 253.07 79.48 214.46 15.331 7 2 J8 74.50 197.83 19.766 247.49 7 9 3 9 214.81 6.726 18.96 74.60 198.16 14.283 116.15 79.69 215.15 17.693 88.47 74.70 198.51 10.475 199.54 79.79 215.47 12.073 77.73 74.81 198.86 4.533 31.35 79.88 215.71 21.348 158.21 74.91 199.16 14.999 97.39 79.93 215.98 7.629 29.95 74.99 199.39 6.183 22.84 80.04 216.42 17.56 91.05 75.05 199.65 25.704 219.40 80.19 216.98 20.846 122.96 75.15 199.98 11.331 125.35 80.37 217.47 14.188 310.46 75.25 200JO 16.397 162.41 80.48 217.81 25.628 594.60 75.34 200.58 18.763 94.35 80.57 218.08 22.184 455.18 75.42 200.86 13.687 128.92 80.64 218.41 13.995 272.94 75.51 201.16 15.704 67.83 80.76 218.81 8.865 59.61 75.60 201.46 26.267 310.43 80.88 219.15 14.699 98.69 75.69 201.74 6.856 26.29 80.96 219.46 7.939 52.24 75.88 202.36 10.42 45.51 81.06 219.80 10.773 57.81 75.97 202.68 20.027 91.84 81.16 220.12 16.397 189.39 76.07 203.02 11.023 54.10 81.25 220.43 24.06 177.14 76.18 203.37 21.101 344.56 81.34 220.75 49.813 602.79 76.28 203.71 22.859 408.05 81.44 221.06 11.3 47.78 76.38 204.04 9.863 60.09 81.52 221.36 18.23 168.71 76.48 204.39 25.891 224.68 81.62 221.72 20.151 226.48 76.59 204.74 15.407 295.48 81.73 222.10 11.491 55.90 76.69 205.09 15.98 98.96 81.84 222.47 7.283 86.89 76.80 205.44 100.72 860.40 81.95 222.85 18.71 86.80 76.90 205.79 36.582 288.99 82.06 223.22 30.297 716.71 77.01 206.16 14.283 55.89 82.17 223.62 14.318 111.97 77.12 206.51 21.574 125.83 82.29 224.15 14.594 389.23 77.22 206.84 14.38 271.41 82.48 224.63 8.088 127.38 77.32 207.16 8.631 90.05 82.57 224.99 17.173 332.68 77.41 207.48 37.293 269.56 82.69 225.33 8.689 56.69 77.51 207.82 19.515 99.22 82.77 225.62 18.859 90.87 77.61 208.15 14.075 194.47 82.86 226.03 5.396 86.12 77.71 208.49 47.851 263.37 83.01 226.43 16.059 104.72 77.81 208.84 6.844 20.83 83.09 226.70 9.339 55.31 77.92 209.22 9.338 43.66 83.17 227.01 17.317 732.27 78.04 209.61 6.969 19.13 83.27 227.35 29.838 507.14 78.15 209.96 6.557 23.56 83.37 227.70 12.312 266.59 78.25 210.31 11.51 234.10 83.47 228.06 28.495 350.68 78.36 210.68 21.599 314.85 83.58 228.43 13.167 561.65 78.47 211.03 12.631 202.76 83.69 228.78 25.113 118.58 78.57 211.37 11.604 161.33 83.78 229.11 17.919 66.45 78.67 211.72 7.817 148.61 83.88 229.40 22.173 134.69 78.78 212.09 36.887 395.88 83.95 229.71 12.306 442.06 78.89 212.44 11.109 38.61 84.06 230.09 22.557 99.69 78.99 212.77 10.773 64.76 84.17 230.43 12.916 171.48 79.08 213.09 16.78 68.81 84.26 230.78 8.821 156.35 79.18 213.43 14.184 80.55 84.37 231.14 11.741 42.49 79.28 213.76 7.905 23.89 84.47 231.86 8.489 28.71 *yrb2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 153 Appendix B. (continued) Depth A ge N M Depth Age N M (m) (vr b2k)* (103 m l1) (H g k g ') (m) (vrb2k)* (103 m l’1) (Ug k g ') 84.79 232-59 50.777 888.60 90.42 25256 8.207 142.72 84.89 232.93 25.616 127.08 9 056 252.82 10.654 1076.65 84.99 233.28 24.037 169.47 90.68 253.17 50.796 282.16 85.09 233.62 84.921 6362.14 90.76 253.48 15.837 155.60 85.19 233.97 46.208 1750.48 90.85 253.78 14.033 43.75 85.29 234.34 22.786 553.75 90.93 254.18 5.127 12.20 85.40 234.71 9.453 210.09 91.07 254.61 21.242 122.19 85.50 235.06 19.343 240.92 91.17 255.02 10.742 367.99 85.60 235.42 8.819 121.59 9 152 256.23 29.66 143.43 85.71 235.77 13.165 217.88 91.63 256.61 5 5 9 8 58.05 85.80 236.08 8.865 150.95 91.73 256.99 20.062 2 8854 85.89 236.48 10.652 74.27 91.85 257.46 19.761 122.24 86.03 236.93 10.485 83.65 91.99 257.89 4.952 200.95 86.15 237.30 13.304 91.17 92.08 258.23 13.834 131.34 86.25 237.65 15.02 132.64 92.18 25859 7.219 23.68 86.35 238.00 14.626 93.10 92.28 258.95 8.425 42.70 86.45 238.35 14.603 56.54 92.47 259.63 8 5 1 9 538.73 86.55 238.70 6.79 44.60 9 257 260.07 9.024 25.95 86.65 239.04 18.098 114.47 92.72 260.65 9.334 95.03 86.75 239.43 17.643 88.95 92.90 261.01 11.375 181.53 86.87 239.83 11.859 161.92 92.92 261.23 11.288 219.01 86.98 240.22 29.071 575.03 93.02 261.60 8.058 63.40 87.09 240.65 18.932 776.74 93.13 262.00 19.691 455.34 87.22 241.19 12.445 164.45 93.24 262.37 10.444 64.91 87.76 242.94 29.66 143.43 93.34 262.73 6.921 22.34 87.87 243.36 5.598 58.05 93.44 263.09 12577 52.10 88.00 243.77 20.062 288.34 93.54 263.41 12.878 75.40 88.10 244.12 19.761 122.24 93.62 263.71 8.531 85.02 88.20 244.47 4.952 200.95 93.71 264.08 25.596 116.02 88.30 244.82 13.834 131.34 93.83 264.48 7.803 28.94 88.40 245.23 7.219 23.68 93.93 264.93 6.057 14.89 88.54 245.65 8.425 42.70 94.08 265.38 11.189 38.76 88.64 246.01 16.112 51.89 94.18 265.82 7.575 17.53 88.75 246.38 8.319 538.73 9 452 266.20 8.207 142.72 88.85 246.74 9.024 25.95 94.39 2 6652 10.654 1076.65 88.95 247.09 9.334 95.03 94.49 266.88 50.796 282.16 89.05 247.44 11.375 181.53 94.59 267.24 15.837 155.60 89.15 247.79 11.288 219.01 94.69 267.62 14.033 43.75 89.25 248.15 8.058 63.40 94.80 268.00 20.27 240.85 89.35 248.46 19.691 455.34 94.90 268.42 22.256 180.05 89.43 248.74 10.444 64.91 95.03 268.81 10.714 102.11 89.50 249.04 6.921 22.34 95.12 269.35 5.249 159.92 89.60 249.41 12.577 52.10 95.33 269.95 7.501 30.24 89.71 249.77 12.878 75.40 95.45 270.33 10.124 47.02 89.80 250.12 8-531 85.02 95.78 271.65 23.707 337.16 89.91 250.49 25.596 116.02 95.93 272.11 10.439 524.91 90.01 250.85 7.803 28.94 96.03 272.49 9.254 45.80 90.11 251.19 6.057 14.89 96.14 272.93 13.362 103.82 90.21 251.54 11.189 38.76 96.27 273.35 10.327 44.40 90.31 251.91 7.575 1753 96.37 273.71 15.459 82.78 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 154 Appendix B. (continued) Depth Age N M Depth Age N M (m) (vr b2k)* (1 0 s ml*1) (Ug k g ') (m) (vr b2k)* CIO3 mT1) O ig k g ') 96.47 274.04 9331 44.15 102.07 294.76 5 0 3 5 5 208.92 96.78 275.19 14.806 2023.14 102.16 295.13 9.533 3134 96.88 275.60 29.621 1187.09 102.27 29531 7.9 20.47 97.00 276.02 15.505 141.03 102.36 295.84 12.582 122.47 9 7 3 2 277.15 19.369 237.49 102.45 296.22 12.735 50.74 97.49 277.78 9 3 5 4 79.88 10236 296.62 28.732 1060.08 97.57 278.11 16.752 7632 102.66 297.03 9.912 162.52 97.67 278.49 7.711 2631 102.77 29737 30.42 233.92 97.78 278.86 10.024 31.86 102.95 297.93 19.73 290.90 97.98 279.61 12.978 653.39 102.96 298.14 26.333 203.76 98.08 279.96 18.149 13533 103.06 298.51 19.898 480.23 98.17 280.30 10.112 37.16 103.16 298.87 21.191 214.76 98.27 280.66 13.846 89.62 103.25 299.23 36.418 165.94 98.37 281.01 8.799 23.15 10335 299.62 8.053 45.08 98.46 281.38 9.661 30.60 103.46 299.96 23.121 171.11 98.57 281.77 8.012 25.14 10334 300.34 19.279 842.07 98.67 282.14 5.407 15.18 103.66 300.76 19.385 151.25 98.77 282.51 9.92 84.47 103.76 301.13 13.359 251.10 98.87 282.87 23.935 213.54 103.86 30135 15.463 81.96 98.97 283.26 9.433 50.58 103.98 301.93 14.831 88.18 99.08 283.60 14.036 105.03 104.06 30230 7.395 50.81 99.15 283.91 29.836 314.72 104.17 302.88 16.821 61.88 99.24 284.22 9.155 58.60 104.26 303.15 7.734 44.70 99.42 284.94 22.746 165.34 104.36 303.43 21.994 180.92 99.53 285.35 15.553 208.77 104.46 303.81 15.865 119.21 99.64 285.74 22.008 144.50 104.56 304.19 5.332 34.04 99.74 286.10 5.174 78.71 104.66 304.55 38.426 262.49 99.84 286.45 18.891 561.97 104.75 304.91 12.13 104.63 99.93 286.76 12.131 63.32 104.85 305.29 30.939 179.26 100.01 287.07 7.822 29.70 104.95 305.65 13.198 43.79 100.10 287.45 12.417 83.92 105.04 305.97 11.977 215.51 100.21 287.85 63.15 1218.06 105.12 306.31 9.893 36.89 100.32 288.26 15.094 7031 105.22 306.71 8.926 28.01 100.43 288.65 6.069 27.23 10533 307.11 11.067 54.07 100.53 289.03 37.537 213.24 105.43 307.49 20.458 138.66 100.63 289.40 10.807 80.28 10533 307.87 15.821 85.20 100.73 289.77 26.687 520.14 105.63 308.26 12.22 40.34 100.83 290.10 18.59 224.71 105.73 308.64 16.036 53.12 100.90 290.42 29.207 451.03 105.84 309.03 9.234 25.93 101.00 290.81 13.519 112.63 105.94 309.40 7.604 105.17 101.11 291.20 30.154 148.73 106.03 309.76 14.826 60.34 101.21 291.60 13.37 135.65 106.13 310.12 10318 100.94 101.32 291.99 17.465 534.89 106.22 310.47 15.041 49.06 101.42 292.36 9.853 31.45 106.31 310.81 18.461 72.63 101.52 292.71 6.258 77.16 106.40 311.21 6.712 4733 101.61 293.02 19.66 112.86 10632 311.52 13.726 224.71 101.69 29330 12.737 287.13 10636 311.89 10308 84.83 101.76 293.61 7.629 50.02 106.71 312.37 15.998 12831 101.86 294.01 11.522 33.85 106.81 312.79 4.888 11.64 101.97 294.40 7.523 15.70 106.93 313.22 24.066 17937 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 155 Appendix B. (continued) D epth Age N M Depth Age N M (m ) (yr b2k)* (10* ml*1) (Ug k g 1) (m) (yr b2k)* (10* ml*1) (Ug k g ') 107.03 313.60 5.568 11J1 113.71 339.64 8.701 55.99 107.13 313.98 30.88 199.81 113.80 340.00 7336 154.72 107.23 314.40 19.507 46.75 113.89 34032 39.493 436.96 107.35 314.81 2 0 J 8 16135 113.96 340.65 46 3 3 2 420.81 107.45 315.19 29.56 26035 114.05 341.01 50.687 625.89 107.55 315.58 9.556 37.09 114.14 34138 6.149 37.21 107.65 315.96 31.396 686.08 114.24 341.84 9.529 77.61 107.75 316.39 13.776 8833 11437 34230 15.615 339.89 107.87 316.81 30.757 162.28 114.47 342.68 12383 66.89 107.97 317.20 12.543 41.17 11436 343.06 11309 340.01 108.07 317.56 14.962 48.08 114.66 343.47 24.46 103.24 108.16 317.91 20.409 334.90 114.77 343.89 9 3 0 4 24.24 108.25 318.19 11.708 28.13 114.87 344.34 15.227 98.40 108 JO 318.48 24.903 241.25 115.00 344.82 14.837 47.09 108.40 319.08 21.96 296.02 115.11 345.18 14.171 33.97 108.50 319.42 27.49 783.75 115.18 34532 15.444 51.45 108.61 319.75 11.707 119.00 115.28 345.92 6.918 18.23 108.75 320.18 12.793 116.28 115.38 346.32 35.029 119.01 108.83 320.57 57.921 461.01 115.48 346.77 9.126 33.90 108.95 321.04 11.09 29.51 115.60 347.24 4.853 7.82 109.07 321.47 24.476 119.67 115.71 347.66 14.235 59.62 109.17 321.88 35.058 95133 115.81 348.08 12.435 58.66 109.50 323.14 57.982 59134 115.92 348.58 10.33 89.58 109.60 323.53 14.95 564.30 116.06 349.08 5.496 13.67 109.70 323.99 11.293 56.06 116.17 34934 17.862 336.39 109.84 324.48 9.906 31.65 116.29 350.01 6.958 61.69 109.96 324.99 12.523 34.18 116.41 350.48 42.954 570.39 110.10 325.51 19.529 106.26 116.53 350.90 13.639 623.90 110.23 325.98 10.34 32.21 116.62 351.26 5.994 21.56 110.34 326.45 9.475 21.63 116.71 351.63 11.745 239.59 110.47 327.10 16.135 50.84 116.80 352.03 9.214 25.26 110.57 327.41 9.839 101.83 116.91 352.43 13.156 116.06 110.67 327.73 32.602 564.93 117.00 352.80 12.11 49.06 110.79 328.22 15.995 168.49 117.09 353.11 27.401 178.91 110.92 328.69 8.042 35.20 117.15 35332 3.557 3.32 111.03 329.08 69.436 1509.48 117.29 354.00 13.258 73.57 111.12 329.45 16.752 163.14 117.39 354.41 29.214 100.81 111.22 329.86 20.728 88.25 117.49 354.81 14.515 44.47 111.33 330.22 6.264 21.98 11739 355.26 8.366 26.75 111.40 330.59 14.328 48.76 117.71 355.87 5.795 10.22 111.52 331.11 16.692 8 9 3 4 117.89 356.51 4.352 10.10 111.66 331.62 23.064 78.68 118.02 357.02 21.986 85.26 111.78 332.05 7.418 19.92 118.14 357.46 9.549 155.59 111.88 332.49 4.53 7.42 118.24 357.87 7.099 152.70 113.08 337.19 11.07 55.99 118.34 358.25 22.208 670.33 113.19 337.64 8.166 17.01 118.43 358.64 71.934 805.20 113.31 338.08 40.279 457 3 6 11833 359.01 11.103 81.44 113.41 338.51 8.467 18.22 118.62 359.45 41.217 455.13 113.53 338.93 17.651 182.01 118.75 359.92 33.711 296.74 113.62 339.29 6.171 43.44 118.85 360.33 18.004 190.11 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 156 Appendix B. (continued) Depth Age N M Depth Age N M (m) (yr b2k)* (103 m l1) frg fc g '1) JrsL (yr b2k>* (10* m l1) («fcg") 118.95 360.75 15.842 157.03 124.65 384.34 7.084 22.05 119.06 361.18 44.336 328.10 124.76 385.17 11.706 49.91 119.16 361.61 9.685 38.58 125.04 385.92 22.83 189.72 119.27 362.03 36.229 500.13 125.12 386.27 20.146 170.05 11936 362.42 10.438 53.84 125.21 386.64 18.685 163.87 119.46 362.81 6.404 29.21 125.30 387.04 40.986 484.17 11935 363.20 11.657 65.78 125.40 38732 18.935 100.08 119.65 36337 55.902 402.56 125.52 387.98 11361 47.75 119.73 363.93 16.491 87.08 125.61 388.30 42.264 27339 119.83 364.32 25.194 110.74 125.67 388.61 19.444 89.08 119.92 364.67 21.383 710.05 125.76 389.04 47.24 325.10 120.00 365.02 21.644 788.58 125.87 389.46 11.07 51.06 120.09 365.37 22.612 911.39 125.96 389.84 16355 81.04 120.17 365.80 31.803 526.61 126.05 390.33 19.237 94.76 120.30 366.26 14.589 233.80 126.20 390.85 4383 3 0 3 9 120.39 366.67 8.687 115.46 12630 391.27 10.371 141.90 120.50 367.16 7.48 59.91 126.40 391.76 31.735 132.43 120.63 367.68 7.235 96.23 126.53 392.23 12.815 6231 120.75 368.15 15.229 210.76 126.62 392.68 20.335 95.00 120.86 368.59 18.995 187.99 126.74 393.12 14.46 364.98 120.97 369.10 18.537 333.08 126.83 39331 14.755 158.17 121.11 369.76 12.864 93.49 126.92 393.93 15.89 182.66 121.29 370.33 34.637 1182.67 127.03 394.45 15.903 793.29 121.39 370.81 19.812 217.19 127.17 395.02 27.054 321.06 121.52 371.41 5.309 91.96 127.30 395.54 25.22 515.38 121.68 372.04 9.469 49.65 127.41 396.00 9.614 85.74 121.82 372.64j 21.727 258.94 127.52 396.45 26.566 225.19 121.97 373.22 20.992 262.50 127.62 396.78 35.545 2888.66 122.10 373.74 23.219 114.77 127.67 397.26 7.139 19.19 122.22 374.60 9.015 124.37 127.84 397.88 7.8 158.26 122.37 375.04 44.076 362.27 127.96 398.41 7.269 94.48 122.52 375.47 17.353 372.95 128.09 398.90 19.597 1498.59 122.64 376.01 7.039 133.18 128.19 399.42 6.275 31.22 122.78 376.52 3.324 3.64 128.33 399.94 3.997 16.49 122.89 377.02 6.822 23.16 128.43 400.37 14.042 132.78 123.02 377.50 55.422 1317.24 128.53 400.78 10.415 103.09 123.12 377.90 36.635 1053.64 128.62 401.23 17.294 231.65 123.21 378.30 16.264 110.45 128.74 401.75 4.195 5.63 123.31 378.75 9.095 213.13 128.86 402.10 12.611 93.46 123.42 379.25 16.844 118.18 128.91 402.39 9.428 46.32 12335 379.73 8.386 66.80 129.00 402.78 6.886 100.60 123.65 380.13 13.572 86.86 129.09 403.19 19.126 1025.40 123.74 380.48 29.316 378.15 129.19 403.64 13.929 98.59 123.82 380.88 12.914 64.30 12930 404.07 22.374 180.56 123.93 381.45 10.621 45.88 12939 404.46 12.518 67.36 124.10 382.02 8.476 30.85 129.48 404.80 35.662 316.63 124.21 382.44 13.16 83.02 12935 405.23 49.972 1361.49 124.30 382.95 33.179 578.21 129.68 405.90 15.413 62.84 124.45 383.47 5.655 10.44 129.86 40 6 3 3 17.779 84.66 124.55 383.89 10.297 45.10 129.97 407.09 21.113 160.91 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 157 Appendix B. (continued) Depth Age N M Depth Age N M (m) (v r b2k)* (10* m l') (MB kg'1) (m) (vrb2k)* (103 ml*1) (UK k g 1) 130.12 407.65 6.6 2735 135.57 431.61 19.595 151.89 130.23 408.13 17.669 87.10 135.69 432.21 8.122 158.02 130.34 408.59 4.48 10.31 135.84 432.82 9.457 75.08 130.44 409.03 8.066 30.79 135.96 433-33 11.138 244.69 130.54 409.46 11.654 33.07 136.07 433.77 38.526 560.27 130.64 409.96 19.631 422.19 136.16 434.22 10.226 45.95 130.77 410.52 21.403 208.99 136.27 434.62 18.436 220.46 130.90 411.01 29.089 129.72 13634 435.05 30.238 271.00 130.99 411.47 8.971 27.40 136.46 435.73 31.081 390.01 131.11 411.97 6.54 17.25 136.46 435.73 9.976 80.96 131.22 412.49 3.562 3.27 136.64 436.34 28.018 203.57 13135 413.01 19.159 315.39 136.73 436.83 15.49 117.99 131.46 413.53 6.993 132.71 136.86 437.31 11.865 70.93 13139 414.00 6.818 152.70 136.94 437.67 29.254 659.61 131.68 414.43 13.438 114.87 137.02 438.09 12.133 203.09 131.79 414.93 12.979 135.79 137.13 438.56 20.382 443.72 131.91 415.41 7.061 25.05 137.23 438.98 32.965 203.82 132.01 415.83 14.108 208.17 137.31 439.43 9.483 10139 132.10 416.22 19.922 302.69 137.43 440.00 11.213 59.29 132.19 416.56 28.096 306.43 13736 440.52 11.029 111.24 132.25 416.89 11.636 163.58 137.66 440.97 5.958 20.97 132.34 417.29 7.622 91.22 137.76 441.42 14.457 130.58 132.43 417.70 14.37 401.07 137.86 441.82 14.139 16732 132.53 418.16 9.514 79.65 137.94 442.20 5.138 22.15 132.64 418.73 8.125 24.33 138.03 442.67 23.5 46.56 132.79 419.29 31.599 246.28 138.15 443.35 13.384 233.79 132.90 419.74 12.487 1622 138.24 443.64 6.327 66.73 133.00 420.18 41.876 262.85 138.33 443.94 52.375 947.87 133.10 420.62 7.949 76.91 138.41 444.34 15.316 141.72 133.20 421.06 20.745 407.98 138.51 444.84 12.523 6431 133.30 421.56 16.552 217.42 138.63 445.37 11.314 55.76 133.43 422.19 9.496 175.11 138.74 445.85 11.425 226.16 133.58 422.74 18.604 264.87 138.84 446.31 16.305 62.43 133.68 423.30 7.754 65.90 138.94 446.78 10.67 36.84 133.83 423.94 17.674 225.50 139.05 447.26 10.441 122.64 133.97 424.53 30.369 637.35 139.15 447.72 7.261 43.17 134.10 425.08 9.463 42.96 139.25 448.17 7.17 31.48 134.22 425.55 14.535 87.77 139.35 448.65 7.121 30.32 134.31 425.97 10.896 169.28 139.47 449.25 7.733 61.07 134.41 426.39 15.433 137.61 139.62 449.82 16.717 115.81 134.50 426.93 5.656 38.73 139.72 450.32 18 88.66 134.65 427.57 10.061 32.91 139.84 450.83 18.231 484.09 134.79 428.10 11.999 180.11 139.94 451.31 10.749 29.12 134.89 428.55 13.647 85.31 140.05 451.86 27.181 125.00 134.99 428.96 10.594 63.99 140.18 452.41 85.255 253.70 135.07 42931 10.101 42.21 140.29 452.96 6.722 41.03 135.15 429.67 13.447 90.69 140.42 453.51 9.147 70.33 135.23 430.07 26.391 171.75 140.53 453.99 6.46 19939 135.33 430.61 17.215 88.16 140.63 454.43 11.033 34.68 135.47 431.14 5.216 11.96 140.72 454.84 9.338 237.75 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 158 Appendix B. (continued) Depth Age M Depth Age N M (m> (vr b2k)* ) (^8 kg') (m> (yr b2k)* (103 m l1) (Hg*g‘>- 140.81 455.22 32.115 251.04 14631 480.98 12.261 73.44 140.88 455.68 38.438 719.46 146.40 481.41 17.231 99.26 141.01 456.35 21.041 44133 146.49 481.88 7.281 34.93 141.17 456.97 40.503 242.94 146.60 48233 10302 31.61 141.28 457.43 16.618 295.75 146.68 482.81 3316 3.29 141.37 457.94 17.519 1055.16 146.80 48 3 3 5 5.236 7.00 141.50 458.40 10.613 201.86 146.91 483.78 7.054 38.70 141.57 458.80 14.571 112.37 146.98 484.23 63 2 2 12.98 141.67 459.24 4.445 36.25 147.10 484.84 15.469 136.20 141.76 459.65 6.849 144.00 147.24 485.35 9.394 33.15 141.85 460.09 9.928 61.93 14732 485.71 12.491 17630 141.95 460.65 7.631 7931 14739 486.24 10.923 45.06 142.09 461.16 23.481 798.15 14734 486.88 73 8 7 50.41 142.17 461.47 32.939 301.25 147.66 487.38 9.633 32.69 142.22 461.84 13.177 138.47 147.86 488.46 12345 125.72 142.33 462.38 8.298 44.90 147.99 488.99 5.352 7.63 142.45 462.93 8.17 151.46 148.08 489.45 8.829 19.34 142.57 463.47 3.543 4.37 148.28 49035 7.485 19.30 142.68 463.95 8.166 43.65 148.44 491.13 14.892 70.94 142.78 464.42 12.4 81.43 148.62 492.06 13.201 111.44 142.88 464.84 8.291 47.44 148.72 492.47 4 3 3 5 9.38 142.97 465.33 12.259 81.23 148.79 492.95 7.137 342.95 143.10 465.94 3.909 3.76 148.92 493.58 12.694 72.48 143.23 466.50 10.06 94.44 149.05 494.08 6.081 46.84 143.34 467.08 12.844 48.82 149.22 495.02 6.208 14.10 143.48 467.64 8.164 33.81 149.36 495.75 5.458 53.15 143.58 468.06 64.413 597.03 14932 496.38 15.232 139.83 143.66 468.58 7.685 20.25 149.62 496.86 4.751 7.17 143.80 469.19 7.656 19.06 149.72 49735 6.16 21.11 143.92 469.68 11.886 177.25 149.82 497.80 10.801 42.22 144.01 470.13 14.815 73.29 149.90 498.32 21.619 110.98 144.11 470.711 4.114 9.49 150.03 498.88 8.408 46.71 144.26 471.34 10.375 56.94 150.13 499.41 15.686 149.04 144.37 471.89 14.587 73.95 150.25 500.07 13.074 98.87 144.49 472.46 10.177 59.87 150.40 500.69 10.56 58.36 144.61 473.02 15.576 133.94 150.51 501.32 6.315 25.46 144.73 473.56 14.774 10530 150.66 501.93 12.811 155.43 144.84 474.10 10.628 109.47 150.76 502.44 16.959 154.85 144.96 474.65 7.113 48.47 151.00 503.66 9.382 38.12 145.08 475.13 6.811 100.66 151.13 504.19 11.156 35.53 145.17 475.55 8.356 34.92 151.22 504.72 9.035 31.39 145.26 476.00 12.819 61.28 151.35 505.28 18.606 234.53 145.36 476.52 11.119 76.81 151.45 505.74 14.333 61.88 145.48 477.09 6.947 22.87 15134 506.16 15337 184.99 145.60 477.72 12.547 75.74 151.62 50638 15.895 237.29 145.74 478.31 6.596 15.59 151.81 507.40 17.966 98.39 145.84 478.85 6.567 17.32 151.85 507.81 7.887 43.21 145.97 479.37 9.739 151.44 151.97 508.47 8.848 36.39 146.06 479.89 9.744 56.64 152.21 509.48 7.92 38.90 146.19 480.49 6.565 18.90 152.29 509.93 25.421 259.27 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 159 Appendix B. (continued) Depth Age N M Depth Age N M J n H __ (yrb2k)* (IQ3 ml'1) -■tegfcg1)- (m) (vr b2k)* (IQ3 ml'1) (Hgfcg'U. 152.39 510.29 8.059 37.61 157.97 53837 5.627 17.06 152.44 510.73 6.615 105.25 158.13 539.23 15.44 6 9 3 6 152.57 511.34 11.428 70.80 15833 539.72 21.126 105.18 152.69 511.91 10.535 55.53 15832 540.15 19.294 120.84 152.80 512.43 16.848 97.54 158.40 540.69 21.972 109.02 152.90 512.92 6.539 22.70 15833 541.19 12.651 87.09 153.00 513.41 9.842 35.48 158.60 541.71 18.297 1087.64 153.10 513.83 8.319 93.56 158.73 542.32 12.498 133.64 153.17 514.20 9.421 20.54 158.84 542.94 19.666 230.71 153.25 514.62 45.132 977.89 158.97 543.48 14.375 288.84 153.44 515.68 21.97 168.04 159.05 543.91 16.173 321.92 153.57 516.47 17.421 216.63 159.13 544.49 8.903 145.45 153.75 517.17 12.413 286.45 15937 545.22 5 3 6 2831 153.85 517.79 10.121 64.50 159.41 545.91 10.192 130.31 154.00 518.51 10.118 53.02 15934 546.46 8 3 7 4 37 3 9 154.14 519.10 41.786 626.23 159.62 547.01 7.07 30.48 154.24 519.58 14.59 240.47 159.76 54735 13.9 367.71 154.34 520.11 20.242 408.15 159.83 548.06 17.457 11139 154.45 520.63 23.079 187.43 159.96 548.74 9.431 44.37 154.55 521.28 13.803 121.97 160.09 549.33 22.374 396.99 154.71 521.91 18.46 189.85 160.19 549.90 11.911 42.46 154.80 522.38 8.26 40.97 160.31 550.41 11.475 176.08 154.90 522.86 15.368 81.44 160.39 550.93 8.553 83.41 154.99 523.41 7.052 27.71 16031 55133 17.273 107.05 155.12 524.11 41.218 20233 160.62 552.07 29.362 30532 155.27 524.68 22.905 229.98 160.72 5 52 3 7 17.894 204.22 155.35 525.09 114.18 5314.69 160.81 553.03 47.442 1157.80 155.44 525.55 48.826 1791.32 160.89 553.52 13.135 16735 155.53 526.05 25.444 860.82 160.99 554.04 18.03 211.17 155.64 526.65 9.899 181.58 161.09 55431 14.92 115.68 155.77 527.31 25.79 1687.26 161.17 554.92 10.102 186.29 155.90 527.96 36.126 2032.31 161.25 555.37 24.587 140.00 156.03 528.54 29.77 968.61 161.34 555.99 14.923 92.42 156.13 528.98 34.248 1901.24 161.49 556.66 16.561 414.21 156.20 529.54 25.844 425.44 161.60 557.18 10.856 40.50 156.35 530.12 75.375 2485.22 161.69 557.66 4.715 19.80 156.43 530.63 6.888 43.03 161.78 558.07 19.859 379.07 156.55 531.31 10.447 549.97 161.85 558.49 12.15 62.89 156.70 531.96 17.284 394.80 161.94 558.96 12.715 220.06 156.80 532.49 13.15 107.06 162.03 559.40 20.303 108.21 156.90 532.99 14.485 77.57 162.11 559.82 12.888 117.19 157.00 533.48 16.86 151.74 162.19 560.24 10.977 106.13 157.09 533.93 11.291 151.81 162.27 560.79 11.92 251.20 157.18 534.44 16.801 234.63 162.40 561.37 6.424 73.94 157.29 534.94 9.823 6 8 3 2 162.49 561.85 12.744 4931 157.38 535.50 7.804 36.14 16238 562.39 13.446 107.57 157.51 536.18 7.073 17.09 162.69 563.01 14.734 84.79 157.65 536.87 10.415 65.07 162.81 56 3 3 6 11.113 45.61 157.78 537.46 6.205 58.18 162.90 564.04 12.056 5733 157.88 537.94 24.85 114.03 162.99 564.59 8.845 15.60 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 160 Appendix B. (continued) Depth Age N M Depth Age N M ’(m) (yrb2k)* (103 m l1) (Hgkg‘) (m) (vrb2k)* (105 ml'*) (Ug kg'*) 163.11 565.26 7.371 48.74 168.44 593.96 17.99 41835 163.25 565.93 5.283 6 3 3 5 16837 594.63 23.824 838.24 163.37 566.51 19.133 24031 168.69 595.25 9.912 91.21 163.47 567.07 11.087 58.07 168.79 595.84 18.422 111.78 163.58 567.63 7.425 514.84 168.90 59632 37.159 402.62 163.68 568.13 22.383 22830 169.04 597.26 20.937 434.82 163.77 568.68 27.192 422.85 169.17 597.95 9.745 61.48 163.89 569.32 17.384 24831 169.29 59836 14.061 54.71 164.01 569.96 11.402 104.15 16939 599.14 19.348 229.29 164.13 570.55 10329 60.40 16930 599.81 17.463 126.94 164.23 571.07 19.498 395.00 169.63 60031 6.164 33.34 164.32 571.74 16.978 136.23 169.75 601.21 21.179 121.86 164.47 572.51 19.38 304.16 169.88 601.96 11.156 33.18 164.61 573.20 15.965 193.43 170.02 602.68 11.686 32.93 164.73 573.79 19.13 117.80 170.15 60331 4.62 7 3 2 164.83 574.51 13.777 106.97 170.25 603.93 9.235 23.27 165.00 575.17 16.037 115.49 170.37 60432 7.326 36.71 165.08 575.62 16.308 97.67 170.47 605.02 10.729 96.69 165.17 576.08 7.793 57.73 170.55 605.61 10.295 54.46 165.25 576.51 16.244 452.09 170.68 606.26 7.894 120.69 165.33 576.97 11.383 145.99 170.78 606.87 8.67 74.02 165.42 577.44 18.937 382.75 170.90 607.60 9.011 66.45 165.51 577.94 12.967 80.51 171.04 608.21 13.305 95.44 165.61 578.48 9.354 25.08 171.12 609.03 12.143 45.77 165.71 579.10 16.64 75.56 171.25 609.45 17.853 115.47 165.84 579.80 8.069 53.52 171.33 609.87 7.456 59.85 165.97 580.47 15.49 217.87 171.42 610.40 17.262 197.29 166.09 581.05 15.49 7 2 3 6 17132 610.93 11.16 147.47 166.19 581.62 18.742 138.50 171.61 611.44 14.231 204.41 166.30 582.30 18.214 511.61 171.70 612.06 7.295 48.20 166.44 582.89 11.728 109.08 171.83 612.77 10.645 162.13 166.52 583.32 22.476 670.73 171.95 613.44 11.293 39.66 166.59 583.86 18.556 355.01 172.07 614.15 5.171 17.89 166.71 584.40 13.671 137.94 172.20 614.74 20.461 379.28 166.79 584.88 13.746 172.11 172.28 615.21 30.647 288.47 166.89 585.42 14.38 252.16 172.37 615.70 15.968 413.18 166.99 585.98 12.556 81.30 172.46 616.18 5.77 270.26 167.09 586.47 10.881 57.07 17234 617.03 1031 107.16 167.17 586.86 15.295 126.43 172.76 617.68 18.637 242.04 167.24 587.25 10.618 163.67 172.77 618.11 15368 189.06 167.32 587.72 9.868 34.80 172.91 618.79 12373 215.38 167.42 588.30 23.113 207.11 173.01 61930 7.72 348.43 167.53 588.91 10.686 81.72 173.16 620.32 6.387 31.39 167.64 589.50 12.838 74.28 173.30 620.98 11.314 227.16 167.74 590.09 8.11 59.85 173.39 . 621.65 13.429 108.43 167.86 590.73 11.366 36.78 173.53 622.28 15.968 319.69 167.98 591.39 18.436 86.72 173.61 622.90 10.457 87.41 168.10 591.99 27.957 573.72 173.75 62339 12.755 214.79 168.20 592.67 11.102 123.22 173.85 624.22 13.857 135.38 168.35 593.35 5.916 31.77 173.97 624.82 19.873 203.45 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 161 Appendix B. (continued) Depth Age N M Depth Age N M (m) (vrb2k)* (103 m ll) (pg k g'1) (m) (vr b2k)* (K fm T1) frgfcg1) 174.06 625.48 8.776 66.55 179.62 657.82 10.266 430.76 174.20 626.28 12.775 194.71 179.71 658.47 14.096 19139 174.34 627.02 12.081 27139 179.84 659.15 2134 125.91 174.46 627.77 9.305 45.90 179.94 659.78 9.465 6 3 3 5 174.60 628.54 14.055 108.14 180.05 6 6 0 3 0 29.906 710.27 174.73 629.32 9.863 36.97 180.18 6 6 1 3 0 7.446 42.69 174.87 630.01 833 32.78 180.32 661.99 16.641 87.37 174.97 630.70 10.565 75.77 180.41 662.62 13.2 417.27 175.11 631.42 5.473 11.83 18033 663.27 20348 509.78 175.22 631.96 8.44 122.64 180.63 663.87 11.646 301.99 175.30 632.57 5.423 48.62 180.73 664.41 32.562 858.25 175.43 633.35 10.456 78.47 180.81 665.01 23309 794.02 175.57 634.04 8.798 340.23 180.93 665.67 14351 24138 175.67 634.62 30.989 170.80 181.03 6 6 6 3 7 7.556 48.61 175.77 635.26 20307 296.09 181.16 667.03 2037 599.47 175.89 635.84 14301 137.28 181.25 667.63 . 16.947 141.33 175.97 636.26 21.378 124.01 181.36 668.20 26.881 347.46 176.04 636.67 10.46 70.28 181.44 668.70 13.204 179.34 176.11 637.27 11.57 91.07 181.53 6 6 9 3 4 8.015 59.23 176.25 638.09 8.103 39.96 181.65 669.97 21.112 399.08 176.39 638.93 12.185 51.15 181.74 670.61 13315 65.35 176.54 639.69 11.064 231.48 181.86 671.25 10.946 52.39 176.65 640.25 10.715 164.75 181.95 671.92 4.776 18.10 176.73 640.76 10.935 45.40 182.08 672.71 5.683 77.84 176.82 641.28 23.238 315.81 182.21 673.39 11.324 496.70 176.91 641.91 15.582 129.71 182.30 674.09 8.309 79.56 177.04 642.58 17.176 86.14 182.44 674.82 14.47 113.91 177.14 643.11 28.678 837.13 182.54 675.37 18.251 753.99 177.22 643.70 7.374 239.82 182.62 675.92 4.8 35.15 177.34 644.25 14.061 375.26 182.72 676.62 5.239 72.33 177.41 644.75 6.654 221.23 182.85 677.32 10.7 100.13 177.51 645.39 9.555 41.84 182.95 678.01 5.587 23.72 177.63 646.04 15.154 163.97 183.07 678.64 9.856 72.83 177.73 646.53 17.531 102.43 183.15 679.20 8.908 122.43 177.80 646.98 7.886 41.17 183.25 679.75 14.436 311.70 177.88 647.65 10.606 179.42 18333 680.30 7.48 15.94 178.03 648.54 10.325 96.98 183.43 680.95 6.421 17.72 178.18 649.44 9.503 63.31 18334 6 8 1 3 6 10.629 56.33 178.34 650.29 5.185 54.63 183.63 682.11 23.962 1057.27 178.47 651.00 5.173 55.81 183.72 682.64 31.267 606.60 178.58 651.59 10.418 75.34 183.80 683.32 9.758 87.66 178.67 652.10 8.254 331.48 183.94 684.09 10.073 128.07 178.75 652.63 5373 56.17 184.05 684.80 11335 455.65 178.85 653.34 6.877 137.69 184.17 685.58 8.861 295.65 178.99 654.02 6.882 22.01 18430 686.41 14.358 8 335 179.07 654.61 8.962 164.77 184.44 687.31 7.313 31.08 179.18 655.17 14.259 50.82 18439 688.12 7.044 125.34 179.26 655.70 14.062 13639 184.70 688.86 10.292 56.43 179.36 656.30 4.178 25.90 184.84 689.67 14317 1340.80 179.46 657.07 13.471 227.13 184.97 690.42 11.48 321.99 *yrb2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 162 Appendix B. (continued) Depth Age N M Depth A ge N M (m) (yr b2k)* (10* m f1) O ig k g 1) (m) (v r b2k)* (10* mT1) (H g k g 1) 185.08 691.11 6 3 7 75.44 19032 725.78 23.805 619.24 185.19 691.79 6.299 14.71 190.62 72630 18.265 468.69 185.30 692.38 32.429 899.63 190.68 726.83 13.835 4 1 4 3 8 18538 693.01 17.992 495.33 190.79 7 2 7 3 6 7.169 292.23 18530 693.60 38.775 958.60 190.91 7 2 8 3 8 8 3 6 6 375.19 18537 694.08 20.361 259.65 191.04 729.23 7.731 3 2 3 6 185.65 694.74 8.223 232.42 191.17 729.98 9321 98.99 185.78 69535 9 3 5 3 109.64 191.27 730.70 5 3 9 6 29.43 185.91 696.24 7.103 223.06 191.39 731.46 8.864 103.01 186.00 696.96 5.379 18.46 19130 73 2 3 3 8.438 40.21 186.14 697.68 7.34 2 8 3 4 191.62 733.09 9.057 2 8 3 8 186.23 698.31 6.217 25.87 191.76 733.98 9 3 8 8 124.77 186.34 698.88 8.837 11938 191.89 734.71 9.088 181.43 186.41 699.41 16.118 5 2 3 0 191.98 7 3 5 3 3 9.946 87.13 18631 699.93 11392 2931 192.14 736.49 8.624 555.06 186.57 700.49 10.391 216.60 192.27 737.18 20.042 1010.91 186.68 701.21 6.62 27.84 19235 737.82 9.74 477.14 186.80 701.97 9.86 49.86 192.46 738.63 13.44 94.96 186.92 702.66 10.983 57.62 19239 739.32 18.432 541.73 187.02 703.45 6.709 116.96 192.67 740.05 23.995 132.96 187.17 704.31 15.083 155.02 192.81 740.98 17.977 229.66 187.29 705.06 16.254 217.04 192.95 741.88 15.456 338.70 187.41 705.81 15.951 21835 193.08 742.65 13.724 520.46 18733 7 0 6 3 4 9.47 138.67 193.18 743.24 23.665 780.06 187.64 707.24 9.104 60.06 193.26 743.76 25.852 956.05 187.75 707.94 12.076 338.85 193.34 74430 19.808 439.11 187.86 708.54 14.252 75.99 193.43 744.90 20.848 810.97 187.94 709.31 11.771 3631 19332 745.47 178.291 567.45 188.10 709.94 21.296 133.06 193.60 746.10 10.124 51.70 188.14 710.41 9.721 52.11 193.71 746.81 20.324 174.62 188.24 711.07 15.871 54.49 193.81 747.61 14.149 119.71 188.34 711.71 6.69 24.51 193.95 748.45 22335 14537 188.44 712.31 1539 7 0 3 7 194.06 749.30 8.01 59.11 18833 712.89 29368 379.80 194.20 750.11 12.715 80.67 188.62 713.60 9.231 30.76 19430 750.72 12.529 113.00 188.75 714.40 19.653 83.08 194.38 751.43 15.385 180.75 188.87 715.04 21.105 579.37 19431 752.37 9.875 45.85 188.95 715.70 6.244 27.03 194.66 753.18 16.047 150.30 189.08 716.53 14.185 68.63 194.75 753.96 8.245 98.62 189.21 717.17 21.246 201.98 194.89 754.77 12.781 65.07 189.28 717.69 27.165 246.81 194.99 755.39 10301 645.41 189.37 718.43 7.472 35.96 195.07 756.01 16373 198.92 18931 719.36 6.879 42.96 195.17 756.76 7.704 2 6 3 6 189.66 720.20 11.784 222.54 195.29 757.54 6.688 22.28 189.77 721.06 6.48 146.61 195.40 758.35 8.508 28.13 189.92 722.04 8.123 10936 19533 759.24 9.121 18937 190.07 722.98 4.863 8 3 1 195.66 760.02 7.752 26.26 190.21 723.67 34317 1111.00 195.76 760.67 19.991 207.99 190.28 724.19 19.764 461.28 195.85 76132 10.312 356.45 190.37 724.97 16.083 200.28 195.93 761.92 7.624 54.87 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 163 Appendix B. (continued) Depth Age j N M Depth Age N M __ (yr b2k)* I (10* ml'1) ii& M l (yr b2k)* (105 ml*) (Ug leg'1) 196.06 762.67 8.525 51.82 201.20 798.67 22324 282.82 196.15 763.25 23.465 37133 201.29 799.46 16.655 138.57 196.23 763.93 8.293 129.98 201.42 80032 12.013 70.67 196.35 764.72 7.449 99.63 20133 801.08 7.295 5833 196.46 765.51 14.463 295.93 201.63 801.79 16322 117.28 196.58 766.25 18.562 271.06 201.73 80233 8.896 116.76 196.67 766.85 30.287 191.34 201.84 803.30 18.093 91.36 196.75 767.50 30.346 847.34 201.95 804.26 23.267 103.18 196.86 768.19 39.47 443.98 202.10 805.30 13.273 68.27 196.95 768.81 17.924 122.74 202.24 806.08 18.658 143.01 197.04 769.40 12.968 220.93 202.32 806.64 16.494 101.11 197.12 770.02 14.752 110.89 20239 807.22 23.097 94.02 197.22 770.71 9.095 42.72 202.48 807.93 22.01 186.36 197.32 77136 9.32 107.72 20239 808.63 53.28 330.79 197.41 772.07 8.74 12739 202.67 809.48 12.299 70.35 197.53 772.87 11.97 635.08 202.82 810.43 16.899 108.37 197.65 773.64 11345 87.13 202.93 811.19 12.418 79.42 197.75 774.30 21.235 25135 203.03 811.96 15.646 67.92 197.84 775.13 10.618 42.97 203.14 812.72 15.831 95.35 197.99 775.93 5.605 56.13 203.24 813.49 8.749 49.29 198.07 776.49 6.275 17.54 203.35 814.42 7.754 36.33 198.15 777.18 8.425 20.03 203.49 815.31 10.901 50.87 198.27 777.95 9.441 23132 203.59 815.94 300.325 4791.48 198.37 778.48 12.41 74.20 203.66 816.74 7.201 49.30 198.42 778.97 7.365 212.65 203.81 817.66 15.96 53.88 198.51 779.74 7.805 54.88 203.91 818.40 18.382 44.13 198.64 780.55 21.832 79.73 204.01 819.06 14325 117.06 198.74 781.21 10.293 28.81 204.09 819.87 9.88 43.36 198.83 781.84 14.368 116.60 204.23 820.89 15.11 158.98 198.92 782.48 20.618 243.26 204.37 821.96 34.289 122.61 199.01 783.14 10.338 49.77 204.52 822.82 18.653 666.53 199.11 783.81 9.801 84.56 204.61 823.53 19.153 69.57 199.20 784.42 20.162 549.49 204.71 824.29 15.269 117.99 199.28 785.24 13.031 208.94 204.81 825.01 25.974 169.08 199.43 786.15 13.245 80.76 204.91 825.71 8.809 43.99 199.54 786.82 16.753 7138 205.00 826.48 10.737 89.93 199.62 787.42 12.872 81.38 205.11 827.20 8.607 297.58 199.71 788.24 15.116 155.95 205.20 828.07 12303 134.05 199.85 789.12 10.802 196.19 205.35 829.00 6.731 87.53 199.96 789.90 12.662 87.59 205.45 829.78 14.749 128.67 200.07 790.51 16.47 212.24 205.56 830.64 17.118 135.14 200.13 791.23 9.897 60.17 205.68 831.46 15.091 104.47 200.27 792.23 9.753 55.75 205.78 832.21 26.791 110.38 200.41 793.22 3.763 27.99 205.88 832.96 10.818 59.89 200.55 794.04 8.845 65.08 205.98 833.61 26.605 120.09 200.64 794.79 8.53 51.75 206.05 834.26 24.59 125.90 200.76 795.61 14.603 69.56 206.15 835.09 18.937 138.86 200.87 796.46 11.884 110.78 206.27 835.95 13.62 118.93 201.00 797.17 13.134 111.77 206.38 836.67 15.419 492.01 201.07 797.88 18.529 68.75 206.46 837.34 18.255 166.07 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 164 Appendix B. (continued) Depth Age N M Depth Age N M (m) (y r b2k)* ( 103 m l'1) (H g k g 1) (m) (vrb2k)* (103 m l1) (H g k g ') 206.56 838.17 9.283 45.57 211.58 877.05 12.474 86.13 206.68 839.04 13309 83.78 211.71 878.04 28.215 202.14 206.79 839.89 9.916 1180.26 211.83 879.04 8.198 78.38 206.90 840.69 4.875 32.28 211.96 879.87 31.691 13833 207.00 841.37 13.634 152.50 212.04 88031 15.043 132.79 207.08 842.02 12.031 57.94 212.12 88135 29.467 120.44 207.17 842.89 12.382 96.20 212.25 882.07 21.75 121.94 207.31 843.80 24.357 106.56 212 JO 88239 25.736 103.26 207.41 844.56 19.577 54.65 21238 883.19 9.335 6433 207.51 845.29 23.004 114.37 212.45 883.75 12399 70.81 207.60 846.01 13.333 54.61 21232 884.43 23.138 128.66 207.70 846.65 16.386 80.57 212.62 885.19 16.904 92.77 207.77 847.29 22.97 130.78 212.71 885.92 17.638 100.96 207.87 848.10 11.177 73.56 212.80 886.51 13.612 411.18 207.98 848.90 21.271 167.51 212.85 887.19 16.183 182.48 208.08 849.66 12.33 95.25 212.96 888.03 23.11 134.30 208.18 850.43 19.102 104.48 213.06 888.80 82.659 538.29 208.28 851.16 16.89 105.72 213.15 889.69 11379 50.86 208.37 851.85 17.298 111.31 213.28 890.74 7.992 36.28 208.46 852.65 12.208 67.48 213.41 891.75 3.47 23.99 208.58 853.54 27.719 127.51 213.53 892.62 10.88 1542.58 208.69 854.34 9.371 47.28 213.63 893.54 7.977 78.80 208.79 855.08 8.827 70.06 213.76 894.51 4.237 26.10 208.88 855.96 14.046 96.48 213.87 895.33 18.101 65.42 209.02 856.82 8.318 37.73 213.96 896.10 8.721 56.71 209.10 857.51 17.96 135.15 214.06 896.83 18.265 12335 209.20 858.21 12.782 109.86 214.14 897.49 18.529 1164.58 209.28 858.87 13.398 70.91 214.22 898.34 10.899 69.91 209.37 859.65 4.896 29.45 214.35 899.32 14.679 79.17 209.48 860.47 8.449 42.92 214.46 900.22 5.573 58.84 209.58 861.21 17.263 85.34 214.57 901.25 7.523 46.44 209.67 862.03 5.879 39.72 214.71 902.31 1.773 20.81 209.79 863.00 9.376 40.84 214.83 903.34 7.969 38.28 209.92 863.90 7.784 40.67 214.96 904.29 13.789 218.85 210.02 864.68 8.678 276.86 215.15 905.77 14.278 49.62 210.12 865.35 36.154 256.27 215.23 90631 20.409 160.38 210.19 865.93 33.338 607.54 215.33 907.29 24.22 188.49 210.27 866.45 17.274 133.71 215.42 908.20 6 3 7 101.25 210.32 867.17 15.709 124.09 215.55 909.11 10.276 102.07 210.45 868.11 8.621 44.35 215.64 909.81 7.498 87.06 210.56 868.94 11.26 48.39 215.72 9 1 0 3 2 10.515 89.28 210.66 869.76 14.305 72.59 215.81 91135 6.755 35.44 210.77 870.67 12.585 54.44 215.92 912.35 12.881 69.39 210.89 871.57 15.404 326.28 216.05 913.22 15.333 123.08 211.00 872.49 14.105 81.87 216.13 913.80 7.635 36.19 211.13 873.41 14.682 78.72 216.19 914.46 12.998 491.65 211.24 874.20 11.206 45.78 216.29 915.34 6.737 39.00 211.33 874.99 10.603 144.10 216.40 916.05 10.693 93.77 211.44 875.82 22.664 388.20 216.46 916.68 34.822 146.26 211.54 876.38 39.616 307.58 21635 917 3 9 23.956 193.13 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 165 Appendix B. (continued) Depth Age N M Depth Age N M (m) (vrb2k)* (10* ml'1) (m) (yr b2k)« ( 103 ml-1) (Ug kg'*L_ 216.63 918.10 6.372 41.64 221.84 962.97 19.665 516.18 216.72 919.02 9.251 3435 221.91 963.77 6.799 287.31 216.85 919.95 12.78 48.67 222.02 964.71 5.972 69.21 216.94 920.58 22.756 85.96 222.12 965.82 8.214 39.05 217.00 921.32 22396 87.98 222.27 967.07 9.022 8 0 3 3 217.11 922.28 11391 78.09 222.40 968.00 17.654 104.00 217.22 92337 4.149 21.75 222.47 968.80 10.406 123.45 21737 924.30 7.13 46.25 22237 969.74 16.987 106.85 217.44 925.15 9.098 40.45 222.68 97035 11.073 54.70 21737 926.12 59.791 288.46 222.75 971.40 11.187 63.45 217.67 926.88 14.346 277.02 222.87 972.44 13.215 80.72 217.75 927.73 16.032 101.55 222.98 9 7 3 3 4 14.115 98.31 217.87 928.54 21.6 596.14 223.07 974.15 13.788 139.87 217.94 929.17 31.718 14736 223.16 974.96 17.295 152.31 218.02 930.14 12.969 86.03 223.25 975.90 12.447 120.16 218.17 931.07 16.943 184.06 223.37 976.75 22.592 203.76 218.24 931.89 9 313 79.62 223.44 977.48 19.739 163.67 218.36 932.82 6.235 46.43 223.53 978.16 16.425 131.56 218.46 933.68 19.665 174.03 223.59 978.79 14.981 125.87 218.56 934.75 6.107 68.38 223.67 979.61 17.622 131.37 218.71 935.82 22.458 277.02 223.77 98036 9.191 84.51 218.81 936.71 16.316 177.96 223.88 981.43 5.633 57.97 218.92 937.59 19.459 15732 223.96 982.07 19.316 119.81 219.02 938.32 20.175 224.02 224.02 982.98 9.66 46.25 219.09 939.20 14.517 96.81 224.16 984.06 10.601 55.22 219.22 940.32 13.936 372.72 224.26 984.97 13336 58.69 219.35 941.44 7.889 6333 224.36 985.89 22.614 130.64 219.48 942.53 11.869 87.25 224.46 986.76 9.797 49.22 219.60 943.15 11.716 63.80 224.55 987.54 18.648 116.75 219.63 944.14 4.082 76.28 224.63 988.36 14.057 164.52 219.83 945.37 26.33 496.95 224.73 989.33 15.522 98.78 219.91 946.33 18.451 125.05 224.84 990.34 13.431 79.84 220.05 947.37 28.071 247.96 224.95 991.22 14.823 137.74 220.15 948.26 25.896 137.37 225.03 991.91 29.082 293.54 220.25 949.22 22.572 139.18 225.10 992.62 9.739 36.14 220.37 950.07 41.373 877.36 225.18 993.46 21.459 111.79 220.45 950.91 32.357 243.28 225.28 994.39 11.776 81.12 220.56 951.95 19.593 133.05 225.38 995.22 15.949 129.48 220.69 952.87 21.38 232.22 225.46 995.92 16.243 118.54 220.77 953.70 9.952 56.48 22533 996.80 20.519 130.41 220.88 954.54 22.409 400.80 225.65 997.69 16.128 112.27 220.96 955.24 32.407 474.43 225.72 998.48 14.35 83.87 221.04 955.95 25.178 250.72 225.82 999.41 16.221 57.16 221.12 956.87 9.891 81.68 225.92 1000.25 14.959 73.22 221.25 957.84 18.159 15330 226.00 1000.94 10.3 108.93 221.34 958.77 4.717 62.24 226.07 1001.82 21.812 262.92 221.46 959.78 21.655 1398.15 226.19 1002.71 51.999 305.71 221.57 960.66 13.86 8637 226.26 1003.41 23.643 14935 221.66 961.51 16.753 91.89 226.34 1004.21 31.226 339.13 221.76 962.31 12.659 7439 226.43 1005.10 19.323 20731 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 166 Appendix B. (continued) Depth Age N M Depth Age N M __ (yr b2k)* (103 ml'1) fcg kg JmL (yr b2k)* (103 tnl *) QMgfcg'1) 226-53 1006.00 19.507 209.44 231.19 I0 5 I3 1 16.167 68.14 226.62 1006.75 16.634 240.41 23131 1052.46 5.248 6 8 3 9 226.69 1007.45 16.202 171.51 231.42 105335 13.019 8 0 3 0 226.77 1008.40 13.817 349.50 2 3133 1054.48 38.904 215.93 226.89 1009.43 19.297 124.48 231.61 1055.49 11.828 85.75 226.99 1010.65 24.296 217.91 231.73 105634 10.384 78.91 227.15 1011.78 119.615 1407.74 231.82 1057.45 10.543 88.63 227.23 1012.64 57.353 528.98 231.91 1058.60 9.953 51.88 227.33 1013.49 18.318 157.66 232.05 1059.66 26.458 238.31 227.41 1014.30 13.755 8037 232.12 106032 9.295 67.08 227JO 1015.35 7.062 81.92 232.22 106133 10.011 87.62 227.63 1016.35 26.525 139.99 232.32 1062.68 19.696 3 3 8 3 2 227.71 1017.02 23.865 164.71 232.45 1063.88 10.204 93.19 227.77 1017.78 7.274 38.51 2 3 2 3 6 1065.15 10.328 48.85 227.87 1018.53 9.685 53.61 232.70 1066.49 20.237 74.62 227.93 1019.14 33.255 171.61 232.82 106736 12.39 112.87 228.00 1019.95 9.709 115.78 232.91 1068.41 17.762 208.09 228.10 1021.05 6.882 148.07 232.99 1069.38 7.784 66.85 228.23 1022.26 12.141 66.77 233.10 1070.40 27.346 13430 228.35 1023.22 10.753 81.07 233.19 1071.27 23.422 221.80 228.43 1024.13 6.355 35.47 233.27 1072.12 30.405 229.12 228.54 1025.10 27.314 150.22 2 3 3 3 5 1073.32 10.834 56.99 228.63 1026.16 11.889 54.67 2 3 3 3 0 1074.71 5.874 34.92 228.76 1027.21 7.823 60.44 233.62 1075.85 7.298 74.53 228.84 1028.12 13.568 54.48 233.72 1077.03 16.412 111.31 228.94 1029.28 7.728 82.82 233.85 1078.38 8.236 72.99 229.08 1030.50 9.78 64.04 233.98 1079.47 18.362 885.44 229.19 1031.37 9.135 9 1 3 0 234.06 1080.35 20.71 218.55 229.26 1032.10 18.774 110.93 234.15 1081.36 9.253 96.95 229.34 1032.88 17.605 92.17 234.26 1082.37 17.905 206.13 229.42 1033.71 11.545 197.81 234.35 1083.21 11.063 164.75 229.51 1034.54 25.414 193.49 234.42 1084.01 12.034 281.16 229.59 1035.32 14.721 81.88 2 3 4 3 0 1084.95 11.167 60.15 229.67 1036.20 31.502 1194.34 234.60 1085.87 18.192 10439 229.77 1037.18 13.059 156.02 234.68 1086.81 25.757 282.52 229.87 1038.11 16.06 583.88 234.78 1087.91 34.019 389.85 229.96 1039.39 21.15 103.25 234.89 1089.06 19.886 255.86 230.13 1040.33 11.226 86.17 235.00 1090.14 27.442 447.60 230.15 1040.82 6.639 51.75 235.20 1092.53 14.717 71.84 230.23 1041.70 14.813 165.38 2 3 5 3 4 1093.69 26.007 159.19 230.33 1042.89 6.22 30.81 235.42 1094.56 14.781 204.05 230.47 1043.93 12.358 64.32 23531 1095.78 15308 266.91 230.54 1044.51 9.273 62.69 235.65 1097.08 21.992 277.03 230.59 1045.24 7.699 90.55 235.75 1098.40 13366 81.38 230.69 1046.09 16.897 118.72 235.90 1099.73 9.852 93.26 230.76 1046.88 9.752 45.27 236.00 1100.66 22.787 251.02 230.85 1047.72 9.32 52.56 236.08 1101.65 19.054 353.82 230.93 1048.97 14.404 87.38 236.19 1102.72 27.27 256.68 231.02 1049.61 18.673 96.12 236.28 1103.73 15.622 222.80 231.10 1050.26 12.384 111.00 236.38 1104.75 13.057 100.01 *yr b2k = years before AD 2000; n/d — no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 167 Appendix B. (continued) Depth Age N M Depth Age N M (m) (y r b2k)* (105 m l'1) (H g k g 1) (m) (yr b2k)* (10* m r1) (H g k g ‘) 236.47 1105.88 8.537 45.76 241.42 1160.66 41.662 428.42 236.59 1107.00 23.484 19939 241.49 1161.70 14337 239.00 236.68 1108.13 21.541 265.01 241.60 1162.74 22.35 10933 236.80 1109.21 15.188 114.45 241.67 1163.60 7.716 12432 236.88 1110.02 27.763 284.18 241.75 116433 15.605 132.20 236.95 1110.69 19.223 217.71 241.83 1165.46 7.315 66.93 237.00 1111.37 42.33 1435.85 241.91 1166.39 12.797 124.44 237.07 1112.23 14.309 401.82 241.99 116735 30.362 305.40 237.16 1113.26 15.761 811.79 242.11 1168.95 12.615 60.63 237.26 1114.35 10.13 94.38 242.23 1170.06 24.204 284.83 23736 1115.60 10.244 113.85 2 4 2 3 0 1170.84 15.456 112.88 237.49 1116.96 15.945 303.92 242.36 1172.03 6.9 70.67 237.61 1118.21 13.46 325.84 24230 1173.61 9388 6 3 3 2 237.72 1119.19 50.474 704.92 242.63 1174.91 14.056 105.67 237.79 1119.93 38.017 285.18 242.72 1176.08 15.969 12237 237.86 1120.84 20398 105.77 242.83 1177.26 13.234 154.51 237.96 1121.83 17.141 256.83 242.92 117832 22.174 157.07 238.04 1122.76 5.665 68.47 243.01 1179.38 11.362 62.11 238.13 1123.91 6.307 42.08 243.10 1180.45 16.306 107.76 238.25 1125.23 5.185 75.41 243.19 1181.43 11.965 73.88 238.37 1126.50 14.511 89.88 243.27 1182.52 11.918 136.26 238.48 1127.60 10.394 76.46 243.38 1184.13 6.858 64.15 238.57 1128.65 8.762 62.84 243.54 1185.73 4.835 45.36 238.67 1129.56 6.75 47.11 243.65 1187.17 11.625 57.43 238.73 1130.48 10.428 111.17 243.78 118834 12.656 91.33 238.83 1131.64 9.072 112.91 243.88 1189.86 4.231 30.13 238.94 1132.92 9.674 106.87 244.00 1191.45 5.783 28.75 239.06 1134.14 14.555 76.05 244.14 1192.92 11.087 147.81 239.16 1135.26 15.809 147.14 244.24 1194.06 14.243 111.86 239.26 1136.37 10.48 63.42 244.33 1195.15 13.63 123.94 239.36 1137.49 7.912 267.64 244.42 1196.17 11.951 96.26 239.46 1138.61 8.142 135.62 244 3 0 1197.08 9.669 74.80 239.56 1139.65 9.936 84.98 24437 1198.05 5326 77.69 239.65 1140.63 13.873 118.82 244.66 1199.08 8.745 46.21 239.74 1141.64 10.78 100.75 244.74 1200.05 11.683 28 6 3 7 239.83 1142.71 30.559 242.76 244.82 1201.27 6.286 176.45 239.93 1143.78 6.016 116.61 244.94 1202.64 8.245 42.16 240.02 1144.80 33.395 138.77 245.05 1203.76 10.765 103.11 240.11 1145.81 13.325 58.87 245.13 1205.11 8.198 77.72 240.20 1147.45 10.866 120.39 245.27 1206.70 11.65 221.59 240.31 1148.38 45.226 289.41 245.39 1208.17 11.659 82.68 240.40 1149.30 15.088 136.18 24531 1209.34 13.722 204.62 240.52 1150.86 12.602 521.20 245.58 1210.26 15.611 244.74 240.67 1152.40 7.018 54.83 245.66 1211.25 16331 83.45 240.79 1153.83 7.287 47.62 245.74 1212.23 32.037 589.06 240.92 1155.31 9325 68.44 245.82 121335 26.925 378.47 241.05 1156.52 9.867 395.95 245.92 121434 40.294 341.62 241.13 1157.49 10.869 171.21 246.01 121536 31.744 417.29 241.22 1158.59 12.812 183.34 246.08 1216.55 21.334 314.43 241.32 1159.71 19.516 202.79 246.17 1217.73 22.853 197.90 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 168 Appendix B. (continued) Depth Age N M Depth Age N M (m) (yr b2k)* (10* m l'1) (H gkg1) (m) (vr b2k)* ( 103 m l'1) (H g k g 1) 246.27 1218.85 26.258 307.65 251.03 1280.90 7.73 109.96 246.35 1219.79 20.598 342.43 251.15 128239 9.527 124.69 246.42 1220.85 13358 108.87 251.28 1284.08 16331 145.79 246.52 1222.03 17.048 18231 25137 1285.33 12.163 144.64 246.61 1223.29 12394 114.11 251.47 1286.66 8.812 80.06 246.72 1224.54 8 3 7 216.15 25 1 3 7 1288.16 12.92 147.83 246.81 1225.52 13.737 122.78 251.69 1289.45 21.653 242.47 246.88 1226.44 15.705 88.70 251.76 1290.69 18.05 124438 246.96 1227.63 8.954 636.94 251.87 1291.99 9.63 143.65 247.07 1229.21 9.659 98.62 251.95 1293.02 13.175 142.54 247.21 1230.85 13.157 197.61 252.02 1294.18 11.297 66.80 247.33 1232.12 26.793 184.05 252.12 129536 11.913 114.71 247.41 1233.07 19.447 239.38 252.22 1296.80 21.647 157.38 247.48 1234.21 18.069 197.11 252.30 1297.94 15.675 71.19 247.59 1235.61 16377 177.81 25238 1299.08 16.735 125.21 247.70 1236.91 11.991 124.62 252.46 1300.12 10.177 146.51 247.79 1238.03 16.384 375.35 25233 130130 2 8 3 183.01 247.87 1239.05 13.376 149.41 252.63 1302.48 23.177 1273.66 247.95 1240.01 21.24 251.71 252.70 1303.66 15.265 319.11 248.02 1241.10 23.07 161.72 252.80 1305.19 24.667 631.05 248.12 1242.45 11.961 53.24 252.92 1306.66 20.485 225.25 248.23 1243.73 13.734 661.58 253.01 1307.99 20.74 199.93 248.32 1244.89 12.083 114.60 253.11 1309.39 10.788 132.76 248.41 1246.12 11.081 83.68 253.21 1310.59 10.268 156.15 248.51 1247.34 18.169 209.57 253.29 1311.93 9.844 76.71 248.60 1248.73 11.328 118.07 253.41 1313.62 12.415 133.51 248.72 1250.18 8.998 53.49 25333 1314.97 13.225 99.05 248.82 1251.54 10.277 157.18 253.60 1316.10 13.21 106.92 248.93 1252.71 19.774 346.02 253.69 1317.66 6.675 35.79 249.00 1253.69 22.497 154.15 253.82 1319.43 9.748 159.79 249.08 1254.74 12.9 123.20 253.94 1320.78 24.24 223.96 249.16 1256.04 12.644 188.22 254.01 1321.92 12.35 286.89 249.28 1257.42 12.311 133.81 254.10 1323.31 11.82 91.53 249.37 1258.53 9.659 69.77 254.20 1324.78 9.505 139.90 249.45 1259.95 11.313 153.30 254.30 1326.21 19.598 77.38 249.59 1261.57 4.04 55.95 254.40 1327.43 26.65 906.34 249.70 1262.95 12.138 239.12 254.47 1328.58 19.327 166.45 249.80 1264.14 31.685 501.13 254.56 1329.73 27.49 654.01 249.88 1265.26 19.121 224.69 254.63 1330.82 17.523 777.19 249.97 1266.32 32.968 17038 254.71 1331.97 15.448 313.72 250.04 1267.32 31.523 241.30 254.79 1333.06 22.886 127.79 250.12 1268.51 29.252 862.18 254.86 1334.07 13.422 105.00 250.22 1269.71 20.163 162.62 254.93 1335.08 33.561 381.03 250.30 1270.98 17.842 67.67 255.00 1336.07 15.845 19830 250.41 1272.60 31.305 216.82 255.07 1337.57 11.282 96.28 250.54 1274.24 28.931 389.57 255.21 1339.10 23.302 335.41 250.65 1275.38 26.669 1094.97 255.28 1340.19 20.453 158.00 250.71 1276.52 15.619 120.02 255.36 1341.58 12.689 78.46 250.82 1277.86 24.872 243.37 255.47 1343.12 14.11 148.34 250.91 1279.28 14.625 112.17 25537 1344.37 12.608 225.93 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 169 Appendix B. (continued) Depth Age N M Depth Age N M (103 m l1) (vr b2k)* (103 m l1) (m) (yr b2k)* (Hgfcg1) i s L (ngfcg1) - 255.64 1345.55 13.373 223.19 260.68 1423.82 11.046 107.03 255.73 1347.17' 9.151 58.88 260.79 1425.69 14.036 185.20 255.86 1348.69 13.028 15733 260.91 1427.74 13.335 249.69 255.93 1349.91 10.264 145.62 261.04 1429.71 13.43 143.29 256.02 1351.99 1239 93.81 261.15 1431.27 11.813 320.14 256.12 1352.92 9.52 89.08 26133 143236 14.879 68.19 256.21 1353.84 12.938 11430 261.31 1434.01 13.025 86.10 256.27 1354.96 9.843 147.96 261.41 1435.63 15.69 5129 256.36 1356.60 7.043 55.41 261.50 1438.03 10.583 64.65 256.49 135832 7.87 69.78 26139 1439.20 9.872 103.60 256.59 1359.67 13.82 122.91 261.70 1440.36 17.958 75 3 3 256.67 1360.99 8.944 170.91 261.78 1441.95 16.993 793.22 256.77 1362.55 8.738 78.10 261.89 1443.66 11.249 235.14 256.88 1364.06 11.657 164.82 261.99 1445.34 1334 109.87 256.97 1365.49 12.988 78.04 262.09 1446.98 10.774 127.74 257.07 1366.77 19.362 130.27 262.18 144835 7.837 132.99 257.14 1368.29 10.863 382.08 262.27 1450.15 26.647 129.71 257.27 1370.19 13.026 503.00 26237 1451.72 18.917 150.67 257.39 1371.94 11.757 44.08 262.46 1453.16 11.013 71.79 257.50 1373.46 10.456 64.07 26234 1454.73 15.67 137.10 257.59 1375.03 33.595 243.39 262.64 1456.60 12.224 132.00 257.70 1376.75 12.205 98.19 262.76 1458.73 35.959 269.96 257.81 137831 17.53 126.44 262.89 146032 76.61 293.03 257.93 1380.13 17.268 142.32 262.97 1462.28 35.153 498.11 258.02 1381.83 17.411 123.11 263.10 1464.73 36.973 188.89 258.15 1383.52 24325 251.94 263.26 1467.23 24.724 135.26 258.24 1385.15 9.498 38.86 26339 1469.05 41.615 497.96 258.36 1386.86 5.398 7239 263.47 1470.43 17.179 136.00 258.46 1388.18 27.124 79.26 263.55 1471.99 10.08 48.03 258.53 1389.24 13.634 183.83 263.65 1473.65 9.18 362.85 258.60 1390.38 16.463 333.16 263.74 147537 10.937 65.73 258.68 1391.94 11.74 108.21 263.87 1477.89 12.662 77.44 258.80 1393.58 12.555 145.07 264.00 1480.14 6.03 35.26 258.89 1395.311 6.205 39.97 264.12 1482.25 8.74 53.81 259.02 1397.28 6.435 59.22 264.24 148434 10.834 68.98 259.14 1399.25 10.008 94.99 264.38 1486.49 8.889 76.55 259.27 1401.06 11.541 243.89 264.46 1488.26 19.049 211.65 259.37 140234 7.353 141.35 26438 1490.39 18.59 268.93 259.46 1404.01 16.274 25638 264.70 1492.36 27.179 108.01 259.56 1405.76 30.719 14932 264.80 1493.84 21.623 138.79 259.68 1407.52 12.885 172.32 264.87 149530 50.628 145.63 259.78 1409.20 6.609 67.10 264.99 1497.75 14.119 184.07 259.89 1410.96 6.127 36.99 265.12 1499.91 11.91 149.74 260.00 1412.72 13388 80.92 265.23 1501.62 20.928 24533 260.11 1414.49 11.077 71.94 265.31 150334 26329 170.83 260.22 1415.95 10.925 72.09 265.42 1505.43 2138 204.70 260.29 1417.44 12.781 137.84 26 5 3 4 1507.25 33.612 264.04 260.40 1418.86 20.841 159.82 265.62 1508.71 45.26 500.33 260.46 1420.32 15.834 11437 265.70 1509.86 23.854 343.67 260.58 1422.11 20.945 195.74 265.75 1511.10 10.759 72.68 *yrb2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 170 Appendix B. (continued) Depth Age N M Depth Age N M (m) (v r b2k)* (lO’ m l1) (Hg kg ') (m) (v r b2k)* (10* ml’1) (H g k g 1) 265.84 1513.02 24.209 8 9 4 3 7 27034 1604.62 10381 48.04 265.96 1515.14 15.311 221.25 270.66 1606.65 13.047 104.77 266.07 1516.89 31.243 308.63 270.74 1608.20 15.757 863.98 266.15 1518.64 17325 100.73 270.81 1610.76 14.485 4 4 8 3 9 266.26 1520.58 33.277 215.48 270.98 1612.74 5.384 42.44 266.36 152234 33.277 215.48 271.00 1614.15 8.499 84.41 266.45 1524.11 17.277 179.74 271.12 1616.41 9.07 259.86 266.55 1525.56 10.873 157.20 271.21 1618.15 36.448 31531 266.60 1527.21 17.984 135.89 271.28 1619.73 17.428 78.04 266.72 1528.89 31.453 135.87 27136 1621.42 11.199 60.01 266.78 1530.11 40.615 579.00 271.44 1623.12 20.033 77.49 266.85 1531.71 38.984 321.92 27132 1625.03 13.099 722.23 266.95 153339 18.928 175.34 271.62 1627.05 17.417 161.22 267.05 1535.67 17.664 115.84 271.71 1629.19 12.576 137.44 267.17 1537.37 21.37 139.44 271.82 1631.11 30385 1515.95 267.23 1538.60 11.333 133.02 271.89 1633.04 13.848 135.68 267.30 1540.41 7.9 58.43 272.00 1635.79 9.991 315.44 267.42 1542.55 11361 50.70 272.15 1638.98 10.125 508.77 267.53 1544.51 13.679 105.84 272.30 1642.01 13.03 481.31 267.63 1546.23 18.634 157.41 272.43 164430 11.752 78.43 267.71 1547.96 22.998 2 2 3 3 6 27231 1646.38 6.302 76.82 267.81 1549.78 8.89 56.60 272.62 1648.90 6.302 76.82 267.90 1551.71 18.096 198.16 272.74 1651.20 9.556 52.72 268.01 1553.84 26.815 526.83 272.83 1653.74 9.089 105.15 268.12 1555.58 28.828 24331 272.97 1656.45 14.139 144.21 268.19 1556.94 14.241 89.18 273.07 1658.61 10.681 77.70 268.26 1558.60 13.946 127.54 273.16 1660.73 5.929 89.75 268.36 1560.40 18.005 157.48 273.26 1662.96 8.776 53.23 268.44 1562.40 12.048 299.80 273.36 1665.65 3.803 32.39 268.56 1564.56 31.465 210.05 273.50 1668.46 12.872 101.23 268.66 1566.23 18.963 423.87 273.61 1670.60 13.662 351.43 268.73 1567.61 13.857 136.14 273.69 1672.52 12.501 140.84 268.80 1569.49 3.725 60.52 273.78 1674.33 9.183 105.29 268.92 1571.86 12.866 116.64 273.85 1676.64 10.151 103.35 269.04 1573.75 12.892 67.35 273.99 1679.01 17.015 237.14 269.11 1575.74 13.159 299.27 274.06 1680.95 15.856 597.95 269.24 1577.73 13.131 236.65 274.16 1683.19 17316 116.77 269.31 1578.93 18.339 119.16 274.26 1685.60 10.865 119.71 269.36 1580.03 20.893 81.36 274.37 1688.03 8324 127.10 269.42 158134 13.463 78.71 274.47 1690.69 17.336 96.66 269.51 1583.45 18.16 1688.65 274.60 1693.71 7.428 71.08 269.61 1585.56 5.83 39.88 274.73 1696.21 7.993 122.15 269.72 1587.69 10.651 217.39 274.81 1698.42 22.773 181.50 269.82 1589.92 8.896 58.73 274.91 1700.52 37.674 260.22 269.94 1592.05 10.062 60.35 274.99 1702.46 16.592 340.71 270.03 1594.29 1032 148139 275.08 1704.88 13.345 59.91 270.16 1597.00 22.24 289.47 275.19 170734 11.49 54.53 270.30 1599.21 12.751 102.71 27530 1710.14 4.215 22.74 270.38 1600.81 13.619 80.42 275.41 1712.63 10.343 62.96 270.45 1602.51 8.288 129.24 27531 1714.90 16.909 159.16 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 171 Appendix B. (continued) Depth Age N M Depth Age N M _ iE ) __ (vr b2k)* (103 ml'1) Q*gfcg‘> i s L (yr b2k)* (IQ3 m l1) frgfcg') 275.60 1717.66 14.03 716.45 280.27 1838.94 8.616 118.96 275.74 1720.43 2 1 5 0 8 184.26 280.40 1842.61 6 5 4 4 222.64 275.83 1722.60 8.094 90.24 28053 1845.45 7.478 86.97 275.92 1724.90 9.331 54.68 280.60 1845.76 4.106 5355 276.02 1726.97 11.729 8052 280.67 1848.62 5.835 11151 276.09 1729.04 14.251 80.68 280.80 185120 4.268 66.44 276.19 1730.94 10.759 97.71 280.92 1855.23 13.483 280.72 276.25 1732.98 14.89 107.82 281.01 1857.83 7553 67.63 276.36 1735.55 6.706 4 1 5 8 281.10 186052 7515 80.44 276.46 1738-51 2.963 30.68 281.20 1863.28 10.756 121.27 276.60 1741.11 13.164 160.19 281.29 1866.72 3.832 304.94 276.67 1743.34 15.23 175955 281.43 1870.24 5.731 26.08 276.78 1745.83 2 1 5 5 5 277.09 28153 1873.93 4.911 50.47 276.87 1748.08 14.311 110.61 281.68 1876.59 7.805 73.34 276.96 1750.33 4.824 60.04 281.71 1878.38 5 5 4 8 289.10 277.05 1752.78 4.759 255.11 281.80 1880.91 10 788.81 277.15 1755.62 6.316 115.01 281.88 1883.30 9.742 91.66 277.27 1758.02 11.066 1502.21 281.96 1886.00 8.916 65.09 277.34 1760.18 8.116 1332.31 282.06 1889.01 12.751 451.71 277.44 1762.60 5.227 59.34 282.16 1891.88 23.355 247.24 277.53 1765.02 11554 55.81 282.25 1894.61 8.013 57.34 277.63 1767.20 10.695 319.91 282.34 1897.19 9.806 112.55 277.70 1769.77 15535 379.97 282.42 1899.63 12.991 85.04 277.83 1772.35 12.3 84.09 28250 1902.47 7.042 54.17 277.90 1774.16 19.955 141.59 282.61 1905.46 8.13 617.43 277.97 1776.61 3.856 25.27 282.70 1908.24 14.683 129.67 278.09 1779.06 22.456 209.19 282.79 191056 10.94 867.47 278.16 1780.89 6.294 75.22 282.85 1913.20 10.813 73.12 278.23 1783.37 8.917 67.28 282.96 1916.78 22.345 111.06 278.35 1786.26 8.9 72.64 283.08 1920.23 14.635 85.70 278.45 1788.90j 11.967 259.03 283.18 1923.69 7.804 104.02 278.55 1791.27! 23.616 299.72 283.30 1927.16 5.138 71.18 278.63 1793.53 7.973 88.85 283.40 1929.87 17.004 176.13 278.72 1795.79 19.764 222.00 283.47 1932.75 7.442 114.01 278.80 1797.79 9.003 68.82 28358 1935.62 9.147 153.30 278.87 179954 11.611 84.93 283.65 1938.99 6.749 154.28 278.93 1801.43 11.089 121.92 283.79 1942.85 17.207 110.16 279.01 1803.44 41.281 426.32 283.89 1946.41 6.204 108.43 279.08 1806.27 23.745 126.66 284.01 1949.66 16.546 82.91 279.22 1809.79 26.48 152.18 284.09 1952.92 14 73.45 279.34 1812-51 14.19 171.81 284.21 1956.19 4.727 31.31 279.42 181455 7.83 81.48 284.29 1958.49 15.852 118.78 279.49 1817.15 12.002 177.48 284.35 1960.96 12.076 75.07 279.61 1819.90 13.077 138.40 284.44 1963.77 13.286 79.65 279.69 1822.37 4.898 66.36 28452 1966.42 13.703 29450 279.79 1824.98 11.823 109.25 284.60 1969.75 11.937 79.93 279.88 1827.74 12.433 130.34 284.72 1973.92 5.773 134.83 279.99 1830.39 11.913 94.60 284.85 1977.76 9.742 2319.61 280.07 1832.90 5.202 3051 284.95 1981.14 10.86 296.45 280.17 1835.70 8.901 178.02 285.05 1984.36 15.499 438.17 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 172 Appendix B. (continued) Depth Age N M Depth Age N M (rn) (v rb 2 k V (10* ml*1) ( p g k g 1) (m) (vrb2k)* (10s mT1) (Ug k g ') 285.14 1987.76 12.441 453.77 289.65 2156.55 15.222 306.03 285.25 1990.49 18.97 159.46 289.72 2159.60 14J83 269.05 285JO 1992.55 23.498 158.87 289.80 2164.01 20.679 523.49 285.37 1994.95 21.518 176.28 289.93 2168.61 12.906 107.31 285.44 1998.22 13.849 1 5 2 0 290.02 2172J9 12.906 107.31 285.56 2002.20 14.461 141.45 290.11 2176.40 14.177 92.21 285.67 2006.37 12.456 869.47 290.21 2180.53 9 J3 6 94.84 285.80 2010.04 6.71 197.45 290.31 2184.49 28.125 3519.70 285.88 2013.20 9.955 85.65 290.40 2186.75 5.891 17.69 285.98 2016.55 24.256 160.66 290.44 2188.46 6.356 15.37 286.07 2019.92 10.206 57.60 290.48 2190.40 14.639 37.64 286.17 2024.15 10.142 100.58 290J 2 2191.96 16.012 66.35 286.31 2028.74 15.301 702.66 290J7 2194.05 16.125 239.90 286.43 2033.22 15.91 184.89 290.61 2195.78 15.826 74.98 286.56 2037.37 10.191 51.68 290.65 2197 JO 14.232 130.18 286.66 2040.99 10.261 46.35 290.69 2199.24 28.383 326.06 286.76 2044.09 10.246 66 JI 290.73 2201.19 15.676 149J5 286.83 2046.82 6.457 49.42 290.77 2203.07 35J29 483.76 286.91 2050.30 5.613 39.37 290.81 2204.67 37.997 348.68 287.02 2053.98 9.758 72.17 290.86 2206.85 23.291 59.60 287.11 2056.94 8.834 47.95 290.90 2208.60 24.001 127.75 287.18 2059.16 12.213 61 JO 290.94 2210.36 9.233 24.58 287.23 2061 J7 10.308 732.62 290.98 2212.11 14.904 158.70 287.31 2064.37 16.034 55.88 291.02 2213.87 41.662 439.22 287.38 2066.98 7.062 43.43 291.06 2215.63 21.074 134.98 287.45 2070.17 15.853 80.47 291.11 2218.06 18.556 162.32 287.55 2073.56 21.036 95.96 291.15 2219.83 6.058 13.11 287.63 2076.58 13.785 282.66 291.19 2221.61 11.232 41.43 287.71 2078.47 21.881 136.82 291.24 2223 J6 9.225 34.35 287.73 2081.32 19.067 143.13 291.28 2225.34 20.825 222.19 287.86 2085.52 18.519 165.61 291.32 2227.35 23.941 161.03 287.95 2089.54 11.148 60.77 291.37 2229.47 12.977 59.61 288.07 2093.00 10.064 73.75 291.41 2231.15 17.417 588.37 288.13 2095.70 30.296 991.21 291.45 2232.94 17.083 231.65 288.21 2099.58 30.296 991.21 291.49 2234.74 14.907 304.09 288.33 2103.28 56.856 1386.01 291.54 2237.11 17.183 142.44 288.40 2106.60 15.791 305.46 291.58 2238.80 13.42 166J8 288.50 2110.33 20.127 153.98 291.62 2241.29 11.071 111.27 288.59 2114.27 11.187 80.57 291.66 2242.56 10.001 54.03 288.70 2118.42 18.525 221.30 291.71 2244.81 4.58 11.31 288.80 2122.00 16.029 166.13 291.75 2246.97 63.33 1500.72 288.88 2125.19 20.725 425.34 291.79 22 4 8 J7 21.879 207.43 288.96 2127.79 32.491 599.45 291.83 2250.39 13.959 281.11 289.01 2130.20 31.265 574.85 291.88 2252.69 25.621 744.24 289.08 2133.02 25.997 275.85 291.92 2254.52 22.478 570.02 289.15 2136.46 19.837 150.71 291.96 2256.13 14.781 169.76 289.25 2140.31 35.289 318.56 292.01 2258.43 27.542 532.59 289.34 2144.18 20.722 780.15 292.05 2260.28 21.605 438.64 289.44 2148.68 17.536 434.02 292.09 2262.13 8 J1 5 23.61 289.56 2153.12 12.39 99.17 292.14 2264.45 6.469 19.00 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 173 Appendix B. (continued) Depth Age N M Depth Age N M (m) (vr b2k)* (103 ml*) (M gkg1) (m) (vr b2k)* (103 m l'1) (Mg k g ') 292.18 226631 6.97 28.10 29 4 3 7 2373.64 7.146 18.08 292.22 2268.17 6.947 1539 294.41 2376.16 6.094 14.25 292.27 2270.73 2.866 4.96 294.46 2378.63 28.339 238.61 29231 2272.60 5.814 3239 2 9 4 3 0 2380.46 9.772 39.08 29235 2274.48 16.073 70837 2 9 4 3 4 238234 41.159 109132 292.40 2276.83 23.617 261.28 29 4 3 9 2385.16 55.202 1969.87 292.43 2278.24 14.117 274.73 294.63 2387.52 27.447 909.52 292.47 2280.12 14.657 157.02 294.67 2389.62 14.073 68.00 29232 2282.25 6.849 40.28 294.72 2392.19 41.162 486.98 292.56 2284.14 7.725 35.79 294.76 2394.11 28.109 421.43 292.60 2286.04 20.69 137.13 294.81 2396.75 13.34 236.16 292.65 2288.65 3.813 7.71 294.86 2399.67 21.15 423.90 292.69 2290.56 15.841 120.19 294.91 2402.33 24.926 490.81 292.73 2292.94 25.13 266.25 294.95 2404.47 11.739 4 0 3 9 292.78 2294.86 23.605 351.93 295.00 2407.13 51.081 1368.52 292.82 2296.77 21.346 993.23 295.04 2409.28 14.273 255.46 292.86 2298.45 19.795 140.78 295.09 2411.96 30.281 605.35 292.91 2300.86 9.857 143.05 295.13 2413.91 5.236 12.60 292.99 2304.72 10.108 1738 295.18 241634 2.2 11.60 293.03 2306.66 7.624 13.21 295.22 2418.70 3.339 6 5 3 6 293.08 2309.33 7.397 25.73 295.27 2421.42 5.446 13.92 293.12 2311.27 29.692 663.27 295.31 2423.86 4.262 15.92 293.16 2313.22 15.492 5734 295.36 2426.58 7.61 113.28 293.21 2315.65 4.523 15.07 295.41 2429.17 8.209 28.70 293.24 2317.08 25.393 1263.40 295.45 2431.22 3 3 4 6 11.05 293.28 2319.12 2 5 3 438.13 29 5 3 0 2433.97 7.698 25.61 293.33 2321.16 15.159 277.82 29533 2435.61 6.645 191.17 293.37 2323.13 7.117 17.59 29 5 3 8 2438.37 5.25 107.45 293.42 2325.84 7.961 39.18 295.62 2440.85 24.693 1069.03 293.46 2327.82 5.541 14.15 295.67 2443.69 10.695 211.82 293.51 2330.30 8.27 2835 295.72 2446.12 7.443 27.85 293.55 2332.53 8.536 35.40 295.76 2448.48 8.755 27.91 293.60 2334.77 4.22 1038 295.81 2451.13 7.639 23.92 293.64 2336.77 11.933 45.45 295.86 2453.92 18.35 225.84 293.68 2338.77 7.727 25.12 295.90 2456.44 9.332 3 6 3 7 293.73 2341.39 9.934 24.72 295.95 2458.97 27.763 505.99 293.77 2343.44 8.444 25.85 295.99 2461.50 16.306 228.27 293.82 2345.95 11.718 35.70 296.04 2464.40 13.367 31.24 293.86 2347.97 4.241 8.34 296.09 2466.94 9 3 3 4 94.11 293.91 2350.63 5.804 13.21 296.13 2469.42 5.67 16.53 293.95 2352.52 12.593 108.92 296.18 2472.26 9.388 17.18 293.99 2354.56 8.363 27.17 296.23 2475.21 7.298 20.23 294.04 2357.23 12.622 5034 296.27 2477.47 7.327 22.87 294.08 2359.14 18.656 169.39 296.31 2479.40 8.444 27.04 294.12 2361.17 12.237 42.07 29 6 3 6 2482.28 10.944 112.27 294.15 2362.62 12.237 42.07 296.41 2485.15 8.157 22.73 294.19 2364.74 33.692 92633 296.45 2487.45 5.161 11.36 294.24 2366.99 11.182 130.01 29 6 3 0 2490.43 10.733 38.77 294.28 2369.18 3.897 7.23 29 6 3 4 2492.90 6 3 4 7 1831 294.32 2371.11 7.891 24.18 296 3 9 2495.95 6.064 17.94 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 174 Appendix B. (continued) Depth Age N M D epth Age N M (m ) (vr b 2 k )* (103 m l'1) ( fig k g ' ) (m) (y r b 2 k )* (10* m l'1) (UK k g ') 296.63 2497.84 11.665 104.74 298.84 2635.41 26.948 265.37 296.68 2501.22 9.496 55.99 298.88 2638.05 27322 35951 296.73 2503.86 9.413 40.05 298.92 2640.69 6.939 12.53 296.77 2506.21 20.528 29456 298.97 264434 11.654 82.25 296.82 2509.15 12.891 99.13 299.01 2646.83 37.93 892.98 296.86 2511.51 29.144 92.67 299.06 2650.00 3.009 6 5 0 296.90 2513.87 16.622 58.59 299.10 2652.84 33.206 403.45 296.95 2516.83 10.171 57.67 299.15 2657.20 4.136 12.03 296.99 2519.21 8.734 34.17 299.20 2659.30 5.275 71.35 297.04 2522.41 24.146 460.65 299.24 2661.75 6 5 5 20.79 297.08 2524.95 11.841 70.35 299.29 2665.12 9.169 4132 297.13 2527.65 6.289 20.93 299.33 2667.83 2.564 4.91 297.17 2530.08 9.052 30.07 299.38 2671.70 15.677 411.76 297.21 2532.49 16.443 54.15 299.42 2674.29 7.079 39.69 297.26 2535.70 7.132 22.49 299.47 2677.70 15509 110.01 297.30 2538.22 14.259 194.49 2 9 9 5 2 2680.79 31501 68151 297.34 2540.34 20.123 140.07 2 9 9 5 6 268353 33.245 681.73 297.37 2541.85 8.963 22.25 299.61 2687.06 19524 7654 297.41 2544.28 5.137 12.04 299.64 268956 9.931 69.38 297.46 2547.33 4.377 9.39 299.69 2692.67 46.4 1384.19 297.50 2549.77 7.064 2552 299.73 2695.45 8.799 29.25 297.55 2552.98 12.709 83.71 299.78 2698.75 9.488 62.85 297.59 2556.21 8.812 30.41 299.82 2702.06 48.019 1106.87 297.63 2558.05 10.269 37.02 299.87 2705.03 38.861 413.31 297.68 2561.13 10.41 43.99 299.92 2708.62 34.365 265.46 297.72 2563.30 7.045 22.32 299.96 2711.70 37.008 928.06 297.77 2566.40 2 1 .8 8 6 309.50 300.01 2714.96 35 5 2 522.90 297.81 2568.88 52.605 246.52 300.05 2718.04 35.52 522.90 297.85 2571.69 44.172 432.59 300.10 2721.23 35.52 522.90 297.90 2574.49 11.716 35.01 300.14 2724.16 5.175 13.41 297.94 2576.99 35.189 244.70 300.19 2727.81 11.805 90.94 297.99 2580.44 14.272 39.23 300.24 2731.21 9.403 30.79 298.03 2582.96 41.563 1231.57 300.28 2734.25 5.627 12.84 298.07 2585.48 20.08 104.67 300.33 2737.66 5.249 15.21 298.12 2588.80 52.7 1238.10 300.37 2740.72 17.599 428.77 298.16 2590.86 52.658 1218.27 300.42 2744.15 10556 52.82 298.21 2594.19 6.041 14.02 300.47 2747.78 16.071 245.97 298.25 2597.15 40.932 242.68 30051 2750.68 3.523 1057 298.30 2600.02 84.885 114652 30 0 5 6 2754.68 5.567 32.00 298.34 2602.58 88.386 174654 300.61 2758.24 2.097 3.42 298.39 2605.79 33.228 649.36 300.65 2761.18 3.893 56.73 298.43 2608.37 48.234 700.12 300.70 2764.93 4.452 18.82 298.48 2611.75 17.698 107.87 300.75 2768.43 8.632 277.84 298.52 2614.50 80.006 1168.98 300.79 2771.57 4.004 958 298.57 2617.74 11.019 28.23 300.84 2775.46 3.246 5.67 298.61 2620.83 74.744 119451 300.88 2778.43 4.86 19.16 298.66 2623.79 55.845 699.96 300.93 2781.60 4.224 13.25 298.70 2626.22 20.831 51.68 300.98 2785.43 6.331 25.04 298.75 2629.65 13-535 41.74 301.02 2788.70 5 5 8 23.10 298.79 2632.03 17.786 45.14 301.07 2792.08 8.967 54.01 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 175 Appendix B. (continued) Depth Age N M Depth Age N M (m) (vrb2k)* (103 ml"1) (Ug k g '1) (m) (vrb2kV* (103 m l1) (p g k g ‘) 301.12 2795.85 10.083 46.24 30333 2974.80 8.188 19.65 301.16 2799.12 10.107 28.42 30337 2978.49 7 3 1 9 73.94 301.21 2802.84 7.861 25.06 303.41 2982.42 16.464 62131 301.25 2805.69 7.129 22.79 303.46 2986.64 26.645 501.28 301.30 2809.69 5.782 247.13 30330 2989.86 5.781 43.23 301.35 2813.17 6.955 217.58 303.54 299337 23.219 1625.91 301.39 2816.23 6.612 72.90 30338 2997.34 18.751 921.47 301.44 2820.07 8.926 26.53 303.63 3001.32 15.829 41930 301.49 2826.12 8.001 435.72 303.79 3016.46 9.642 80.32 301.52 2827.61 4.238 10.45 303.83 3019.15 13.32 145.30 301.57 2830.49 6.944 48.82 303.88 302432 7.691 1935 301.61 2833.69 4.184 9.10 303.92 3027.02 27.768 566.11 301.66 2836.89 5.065 13.11 304.06 3039.49 8 3 4 6 2538 301.70 2840.09 232 4.83 304.10 3043.83 10.255 39.90 301.75 2844.43 2.957 6.58 304.15 3047.72 8.567 25.23 301.79 2847.76 7.709 133.92 304.19 3051.50 23.958 306.48 301.83 2850.91 4.981 11.81 304.24 305637 49.949 110738 301.88 2854.96 3.022 46.46 304.28 3060.68 5.375 11.40 301.92 2857.63 7.923 37.05 30435 3066.63 11.418 111.03 301.97 2862.20 4.898 14.14 304.39 3070.82 23.402 274.22 302.02 2866.38 14.114 602.85 304.43 3074.09 7.673 43.68 302.07 2870.08 8.244 53.83 304.47 3077.84 6.38 24.75 302.12 2874.20 5.39 13.20 304.51 3081.59 10.433 187.71 302.17 2877.61 11.41 90.91 304.56 3086.53 15.432 361.43 302.22 2881.64 14.984 161.69 304.60 3090.07 3.663 12.44 302.26 2885.49 9.749 144.48 304.64 3093.62 17.245 318.06 302.31 2889.14 5.333 13.08 304.68 309737 10.561 300.75 302.35 2892.59 12.393 207.06 304.72 3101.46 13.062 340.51 302.40 2896.88 16.111 352.45 304.76 3105.28 4.051 15.79 302.44 2899.95 21.823 342.26 304.80 3109.11 10.734 87.90 302.48 2902.82 6.055 22.95 304.84 3113.07 13.859 276.01 302.53 2906.94 17.901 295.52 304.89 3117.28 12.178 116.88 302.57 2910.44 9.633 62.50 304.93 3121.14 12.932 202.66 302.62 2914.68 5.926 16.25 304.97 3125.13 16.058 251.43 302.66 2918.21 37.643 1170.85 305.01 3129.81 8.879 196.93 302.70 2921.02 25.847 770.42 305.05 3132.91 18.322 792.64 302.75 2925.29 60.868 1763.04 305.09 3137.61 13.192 492.32 302.79 2928.96 6.184 26.93 305.13 3140.61 9.828 100.18 302.83 2931.89 8.119 19.66 305.18 3145.72 6.766 38.55 302.88 2936.10 11.546 3 2 3 7 305.27 3154.30 5.58 64.58 302.92 2939.90 22.89 597.18 30535 3162.99 4.288 26.09 302.96 2942.86 15.318 1321.65 305.44 3171.73 17.633 107.11 303.00 2946.67 10.911 176.62 30533 3180.28 10.151 75.67 303.03 2949.23 13.152 25.81 305.62 3189.64 6.831 107.12 303.07 2952.21 7.909 8235 305.71 319835 30.245 139936 303.12 2956.70 3.959 8 3 7 305.80 3208.28 12.955 141.05 303.16 2960.13 4.05 9.00 305.88 3216.27 10.131 54.71 303.20 2963.35 3.805 6.93 305.97 3225.87 7.865 19738 303.24 2966.80 9.147 129.09 306.06 3234.75 16.469 267.86 303.29 2971.55 18.621 352.18 306.12 3241.83 5.172 33.20 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 176 Appendix B. (continued) Depth Age N M Depth Age N M (m) (vr b2k)* (103 ml*1) (Ug kg'1) (m) (yrb2k)* (103 m l1) (Ug k g'1) 306.16 3245.26 14.679 292.31 30838 3499.67 23.667 549.65 306.20 3249.48 6.724 6437 308.43 3505.92 13.147 102.02 306.24 3253.72 9354 7737 308.47 3510.94 22.18 514.71 306.28 3258.50 7.952 174.44 30831 3516.13 25.479 274.08 306.33 3263.30 9.354 42.08 30836 3522.81 13.838 225.09 30637 3267.84 12.414 260.07 308.60 3528.09 9.484 49.09 306.41 3272.13 15.778 29630 308.65 3534.45 8.751 47.07 306.45 3277.25 25.716 449.66 308.69 3539.77 38.695 417.85 306.49 3281.02 38.049 117434 308.74 3546.18 28.088 152.05 306.53 3284.81 15.175 490.42 308.78 3551.00 5.947 46.79 306.57 3289.51 29.446 956.86 308.83 3557.43 4.676 107.43 306.61 3294.05 20.672 438.23 308.86 3562.18 23.043 303.60 306.65 3298.56 45.572 1630.97 308.91 3567.70 34.126 683.13 306.70 3303.77 14.376 165.91 308.95 3572.92 37.23 852.98 306.74 3308.30 16.941 402.41 309.00 3579.96 19.12 145.83 306.78 3312.80 28.347 501.85 309.04 3585.70 18.773 161.96 306.82 3317.13 32395 52432 309.09 359130 21.514 96.10 306.86 3321.57 36.842 656.47 309.13 3596.93 49.433 1209.92 306.90 3326.02 27.032 589.37 309.18 3606.12 6.658 95.82 306.94 3330.48 4.396 18.57 309.23 3610.56 13.32 417.38 307.02 3339.45 17.544 340.88 309.27 3616.92 5.625 24.70 307.07 3345.25 17344 340.88 309.32 3622.64 27.938 973.80 307.11 3349.21 39.816 704.73 309.36 3627.95 12.157 90.71 307.16 3355.16 13.428 107.86 309.41 3635.13 19.12 94.92 307.20 3359.64 10.129 34.07 309.46 3642.62 5.516 35.90 307.25 3365.42 26.213 295.43 309.50 3647.27 16.964 96.14 307.29 3370.00 39.083 685.34 309.55 3653.89 14.227 116.69 307.34 3376.32 15.433 133.06 309.59 3658.70 10.538 11037 307.38 3380.21 31.645 627.36 309.64 3666.29 9.569 45.76 307.42 3385.13 34.297 754.45 309.68 3671.47 15.089 209.03 307.47 3390.65 11.164 94.70 309.73 3678.42 18.43 192.82 307.51 3395.45 24.553 727.19 309.78 3686.03 41.499 568.66 307.56 3401.69 19.917 393.60 309.81 3690.16 25.07 204.58 307.60 3405.40 23.173 812.38 309.85 3695.78 56.179 489.84 307.65 3411.72 18.796 72.25 309.90 3701.76 12.027 103.79 307.69 3416.89 28.283 443.12 309.99 3714.70 7.909 52.98 307.73 3420.74 16.576 255.27 310.03 3720.93 i 8.257 11538 307.78 3426.68 33.069 769.46 310.07 3725.93 12.263 249.87 307.82 3431.74 33.758 43937 310.12 3733.11 13.557 200.25 307.89 3440.61 31.494 409.66 310.16 3739.24 10.776 10035 307.93 3444.52 6.552 34.99 310.20 3745.02 10389 51.03 307.98 3450.55 7 3 7 40.54 310.25 3752.64 9.44 73.68 308.02 3455.39 35.828 471.92 310.29 3758.47 13.752 369.45 308.07 3461.62 13.234 5139 310.34 3766.27 8.016 69.68 308.11 3466.96 13.234 5139 310.38 3770.92 9 3 2 7 76.06 308.16 3472.77 45.529 745.49 310.42 3776.81 7.995 265.85 308.20 3477.68 20.802 601.80 310.47 3784.57 10.259 31438 308.25 3484.66 18.645 504.49 310.56 3798.86 10.281 30.44 308.29 3488.79 10.043 72.80 310.65 3811.23 17324 596.61 308.34 3495.62 33.995 680.19 310.69 3817.26 31.193 999.43 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 177 Appendix B. (continued) Age N M Depth Age N Inn (vrb2kV* (101 m l'1) k g 1) (m> (yrb2k)« (103 m l'1) kg' 310. 3825.46 68.662 1921.93 312.91 4189 JO 8.837 127. 310. 3831.67 7.156 58.21 312.95 4196.62 17.072 292 310. 3839JO 9.763 40 JO 313.00 4205.93 60.728 518. 310. 3846.01 33.973 601.62 313.04 4213.87 8.47 200 . 310. 3851.58 45.831 547.73 313.09 4222.80 15.843 98. 310. 3859.30 14.226 207.61 313.13 4230.34 12.867 110. 311. 3865.49 18.689 353.94 313.18 4238.30 10.281 61. 311. 3873.28 8.017 44.10 313.22 4246J8 16.382 229. 311. 3879.53 9.979 122.09 313.26 4254.49 45.055 543. 311. 3 887J6 14.053 52.88 313.31 4264.24 34.082 500. 311. 3894.69 17.783 389.95 313.35 4271.79 17.05 191. 311. 3899.78 32.831 545.45 313.40 4281.71 50.833 816. 311. 3907.91 39.73 635.06 313.44 4288.27 40.721 457. 311. 3914.28 15.434 184.73 313.48 4297.54 1 6 J1 1 82. 311. 3922.28 15.045 224.03 313.53 4305.87 11.616 168. 311. 3928.71 41.67 529.67 313.57 4313.74 33.003 425. 311. 3936.36 41.304 405.64 313.61 4323.13 40.549 188. 311. 394251 3.102 9.96 313.66 4331J7 27.27 320. 311. 3949.41 62.927 848J 1 313.70 4339.54 17.266 282. 311. 3957.16 42.728 501.42 313.75 4351.06 30.116 573. 311. 3962.06 47.684 568.00 313.80 4359.61 26.643 657. 311. 3970.69 14.745 45.68 313.84 4369.22 25.997 287. 311. 3977.43 50.511 764.68 313.88 4376.08 11.598 110. 311. 3983.91 48.937 705.22 313.93 4386.87 18.387 211. 311. 3990.41 49.561 894.99 313.97 4395.40 15.799 323. 311. 3997.22 50.077 1189.40 314.02 4405.53 8 J 1 3 53. 311. 4003.92 28.023 411.52 314.07 4416.39 14.139 378. 311. 4009.79 14.118 270.10 314.11 4423.15 25.113 463. 311. 4018.22 16.145 119.07 314.15 4431.49 10.841 167. 311. 4025.84 11.273 125.14 314.19 4439.87 19.853 99. 312. 4031.79 21.814 805.36 314.24 4451.98 11.1 41. 312. 4038.61 17.373 185.31 314.28 4458.85 53.808 533. 312. 4045.46 14.549 113.45 314.32 4468.05 10.347 167. 312. 4052.33 13.581 158.71 314.36 4476.94 51.631 356. 312. 4058.97 6.96 62.12 314.40 4485JO 16.662 61. 312. 4067.80 4.115 61.20 314.44 4495.00 9.635 46. 312. 4076.06 15.498 116.87 314.48 4502.20 40.701 463. 312. 4082.83 12.566 119.20 314.52 4511.14 17.675 95. 312. 4091.81 14.853 63.12 314.57 4522.30 22.223 256. 312. 4098.86 13.515 106.22 314.61 4529.96 19.94 240. 312. 4107.70 27.334 186.11 314.65 4539.30 21.124 170. 312. 4115.70 14.442 109.98 314.69 4549.23 24.293 262. 312. 4123.72 13.557 1202.38 314.73 4558.10 45.833 240. 312. 4130.89 14.894 112.00 314.77 4566.45 27.766 90. 312. 4140.79 10.648 40.72 314.81 4574.82 19.572 883. 312. 4146.89 10.97 293.84 314.85 4584.18 7.435 30. 312. 4156.18 16.92 793.75 314.90 4595.46 15.131 60. 312. 4163.47 11.704 79.77 314.94 4604.70 30.869 308. 312. 4172.77 29.749 576.62 314.98 4612.67 33.845 427. 3 12 4179.97 20.005 218.78 315.02 4623.06 41.152 755. * y rb 2 k = years before AD 2000; n/d = no data copyright owner. Further reproduction prohibited without permission. 178 Appendix B. (continued) Depth Age N M Depth A ge N M (m) (vrb2k)* (103 m l1) d ig k g 1) (m) (vr b2k)* (103 m l'1) (ug k g '1) 315.06 4632.82 38.049 362.06 317.22 5 1 9 5 5 6 17.589 379.24 315.11 4644.36 49.668 91856 317.27 5209.89 11.035 276.17 315.15 4653.63 68.425 669.45 31751 5222.26 9.547 111.01 315.19 4663.24 25.651 204.19 31755 5234.19 19.142 475.46 315.24 4674.35 47.125 452.78 317.40 5249.19 6.184 63.18 315.28 4684.05 26.946 287.60 317.44 5260.75 5.883 8 4 3 0 315.32 4694.09 12.76 129.05 317.49 5275.66 9.267 111.40 315.36 4702.98 15.735 320.04 31754 5 2 9 1 5 7 14.118 3 0 8 3 2 315.41 4715.20 11.466 161.47 31758 5 3 0 1 5 4 17.049 224.35 315.46 4725.68 12.479 94.83 317.63 5319.07 7.63 62.21 315.50 4735.31 25.222 175.17 317.67 5330.33 38.09 2 2 7 3 6 315.54 4744.98 17.223 22058 317.71 5 3 4 5 5 2 30352 179.64 315.58 4754.69 13.666 158.95 317.75 5354.14 59.392 1028.70 315.63 4767.50 26.924 576.71 317.80 5373.24 15.886 71.40 315.67 4777.72 14.852 154.27 317.84 5383.87 14.788 90.71 315.71 4787.13 11.661 125.49 317.88 5397.67 80.606 2438.61 315.76 4798.97 16.123 729.00 317.93 5412.89 14.982 64.03 315.80 4809.13 33.09 255.50 317.97 5425.78 26.084 568.72 315.84 4819.12 6.034 26.11 318.01 5439.95 9.484 109.25 315.88 4829.38 14.742 387.72 318.05 5451.75 9.095 7 0 3 8 315.93 4841.47 12.351 95.60 318.10 5468.10 6.184 53.01 315.97 4851.93 10.561 41.90 318.14 5482.09 15.734 149.49 316.02 4865.31 31.989 357.77 318.18 5494.09 18.839 365.81 316.06 4874.28 19.853 293.15 318.23 5511.14 25.932 285.81 316.10 4884.57 18.668 171.70 318.27 5524.53 10.13 43.26 316.14 4895.55 22.742 377.30 318.31 5538.83 11.983 125.11 316.18 4905.29 4.417 2153 318.35 5551.10 36.216 917.66 316.22 4915.08 20.154 320.03 318.43 5577.59 11395 100.53 316.26 4925.55 37.897 344.27 318.47 5592.18 5.15 37.79 316.30 4937.07 8.6 53.49 318.52 5609.90 24.099 1 1 1 3 0 316.34 4947.98 17.05 401.79 318.56 5621.62 53.829 790.04 316.38 4958.61 19.808 457.13 318.60 5638.22 13.17 96.16 316.42 4969.29 36.39 1897.69 318.65 5654.62 5.28 31.70 316.47 4983.59 85.284 2061.29 318.69 5669.06 14.658 81.42 316.51 4992.13 33.672 963.51 318.73 5684.17 14.42 70.09 316.55 5002.97 35.203 1087.88 318.78 5700.56 12.609 56.54 316.59 5013.85 22.85 288.23 318.82 5715.56 8.255 68.53 316.65 5032.06 23.389 64.21 318.86 5728.67 36.239 568.92 316.69 5043.77 33.522 1378.95 318.90 5745.49 12.976 153.21 316.74 5057.63 13.557 413.23 318.95 5761.03 1131 37.04 316.78 5069.12 28.865 1155.23 318.99 5775.74 28.175 385.24 316.83 5082.42 44.193 184250 319.03 5793.32 2.736 23.88 316.87 5094.39 20.392 11455 319.08 5809.15 4.159 33.24 316.91 5103.92 25.824 359.77 319.12 5824.13 6.939 27.86 316.96 5118.14 18.474 75.62 319.16 5839.19 12.782 54.92 317.00 5129.92 15.367 238.17 319.21 5859.08 7.133 73.49 317.05 5145.37 11.509 254.35 319.25 5876.25 29.424 552.93 317.09 5157.89 34.729 1705.21 319.29 5888.72 10.863 90.46 317.13 5167.09 22.44 747.67 319.34 5909.93 10.797 65.00 317.18 5181.68 32.53 160.15 31958 5925.47 7.069 40.30 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 179 Appendix B. (continued) Depth Age N M Depth Age N M (m) (vrb2k)* CIO3 m l1) (US k g ') (m) (yr b2k)* (10* mT1) (H g k g ‘) 319.43 5944.53 23.95 324.71 32155 6922.46 10.281 48.49 319.47 5961.41 41.326 549.81 321.60 6952.62 30.46 2 1 0 J4 319.52 5979.54 7.197 39.96 321.64 6968.76 22.461 105.47 319.56 5995.47 52.471 1012.23 321.68 699354 8.708 36.31 319.61 6014.50 4859 709.76 321.72 7012.94 7565 63.89 319.65 6032.15 19.616 141.95 321.76 7036.65 8.082 32.62 319.70 6050.91 33.176 36057 321.81 706355 9.548 37.61 319.74 6069.30 11.123 32.80 321.85 708458 8.342 36.43 319.79 608952 10539 5051 321.89 7113.10 4.957 22.47 319.83 6106.42 4.848 18.04 321.93 7131.77 4.008 18.34 319.88 6128.29 16.986 132.23 321.97 7154.88 5558 4 9 5 5 319.92 614350 14.225 5956 322.01 7181.81 3.296 23.46 319.97 6165.13 7.069 34.11 322.06 7210.41 2.694 15.11 320.01 6182.12 7.845 40.62 322.10 7237.03 6.896 43.87 320.06 6202.43 12.414 9351 322.14 7259.38 8.577 4 5 5 5 320.10 6229.37 6.251 30.78 322.18 7281.87 4.999 22.70 320.14 6240.96 10.863 23.81 322.22 7302.99 6.184 34.22 320.18 6255.47 556 57.90 322.26 7331.86 7.047 4 3 5 5 320.23 6277.40 6.314 64.05 322.30 7351.76 5.387 32.34 320.27 6292.84 11317 101.03 322.34 7376.40 7.824 32.21 320.31 6313.93 12.934 104.11 322.39 7409.00 16.641 93.42 320.35 6330.69 13.213 95.39 322.43 7434.05 15.088 153.79 320.39 6346.41 19.054 149.35 322.47 7457.69 14.529 62.25 320.43 6364.48 69.503 679.01 32251 7484.68 12.136 63.16 320.47 6382.66 15.541 61.05 322.55 7510.25 13.86 122.80 320.51 6400.95 28.908 419.48 32259 7537.63 23.28 30657 320.56 6427.05 56.804 1042.49 322.63 7563.60 8.901 72.37 320.60 6444.83 9.483 37.53 322.67 7589.75 6.68 62.07 320.64 6463.50 7.846 30.97 322.71 7616.10 6.422 36.70 320.68 6483.46 6.228 23.19 322.75 7648.65 9.009 36.85 320.72 6498.82 14.097 81.51 322.79 7669.38 5.301 33.85 320.76 6518.42 12.76 44.74 322.83 7696.30 3.618 37.13 320.80 6539.33 10.411 42.76 322.87 7723.43 6.142 31.66 320.84 6556.17 6.788 61.87 322.91 7751.33 8.276 39.28 320.89 6582.82 15.283 139.68 322.95 7778.28 7.089 43.20 320.93 6599.89 7.781 44.22 322.99 7806.01 5.172 30.47 320.97 6623.22 8.75 128.94 323.03 7833.95 9.527 59.86 321.01 6642.01 4.523 36.09 323.06 7855.64 6.229 75.99 321.05 6661.40 6.272 39.32 323.10 7883.36 6.187 22.28 321.09 6686.45 5.408 62.17 323.14 7911.89 4.611 42.48 321.13 6701.57 11.553 60.78 323.18 7940.63 13.946 88.73 321.18 6729.06 10.928 72.93 323.22 7971.41 9.527 51.50 321.22 6747.80 8.493 36.44 323.26 7997.87 8557 69.12 321.26 6773.11 8.448 7551 323.30 8028.19 10.088 43.01 321.30 6789.94 13.472 100.23 323.34 8058.76 3.339 23.41 321.34 6812.09 11.79 6551 32358 8083.93 3.9 14.26 321.39 6838.34 6.918 84.56 323.42 8114.01 6.573 35.66 321.43 6855.52 17.093 12951 323.46 8142.40 7.305 45.01 321.47 6877.46 40.786 299.20 3 2 3 5 0 8173.69 5.387 2753 321-51 6900.89 8.642 56.18 32354 8206.39 4.677 28.89 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 180 Appendix B. (continued) Depth Age N M Depth Age N M (m) (vrb2kV* (10* mT1) (H gkg'1) (m) (yr b2k)* (103 m l'1) (H g k g ‘) 323.59 8245.22 3356 16.17 325.73 1036437 3.684 19.02 323.63 8279.84 3382 34.66 325.78 10429.28 6.401 40.65 323.68 8312.10 5.386 6 5 3 5 325.82 1048339 3.295 28.26 323.72 8343.97 7.694 4 6 3 2 325.86 10530.41 5.107 52.84 323.77 8387.21 9.57 210.07 325.90 10585.82 6.422 56.91 323.81 8420.70 5.214 24.08 325.94 1063334 4.396 18.83 323.85 8456.87 12.242 45.74 325.99 10703.48 11.487 98.17 323.90 8490.59 8.275 62.88 326.03 10757.41 11331 72.05 323.94 8525.99 8.771 79.45 326.07 10812.59 4.526 20.10 323.99 8568.04 7.974 114.25 326.12 10881.52 38.2 18131 324.03 8604.13 8377 146.43 326.16 10933.84 16.146 79.34 324.08 8646.99 6.421 74.27 326.21 11002.63 5.97 22.01 324.12 8680.29 7.976 41.69 326.26 11079.49 11375 65.28 324.16 8717.37 12.458 96.84 32630 11137.42 12.459 49.41 324.20 8752.57 6.745 5637 326.35 11199.64 8.686 43.67 324.24 8790.32 6.032 82.99 326.40 11273.76 8.362 26.18 324.29 8832.87 4.482 21.04 326.44 11333.80 5.604 54.92 324.33 8869.81 3.727 47.03 326.49 11409.82 11.057 50.35 324.37 8905.53 5.387 46.74 326.54 1148635 ^ 15391 52.01 324.41 894233 3.899 39.67 324.45 8979.45 4.159 23.05 326.59 n/d 20.01 59.56 324.49 9016.89 4.59 30.40 326.63 n/d 19.10 60.63 324.53 9057.03 5.624 35.67 326.68 n/d 165.44 335.63 324.57 9091.58 6.293 64.23 326.73 n/d 105.70 226.83 324.62 9140.85 3.684 3530 326.77 n/d 65.48 137.18 324.66 9179.71 3.814 58.24 326.82 n/d 31.18 95.71 324.70 9218.91 4.438 64.16 326.87 n/d 39.87 159.82 324.74 9258.46 11396 236.19 326.91 n/d 68.54 156.27 324.78 9301.73 15.346 261.04 326.96 n/d 43.10 117.98 324.82 9333.58 5.129 27.34 327.00 n/d 45.58 300.36 324.86 9374.16 25.846 858.18 327.05 n/d 43.21 210.18 324.91 9426.71 11.748 133.12 327.09 n/d 32.17 124.86 324.95 9472.91 32.68 378.39 327.14 n/d 35.45 329.61 324.99 9516.50 6.443 44.49 327.18 n/d 12.05 45.13 325.03 9556.12 11.079 189.00 327.23 n/d 19.32 183.47 325.07 9593.37 6.141 40.22 327.27 n/d 15.31 156.27 325.11 9638.16 4.503 29.25 32732 n/d 24.39 318.96 325.15 9684.37 6.939 87.19 327.36 n/d 15.85 192.96 325.19 9733.94 6.121 35.32 327.41 n/d 18.52 178.65 325.23 9769.91 7.004 97.20 327.45 n/d 22.12 119.29 325.27 9815.94 12.998 256.52 327.49 n/d 22.64 10558 325.32 9873.75 8.04 145.12 327.54 n/d 26.63 256.44 325.36 9916.51 14.096 56.11 32738 n/d 25.12 143.93 325.40 9968.33 14.658 67.45 327.63 n/d 29.60 211.43 325.48 10058.86 3.944 31.84 327.67 n/d 17.16 117.27 325.53 10125.19 2.909 18.69 327.72 n/d 2 1 3 6 111.45 325.57 10169.21 3.878 25.96 327.76 n/d 18.85 84.75 325.61 10217.71 4.028 33.88 327.81 n/d 14.47 75.11 325.65 10266.69 4.914 38.65 327.85 n/d 13.02 132.40 325.69 10319.26 6.292 78.57 327.90 n/d 11.00 111.63 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 181 Appendix B. (continued) Depth Age N M Depth Age N M (m) (y r b2k)* (10* mT1) (US kg'1) (m) (yr b2k)* (103 m l'1) (Ug k g '1) 327.94 n/d 28.09 192.70 330.05 n/d 25.03 382.77 327.99 n/d 18.71 115-58 330.09 n/d 28.29 11959 328.03 n/d 50.96 481.57 330.13 n/d 31.26 212.72 328.08 n/d 18.69 167.87 330.17 n/d 42.90 1076.37 328.12 n/d 12.89 214.20 330.23 n/d 18.17 141.44 328.17 n/d 8.39 53.51 330.27 n/d 18.22 15652 328.21 n/d 10.76 58.61 330.31 n/d 12.79 128.14 328.26 n/d 8.71 50.60 330.35 n/d 16.26 179.73 328.30 n/d 10.01 64.25 330.42 n/d 9.49 100.39 328.35 n/d 6.84 91.10 330.46 n/d 13.67 45.75 328.39 n/d 9.77 101.64 33053 n/d 16.67 253.20 328.44 n/d 5.54 56.26 330.57 n/d 7.72 83.82 328.48 n/d 6.21 33.10 330.61 n/d 4.62 15.14 328.53 n/d 8.17 52.86 330.65 n/d 17.44 173.42 328.57 n/d 7.74 163.29 330.71 n/d 10.74 59.32 328.62 n/d 10.26 35.05 330.75 n/d 29.28 116157 328.66 n/d 7.05 67.50 330.79 n/d 17.12 23651 328.71 n/d 7.85 48.78 330.83 n/d 9.04 58.02 328.75 n/d 18.52 226.95 330.87 n/d 8.19 91.62 328.79 n/d 16.19 375.91 330.91 n/d 9.10 37.35 328.82 n/d 10.66 80.48 330.95 n/d 7.87 37.45 328.86 n/d 7.44 54.49 331.00 n/d 11.41 42.38 328.90 n/d 20.03 120.86 331.04 n/d 11.84 37.99 328.94 n/d 17.12 81.81 331.09 n/d 8.52 54.64 328.98 n/d 14.84 73.86 331.13 n/d 8.90 98.20 329.02 n/d 11.75 92.46 331.17 n/d 12.48 140.70 329.06 n/d 14.23 135.14 331.20 n/d 7.78 338.68 329.10 n/d 14.77 62.78 331.24 n/d 9.25 43.30 329.14 n/d 13.80 103.02 331.28 n/d 8.71 36.79 329.18 n/d 10.35 94.30 331.31 n/d 4.96 17.57 329.21 n/d 17.01 144.47 331.35 n/d 6.68 200.47 329.25 n/d 38.59 440.59 331.39 n/d 19.26 113.03 329.29 n/d 15.31 82.37 331.42 n/d 24.21 300.90 329.34 n/d 20.37 735.63 331.46 n/d 17.57 826.89 329.37 n/d 24.09 194.10 33150 n/d 35.25 519.88 329.41 n/d 11.97 56.76 331.54 n/d 30.46 785.78 329.45 n/d 15.14 96.46 33159 n/d 17.59 3 6 7 5 2 329.49 n/d 19.08 104.73 331.63 n/d 8.08 32.02 329.53 n/d 15.14 135.18 331.67 n/d 6.02 37.49 329.57 n/d 12.94 85.33 331.71 n/d 4.27 48.41 329.63 n/d 20.22 110.20 331.76 n/d 3.41 73.64 329.67 n/d 13.59 180.12 331.80 n/d 9.88 112.52 329.71 n/d 15.09 176.86 331.85 n/d 10.54 42.06 329.75 n/d 28.98 238.87 331.89 n/d 6.69 34.94 329.79 n/d 10.44 80.07 331.93 n/d 2 5 0 10.68 329.83 n/d 8.48 36.27 331.97 n/d 4.42 161.80 329.88 n/d 8.91 35.42 332.01 n/d 4.88 131.49 329.92 n/d 16.00 174.60 332.05 n/d 2.68 13.91 329.96 n/d 20.64 91.78 332.09 n/d 3.07 23.15 330.00 n/d 14.12 101.41 332.13 n/d 6 5 3 20.57 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 182 Appendix B. (continued) Depth Age N M Depth Age NM (m) (yr b2k)* (10* ml*1) (fig k g 1) (vr b2k)* (103 ml*1) (Hgkg'_l) 332.17 n/d 14.04 243.75 332.21 n/d 18.16 475.49 332.27 n/d 14.41 361.97 332.32 n/d 16.52 368.46 3 3 2 3 6 n/d 14.69 176.50 332.40 n/d 22.04 621.77 332.43 n/d 13.54 40.60 332.47 n/d 18.11 600.76 332.51 n/d 5.87 29.61 332.55 n/d 8.86 45.02 332.59 n/d 12.86 170.55 332.63 n/d 14.58 50.94 332.66 n/d 57.35 211.53 332.70 n/d 74.32 224.87 332.74 n/d 67.80 145.41 332.79 n/d 110.02 276.59 332.85 n/d 102.45 199.01 332.90 n/d 58.00 123.92 332.94 n/d 75.24 323.47 332.99 n/d 77.51 199.10 333.03 n/d 64.23 175.53 333.07 n/d 68.43 198.75 333.11 n/d 55.91 305.83 333.15 n/d 46.12 100.57 333.20 n/d 7.96 56.87 333.24 n/d 39.48 606.38 333.30 n/d 16.76 109.12 333.34 n/d 35.03 206.98 *yr b2k = years before AD 2000; n/d = no data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IMAGE EVALUATION TEST TARGET (Q A -3 ) <£> & /, S? 6/ w >c V- 150mm IIVUGE. Inc 1653 East Main Street Rochester. NY 14609 USA Phone: 716/482-0300 Fax: 716/288-5989 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.