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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. AN ICE CORE PALEOCLIMATE STUDY OF WINDY DOME, FRANZ JOSEF LAND (RUSSIA): DEVELOPMENT OF A RECENT CLIMATE HISTORY FOR THE BARENTS SEA

DISSERTATION

Presented in Partial Fulfillment of the Requirements for

the Degree Doctor of Philosophy in the Graduate

School of the Ohio State University

Keith A. Henderson. M.S.

The Ohio State University 2002

Dissertation Committee:

Dr. Lonnie G. Thompson. Adviser

Approved by Dr. W. Berrv Lyons

Dr. E. Scott Bair 1^ g 6>vr >vr vJ’ ' rr)\f JY\\ ttj

Adviser Dr. Claire L. Parkinson, NASA Goddard Department of Geological Sciences

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT

A 315-meter ice core obtained in April-May, 1997 from the summit of Windy Dome, Franz Josef

Land in the Russian high Arctic (81°N, 64°E, 509 masl) reflects 772 years of climate variability in the

Barents Sea region. Paleotemperatures inferred from oxygen isotope (8ihO) calibration indicate a

dramatic and sustained wintertime warming of more than 8°C occurring abruptly around 1910. halting

the persistent cold temperatures of the Little Ice Age (LIA, -1450 to -1870 A.D.). Summer temperatures,

related to meltwatcr formation, rose earlier (-1850) but only by approximately 0.5°C relative to the LIA

mean, consistent with regional tree-ring histories.

The age scale for the finely-sampled Windy Dome ice core was generated by three-parameter

(chloride. 6 ix O, and melt-stratigraphv) reconciled layer counting, guided by the detection of recent nuclear

testing horizons and nine known volcanic eruptions, and confirmed by duplicating the cosmogenic record

of solar variability. Accordingly, a proposed common time scale based on this superior chronology is

presented, that realigns previous Eurasian Arctic ice core records to illustrate a consistent pattern of

climate change along the northern Barents continental margin from NordauslandeL Svalbard to Severnaya

Zemlva. While the temporal climate changes fit a global paradigm, it is cautioned that the wintertime

fluctuations that occurred here represent a threshold change in the position of the polar front and should

be weighted accordingly when considering hemispheric-scale climatology.

Soluble ionic constituents in the ice core reveal a strong signature of anthropogenic emissions by

rising sulfate and nitrate levels, and also 20th century agricultural activity via ammonium. The degree of

post-depositional modification of core parameters was quantified, with ion fractionation and multi-year

percolation indicated to reduce concentrations of more mobile ions {e.g., SO.,2'. Mg2*) by up to 10-15%.

and solid-liquid stable isotope fractionation currently responsible for a ~0.9%o difference between bubbly

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and melt-infiltrated ice. Regular oscillations in pH values suggest a succession of "stacked percolation

cells" that are sealed and archived every 13-14 years on average. Periodicities of 40-70 years were

detected by Singular-Spectrum Analysis (SSA) in several parameters, and the annual signal strength of

5uO and chloride is shown to be related to the extent of meltwater formation and thereby summer

temperatures.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGMENTS

Primary financial support for this research was provided by the Polar Research Program of the

National Aeronautical and Space Administration (NASA), then under the direction of Robert H. Thomas.

Additional support was provided through the NASA Earth System Science Fellowship program,

supervised at the time by Ghassam Asrar. I'd like to express my appreciation to all those, past and

present, who have contributed to these excellent funding programs at NASA in supporting research

directed at our own planet Earth. In addition. I wish to express my personal thanks to Claire L. Parkinson

of the Oceans and Ice Branch of the NASA Goddard Space Flight Center for her interest in and

contributions to this project.

f am particularly indebted to Victor S. Zagorodnov and a team of talented researchers from the

Institute of Geography at the Russian Academy of Sciences (IG-RAN). Moscow including, but not limited

to. Sergei Arkhipov. Vladimir Mikhalcnko. Misha Kunakhovitch. Andrei Glazovskiv. and IG-RAN

director Vladimir Kotlyakov. Due to the vagaries of certain nameless government agencies, it was only

with their tireless effort that the 1997 field program came to pass. Many of these fine folks were also in

Franz Josef Land with myself and L.G. Thompson in 1994 when this program first saw the light of day.

and were good comrades as well as being evermore industrious. I also wish to thank the radio-echo

sounding team of Julian Dowdeswell, Michael Gorman, and Yuri Macheret. whose cooperation in

logistics sharing and research objective in 1994 was much appreciated. I also wish to acknowledge

Konstantin Smirnov and Vladimir Baranov who were essential in organizing the logistics for that initial

expedition.

I would like to recognize the entire Ice Core Paleoclimate Research Group at the Byrd Polar

Research Center (BPRC) at the Ohio State University, under the co-direction of Lonnie G. Thompson and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ellen Mosley-Thompson, who have been a never-ending source of assistance, encouragement, and

intellectual debate. In particular, I wish to personally thank Mary E. Davis and Ahnan & Sherry Lin. who

completed all the analytical work on both the 1994 and 1997 ice cores from Franz Josef Land for dust and

oxygen isotopes, respectively. The administrative staff at Byrd Polar, including librarian Lynn Lay. have

been of great assistance to myself and the (ce Core Group as a whole. I also wish to recognize the other

employees, graduate students, and vagrants that have come through the doors of BPRC over the years and

made our windowless home tolerable, including Rob Hclistrom. Shawn Wight, Jihong Cole-Dai. John

Bolzan. Henry Brecher, W. David Lape, Deb Bathke, Tracy Mashiotta, Ross Edwards, Li Zhongqin.

Patrick Ginot. Chris Readingcr. Wang Ninglian, and Amanda Cavin.

I am also indebted to Jiirg Beer of the Swiss Federal Institute for Environmental Science and

Techonology (EAWAG) in Diibcndorf. Switzerland who conducted the mass spectrometry measurements

of beryllium-10 and chlorinc-36 on the GB97C1 core samples. I also thank Ulrich Schottcrcr of the

University of Berne. Switzerland, who measured the tritium concentrations of near-surface samples from

the 1997 core as well.

Finally I wish to thank those who have served on my advisory committee. E. Scott Bair. Gariy D.

McKenzie, W. Berry Lyons, and of course. Drs. Parkinson and Thompson once again. Finally. I wish to

express my appreciation once more to Lonnie G. Thompson, who has (for a change) thought "polar" for a

second or two. and has continually encouraged me in this challenging undertaking in the Great White

North. It has only been because of his tolerance of my eccentric research methodology (or indeed lifesty le

habits) that allowed me to complete such a task that had long seemed impossible, given such strong

personal inclination in the opposite direction from success.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. VITA

May 17. 1964 ...... Bom - Newark, Ohio

1986 ...... B.S. Chemistry, The Pennsylvania State University

1986 - 1987 ...... Laboratory Technician, Dynamit Nobel (Petrarch Systems), Bristol, PA

1988 - 1992 ...... Product Development Chemist, The Lubrizol Corporation, Wickliffe, OH

1993-1996. 2000-present ...... Graduate Research Associate. Byrd Polar Research Center, The Ohio State University

1996 ...... M.S. Geological Sciences. The Ohio State University

1997-2000 ...... Graduate Research Fellow. Byrd Polar Research Center, The Ohio State University

PUBLICATIONS

1. Thompson. L.G.. E. Mosley-Thompson. M.E. Davis, P.-N. Lin. K. Henderson. andT.A. Mashiotta. Tropical glacier and ice core evidence of climate change on annual to millennial time scales, submitted to Climatic Change . 2002.

2. Thompson. L.G., E. Mosley-Thompson, M.E. Davis, K.A. Henderson. H. Brecher. V.S. Zagordnov. P.-N. Lin, T. Mashiotta. V.N. Mikhalcnko. D.R. Hardy, and J. Beer, Kilimanjaro ice core records: Evidence of Holoccne climate change in tropical Africa. Science, in press. 2002.

3. Wang. N„ T. Yao. L.G. Thompson, K.A. Henderson, and M.E. Davis, Evidence for cold events in the early Holocene from the Guliya ice core. Tibetan Plateau. China. Chinese Sci. Bull.. 47. 1422-1427.

2002 .

3. Thompson. L.G., T. Yao, E. Mosley-Thompson. M.E. Davis, K.A. Henderson, and P.-N. Lin. A high-resolution millennial record of the South Asian Monsoon from Himalayan ice cores. Science. 289. 1916-1919. 2000.

4. Thompson. L.G., K. Henderson. P.-N. Lin, and E. Mosley-Thompson. The tropical ice core record of ENSO. in El N'iho and the Southern Oscillation; Multiscale variability and global and regional impacts , edited by H.F. Diaz. pp. 325-356. Cambridge University Press, 2000.

5. Thompson, L.G.. E. Mosley-Thompson. and K.A. Henderson, Ice core paleoclimate records in tropical South America since the Last Glacial Maximum. J. Ouater. Sci., 15, 377-394, 2000.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6. Henderson, K.A., L.G. Thompson, and P.-N. Lin, The recording of El Nifio in ice core records from Nevado Huascaran, Peru, J. Geophys. Res., 104 , 31,053-31,065, 1999.

7. Thompson. L.G., M.E. Davis, E. Mosley-Thompson. T.A. Sowers, K.A. Henderson. V.S. Zagorodnov, P.-N. Lin, V.N. Mikhalenko, R.K.. Campen, J.F. Bolzan. J. Cole-Dai, and B. Francou. A 25,000-year tropical climate history from Bolivian ice cores. Science, 282, 1858-1864, 1998.

8. Thompson, L.G., T. Yao. M.E. Davis, K.A. Henderson, E. Mosley-Thompson, P.-N. Lin. J. Beer. H.-A. Synai. J. Cole-Dai, and J.F. Bolzan, Tropical climate instability: The last glacial cycle from a Qinghai-Tibetan ice core. Science, 276, 1821-1825, 1997.

9. Mikhalenko, V.N., L.G. Thompson. K..A. Henderson. M.E. Davis. P.-N. Lin. and J. Dai, Ice-core studies from the Windy ice dome. Graham Bell Island. Franz Josef Land, Materialy Glyatsiol. Issled.. HQ. 243-247. 1996.

10. Thompson, L.G., E. Mosley-Thompson, M.E. Davis, P.-N. Lin, K.A. Henderson. J. Cole-Dai, J.F. Bolzan. and K.-b. Liu. Late glacial stage and Holocene tropical ice core records from Huascaran. Peru. Science. 269. 46-50. 1995.

FIELDS OF STUDY

Major Field: Geological Sciences

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS

Page

Abstract...... ii

Acknowledgments ...... iv

Vita...... vi

List of Tables ...... x

List of Figures ...... xi

Chapters:

1. Introduction ...... 1

1.1 Site introduction ...... I 1.2 Project overview ...... 5

2. The 1994 reconnaissance program ...... 9

2.1 The 1994 field program and core analysis ...... 9 2.2 Dating of 1994 short cores ...... 11 2.3 Graham Bell 1994 ice core data ...... 16

3. The 1997 deep drilling program ...... 22

3.1 Deep ice core drilling and sampling ...... 22 3.2 Analytical procedures ...... 34 3.2.1 Ion chromatography (IC) methodology' ...... 34 3.2.2 Stable isotope and microparticle analysis ...... 41

4. Time scale development and accumulation reconstruction ...... 45

4.1 Time scale development ...... 45 4.1.1 Blanket statement of dating rationale ...... 45 4.1.2 The annual signal preserved in the Windy Dome ice cores ...... 45 4.1.3 Final time scale determination ...... 56 4.1.4 Time scale verification ...... 69 4.2 Creation of Windy Dome time series...... 72 4.3 Time/depth modelling and accumulation reconstruction ...... 73 4.3.1 Annual layer thickness modifications ...... 73 4.3.2 Row modelling ...... 73 4.3.3 Accumulation reconstruction...... 74 viii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5. Calibration and application of the GB97C1 6uO and melt records as paleothermometers 77

5.1 Historical temperature records in the Eurasian Arctic sector ...... 77 5.2 Spatial correlation of temperatures and generation of a representative temperature history for Franz Josef Land ...... 80 5.3 Calibration of GB97C1 5180 as a paleothermometer ...... 93 5.4 Application of the GB97C1 melt percent record as a summer temperature proxy ...... 97 5.4.1 Post-depositional influences on the GB97C1 melt percent record ...... 99 5.5 Multi-proxy method for estimating DJF temperatures from GB97C1 ...... 103

6. Interpretation of GB97C1 ion chemistry and microparticle records ...... 105

6.1 Overview of the soluble chemistry records ...... 105 6.2 Basis of interpretation of ion chemistry records according to conservation in GB97C1 ice ...... 112 6.3 Interpretation of the SO f' and N 03‘ profiles as an anthropogenic pollution recorder. 118 6.4 Other aspects of the GB97C1 chemistry record ...... 119 6.5 Characteristics of the history of dust deposition and size distribution in GB97C1 ...... 123

7. Spectral properties of the GB97C1 time series and comparison to other palcohistorics ...... 128

7.1 Spectral analysis of the GB97C1 melt, chemistry, and isotope records ...... 128 7.2 The strength of the annual signal as determined by spectral analysis for the chemistry and isotope records ...... 137 7.3 Comparison of the GB97CI core result to other paleohistorics ...... 139 7.3.1 Arctic and Northern Hemispheric temperature proxy compilations ...... 139 7.3.2 Northern Eurasia tree-ring records ...... 141 7.3.3 Sea ice records and historical reconstructions ...... 144 7.3.4 Precipitation history from Scotland ...... 147

8. A proposal for a common Eurasian Arctic ice core time scale based upon the GB97C1 dating ...... 150

8.1 The Windy Dome record in the perspective of the history of Eurasian Arctic ice coring 150 8.2 Isotopic and melt percent matching with GB97C1 ...... 156 8.2.1 Consideration of the pre-1225 history of ice cores from Severnaya Zemlya ...... 162 8.3 Evidence of support from qualitative accumulation reconstructions ...... 166 8.4 Summary of environmental history from the north margin of the Barents/Kara sea (excluding West Spitsbergen) ...... 168

9. Conclusions ...... 172

9.1 Final discussion ...... 178

Bibliography ...... 184

Appendix A. 1994 Franz Josef Land short core results ...... 207

Appendix B. Depth-depth and depth-age matchpoints for Eurasian Arctic common chronology ...... 214

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES

Table Page

1.1 World Glacier Inventory classification for Windy Dome. Franz Josef Land ...... 7

3.1 GB97C1 IC analytical parameters ...... 34

4.1 GB97C1 Laki eruption results ...... 63

4.2 List of horizons identified in the GB97C1 record ...... 68

4.3 GB97C1 cosmogenic isotope results ...... 71

5.1 Names and locations of sites in the North Atlantic/Eurasian Arctic region from which temperature data were compiled for creating spatial correlation maps (including those in italics) and a single representative temperature history (including only those in boldface) for the Barents Sea region ...... 78

6.1 Visible dust stratigraphy from GB97C1 ...... 124

8.1 Sites, coordinates, and summary information about ice cores obtained in the Eurasian Arctic ...... 15 1

8.2 Summary of characteristics of ice cores obtained in the Eurasian Arctic ...... 152

B. 1 Depth-time matchpoints used to rescale the Akademii Nauk '86 ice core (and the Vavilov cores by the relationships given in Table B.2 below) and the second generation (1990s) Svalbard 5'*0/ineil records to an equivalent Graham Bell (FJL) '97 time scale, to bedrock or 1225 A.D. horizon ...... 215

B.2 Depth-depth matchpoints used to rescale the Vavilov Dome ice core 51!fO records to equivalent Akademii Nauk '86 depth scale, consistent with individual GB97C1 depth-time matching above 1225 A.D. Graham Bell horizon, as indicated ...... 216

B.3 Depth-time matchpoints used to rescale the West Spitsbergen 5uO/mclt records to equivalent Graham Bell (FJL) '97 time scale, to bedrock or 1225 A.D. horizon ...... 217

B.4 Depth-time matchpoints used to rescale the Nordauslandet S180/melt records to equivalent Graham Bell (FJL) '97 time scale, to bedrock or 1225 A.D. horizon ...... 218

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES

Figure Page

1.1 Mean air pressure field over the North Atlantic-Arctic region for January (top) and July (bottom), after Prik (1959) ...... 2

2.1 Map of Franz Josef Land with 1994 drill site locations ...... 10

2.2 Maximum (February) and minimum (September) sea ice cover in the Arctic basin, as determined by passive microwave measurements from the satellite-borne SMMR and SSM/l instruments...... 10

2.3 Short ice core records from Franz Josef Land (1994). superimposed in time (Alexandra Land. Hall and Graham Bell islands)...... 12

2.4 a. Laver thickness and b. density comparisons for the three 1994 short cores from Franz Josef Land locations on Graham Beil Island. Alexandra Land, and Hall Island ...... 14

2.5 Profiles of GB94C1 b. reconstructed density and c. melt percent by sample, based on a. the separation of bulk density values into individual components (identified by the original stratigraphy) ...... 18

2.6 Bimonthly GBC941 chloride vs. sea ice concentration and air temperatures during the satellite era...... 20

3.1 a. Map of Graham Bell Island, with surface elevation contours indicated for Windy Dome (after Glazovskiy el al .. 1999), b. Map of ice thicknesses (dashed when inferred) from radio echo sounding measurements (after Macheret et al.. 1998) ...... 23

3.2 Initial survey results from 1997 deep ice core drilling on Windy Dome, Graham Bell Island, including a. borehole temperatures, b. melt percent, c. oxygen isotopic ratio, with initial climatic interpretation given. MWP = Medieval Warm Period ...... 25

3.3 Stratigraphy comparison of Graham Bell (1997) Cores 1 and 2. top 24 meters only, showing comparison by analyst for Core 1. Asterisks denote locations of high KF concentration [K>120 ppb and F>10 ppb. or K>200 ppb and F>50 ppb (bold)); see Section 6.3 ...... 27

3.4 Plot of average sample size for each of the 315 1-m sections (tubes) of the GB97C1 ice core ...... 29

3.5 Plot of sampling density (number of samples cut per given year) over the length of GB97C1. compared to the limit of monthly resolution' (SD = 12) ...... 29

3.6 Sampling strategy for Graham Bell (1997) Core 1 ...... 30

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.7 Idealized drawings of common bubble structure within GB97C1 ice samples prepared for IC analysis, and determination of melt percent by visual inspection (estimated to 10%) ...... 34

3.8 Sample chromatogram showing isocratic separation of major anions (non-quantitative for fluoride, organics) from the detailed analysis of GB97CI; Tube 161. Sample 3 (161.852 to 161.887 m), with concentrations as shown, among the lowest levels in the entire core ...... 38

3.9 Comparison of oxygen isotope measurements made on bottled survey samples vs. averages from the detailed analysis over the respective depth ranges ...... 42

4.1 a. Profiles of chloride and 6!i<0 from a 1997 snowpit representing the past year’s accumulation, before alteration by seasonal melting/percolation, and b. Profiles of chloride, dust, and 6ixO from a 3-m section of the deep core, from a particularly low-melt. well- preserved portion of the core. Annual layers are easily discernible in Cl' and 8lsO ...... 47

4.2 Chloride. 8'*0, and density profiles for upper portion of Graham Bell (FJL) 1997 ice core, compared with the 1994 C f record (below). Tritium-adjusted three-parameter reconciliation age dating as indicated. Darker lines are smoothed. 5SRM (1-3-4-3-1) ...... 48

4.3 Daily temperatures (solid line) at Ostrov Vize (79°30'N, 76°50’E) for 1994. compared to the area of sea ice coverage (dots) along the NE-SW transect from (175.213)-( 190.213). and then continuing SW along the diagonal (190.213) to (220.243) in the SSM/1 polar stereographic grid (cells 25 x 25 km): 100% SIC=28.800 km* ...... 51

4.4 Comparison of annually-averaged ice core parameters from GB94C1 and GB97C1 for the entire period of overlap (1960-1994) ...... 52

4.5 Distribution of offset (in terms of number of samples) between identified annual peaks in each of the three datable parameters for GB97C1 (772 years) ...... 53

4.6 Annual signal in GB97C1 as a function of melt % (as indicated) for separate 5-m intervals during 19th-20th century (top), Little Ice Age (middle), and Medieval Warm Period (bottom)...55

4.7 Depth-based profiles of beta-radioactivity for GB94C1 (left) and GB97C1 (right), compared also with GB97C1 chloride and tritium records ...... 58

4.8 Time-based profiles of beta-radioactivity and tritium from Graham Bell ice cores, compared to near real-time tritium records (decay-corrected to time of the ice core measurements) from two IAEA northern hemisphere sites ...... 60

4.9 GB97C1 data for 124.3 - 125.5 m pertinent to the Laki 1783 eruption. Years shown determined jointly by stable isotopes, chloride, and melt layers, and were adjusted slightly to place the largest sulfate between the March 1782 and March 1783 horizons as shown ...... 62

4.10 Graham Bell (FJL) Core 1 (1997) - Identification of nine volcanic horizons in 6180 and/or SO.f \ Annual dating shown for 8lilO by small triangles, determined by Cl' and melt records when necessary, e.g.. MWP < 1450...... 65

4.11 Final layer-counted GB97C1 age/depth relationship, indicating location and dates of identified horizons ...... 67

xii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.12 GB97C1 l0Be and 36C1 records compared to Intcal AUC (Stuvier et al., 1998). Actual layer- counted age scales for both GB97C1 profiles shifted to show maximum correlation: by 50 years for 36C1 and 70 years for l(>Be ...... 70

4.13 Graham Bell (1997) Core 1 accumulation profile, reconstructed from two-parameter model with Laki and 1259 (unknown) eruptions as chosen horizons ...... 76

5.1 Sites and sub-regions used in the determination of a composite temperature record for the Eurasian Arctic from 1840-1993 ...... 79

5.2 Correlation matrix - r values for annual average temperatures over a period of 30 years, nominally 1951-1980 (in some cases. 1947-1976). Asterisk denotes those correlations based on data overlap of less than 25 years. Italic type denotes those correlations based on the time period 1920-1950. Values in boldface are correlations greater than 0.4 (0.5 for under 25 year overlap). Highlighted individual boxes indicate correlations within a particular subregion 79

5.3 Spatial correlation map of annual air temperatures with the Franz Josef Land composite record for two separate 30 yr. periods, when applicable: 1961-90 and 1931-60 ...... 81

5.4 Spatial correlation maps of air temperatures (winter-DJF, summer-JJA) with Krenkel Station, Ostrov Heisa (FJL) temperatures for 1981-90 (individual monthly averages) ...... 82

5.5 Mean change in a) surface atmospheric pressure (mb), and b) surface atmospheric temperature (°C). during the four winter months (DJFM) of 1961-70 vs. 1951-60 over the north Atlantic and north polar regions (after Rodewald. 1977) ...... 84

5.6 Annual average temperatures for Eurasian Arctic by sub-region (all available records combined and scaled to match mean conditions at Rudolf Island. 1951-80) ...... 86

5.7 DJF average temperatures for Eurasian Arctic by sub-region (all available records combined and scaled to match mean conditions at Rudolf Island. 1951-80) ...... 87

5.8 JJA average temperatures for Eurasian Arctic by sub-region (all available records combined and scaled to match mean conditions at Rudolf Island, 1951-80) ...... 89

5.9 Difference in annual average temperatures between Svalbard and Norway (both scaled to match mean conditions at Rudolf Island. 1951-80): subtraction to Norway temperatures: according to regression line from 1947-93 ( r = .04) extrapolated (dashed) back to 1937. continued by 1912-1940 regression (solid) line to 1917 ( r = 0.57). and set constant (dashed) from 1917 back until 1840 ...... 90

5.10 Annual average temperatures (adjusted to Svalbard trend, as indicated) for Eurasian Arctic by sub-region (all available records combined and scaled to match mean conditions at Rudolf Island. 1951-80) ...... 91

5.11 Comparison of: a. Eurasian Arctic composite temperatures (scaled to Rudolf Island. FJL) and b. Graham Bell (1997) Core I f>'*0 for 1840-1993 ...... 92

5.12 Comparison of temperature proxy reconstructions from Graham Bell (1997) Core 1, a. 6lsO-annual temperatures, and b. melt-proxy summer temperatures ...... 95

5.13 Relationship between melt percent and reconstructed accumulation for GB97C1 for a. all years, and b. separated into three climatic periods ...... 100 xiii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.14 Distribution of samples cut from GB97C1 according to estimated melt (infiltration ice) percent, in 10% increments (total 9,029 samples) ...... 102

5.15 Relationship of 6lsO vs. melt (infiltration ice) percent for GB97C1, in 10% increments (total 9,029 samples). Shift values due to solid/liquid fractionation given at right for different time periods ...... 102

6.1 1-meter averaged values (by tube) of all major ionic species from Graham Bell (1997) Core 1. and calculated pH values. Anion values based on detailed samples, cation values from 1-m survey samples ...... 106

6.2 1-m averaged values of eight major ions measured in GB97C1, shown on the layer-counted limescale. Anion values are based on detailed measurements, whereas cation values arc based on the 1-m survey samples. Values indicated at top right represent the pre-industrial (1225-1800) mean concentration and the contribution from sea-salt (ss) based on Na' concentration ...... 107

6.3 Mean ionic composition of GB97C1 ice over the pre-industrial period 1225-1800. and last 30 years (1968-1997): pH and bicarbonate ion concentration determined by simultaneous solution assuming ionic balance with minor constituents (bromide, organic acids) negligible ...... 108

6.4 Average sulfate, nss-sulfate. and calculated pH values (bold line. 1-2-1 filter) from GB97C1 (top 150 m). showing onset of anthropogenic influence (~70 m), and the Laki 1783 eruption (125 m). The number designations on the pH profile indicate perceived stacked percolation cells (see text) roughly 13.5 years in length...... 109

6.5 Detailed profiles of all major (and two minor) soluble species in the upper 25 meters of GB97C1. ordered by the apparent degree of percolation influence, from ammonium (minimum, bottom) to MSA (maximum, top): 1C and F indeterminate ...... 113

6.6 a. Plot of sodium vs. chloride in GB97C1 by 1-m tube core sections: by single measurement (Na*). average of individual samples (Cl~). compared to the relationship from pure sea-salt aerosol: b. the Cl'/Na* ratio (in equivalents) by meter in the ice core, compared with calculated pH values (both 5SRM, 1-3-4-3-1) ...... 115

6.7 Plot of magnesium vs. sodium in GB97C1 by 1-m tube core sections: by single measurement from combined samples, for high-meit zones (top) and low melt zone. i.e.. LIA (bottom) ...... 116

6.8 Plot of logio(dust concentration) vs. average grain size (AGS) in Graham Bell (1997) Core I (all samples), with region including visible layers indicated ...... 125

6.9 Annual melt percent vs. microparticle concentration (corrected for instrument bias) and average grain size (AGS) (all 5SRM, 1-3-4-3-1) in Graham Bell Core 1 (1997). Superimposed on the AGS curve are the trends of GB97C1 6I!tO and logi0(dust concentration) (inverted) both produced by spline functions with stiffness 200 ...... 126

7.1 SSA reconstructed components representing the first 10 eigenvectors for the annual 6lsO anomalies, M=95. Detrended with spline (stiflfness=200) as shown atop raw values ...... 130

7.2 SSA reconstructed components representing the first 12 eigenvectors for the bimonthly 6180 anomalies, M=210, over the period 1775-1997. Detrended with spline (stiffness=1000) as shown atop raw values ...... 131 xiv

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.3 SSA reconstructed components representing the first 10 eigenvectors for the bimonthly 6lsO anomalies, M=360. over the period 1500-1800. Detrended with spline (stiffness=1000) as shown atop raw values ...... 132

7.4 SSA reconstructed components representing the first 12 eigenvectors for the bimonthly 61!fO anomalies, M=390, over the period 1225-1825. Detrended with spline (stiflhess=1000) as shown atop raw values ...... 133

7.5 SSA reconstructed components representing the first 8 eigenvectors for the annual logmCr anomalies, M=120. Detrended with spline (stiffness=200) as shown atop raw values ...... 135

7.6 SSA reconstructed components representing the first 8 eigenvectors for the annual JJA temperature anomalies. M=105. Detrended with spline (stiffness=200) as shown atop raw values...... 136

7.7 Annual signal strengths in GB97C1 6lsO and Cl' as determined by the SSA-filtered component (RC12) from the bimonthly analyses: spliced together from three separate parts, as depicted in Figs. 7.2-7.4 ...... 138

7.8 Comparison of GB97C1 JJA (melt) and annual (5uO) temperature proxy record, to Arctic summer temperature anomaly time series compiled from 20 other paleoclimatc records, and Northern Hemisphere temperatures reconstructed primarily from 12 regional climate indicators (tree-rings, ice cores) ...... 140

7.9 Map of the Northern Hemisphere, showing locations of important ice core studies, selected tree-ring sites, and one cave site, considered in this study ...... 142

7.10 Comparison of summer temperature proxy reconstructions from: a. Sweden (Brifla et al.. 1992). b. Finnish Lapland (Brifla and Schweingruber, 1992), c. Franz Josef Land (this study), d. northern Urals (Brifla et al., 1995). e. central Siberia (Naurzabaev and Vaganov. 1999). and f. northeastern Siberia (Hughes et al.. 1999) ...... 143

7.11 Comparison of three decadally-averaged proxy records from GB97C1 with the history of August sea ice margin positions as determined by Vinje (1997; 1999), and the annual sea ice concentrations from the updated Walsh and Johnson (1979) gridded data set (for 19 grid cells in the Barents Sea between 77.6°N and 81.0°N, and 33.1°E and 70.0°E ...... 146

7.12 Comparison of a. precipitation history from Scotland (Proctor et al.. 2000) inferred from a speleothem record, and b. reconstructed accumulation (5SRM. 1-3-4-3-1) from Graham Beil. FJL (both m water equivalent) ...... 148

8.1 Ice core isotopic records from Eurasian Arctic, on depth scale; arranged (left to right) by longitude from west to east ...... 155

8.2 Isotopic records from Eurasian Arctic ice cores presented on proposed common chronology based on GB97C1 ...... 157

8.3 Melt percent records from Eurasian Arctic ice cores presented on proposed common chronology based on GB97C1 ...... 158

8.4 Severnaya Zemlya deep ice cores, after a proposed depth-depth rescaling referenced to Akademii Nauk '86, via a stable isotope match with GB97C1 over top 772 years ...... 163

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8.5 Map of October Revolution Island, Severnaya Zemlya, including surface and bedrock topography of Vavilov Ice Dome, and locations of ice cores ...... 164

8.6 Qualitative accumulation reconstructions for all applicable Eurasian Arctic ice cores based on GB97C1 chronology ...... 167

8.7 High-quality ice core records from north-central Barents/Kara seas presented on proposed common chronology based on GB97CI ...... 169

9.1 Summary of decadal results from the Graham Bell (1997) ice core study, including from top, a. reconstructed accumulation, b. chloride concentration, c. chloride flux, d. DJF- temperatures from mixed proxy records, e. annual temperatures from 6180 record, and f. JJA-temperatures from melt/accumulation ...... 179

A. 1 Raw data of oxygen isotope ratio, dust concentration, and major anions from GB94C1. Dating of chloride peaks indicated with dots/years ...... 208

A.2 Raw data of oxygen isotope ratio and major anions from GB94C2. Dating of chloride peaks indicated with dots/years ...... 209

A.3 Raw data of oxygen isotope ratio, dust concentration, and major anions from H94C1. Solid, clear mcltwater-ice existed below the super-concentrated dust layer separating a thin snow/ fim layer at .65 m from the 'old' ice below. Dating of Sl80 troughs indicated with dots/years. Ages uncertain ...... 210

A. 4 Raw data of oxygen isotope ratio, dust concentration, and major anions from G94C1. Dating of chloride peaks indicated with dots/years ...... 211

A.5 Raw data of oxygen isotope ratio, dust concentration, and major anions from ZA94C1. Dating of chloride peaks indicated with dots/years ...... 212

A.6 Annual averages of oxygen isotopic ratios and sulfate for the 1994 core from Hayes Island. matched to the 1997 Graham Bell Island core ...... 213

xvi

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER I

INTRODUCTION

1.1 Site introduction

Franz Josef Land (FJL) is a large archipelago positioned between 79°45' and 80°50' N. and

42° 10' and 65°00' E in the Russian high Arctic. FJL is located on the northern portion of the Eurasian

continental shelf that underlies the Barents Sea to the southwest and Kara Sea to the southeast.

Approximately 25 major islands, and numerous smaller islands, cover a total area of roughly 20.000 knr

of which 85 to 90% is covered by glaciers and ice caps. The ice caps covering the larger islands

commonly reach elevations of 300 to 600 m and are generally underlain by 20-30 m thick Crctaccous-agc

basalt flows forming ice-buried mesa-type structures. As a result, many of the ice caps have flat bottoms,

but also a complex system of outlet glaciers and ice cliffs (ty pically 10-30 m high) along their margins as

the ice cascades down the irregular cliffs and steep valleys. Several islands (e.g.. Graham Bell. La

Ronsyer, and Eva-Liv) in the far eastern region, however, have no underlying basalts and the ice caps

have a uniform dome-shape.

The mean annual temperatures on Franz Josef Land currently range between -11 and -15°C.

displaying a strong seasonality (25°C or more) due to the polar night lasting 125 days and the polar day

lasting 140 days. The region is in a zone of negative radiation balance, which is partially compensated for

by the warming effect of the Barents Sea. The dominant wind directions for much of the year are east to

southeast (Fig. 1.1) and are a result of the frequent passage of cyclones to the south of the archipelago,

which also provide the major moisture source. Winds are light and variable during the summer months

(Fig. 1.1), and extensive banks of stratiform cloud cover blanket the archipelago. Because of the storm

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 0 \5 id?W,

Svalbard Greenlani 40°W 80°E

40°E 20°E Mean air pressure, January (mb)

vemaya

ii)io : •• /100’E

Svalbard • ranz Greenland Josef Land ovaya 40 W lya

cel and

20°E Mean air pressure, July (mb)

Fig. 1.1 Mean air pressure field over the North Atlantic-Arctic region for January (top) and Julv (bottom), after Prik (1959).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. track to the south, a precipitation gradient exists (decreasing from southeast to northwest) and as a

consequence generally greater ice extent and volume are found towards the southeast (Grosswald, 1973).

Precipitation increases with elevation also, from values of 200-250 mm/yr in coastal regions to upwards of

500 mm/yr on the higher domes. At least 90% of the precipitation falls as snow. Snow accumulation is

bolstered by precipitation that occurs throughout the year, although the length and severity of the summer

melt season is largely responsible for detcrming the annual mass balance (Glazovskiy. 1996). Maximum

precipitation in the region generally occurs in the late summer (i.e.. August), with a minimum in April

(Zeeberg and Forman, 2001, Hanssen-Bauer and Farland, 1998). The whole of the archipelago lies

between the boundaries of maximum and minimum seasonal sea ice extent, with maximum concentrations

of over 90% in February, and minima of 0-50% in late summer (August-Septcmber). To the southwest,

the influx of warm Atlantic water via the Norwegian current limits the sea ice extent in the southern and

western Barents Sea region, meaning that the sea surrounding Svalbard and along southwestern Novaya

Zcmlya (Fig. 1.1) remains relatively open year round.

All evidence shows that the glaciers of Franz Josef Land arc in a condition of negative mass

balance (Dowdeswell et al.. 1997). Krenke (1982) reported a total accumulation area for the archipelago

of 5300 km \ which yields an accumulation area ratio of approximately 0.35. well below the "rule of

thumb" value of 0.7 required for zero mass balance (Paterson. 1981). Equilibrium line altitudes (ELA)

typically lie between 200 and 300 m. and should increase towards the NW. although the general paucity of

field or remote-sensing data prohibits the detailed placement of ELA contours. Field studies on the

Churylanis, Jackson and Sedova ice domes on Hooker Island in the central part of Franz Josef Land

(Grosswald and Krenke. 1961) observed the ELA at 300 m. with a zone of superimposed ice formation

between 300 and 380 m. and cold infiltration (wct-snow zone) above. Also, boreholes drilled at these

locations as well as on Alexandra Land to the west (Sinkevich et al.. 1991) showed extensive

meltwater/rainfall percolation in the manner of thick layers of superimposed ice, or solid ice below a

shallow fim depth. Also, negative temperature gradients were commonly discovered (-0.6°C in

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Alexandra Land from 20 to 54 m depth), indicating the general increase of meltwater within the snow

pack towards the present.

The position and extent of ice sheets over Franz Josef Land and the entire Russian Arctic region

during the late Weichselian (coincident with the Wisconsinan/Wurm ice age) is still a matter of debate

(Siegert et al., 2002). Evidence from isostatic uplift of shorelines in the Arctic region suggests the

presence of a large ice mass developed in the Kara Sea region covering Novaya Zcmlya. as well as a dome

centered in the north central Barents Sea covering Svalbard and at least the central and western portions

of Franz Josef Land. This ice dome may have been joined with the Fennoscandian and/or Kara Sea ice

sheets at some point in the Weischselian. Dcglaciation of the Russian Arctic region is believed to have

begun relatively early, as evidenced by whale bones and driftwood found in Franz Josef Land dated at 10.4

ka BP. suggesting at least seasonally open sea-icc conditions and dcglaciation of the Russian coastal plain

(Forman et al., 1996). The early Holocenc was likely characterized by restricted ice margins, as

evidenced by a marine mud deposit containing in situ molluscs (dated at 8340 ± 100 yr BP) overlain by

ncoglacial till, suggesting glaciers were at or behind their present margins prior to 8000 yr BP. Lubinski.

et al. (1993) have suggested that during the Hypsithermal (beginning at ca. 8 ka BP), current variations in

the North Atlantic may have enhanced the influx of warm waters into the Barents Sea region, leading to

the retreat of glaciers witnessed in Norway and Svalbard. These current variations would likely have also

controlled regional sea ice and glacier extent in the Franz Josef Land region.

Recent field work on Hooker Island (Forman. 1992 and Miller. 1992) has yielded evidence of two

periods of neoglacial advance of outlet glaciers. Organic remains (wood, moss) found within the

respective moraines have provided radiocarbon age limits of 1165 - 775 yr BP for the initial neoglacial

advance (Yuri I stadial), with a maximum at about 1100 yr BP, followed by a Little Ice Age (LIA)

advance with maxmimum age of 595 yr BP (Yuri II stadial). The last century has then represented a

retreat of glaciers from their LIA maximums. as has been documented in many other regions of the world.

The extent of the decrease in glacier cover of Franz Josef Land in recent years was estimated by

Koryakin (1986) using a combination of Held observations and satellite imagery over the period from

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1954 to 1976. The results showed a loss of ice area extent of 233 km2. roughly 1.7% of the total coverage

of the archipelago, and suggested that the mean lowering of the ice surface since 1900 has been nearly 20

m (by extrapolation). Similar results were observed for Svalbard and Novaya Zemlya, but Koryakin

(1986) reported little to no ice cover shrinkage for Severnaya Zemlya, and only a 3-m lowering of the ice

surface from 1900 to 1976. This result differed from a similar air photo comparison reported by

Govorukha (1988), which detected a decrease in glacier cover of 500 km2 (2.9% of total) for the 50-ycar

period from 1930 to 1980, suggesting that all four of the Arctic archipelagos were experiencing a similar

retreat. Yet a compilation of mass balance data from the whole of the Arctic (Dowdeswell et al.. 1997)

maintained that Severnaya Zemlya and Franz Josef Land experienced only moderate retreat (both at an

average of -0.03 m yr'1) over the past 50 years, compared with a higher rate (-0.14 m yr'1) for Novaya

Zemlya and an extreme rate (by far the highest in the Arctic) of -0.55 m yr'1 for Svalbard glaciers.

Specifically, the mass balance of two cirque glaciers in West Spitsbergen (Lcfauconnicr et al.. 1999) has

been -0.43 m yr'1 (at Breggerbrccn) and -0.34 m yr'1 (at Lovenbreen) since 1966. though rates of ablation

have slowed since the 1920-1940 period (Lcfauconnicr and Hagen. 1990). In addition. Kongsvcgcn

(78°45'N. 13°E), a larger glacier nearby with a recharge area at higher elevation, has maintained a

positive balance of 0.11 m yr'1 since 1986 (Lefauconnier and Hagen. 1990). and highlights the variability

from site to site. However, the vast majority of evidence from glaciological studies in the Eurasian Arctic

is that all glaciers on the four archipelagos have retreated significantly since 1920.

1.2 Project overview

The Franz Josef Land ice coring project began with a reconnaisance program in May-June, 1994

designed to sample several ice caps along an east-west transect of the archipelago with the intent of

identifying a suitable location for subsequent deep drilling. Based on that work (Chapter 2), Windy Dome

on Graham Bell Island was chosen as the best site and in 1997 a second field program to drill a

continuous ice core to bedrock was undertaken. While this operation failed to produce a complete core, a

high-quality 315-m long ice core was successfully extracted and transported to the Byrd Polar Research

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Center (BPRC) for complete analysis. The comprehensive high-resolution study of this ice core record,

which comprises a 772-year history of Eurasian Arctic climate, is expected to provide the scientific means

to produce in the near future a more complete record covering at least the last half of the Holocenc from

Franz Josef Land or nearby. The large quantity of valuable information gleaned from this work about ice

core chronology and the influence of melt on ice chemistry should furnish an instrumental basis for

developing a longer record of similar quality from perhaps several different sites in the Eurasian Arctic.

Furthermore, the proposal of a common chronology based on the Windy Dome ice core presented in

Chapter 8. if verified, should reinforce the usefulness of palcoclimate records obtained from these more

challenging locations, now that improvements in technologies and expertise have transformed sub-polar

ice bodies into viable candidates. While sites in Greenland and the Canadian Arctic will continue to

produce the highest quality ice core records in the high northern latitudes, these cores reflect climatic

variations governed to some extent by the ice masses themselves. In contrast, the Eurasian Arctic, from

what the Windy Dome core suggests, is perhaps the most ciimaticallv-sensitive area on all the globe with

the ice caps existing as relatively minor elements of the environment. The well-documented extreme

warming of more than 2.0°C seen in the Antarctic peninsula over the past 50 years (Comiso. 2000) is

shown herein to be surpassed by an even larger temperature shift that occurred recently over a large

expanse along the 80°N parallel within a single decade.

Windy Dome (Kupol Vyctreniy) is a roughly circular ice dome with a summit elevation of -500

m asl. and extends down to the sea in most directions where calving fronts exist. The World Glacier

Inventory (Hoclzle and Haeberli. 1999) classification of Windy Dome is given in Table 1.1. A smaller

second dome (summit elev. 330 m) exists to the northeast with a saddlepoint in between that guarantees

that the ice in the upper reaches of Windy Dome experiences almost perfectly radial drainage. Average

temperatures currently experienced on the summit are estimated at -16°C based on a lapse rate of -0.5-

0.7°C/100 m (Zeeberg and Forman, 2001). Open water in the region during the late summer, however,

elevates mean air temperatures to near the freezing point such that Windy Dome experiences periods of

melting snow. Without the benefit of regular day-night cycles that could refreeze a limited amount of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Category WGI Entry Description WGI Glacier No. SU4X03001954 Latitude 80.78° N Longitude 63.53° E Area 727.9km: ±1% Peak Elevation 509 m Equilibrium Line Altitude 250m ±2% 8/8/53 Mean Depth (-99) Unknown Orientation of Accumulation Field North Primary Class 3 Ice Cap Form 1 Compound Basin Frontal Characteristic 4 Calving Longitudinal Profile 1 Even, regular Source of Nourishment 1 Snow- Tongue Activity 0 Uncertain Moraines (Contact) 1 Terminal Moraines Moraines (Downstream) 9 Moraines, type uncertain

Tabic 1.1 World Glacier Inventory Classification for Windy Dome. Franz Josef Land.

mcltwatcr, extended periods of relative warmth can persist and cause significant percolation, halted only

by the sharp negative temperature gradient between the surface snow and that of the ice at ~10-m depth

during this time.

The scientific objectives outlined for this program at the outset were: 1) to produce a long

climatic and environmental history that could contribute to circumpolar coverage and aid in diagnosing

relationships between high-latitude climate and low-latitude forcing; 2) to produce a sea ice proxy record

for the Barents Sea that would not only address regional climate variations (eg. SST. salinity, albedo), but

also could be sensitive to ocean circulation changes; for example, the influx of North Atlantic water to the

region, which could be related to the overturning of the thermohaline circulation, an important meridional

heat transport process; 3) to develop a long-term proxy record that could place recent interannual

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. variability into perspective amongst long-term trends; and 4) to prevent loss of quality and length of the

archive (due to the present negative-balance condition of most Eurasian Arctic ice caps) by acting quickly

to recover the ice core in a timely fashion.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 2

THE 1994 RECONNAISSANCE PROGRAM

2.1 The 1994 field program and core analysis

The initial ice core studies took place during a 1994 international cooperative expedition to FJL

(involving researchers from BPRC (including the author), the Institute of Geography - Russian Academy

of Sciences (IG-RAN), and Scott Polar Research Institute (SPRI) in Cambridge. UK) along a west-to-east

transect of the archipelago. During a period of three weeks in May 1994. shallow ice coring (the deepest

hole being 24 m on Windy Dome. Graham Bell Island) was completed on the glaciers of four islands (Fig.

2.1). supported by helicopter transport that was simultaneously engaged in a radio-echo sounding survey

of several large ice caps, including each of those drilled (Dowdeswcll et al.. 1996). The ice cores,

obtained by dry drilling with a lightweight hand-operated 3-inch (diameter) auger, were transported from

each ice cap to the Krcnkel Meteorological Station on Ostrov Heisa (Hayes Island, aka Heiss Island), and

then returned to the facilities at BPRC. One core from each island was returned in a frozen state packed

with dry ice in insulated boxes, whereas shorter secondary cores from the three highest locations were

presampled in the field, measured for density, and then melted and bottled at the Krenkel Station for safe

transport to BPRC. The intent of this reconnaissance mission was to evaluate the potential for extracting

a high resolution climate history from FJL with strong age control, and determining the particular site

where this potential would be greatest. The rationale for extracting the 24 m core on Graham Bell Island

w as to reach the depth of the 1962-64 nuclear bomb test horizon (Koide and Goldberg, 1985) and to verify'

a multi-annual accumulation rate for at least one site.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Graham Bell

Alexandra Land

Approximate Scale Ice cover • Drill sites i ■ 1 o 0 50km

Fig. 2.1 Map of Franz Josef Land with 1994 drill site locations.

,. February September U (1979-2001) (1979-2001)

Fig. 2.2 Maximum (February) and minimum (September) sea ice cover in the Arctic basin, as determined by passive microwave measurements from the satellite-borne SMMR and SSM/I instruments.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In 1995, a complete chemical and microparticle analysis of all short cores from the four 1994

drill sites was completed (Thompson et al.. 1995). Included were a 9.3 m core (ZA94C1) from Luna

Dome (aka Looney Ice Cap), Zemlya Alexandra (Alexandra Land: 80°39'N, 46°49'E, 375 masl). a 5.7 m

core (G94C1) from Ostrov Galiya (Hall Island; 80°23'N. 57°55'E, 350 masl), and a 4.7 m core (H94C1)

from the summit of Ostrov Heisa (Hayes Island: 8()°36'N, 57°37'E. 240 masl). These analyses were in

addition to the initial complete profiles of 51!fO, microparticles, anion chemistry, and beta-radioactivitv

completed in 1994 on two cores (GB94C1 - 24.0 m, and GB94C2 - 10.4 m) from the summit of Ostrov

Grecm Bell (Graham Bell Island; 80°47'N. 63°32'E. 509 masl). Because of its relatively high elevation,

symmetric shape, and high firn-to-superimposed ice ratio (indicating colder conditions), this ice cap

(Kupol Vyetreniy, or Windy Dome) was the favored location for the deep drilling program that

commenced in Spring 1997.

2.2 Dating of 1994 short cores

The most reliable dating tool for the FJL short cores proved to be the regular peaks in Cl*

concentration (Appendix l.l). initially presumed to be a proxy for seasonal sea ice decay and growth in

the Barents Sea (Fig 2.2). However, as detailed in Section 4.1.2, the wintertime buildup of aerosols due to

reduced scavenging (the "Arctic haze" phenomenon) was subsequently discovered to dominate the

seasonal signal over a distance-to-source argument. The chloride signal was strongest in GB94C1. and

yielded an age of 15 years BP (1979) at a depth of about 15 m. Large mcltwater-ice layers below- this

depth made reliable layer counting difficult, though the age at the bottom of the core (24 m) was believed

to be at least 25 years BP. Subsequent information based on the 1997 cores resulted in a revised bottom

age of 1959 for GB94C1 (i.e.. 35 years BP). Without deeper coring, the identification of a peak in the

bcta-radioactivity profile (see Fig. 4.7) representing the concentrated nuclear testing of 1962-64 could not

be confirmed.

Both the Alexandra Land and Hall Island cores also showed annual Cl* peaks that could be dated

and matched with the Graham Bell profile (Fig. 2.3), even with the higher background concentration and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1111 -i 111111111111111111111111111...... iiiiiii.iiiiiii.il

-1 2 -

i ' 1 5 H I o 5 -18 H o

-21 H

9 H E 3 . 3 T _n CO C O£ 0) - 6 A Q . m ^ 0) o O •C x 3 (0 Q_ j y Hr 0 4

E 3 Q. 3 I 2 o 1 P- 0 Graham Bell Core 1 Zemlya Alexandra Core 1 E 3 a . Galiya Core 1 Q. 2 CM o CO 1 H

1994 1993 1992 1991 1990 1989 1988 1987 1986 1985 Year (A.D.)

Fig. 2.3 Short ice core records Grom Franz Josef Land (1994), superimposed in time (Alexandra Land, Hall, and Graham Bell islands).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. greater presence of meltwater ice in the stratigraphy and a presumption of enhanced post-depositional

signal alteration. These matches indicated that both cores have a bottom age of-1985. consisting of nine

years of continuous accumulation. The ice accumulation profiles all show a negative trend over the most

recent decade (1985-1994) (Fig. 2.4). During the nine-year overlap period (1986-1994) the average ice

accumulation values are similar for all three sites, ranging from 0.56 m at Hall Island to 0.72 m at

Alexandra Land. In the period before 1980, the Graham Bell record shows sharply reduced ice

accumulation concomitant with increased density/meltwater infiltration (c/ Figs. 2.4a and 2.4b).

However, model results (Section 4.3) of the depth-age profile from the 1997 deep core indicated that

annual layer thicknesses from the top low-melt portion of the GB94C1 core (ave. = 0.61 m) are more

similar to the long-term accumulation rate (0.64 m).

Some major features in the stratigraphic and particulate profiles arc common among the three

cores. Large meltwater ice layers arc present in both the Alexandra Land and Graham Bell cores during

the year 1990, and elevated dust concentrations are seen in all three cores around 1988-89 and 1993-94

(Fig. 2.3). The 6I80 records, despite not exhibiting a definitive seasonal signal over this time window, do

reveal several common features on an interannual time scale. Short-lived negative excursions are seen in

the respective isotope records in the winters of 1987 and 1989. followed by an enrichment trend

culminating in the year 1991. Large discrepancies in the relative magnitudes of these common events is

apparent, whereas monthly-averaged air temperatures from different sites across the archipelago show

little variation. With a few exceptions, the enriched ("warmer") isotopic values occur during the fim

sequences, whereas the depleted ("colder”) values often correspond with melt layers. Counterintuitive in

terms of a temperature-dependent Rayleigh process for precipitation (Sonntag et al.. 1983). this

relationship is generated by post-depositional processes as discussed in Section 5.4.1. Recognizing

common features and events among these three records from distant sites in the archipelago supports the

premise that a regional climatic signal is preserved in the 6lsO record, even if isotopic composition relates

to forcing factors (e.g., temperature) indirectly.

Density (g cm'3) Layer Thickness (m ice eq.) 1.2 0.8 0.6 1.0 . - 0.4 . - 0.9 0.2 0.6 0.3 1— i — i — i —0.3 | — i — i — i — i — | — i — i — i — i — | — i — i — i — i — | — i — i — i — i — | — i — i — i — i — | — i — 1 — i — r - Fig. 2.4 a. Layer thickness and b. density comparisons for the three 1994 short cores from cores short 1994 three the for comparisons density b. and thickness Layer a. 2.4 Fig. - - - - 95 90 95 90 95 90 95 1960 1965 1970 1975 1980 1985 1990 1995 Franz Josef Land locations on Graham Bell Island, Alexandra Land, and Hall Island. Hall and Land, Alexandra Island, Bell Graham on locations Land Josef Franz Year (A.D.) Year 14 Linear regressions for 1986-1994 for regressions Linear —A— ZA94C1 - O - GB94C1 G94C1 L 13.34ya, 1^=25) 61.3-.0304*year, = (LT L 37.16ya, ^=.05) 23.7-.0116*year, = (LT L 36.37ya, .39) = r 73.6-.0367*year, = (LT ZA94C1 GB94C1 G94C1

The extremely low background chloride concentrations in both Graham Bell cores for the 1988-

89 period, coupled with similarly muted peak values, are not duplicated in the other records. This unusual

event presented a valuable opportunity to quantify the percolation of soluble species by way of comparison

to the 1997 core, as developed in Section 4.1.2. Given this foundation, it was apparent that even if low

concentrations of chloride ion were deposited in all FJL snow during that two-year period, then evidence

of this episode was already erased by melt migration at both the Alexandra Land and Hall Island sites

prior to May, 1994.

As suspected from field observations, the lab analysis of the Hayes Island summit core confirmed

that its ice cap (Hydrographer Dome) is presently undergoing net ablation. During drilling, large dirt

clumps were observed at a depth of-60 cm. at which point the thin (and presumably ephemeral) firn layer

abruptly ended atop solid ice below. The Hayes Island core results (Fig. A. 3 in Appendix) also revealed

several episodes with extremely high concentrations of Cf (8-10 ppm) and SO.)2' (3-4 ppm), levels unseen

in any of the other FJL cores. While the depositional age of the current (1994) surface of Hydrographer

Dome may remain indeterminate, there are several pieces of evidence that suggest that net accumulation

ceased only within the past century. In the absence of significant concentration of sulfate ion by

melt/percolation (an assumption that can by no means be easily substantiated), the elevated levels of SO.f

in the H94C1 core suggest a surface age within the era of widespread anthropogenic pollution, i.e.. post-

1830. Furthermore, mean 5l!*0 ratios within the top 5 to 10 m from cores obtained at the two nearer

islands are similar (-16.8%o for Graham Bell and -16.1%o for Hall Island, compared to -15.9%o at Hayes

Island, while Alexandra Land in the west yielded -14.4%o). Again, this similarity suggests a 20th century

age for the Hayes summit surface, because the 315-m deep core from Graham Bell (obtained in 1997)

displays a marked isotopic shift to far more negative values (-19 to -20%o) in previous centuries.

Attempts to isolate a single multi-parameter cross-match between the Hayes 4.7 m core and the

Graham Beil records (including the 1997 core) were inconclusive, although one particular alignment

appeared more probable than others. As shown on the Hayes Island raw data profile in Fig. A.3. an age

scale beginning with the year 1946 ascribed to the position of the fim boundary/dirt layer and ending with

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the year 1917 at the base of the core, yielded the most plausible match with the Graham Bell record

considering all parameters equally (Fig. A.6). Included in these parameters (though not shown) is the

average grain size (AGS) determined from the 14-channel microparticle data, as outlined in Section 3.2.2.

The Hayes Island core average AGS of 6.5 pm is significantly higher than at any portion of the GB97C1

record, though the highest values for the deep core of S-5.5 pm do occur in the middle portion of the 20th

century, which then sharply decline to -4.5 pm after 1980 (see Fig. 6 .8). Also considered was the 1994

field observation of an accumulation/ablation marker, apparently placed near the Hydrographer Dome

summit during the International Geophysical Year of 1957-58 (Krenke and Psareva. I960; pp. 6, 44-45).

that would further suggest no net accumulation has occurred on the dome for at least several decades. The

proposed Hayes Island age scale produces a fair isotopic match with GB97C1 (Fig. A.6) and would

indicate very' low accumulation (0.14 m ice eq.) for the 30-vcar period indicated. The two large events in

anion concentrations at 1.7 m and 2.7 m (as indicated in Fig. A.3) are also mirrored by similar peaks in

the GB97C1 around 1932 and 1940. though cross-correlation of ion concentrations is more problematic

given the meltwater/pcrcolation effects. However, given all the information available, the most reasonable

conclusion is that the Hydrographer Dome summit began to stagnate at some point around 1950.

2.3 Graham Bell 1994 ice core data

Because of procedural changes in data generation/handling and core dating between the 1994

reconnaissance study and the more extensive 1997 program, several data profiles from cores taken in 1994

were re-parameterized utilizing the same methodology as for the newer core. Originally, melt percent and

density values were not generated on a sample-by-sample bases for GB94C1, so it was necessary to

combine the layer-based descriptive stratigraphy with the available bulk (i.e.. 1-m) densities to produce

analogous profiles. Given four different basis layer descriptions (fim. icy fim. bubbly ice. clear

[meltwater] ice) and only a single density measurement per meter, some assumptions about three of the

four types of ice core were required. 'Meltwater ice' was simply assumed to retain a constant density of

0.92 g cm*3 throughout the core, and 'icy firn' and 'bubbly ice' were estimated by simple linear functions

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (gradually increasing with depth) as shown in Fig. 2.5. The overall density profile was not greatly

affected by the choice of these functions because layers designated 'icy fim' only amounted to 0.74 m

(3.1%) of the 24-m core, and 'bubbly ice' only 2.15 m (9.0%). all in the lower portion where densities were

less variable.

The GB94C1 melt percent profile, analogous to the sample-based melt record generated during

routine ion chromatography (IC) analysis of GB97C1. was created in a similar way. All 'firn' layers were

assumed to contain 0% melt and all 'clear ice' layers were assigned 100% melt, whereas 'icy fim' was

assumed to represent 20% melt and the 'bubbly ice' layers 80% melt. Deeper in the glacier, tighllv-packcd

spherical bubbles in otherwise solid ice were assumed to represent a lack of meltwater saturation.

However, because true fim layers still existed below 28 m in GB97C1 it was apparent that these shallower

'bubbly ice' layers represented significant meltwater infiltration. The depth scale transfer for the melt

record proceeded incrementally: for each depth range representing a single sample, the relative

proportions of the four ice classifications were determined and each multiplied by the percentage of melt

that each layer was assigned (as above), and then summed into a single value. Unlike for GB97C1. these

values (Fig. 2.5c) were not rounded off in 10% increments, because minor fluctuations within multiyear

melt- or fim-layers might have been erased. However, it should be expected that the GB94CI melt record

has (at best) an accuracy' and/or resolution of only 10%. given the uncertainty of the exact sample-by-

sample depth control (only assumed to be within ±1 cm). These uncertainties become minimal when re

averaging the melt values on a yearly basis (as shown in Fig. 4.4).

For long ice cores, annual accumulation values must be reconstructed given both the requisite

knowledge of the age-depih relationship that layer-counting provides, and some understanding of how the

individual layers have undergone thinning with successive burial. Because all of the seven cores hand-

drilled in 1994 represent only a small fraction of the ice archived in each glacier, the thinning of even the

bottom layers of the 24-m Graham Bell core would be minimal (-5%) and so layer thicknesses (reported

in terms of ice equivalent) are adequate for use as accumulation values for these few decades. The ice

equivalent depth scale for GB94C1 was created by multiplying each sample increment by its estimated

Melt % Density (g cm'3) Density (g cm'3) 100 0.4 0.5 0.8 0.9 0.3 0.7 0.6 0.4 0.5 0.3 60 80 20 40 0 Fig. 2.5 Profiles of GB94C1 b. reconstructed density and c. melt percent by sample, sample, by percent melt c. and density reconstructed b. GB94C1 of Profiles 2.5 Fig. — r - icy Modelled fimdensity — a - set constantto cmg 0.92 Meltwater-icedensity based on a. the separation o f bulk density values into individual components components individual into values density f bulk o separation the a. on based (identified by the original visual stratigraphy). visual original the by (identified Modelled bubbly ice density ice bubbly Modelled Reconstructed fim density density fim Reconstructed —i ‘f l—

GB94C1 Depth (m) Depth GB94C1 0 15 10 SM(----) k (1-3-4-3-1) 5SRM Reconstructed sample density (b., above) above) (b., density sample Reconstructed 18 "only 11 cm fim in11 cmfimthis meter "only •only 12.5 cm fim in•onlyfim12.5cmthis meter melt percent (c., below)(c., melt percent 20

a. 25 density value as described above, and dividing by the constant 0.92 g cm'3, again representing the density

of glacier ice. Following this conversion, the cumulative length of GB94C1 became 18.49 m IED (ice

equivalent depth), which represents a shortening of S.49 m relative to actual core depth. Because this

reduction is approximately 1 m greater than the equivalent for the entire fim sequence for GB97CI (4.46

m). it suggests that the sample densities (and hence the original bulk densities) for GB94C1 were

somewhat underestimated. Given the potential for loss of material during transport and handling (bulk

densities were calculated assuming a complete, perfect cylinder of ice without breakage), this result is

conceivable. However, it is also possible that there was a true net densification of the upper fim zone

between 1994 and 1997 because of large melt/percolation cvent(s) during the intervening years. Evidence

for these percolation events exists in the comparison of the annual melt-percent records, as well as in the

chemical records as discussed in Section 4.1.2.

Following the 1994 field program and subsequent laboratory analysis, preliminary findings and

interpretation were presented (Thompson et al.. 1995) that pointed to a perceived relationship (r = 0.37)

between maximum Cf concentration (assumed then to occur during late summer) and the average

September sea ice concentration at individual gridpoints near Graham Bell, over the 16 years of satellite

measurements (Fig. 2.6). However, this method suffered from the static, spatially-limited nature of the

correlation, and analysis of the monthly satellite data (Gloersen at al., 1992) shows that the configuration

of the sea ice margin in the Barents Sea varies greatly from year to year. Therefore, the effective distance

from the open water source to the ice cap during summer is probably very sensitive to changing near-

surface atmospheric circulation patterns. Following the 1997 program, the determination was made that

chloride maxima actually occurred in late winter, and the conspicuous multi-year post-depositional

alteration of the anion record was also detected. This knowledge pointed to the necessary realization that

the promising correlations over this limited number of years were indeed spurious (note the out-of-phase

relationship in Fig. 2.6), and illustrated unequivocally that year-to-year relationships between migratory

ions in Franz Josef Land ice cores and regional environmental parameters are unreliable and

overambitious. However, there might originally have been a true climate link between the GB94C1 multi-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

met stations met (@ sea level) (@ sea Composite of 3 of Composite SSM/I SMMR Cl Cl (ppm) (%) Cone. Ice Sea Mean (°C) Temperature Monthly Air Avg. Annual 0 1 2 3 0 20 40 60 80 100 -16 -14 -12 -10 -8 Fig. Fig. 2.6 Bimonthly GBC941 chloride vs. sea ice concentration and air temperatures during the satellite era. 1993 - 1992 - 1991 - 1990 - 1989 - 1988 - 1987 - 1994 - 1986 - 1983 - 1982 - 1981 - 1985 - 1980 - 1979 - 1984 - Year

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. year trends in chloride and general sea ice/temperature conditions over the decade of the 1980s, but it was

readily apparent that by 1997 this record was no longer reproducible.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 3

THE 1997 DEEP DRILLING PROGRAM

3.1 Deep ice core drilling and sampling

Of the ice core data acquired from the 1994 reconnaissance, the most promising results were

obtained from a 24-meter core taken on Windy Dome. Graham Bell Island as compared to short cores

from three other sites within Franz Josef Land. Therefore in 1997 a deep ice core-drilling expedition to

Windy Dome was undertaken, a joint venture between the Byrd Polar Research Center (BPRC) at The

Ohio State University and the Institute of Geography at the Russian Academy of Science (IG-RAN) in

Moscow. The field party, under the direction of V. Zagorodnov (BPRC). successfully recovered a l()-cm

diameter. 314.8-m core (GB97C1) and a second 8-crn diameter. 36-m core (GB97C2) from the Windy

Dome summit (Fig. 3.1a. 80°47'N. 63°32E. 509 masl) in March-April 1997.

Both cores were obtained using a modified Antifreeze Thermal Electric ice-coring Drill (m-

ATED). with a variable ethanol-water mixture employed as borehole antifreeze. The prototype drilling

apparatus for deep ice core extraction (Zagorodnov et al.. 1998) included a 740 m support/power cable, a

motorized winch system operated through an electric controller, a hoisting mast (supporting and guiding

the cable/drill), and the drill itself. The 2.9 m long m-ATED drill barrel was capable of retrieving a 10

cm diameter core section up to 2.1 m in length in ideal conditions. Modifications in the m-ATED drill-

head construction were made to reduce the heating height of the thermal-electric coring tip (from 47 to 12

mm), and effectively the time of heating during penetration. A self-contained antifreeze

injection/circulation system eliminated the need to remove melt water from the newly-forming borehole

during operation and also prevented refreezing, although this process limited the speed of penetration.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ysxwss. Graham Bell Island, W m w m m m Franz Josef Land, Russia m m A Base station I'"" Kupol Vyetremy, !j|llllilIllpppL Windv Dome m m m r n m m m m m «*« m a m m m w m m m m m wM5»»»5dF*V/«««xxxxx v/s,v/,

# p p ® t 0 llllllI P "

r n Bedrock below sea level 300— Ice surface elev. (m) a*®** Bare landimm contour interval = 50 m

Graham Bell Island, 0V Franz Josef Land, & XXXfiiXi Base station m Russia Xiiiii vMw»»»p?2wS m m m m m . mmmmm imms^sssssssSssm m m illlillllll l i l i i S M ‘M m m t m m v s m m i

ww m m m m x m nO1 W indy Dt>tne 5? mm m m m m M m

[ 1 Ice cover s-400— Ice thickness (m) S&l Bare land contour interval = 50 m, 25 m > 400 m

Fig. 3.1 a. Map of Graham Bell Island, with surface elevation contours indicated for Windy Dome (after Glazovskiy e t al., 1999), b. Map of ice thickness (dashed when inferred) from radio echo sounding measurements (after Macheret et al., 1998). 23

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The 315-m ice core (GB97C1) was obtained in approximately 17 days of drill operation (with three days

of downtime), producing core at an average rate of 18.5 m/day. Very good quality core was extracted

throughout the uppermost 175 m of ice drilling. Increased fracturing was seen in the lower portion of the

315 m core due to the colder ice temperatures (nearly •I2°C) approaching the lower limit of the drill's

operational temperature range (-15°C). However, core segments were of sufficient length and quality to

produce a high-quality physical and chemical record from the entire length of the core, without any

significant gaps or cumulative core loss.

The m-ATED apparatus was also designed with a borehole thermometer/recorder and an internal

depth-recording system that yielded real-time penctration-depth measurements and also borehole

inclination. Borehole depths were recorded at a resolution of 1 mm. and closely matched the cumulative

lengths of ice core segments returned to the glacier surface. Borehole orientation was nearly vertical,

straightening from 11° inclination at 75 m depth to 4° at the core bottom (315 m). During the drilling

operation, the borehole temperature measurements were used to determine the necessary proportion of

ethanol to water required to keep the antifreeze solution from freezing. In the process, it was discovered

that the Windy Dome ice temperatures display a sharply negative gradient, resulting in much colder ice at

depth (-ll.5°C) than near the surface (below the zone of seasonal influence. -6°C) (Fig. 3.2a). This

finding (known from other Eurasian Arctic glaciers, but particularly strong in Windy Dome) dictated that

the budgeted supply of ethanol retained on site was insufficient, and the drilling operation had to be cut

short of completion to bedrock for fear of borehole freezing and loss of the drill. Radio echo sounding

measurements conducted in 1994 (Machcret et al.. 1998) suggested that the ice thickness at the center of

Windy Dome was approximately 500 m (Fig. 3.lb). As a result, the deep core recovered (315 m) does not

represent the complete climate history archived in the ice cap. Because intact and complete core from the

surface snow/fim layer of any ice cap is difficult to obtain with deep-drilling equipment, it is standard

practice to sample snowpits in an area nearby to provide clean material from the most recent

accumulation. Therefore, on the Windy Dome summit, snow pits were prepared and sampled before and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. MWP? ^151 150 Depth (m) Depth M m m m 20th century Warm Period. temperatures, b. melt percent, c. oxygen isotope ratio, climatic ‘ interpretationgiven MWP = Medieval Fig. Fig. 3.2 ey results Initial surv from deep 1997 icecore drillingon Dome,Windy Graliam Bell Island, including a. borcliolc w -18

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. after the main coring operation in 1997. Pit 1 (1.45 m depth) was excavated on April 4, 1997 and a

second summit pit (denoted Pit 6) (1.68 m depth) on April 23. 1997.

Following the field program, both ice cores were transported by helicopter to Sredniy Island.

Severnaya Zemlya and subsequently packed into insulated boxes with frozen gel packs (melting range -15

to -5 C) for a return flight to the ice core freezers at BPRC. A large majority of the ice cores were

received without having been warmed to the melting point and displayed no significant damage otherwise.

However, several core tubes were necessarily housed near the cabin heater of the helicopter during the

initial flight, including several ice core sections that contained fim sequences. Even though these few

sections showed signs of significant narrowing, flattening, and rcfreezing of meltwater within the core

cylinder, selective sampling of the ice from the "good" side of the remaining core provided samples of

acceptable quality and the record was not compromised. Furthermore, because the fim sections were

subject to fluid formation during drilling, core sections representing the top 20 m of accumulation were

subject to addition of pore-filling meltwater. The procedure of turning the core sections to a horizontal

position after extraction (for the sake of completing visual measurements, cutting the core into ~!tn

sections for transport, and the securing of ice into protective tubes), allowed the retained pore fluid to

collect only in the underside of the core as it lay flat. Again, this happenstance allowed for judicious

subsampling of the sections for the major analyses that require uncontaminated ice.

During the coring operation, IG-RAN researcher S. Arkhipov completed stratigraphic profiles for

each core (employing the nomenclature method of Shumskii. 1964). Simultaneously, the team also

produced 330 (approximately meter-long) integrated ice samples from core surface shavings for the

purpose of completing a "survey" profile of stable isotope (51!,0) values, a proxy for air temperature. The

stratigraphy was later repeated by the author (using different nomenclature) and a comparison of the

respective visual records over the upper portion of core (highly simplified in the case of the field profile) is

shown in Fig. 3.3, along with that of GB97C2. The field observations of visible ice stratigraphy were

subsequently reduced to a continuous record of melt percent by S. Arkhipov (Fig. 3.2b), and the 6**0

survey (Fig. 3.2c) was later completed at BPRC by P.-N. Lin. Both records indicate a strong change in

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o> o>.9* 3 1 II i w 0 * * * 1

D Depth (m) III

Depth (m) LUU

Depth (m) I I Fim Dense Icy Fim Icy Firn Bubbly I B Ice Ice Fig. 3.3 Stratigraphy comparison of Graham Bell (1997) Cores 1 and 2, top 24 meters only, showing comparison by analyst for Core 1. Asterisks denote locations of high KF concen tration [K>120 ppb and F>10 ppb, or K>200 ppb and F>50 ppb (bold)]; see Section 6.3.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. character between 60 and 100 m depth. These profiles were the basis of an initial interpretation:

specifically, that this marked change represents the transition from the 20th century back into the Little

Ice Age’ (LIA), the period of colder global temperatures that persisted from approximately 1450 to 1850

A.D. (Grove. 1988). Less apparent was a trend towards less negative 5uO values and higher melting

below 250 m. which was postulated to represent the final stage of the Medieval Warm Period’ (MWP.

1000-1450 A.D.) (Hughes and Diaz, 1994). This hypothesis was later confirmed by fine

sampling/analysis and the counting of annual layers guided by several major volcanic horizons that lias

yielded a bottom age for Core 1 of 1225 A.D.

Given the initial assumption of no more than a thousand years of history represented by 315 m of

ice core, it seemed likely that a subannually-resolvcd record of all major core constituents could be

achieved through continuous fine sampling (under 5 cm) and standard analytical procedures.

Accordingly, a strategy was devised that would yield a inorc-or-less consistent sampling density' (SD.

defined as the number of discrete analyses made within a single year of ice accumulation) throughout the

core. The profile in Fig. 3.4 depicts the resultant pattern of average sample size (in terms of vertical

depth) for GB97C1. Due to fim dcnsification in the uppermost 30 m of core, the reduction in sample size

was more pronounced in this section. Below 120 m depth, sample size was maintained at roughly 3 cm.

which was adequate for retaining subannual resolution (roughly 10 samples/year), while simultaneously

providing a manageable daily analysis routine at a pace of 2 m per work day (maximum ~70 samples/dav)

for much of the core processing. At this accelerated rate, the sampling/chemical analysis phase of the

research project was completed in roughly 15 months between November. 1997 and January. 1999. Fig.

3.5 depicts the temporal profile of SD for the entire GB997C1 core based on the final limescale outlined

in Section 4.1.3. A total of 9,048 samples were analyzed over the entire length of the core, with valid

results generated for all but a few (<~10) in each analysis.

The procedures for sampling the upper fim section differed from those performed on the longer

solid ice section, as shown in Fig. 3.6. Because fim is naturally porous and capable of retaining a large

volume of water, washing of prepared ice core samples was not permissible due to the indeterminate

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0 50 100 150 200 250 300 Tube Number

Fig. 3.4 Plot of average sample size for each of the 3 IS l-m sections (tubes) of the GB97C1 ice core.

Annual values 5SRM (1-3-4-3-1) 20

2000 1900 1800 1700 1600 1500 1400 1300 Year (A.D.)

Fig. 3.5 Sampling density (number of samples cut per given year) over the length of GB97C1, compared to the 'limit of monthly resolution' (SD = 12).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Deep Ice Core, 28-315 meters Firn Section, Top 28 meters

Anion Chemistry & Stratigraphy Particle (Bottle archive Concentration for survey of /.•.••..'.V.V.V.V.V.V.*. \v . pH, Cations) / Total Particle Anion/Cation Total Beta Concentration Chemistry, Beta / Radio $ Distribution Oensity & Radio Pollen, Cosmogenics O ^e,3^!) activity Stratigraphy activity

Core Archive Core Archive \ \

Core Diameter = 9.5 cm Core Diameter = 9.5 cm viewing downcore viewing downcore Sample size: 3-4 cm Sample size: 4-10 cm

Fig. 3.6 Sampling strategy for Graham Bell (1997) Core I. dilution effect that would occur. Hence, fim samples were necessarily taken from the internal portion of

the core for those measurements that are particularly sensitive to contamination (i.e., ion chemistry, dust

analysis). In addition, more stringent contamination-control procedures were undertaken to protect the

samples, including handling core samples only with latex gloves that had been washed thoroughly with

deionized Milli-Q water, and a cutting methodology that protected the samples prepared for ion and dust

analysis from contact with anything except the blade on the band saw table.

Coincidentally, the fim section of GB97C1 also represented the window of time that

measurements of [3-radioactivity and tritium are applicable, because these parameters arc mainly useful for

detecting horizons provided by the well-documented nuclear testing begun in the 1940s by the United

States, the former Soviet Union and other countries such as France (Carter and Moghissi, 1977). Because

these radionuclides arc not currently present in large abundance compared to previous decades,

contamination by modem materials was not expected. For this reason, the outside portion of core was

suitable for these samples. Similarly, the nature of oxygen isotope concentration as a bulk property of the

glacier ice (unlike dust and soluble ions, which are essentially trace elements) also allowed surface fim/icc

samples to be utilized without fear of contamination. In practice, only the removal of frost and extraneous

small bits of ice ("freeze-on") via scraping by hand (or decontaminating the surface by skimming the ice

core along the saw blade) was deemed necessary for these particular analyses.

As depicted in Fig. 3.6a, most of the core was sectioned using a three-step procedure in a single

cutting session for each meter (twice-daily). All sampling work was completed in a 20°F (-7°C) cold

workroom attached to the -30°F (-34°C) cold storage facility at BPRC, equipped with a Sears Craftsman

12" (1 1/8 hp) band saw. (To provide a smooth clean surface for ice preparation, a thin sheet of plexiglass

was fitted to the band saw table.) After cleaning the core surface of all "freeze-on." the superior half of

the core was identified and a continuous slab of ice was produced by feeding the core through the band

saw longitudinally, making sure each core section was identically oriented so that gaps were minimized

between sections with irregular ends. Each slab section was then turned over to rest on the freshly-cut

surface and subsequently divided into three equal-volume ice "planks." The planks were placed together

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. on the preparation table as a final sampling plan was chosen. Each core section was measured and the

number of individual samples to be acquired from each section was determined based on the intended

sample size (e.g., a 22-cm section would provide seven samples if the sample size was to be roughly 3

cm). After removing a small amount of ice (~2 mm) from the rough edges of each end of the

reconstructed slab (the planks still held closely together without offset), the saw guide was then set to the

exact distance from the blade such that the intended number of samples would be generated by repeated

cross-cutting, without significant excess remaining after the final cut. In rare cases where high-anglc

breaks occurred, two adjacent core sections might be treated as one. such that one intermediate sample

would span the break. While this procedure usually resulted in corresponding samples being derived from

different core sections (w ith the central ion chemistry sample generally consisting of two fragments), the

method also proved to be most effective at limiting large gaps due to these irregular breaks and

maintaining consistent sample sizes.

As the cross-cutting progressed, each set of three samples was returned in the proper order to the

preparation table. Upon completion of the cutting, the samples for both anion and microparticle analysis

were transferred to separate samplc-cup trays (numbered in sequence) for transporting the ice from the

cold room to the clean room laboratory for further preparation and melting. The samples for isotopic

analysis were also transferred to a separate tray for melting and bottling, after which they were returned to

the cold storage room to be preserved until they were rcmeltcd and analyzed at a later date by P.-N. Lin.

Immediately upon transfer to the clean room, all of the ice samples were individually washed (handheld

with stainless steel tongs) under a steady stream of deionized Milli-Q water, removing preferentially a

layer of ice from the side representing the original core surface and allowing the water to completely wash

over all six sides of the "cube." After shaking off any excess water, the samples were placed into a second

set of numbered plastic cups that were earlier washed thoroughly with Milli-Q water and left to dry for

approximately 1 hour in the clean room environment. Screw-top lids were then secured onto each cup

and the ice samples were left to melt (1-2 hours). All information about the samples produced for each

meter was recorded, with sample sizes being determined to 1 mm. Because only a small amount of ice

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (with respect to depth) was removed in the cutting/washing procedure, it was assumed that the entire

length of core was analyzed continuously. In practice, to account for most breaks (including the top and

bottom ends of each meter). 2-3 mm of core depth was normally added to the samples on either side. Any

minor disagreement (normally a deficiency) that existed between the sum of the individual samples and

the length of the ~lm core section as originally measured would have been reconciled by small

incremental augmentation of the sample sizes as necessary.

In addition to the layer-based stratigraphy profiles (as in Fig. 3.3). a sample-based stratigraphy

was also recorded to impart ease in comparison with the other physical and chemical properties on that

same interval basis. After each IC sample was washed and readied for melting, a quick examination of

the internal appearance of the ice was made by holding each sample up to the ceiling lights. Physical

disturbances to the ice (e.g., cracks) were recorded to prompt a subsequent check for any possible signs of

contamination, and the average 'melt percent' of each sample was estimated in 10% increments (0% -

bubbly ice. 10%. 20% ...... 90%. 100% - bubble-free) as shown graphically in Fig. 3.7.

For the upper flm layer, density was measured on cut samples (rectangular prisms) from the core

interior, before being melted for IC analysis, by a simple method of measuring the lengths in each

dimension (to within 0.5 mm) and weighing the sample (to within 0.1 g). A total of 84 measurements

were performed on (generally bubble-free) infiltration ice spanning the top 25 meters of the GB97C1 core,

yielding a normal distribution and an average density of 0.939 (± .044, ler) g cm 3. Comparison of this

value with the known densities of glacier ice produced from cold fim sintering (0.917 g cm'3: Paterson.

1994) and pure-water ice (0.998 g cm'3) indicates that either the methodology underestimates the actual

density' or that a certain amount of air is still contained in the ice structure. In fact, occasional large

irregular voids (as depicted in Fig. 3.7) did exist in ice samples that were determined to be 100%

meltwater-infiltrated.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 3.7 Idealized drawings of common bubble structure within GB97CI ice samples prepared for IC analysis, and determination of melt percent by visual inspection (estimated to 10%).

3.2 Analytical procedures

As for many ice core-climatc studies, the analytical phase generated complete high-rcsolution

profiles of oxygen isotope composition (5>!lO). microparticle concentration and size distribution, and

major anion (Cf, N03\ and SO.f) concentration. The author completed all of the required ion analysis

(as well as preparing all of the ice samples), and M.E. Davis (BPRC) analyzed all samples for

microparticles and P.-N. Lin (BPRC) for 6lsO. In each case, well-documented techniques were employed,

including the mass spectroscopy method developed by Craig (1957) for 5lsO and the dust analysis

methods described by Thompson (1975). Concentrations of major soluble anions and cations were

determined separately by standard ion chromatographic (IC) methods, as described in Legrand et al.

(1984) and Buck et al. (1992).

3.2.1 Ion chromatography (IC) methodology

Routine daily analysis of the GB97C1 core was completed over a period of 15 months, beginning

November, 1997 and terminating in January, 1999. At the outset, the lone IC instrument available was a

Dionex Model DX-2010i fitted with a lonPac AS4 anion column, conductivity' detector, H;S04-

regenerated suppressor column, and a manual injection port. Hence, the sample-by-sample operation

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. required the constant presence of the analyst to inject samples from a plastic syringe, and effectively

limited the rate of core processing to 1 m per analysis day. In April 1998, a Dionex Model DX-500 (with

CD20 conductivity detector and ASRS-II Ultra suppressor system) was obtained, additionally equipped

with a AS-40 Autosampler Module capable of storing up to 13 x 6 (78) water-filled 5 ml vials and

executing a continuous automated injection sequence. (For cither IC device, detection limits of all species

were on the order of 0.1 to 1.0 ppb. and hence were not an issue in resolving any of the major ion peaks

from this core.) From this point to its conclusion, core processing accelerated to 2 m per day. However,

because of additional obligations present for the other analysts only the IC evaluation was concluded as

the core was being sampled. Samples for <51>(0 analysis were melted, poured into labeled Nalgcne bottles

(with no head space) and returned to the deep freeze cold room until ready for analysis. Ice samples that

could not be immediately analyzed for microparticles were secured inside dear plastic sleeves and placed

inside the core storage tubes along with the remaining core archive until needed.

Because fim processing (described in Section 2.1 above) required special handling and acquired

skill, the GB97C1 core analysis prudently began at 28 m depth where the samples could be considered as

"solid ice” and therefore thoroughly washed. From this depth, the IC analysis continued downcorc to 106

m depth at which point processing was halted briefly as the DX-500/AS-40 devices were installed and

tested. Core processing resumed at 2 m/day from 106 to 121 m. at which point fim processing began,

working upwards from 28 m to the fragile surface-snow layer. The remainder of the core sampling

continued uninterrupted from 121 m to the core bottom at 314.8 m. The final procedural change occurred

at a depth of 143 m. when the 1C sample loop size was changed from 300 to 500 ul in order to improve

sensitivity for the lower concentrations of anions present in the bottom half of the core. All samples w ere

analyzed at full concentration, except for several samples representing the Laki eruption (Section 4.1.3)

that were diluted 1:100 in Milli-Q water for accurate sulfate determination. Other operational details are

included in Table 3.1.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Depth Device: Column: Baseline Column Row Eluant: Run Injection Output Range: Conduct Pressure: Rate: Time: Volume/ Range: ivity: Spl Loop: 28-106 m Dionex lonPac 11.7- 1190- 2.0 ml 0.28g/0.43g 9.0-9.5 2.5-3.0 ml 100 pS (Cl"). DX-2010i AS4 12.1 pS 1240 psi per NaHCCV min 650 pi 10pS(NO,\ min. Na.CO, so.,2-) per 3.8 L water

1-27 m. Dionex (onPac 15.0- 1600- 1.5 ml 0.135g/1.5g 11.0 2.0-2.5 ml 50 pS (C1-). 106-143 DX-500 AS12 15.5 pS 1750 psi per NaHCCV min. 300 pi 5 pS (NO3’. m min. Na:C 0 3 SO.,2) per 3.8 L water

143-315 Dionex lonPac 14.8- 1650- 1.5 ml 0.133g/1.48g 11.0 2.0-2.5 ml 100 pS (Cl ), m DX-500 AS12 15.0 pS 1720 psi per NaHCCV min. 500 pi 10 pS (NOV, min. Na;CO, SO.,2) per 3.8 L water

1-25 m. Dionex lonPac A)2.5 pS 650 psi 1.0 ml A) 3.0 ml 14.0 2.0-2.5 ml 10 pS m-integ. DX-500 AS12 rising to per - B) 50 ml min. 500 pi (F. MSA). sample B)3.0 pS min. 0.5M NaOH 200 pS (Cl ). anion a t -5 per 3.8 L water 50 pS (NOV. (gradient) min. SO.,2) analysis 1-25 m. Dionex lonPac 0.7-1.0 1100- 1.0 ml 45 ml 14.5 2.0-2.5 ml 200 pS (Na\ m-integ. DX-500 CS12A pS 1150 psi per 1M H;SO., min. 500 pi NR|~). sample min. per 3.8 L water 30 pS (KV. cation Ca; \M g 2') analysis

Tabic 3.1 GB97C1 IC analytical parameters

Calibration of each anion species analyzed was carried out using standard practices, involving

daily formulation of several multi-anion standard solutions, which were each analyzed twice al the

conclusion of the day's run. and then twice each again at the outset of the next day's run. The daily

standards were diluted from an intermediate stock solution of 40 ppm Cl'. 10 ppm NO3'. and 20 ppm

SO42' that was prepared from individual 1000 ppm stock solutions of each anion whenever necessary.

Each day, one of the two standards was held constant at 1:100 dilution of the intermediate stock

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. producing a solution of 400 ppb Cl', 100 ppb N03\ and 200 ppb SO.f\ The second standard rotated

between higher multiples of these values to cover the entire range of concentrations found in the GB97C1

core. For example, standard peak heights and areas representing 800, 1600, 3200, and 6400 ppb Cl' were

generated on average once every four working days. Peak heights and areas for the four repeat

measurements on each standard were tabulated and averaged to yield single values. Statistics from these

daily standards produced estimated measurement errors (for the DX-500 system) at -1% for all three

major anions at this concentration. For each of the five concentrations (the highest two concentrations for

NOj' were not required), daily mean values were again averaged over a longer timeframe to remove any

minor procedural fluctuations in the manual pipetting of solutions between volumetric flasks. The daily

1:100 standard, however, was tracked to make certain that no appreciable instrumental drift was occurring

that would invalidate the use of longer-term calibration. Peak areas were chosen for the final calibrations

over heights because none of the three anions was affected by neighboring peaks (Fig. 3.8). and no

appreciable difference was seen between calibrating each way.

The entire calibration method was reinitiated each time a major change in IC analysis occurred

(as indicated in Table 3.1). so that three separate schemes were used in the end. Discernible instrumental

drift occurred only during the initial analysis period using the older DX-2010i instrument, for which a

minor correction to the results was applied over the entire depth range. Because the peak heights and

areas for all three ions gradually rose over time, a linear function was established to compensate for this

long-term drift. The correction led to a total change of 3.8% to the calibration between 28 and 106 m.

centered at the mid-point of the depth range. The actual percent change represented by the linear trends

of the three anions (Cl\ N 03\ and S04:") between 28 m (1962) and 106 m (1822) is 85%, 45%, and

134%. respectively, so the correction was minimal compared to the natural climate signal.

Although it was not feasible to complete an analogous high-resolution cation record from

GB97C1. integrated samples representing individual meter-long core sections were prepared from the

remaining meltwater following anion analysis. For each meter of ice analyzed below 25 m. -40 ml

portions of "cleaned" ice-meltwater were combined in four separate 60 ml Nalgene bottles (washed with

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Retention time 53 (minutes) ”

Output Range 1 0 0 jiS (S' ^ 10.9 ppb 12.4 ppb 9.7 ppb

Fig. 3.8 Sample chromatogram showing isocratic separation of major anions (non-quantitative for fluoride, organics) from the detailed analysis of GB97C1; Tube 161. Sample 3 (161.852 to 161.887 m). with concentrations as shown, among the lowest levels in the entire core.

Milli-Q water and dried before using), each representing (lengthwise) about a quarter of the given core

section. From each bottle, a smaller volume (~5 ml) was then extracted (weighted according to the

relative lengths of each "quartcr-scction") and then blended together to create a single sample

representing equally the entire core section. All five archival samples were appropriately labeled and

returned to the cold rooms to remain frozen until further use. In contrast, all of the 361 samples derived

from the uppermost 25 m of the GB97C1 core (1967-1997) were bottled individually in order to produce

at a later date high-resolution records of cations, fluoride and methanesulfonate (MSA') over the recent

past. Individual samples were also saved for cation analysis whenever an outstanding sulfate signature

was detected that might indicate a response to a volcanic eruption. Generally, a series of samples (7 to 15)

from both before and after the sulfate peak were reserved for dual analysis to establish a baseline around

the ev ent, although in the case of Laki, more than one entire meter of core was bottled and refrozen.

All of these archived samples were analyzed in a second shorter analysis program during the

summer of 2000, when two DX-500/AS-40 IC systems were available in tandem, allowing simultaneous

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cation and anion analysis. The methodology for determining anion concentrations of the near-surface

samples and 1-m integrated bottles was altered to a gradient IC method such that rapidly-eluting minor

constituents such as fluoride and MSA could also be measured. To achieve this goal, a weakened base

eluant is replaced by a second, more concentrated solution near the midpoint of each run. which quickens

the release of the slower-eluting ions (NCV, SO.t2') from the IC column and shortens the total run time to

under 15 minutes, providing enhanced separation between all minor and major constituents. In order to

cleanly separate the five major cationic species, including the slowly-eluting Ca2' and Mg2* species, a

single-eluant (i.e., isocratic) methodology was retained, which required a similar run time (-15 minutes)

as the gradient anion method. New calibration curves were again established by analyzing a similar set of

standards over the appropriate concentration ranges.

The repetition of the anion analysis of GB97C1 on this lower resolution scale provided the means

for detecting any previously unseen instrumental bias and/or drift as well as determining any potential

effects of long-term storage (two years or more) on ion concentrations. A side-by-sidc comparison of the

1-m integrated sample record (augmented at the top by the complete re-analysis of the uppermost 25 m)

with the analogous high-rcsolution data (appropriately weighted and averaged), detected no significant

biases or discrepancies. Mean values determined from the 1-m samples were within 1.2%. 0.3%. and

2.2% of those determined from the detailed analysis of chloride, nitrate, and sulfate, respectively.

With available data for all major anion and cation species present in the ice core (except

dissolved CO; or H;C03*). it was possible to produce estimates of solution pH for the entire length of the

core at low resolution (again, one value per m of ice). After recalculating all major ion concentrations in

terms of equivalents and summing both the positively and negatively charged ions into single values, a

simple ion balance could be used as an effective pH proxy via the following expressions. Quantification of

minor anions including fluoride and methanesulfonate (MSA') was only accurate for the top 25 m. so

estimates of their average concentrations (7.5 and 12 ppb. respectively) were added in as constants for the

length of the core, and made little difference to the final pH profile. From Morel and Hering (1993: p.

181-185), an aqueous system with open exchange with the atmosphere (CO; T = 10'5 M) yields a linear

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. relationship between pHC03 and pH. (Given expected pHs in the range of 4-6 for meteoric waters,

negligible C O 32' should be present.) The guiding formulae are calculated from the following:

K, = 10-6 3 = [H*][HC03'1/[H2C 0 3], with [H2C0 3] = 10'5 M (Eq. 3.2.1).

Rearranging and solving, produces:

pHCOj- = -pH + 11.3 (Eq. 3.2.2).

In addition, a second equation for pH of the ice core samples can be generated as:

pH = -login ([Sum-Anions|-[Sum-Cations|+(HC03 |) (Eq. 3.2.3).

where the Sums arc the total peq/1 amounts of the five anion and cation species that were either directly

measured or estimated, respectively. The two equations and two unknowns (pH and pHCOi'. effectively)

can then be solved simultaneously to locate a single value of pH that satisfies both expressions, taking into

account that pHC03' = -logio [HC03'|. The general assumptions that are inherent in this method arc: I)

the aqueous [HC03 | is in equilibrium with the atmosphere for the solution pH (without any need to

specify its source). 2) the undetermined minor constituents are cither negligible (H;POr, HCOO'.

CH3COO ) or invariant (F . MSA"), and 3) that the net anion surplus is countered exactly by the [H*|. i.e.,

the solution pH. For GB97C1. the mean [H C 03 | was estimated to be approximately 1.7 ^cq/1 (-100 ppb).

As expected. pH values average ~5.5. resulting from an average (SumAnions-SumCations) difference of

3.0-3.5 fieq/1 in the core overall. Direct measurements on mcltwater with a pH electrode yielded slightly

lower values (~5.2), assumed to be due to a greater CO? concentration in the enclosed environment, and

also an unacceptably large measurement drift and lack of reproducibility. For this reason, a record of

direct pH measurements was not pursued.

In many climate studies, differentiation of soluble ice core constituents by source is desirable for

interpreting variations of the individual ions. In particular, determining the portion from sea-salt aerosol

is beneficial for detection of mineral dust input, volcanic eruptions, marine biological activity, and recent

anthropogenic influences. These non-sea-salt (nss) contributions are determined as deviations from a

reference ion considered to have no other appreciable source, preferably Na* or Mg2*, though Cl’ is often

used when cation concentrations are not available. For detection of volcanic signatures in GB97C1. Cl'

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. was used as the reference ion for nss-SCV determination because cations were only determined for the 1-

m integrated samples. (Although volcanic eruptions also produce HC1, this acid species normally docs not

persist in the environment long enough to be distributed globally; Legrand and Delmas. 1988.) For the

core as a whole, nss-fractions of all species were calculated using the sodium measurements that were

determined from the identical samples. While magnesium has been shown to be the superior reference

ion in marine aerosols (Keene et al., 1986), examination of the Mg2' record for GB97C1 indicated

meltwater influences that placed doubt in this ion as a conservative species in the core. The bulk sea-salt

composition used was that of Wilson (1975), which determined the equivalcnt-ratio scries (from most- to

least-abundant) of the ions (Cf : Na' : Mg'* : SOr : Ca"* : K ) as (1.16 : I : 0.227 : 0.121 : 0.0439 :

0.0218). The nss-fraction C(nss) of any ion, C, is determined by comparison to reference ion, R, by

C(nss) = C,pi - (CJW/R,w) * R,Pi (Eq. 3.2.4),

where the subscripts 'sw' and 'spl' indicate concentrations in bulk sca-water and the sample, respectively.

All concentration values are given in neq/1.

3.2.2 Stable isotope and microparticle analysis

As previously mentioned, sample backlogs from other ice core work led to delays in completing

the detailed 6uO profile from GB97C1. Also, the acquisition of two Finnigan Mat DcltaS+ mass

spectrometers in 1999 meant that measurements were made on separate instruments and with varying

storage time in the freezer. However, again it was possible to gauge any potential biasing effects by

comparing the initial survey profile of 330 bottled samples prepared in the field (measured solely on the

older Finnigan Mat DellaE instrument) with an analogous record produced from the fine sampling. The

comparison of these two records is shown in Fig. 3.9 and indicates very little instrument/procedural bias

was present in the survey data. A discrepancy exists over the top 60 m of the core, where on average a

slight enrichment is apparent for those samples prepared in the field. Because this portion of the core was

physically warmer and comprised of more porous material, it can be surmised that the bottled samples

were subject to a small amount of sublimation during field preparation, accounting for the difference.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Bottled samples Detailed core samples

Fig. 3.9 Comparison of oxygen isotope measurements made on bottled survey samples vs. averages from the detailed analysis over the respective depth ranges.

Also, because the detailed 5l!lO measurements were done non-sequentially (28-100 m completed before 1-

28 m). instrumental bias was not suggested. Deeper in the core at 200-225 m. averages of the detailed

samples were slightly enriched (by ~0.3°/6o) relative to the corresponding bottled samples, for reasons as

yet undetermined. A future project designed to assess deuterium excess in GB97C1 is planned that will

incorporate this section of ice specifically to reconcile the minor differences in this section. At present, it

has been assumed that the lab-prepared ice samples yield the superior record in this region of core.

The two different Coulter Counter models (the TA-II and the Multisizer II) used to analyze

GB97C1. when fitted with 30 pm apertures, provide data on microparticle concentration over the same

series of 14 size ranges, from 0.63 up to 16 pm. Summary data products on microparticle concentration

most commonly used are the "total small fraction" (all counts from 0.63 to 16 pm), and the "total large

fraction" (all counts from 2.0 to 16 pm). Because the larger channels (above 2 pm) generally contain very'

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. few particles relative to the smallest channels, the all-inclusive summary reflects mainly the smallest

particle ranges. Samples from GB97CI were not analyzed with counters outfitted with 100 p.m apertures

for detecting the very largest fractions of dust.

Due to simultaneous ice core processing for other projects in the BPRC laboratories during the

analysis phase of the Windy Dome program, once the IC analysis accelerated to a 2m-pcr day rate, dust

analysis of every other meter of core was commonly delayed until a later date. When the microparticle

measurements were then later completed, the remaining stored samples were analyzed solely on the

Multisizcr II device, whereas much of the core was earlier analyzed by the TA-1I. Considering the core as

a whole. 186 meters of GB97C1 were analyzed on the TA-II with the remaining 129 meters run on the

Multisizer U. Over one particular section of core (Tubes 119-198). fortuitously located in the heart of the

Little Ice Age (-1600-1800 A.D.) when dust concentrations varied little, analyses were done on the

respective devices in a roughly alternating pattern. From this circumstance, it was determined that a

machine-bias of 21% (small fraction) was seen between the two models, with the Multisizcr II reporting

lower concentrations. For this reason, it was deemed appropriate to augment all Multisizcr II

measurements of dust concentration in this size range by this same amount, as was done for the profile in

Fig. 6.9.

Size distribution information can be condensed into a single variable termed "average grain size"

(AGS) calculated from a ratio of two intermediate summary data products. This procedure was adopted

from the Method of Moments described by Folk (1974) for application in sedimentary petrology involving

bulk dry sediment samples. In this revised technique, the instrument channels are used in place of the

screening pans, and diameters are given in pm rather than the classic 'phi' (4>) scale. The total volume of

particles in each channel (size range) /. TotW. is determined by:

TotV; = V; * Ci (Eq. 3.2.5).

where V/ is the midpoint volume (assuming spherical shape) of each channel fraction (0.191 nm3. 0.382

p.m3 , 1547 fim3) and C/ is the respective measured particle counts for any given ice-meltwater

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sample. The product. Pi. is then calculated for each sample by multiplying the total volume of particles

within a given channel by its mean diameter, as:

Pi = TotV; * D/ (Eq. 3.2.6),

where D/' represents the midpoint diameters of the 13 size ranges (0.63-0.80 pm, 0.80-1.0 pm 10.08-

12.7 pm). The average grain size (AGS) is then said to be represented by the sum of the products P»

divided by the sum of the channel volumes V/. as:

AGS = (2 Pi) / (I V/) (Eq. 3.2.7).

If climatically sensitive. AGS can yield information about the provenance of dust in an ice core and the

distance of travel prior to deposition.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 4

TIME SCALE DEVELOPMENT AND ACCUMULATION RECONSTRUCTION

4.1 Time scale development

4.1.1 Blanket statement of dating rationale

From the outset of this research program, age-dating of the Graham Bell ice cores was

intentionally over-ambitious, in order to maximize the potential for gaining insight into the effects of

percolation zone processes on the detailed stratigraphic record. In addition, expertise important for future

ice drilling efforts in the Eurasian Arctic region, perhaps in even more challenging locations, has now

been gained through this laborious process. It is certain that some age-dated episodic features in GB97C1

were discovered only because of the 3-cm sampling resolution, and that these will be utilized as cross-

matching time horizons for other palcoclimate records in the region. However, given the documented

decadal-scale alteration within the active snowpack surface on Windy Dome (during at least most periods

of the last millennium), the final interpretation of many core records will necessarily be later readdressed

over coarser time windows. Hence, the operation of dating the core proceeded with the most ambitious

intentions, and in future chapters the data will be presented with a more prudent approach, in essence

"backing off' to discuss the record as it is actually expressed in the physical archive.

4.1.2 The annual signal preserved in the Windy Dome ice cores

During the 1997 field season, two snow pits were excavated near the Windy Dome summit drill

site, one before the main drilling began (designated Pit 1), and one after drilling concluded (Pit 6). The

basal depths of the two pits (1.4S and 1.68 m, respectively) were limited by the hard icv-fim layer that

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. represented the previous summer melt season. Samples from the pit wall were collected and bagged

individually, and transported in a frozen state along with the cores. Analysis of major anions,

microparticles, and SlilO was completed at BPRC on all 47 pit samples (27 from Pit 1, 20 from Pit 6). and

the results for Pit 6 are shown in Fig. 4.1a. (Results from Pit 1 were similar and the pit sampling,

although finer, also contained several gaps and hence Pit 6 was the superior record.) In both pits, the

highest values of Cl' concentration occur just below the surface, likely representing recent snow

accumulation from February or early March, 1997. Conversely, the highest 6l!tO values occur at -0.9 m

depth, coincident with the initial rise in chloride levels from very low values. Large fluctuations arc seen

within the winter season (0-0.7 m) even though generally the 6ihO values remain more depleted,

indicating that a strong seasonality in the isotopic profile may not always be recognized even in the

unaltered surface snow/fim layer, as also found in Svalbard (Igarashi et al.. 2001).

As previously shown for GB94C1 (Section 2.2). credible layer counting was possible utilizing

regular oscillations in chloride concentration, at least for the uppermost 15 m. At the time, the lack of a

definitive beta-radioaclivity horizon precluded confirmation of the layer-counting for earlier decades.

Based on the finer resolution for GB97C1 and the addition of both high-resolution density measurements

and tritium concentrations (as an additional tool for detecting the 1963-64 nuclear test horizon: Crozaz et

al.. 1966). the original GB94C1 layer-counting (Thompson et al.. 1995) was shown to be inaccurate

below 1980. The revised dating scale, cross-matched from the GB97C1 results, is shown in Fig. 4.2. For

the 1997 core, it was only upon examination of isotopic and stratigraphic profiles from the Little Ice Age

section that it was recognized that these parameters might provide additional dating information

throughout. In the end. it became apparent that a weak, though persistent, annual signature did exist in

the isotopic record even in the upper section of core (Fig. 4.2. middle). For this reason, an iteratively-

reconciled age scale was constructed using all three seasonally-varying parameters guided by definitive

time horizons. In the upper 25 m. the individual density measurements completed on IC samples (as

shown in Fig. 4.2. top) provided the annual counting that was continued to the bottom using the melt

percent estimates. The general inverse phase relationship between chloride and 8lsO seen in the pits

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cl'(ppm) 5,80 (%o) cr (Dpm) Total Particles >0.63 pm 5 ' 80 (% o) r ’ (per ml) (x1 O’) 0 2 4 6 -20 -15 -10 -5 0 1 2 3 4 0 20 40 60 -24 -20 -16 0 0 I 1--1-- 1—I--1—L.

I I Wiwinter 0.5

c 99.5-

.Cl 1.0 100.0 summer f o> O

100.5

1.5- winter 101.0 Graham Bell (FJL) Graham Bell (FJL) Pit 6 (April, 1997) Core 1 (1997)

2.0 101.5 3 1832

Fig. 4 .1 a. Profiles or chloride and 8 u O from a 1997 snowpit representing the past year’s accumulation, before alteration by seasonal melting/percolation, and b. Profiles of chloride, dust, and 6 180 from a 3-m section of tlic deep core, from a particularly low-melt, well-preserved portion of the core. Annual layers arc easily discernible in Cf and fi|B0. et m 19 o -1994 (m) Depth Cl' (ppm) 5180 (%0) Density (g cm*3) Fig. 4.2 Chloride, 6lH0 , and density profiles for upper portion of Graham Bell (FJL) 1997 ice core, compared with the 1994 Cl' record 1994Cl' the with compared ice core, 1997 (FJL) Bell Graham of portion upper for profiles density and 6lH0 , Chloride, 4.2 Fig. (below). Tritium-adjusted three-parameter reconciliation age dating as indicated. Darker lines arc smoothed, 5SRM (1 5SRM -3-4-3-1). smoothed, arc lines Darker indicated. as dating age reconciliation three-parameter Tritium-adjusted (below). 2

4 a 6 years removedyearsfor tritium correction 10

16 ie ie 20

26 continues throughout the ice core, even though some misalignment of related peaks and troughs is evident

(Fig. 4.2). The isotopic profile also illustrates that the interannual variability’ is at least as large as the

annual signal, suggesting that the weakly-recorded primary signature (as in Pit 6) is further influenced by

post-depositional effects.

The indication of an opposite phase relationship between anion concentrations (particularly Cl )

and 61!lO strongly suggests that the availability of open water near Graham Bell Island during the late

summer season is not an important factor in regulating the scasalt component of Windy Dome snowfall on

an annual basis. The inherent stability of the surface inversion layer over the Arctic (witnessed in the

form of persistent banks of stratiform cloud cover over the FJL archipelago in May. 1994) apparently docs

not allow locally-derived scasalt aerosol to be incorporated into snowfall over the higher domes. This

finding verifies that the dominant mechanism of aerosol regulation in FJL is related to residence times,

just as exists in most parts of the Arctic that arc not subject to local sea ice variations of this magnitude,

such as central Greenland (Davidson, et al.. 1987) and the Canadian Archipelago (Barrie. 1986).

Following widespread sampling of atmospheric aerosols during the year 1983 to study the "Arctic Haze"

phenomenon (Schncll. 1984), an understanding of the process of aerosol cntrainment and removal was

developed. Davidson (1989) determined that the low humidity of the wintertime air over Greenland led to

scavaging ratios that were less than half of those during the Arctic summer. While this phenomenon leads

to a summertime increase of Cl* sequestering in snowfall relative to the atmospheric aerosol from which it

was derived, this circumstance also determines that ionic species have a much shorter residence time in

the atmosphere during the summer given that they arc more effectively removed (through riming) during

transport at levels above the zone of continual recharge from below. In the recent past, the pollution

component to the aerosol budget of the far northern latitudes has led to an additional seasonal influence

on atmospheric concentrations of N 03* and SO f supported by strong meridional circulation (Heitzenberg

and Leek. 1994). Although enhanced wintertime transport of these aerosols from northern Europe may

explain results from current seasonal studies, it is apparent from the long Graham Bell ice core record that

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the seasonality of aerosol concentrations was not significantly altered by recent input of pollution

elements.

Over the length of GB97CI, the respective annual signals in chloride. 5lsO, and melt percent

vary in strength, almost certainly due mainly to post-dcpositional processes of mcltwater formation,

percolation, and refreezing. Annual signatures in microparticles, nitrate, and sulfate are either weak or

nonexistent, and were not utilized for limescale development via layer-counting. Whereas the inverse

relationship between chloride and 5lxO could be anticipated given the 'residence time' mechanism outlined

above, the position of meltwater-ice layers in relation to these geochemical species is less certain.

Undoubtedly, near-surface meltwatcr forms only in the mid- to late-summertimc on the Windy Dome

summit, inferred from typical conditions at nearby Ostrov Vizc when nearly all surrounding sea ice is

removed and sea level air temperatures arc fixed at near ()°C (Fig. 4.3). However, the depths at which the

melt forms in the snowpack. and to what depth the downward percolation ceases each consecutive summer

season, is difficult to establish. By comparing the 1994 and 1997 stratigraphic profiles, it was observed

that a continuous ice layer that existed at approximately 4.0-4.5 m depth in GB94C1/2 grew in thickness

from -40 to -60 cm in the intervening three years. Additionally, it can be seen in the comparison of

chloride profiles from GB94C1 and GB97C1 (Fig. 4.2) that while close agreement exists in the deeper

layers, the concentrations were altered drastically in the upper 6 m of fim due to infiltration from above.

A comparison of annual averages from both cores (Fig. 4.4) indicates that only the anion records

(represented here by Cl' alone) were severely affected by the penetration of meltwater from above, as

indicated by the elevated melt percentages in the zone representing accumulation between 1989 and 1994.

Lesser effects of percolation on the dust record (reduced concentrations) and lED-layer thicknesses (net

increase) can also be seen within the upper seven years of accumulation. Inspection of real-time records

of conditions in the Barents Sea region (Parkinson et al.. 1999) suggests that the epsiode of high

melt/percolation probably occurred in the late summer of 1995 when conditions were anomalously ice-

free. thereby yielding effective current percolation depth of -7 m (-8 years). This result agrees well with

the value of 2-6 m (3-10 years) reported by Tarussov (1992) for Svalbard and Severnaya Zemlya glaciers.

Fig. 4.3 Daily temperatures (solid line) at Ostrov Vize (79°30'N, 76°50'E) for 1994. compared compared 1994. for 76°50'E) (79°30'N, Vize Ostrov at line) (solid temperatures Daily 4.3 Fig. Sea ice area along bent 'diagonal' (175,213)-190-(220,243) (103 km2) the SSM/I polar stereographic grid (cells 25 x 25 km): 100% SIC=28,800 km*. SIC=28,800 100% in km): 25 x (220.243) 25 to (cells grid (190.213) diagonal stereographic the polar along SSM/I SW the continuing then and (190,213), to the area of sea ice coverage (dots) along the NE-SW transect from (175,213)- (175,213)- from transect NE-SW the along (dots) coverage ice sea of area the to 1994 51 I * .Vz e peratures Tem Vize O. Area Ice Sea V . t f 0) Q. ° > X a z -40 -

Temperature (°C) -14

-16 -

oo'

__ - 2 0 - 2 100 - OOO' ® 80 - fc >P 3 L 60 - . (I) ^ 5 40 - co oo § 20 -

o 3 - CO T -

0.0 GB97C1 GB94C1

2 -

P o

2000 1990 1980 1970 1960 1950 Year (A.D.)

Fig. 4.4 Comparison of annually-averaged ice core parameters from GB94C1 and GB97CI for the entire period of overlap (1960-1994).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. _ 120 - tn 5 O vs. Chloride 5180 (neg.) peak leads Chloride peak (when +) $ 100 -

i 80 - dc 60 - § 40 - o O 2 0 -

u Q . 12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 Lead / Lag (# samples)

_ 120 Chloride vs. Melt % Chloride peak leads 1 100 Melt % peak (when +) *5 80 1 60 § 40 o O 2 0

0 U Q n -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 Lead / Lag (# samples)

_ 120 510O v s . Melt % 51sO (neg.) peak leads I 100 Melt % peak (when +) *5 80

I . 6 0 § 40 o ° 20

0 D D -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 Lead / Lag (# samples)

Fig. 4.5 Distribution of offset (in terms of number of samples) between identified annual peaks in each of the three datable parameters for GB97C1 (772 years). 53

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Although the formation and growth of melt layers is complex and must involve a multi-year

evolutionary process, on average the bubble-free layers occur with greatest frequency in conjunction with

the peak Cl' levels and minimum 6lt(0 values (Fig. 4.5). suspected to be the late winter months of

February and March. Because grain sizes in fim are known to vary with temperature during snow

formation (Sommerfeld and LaChapclle, 1970; Colbeck. 1982). it is apparent that the tightly-packed

wintertime fim layers are more likely to capture and retain percolating meltwater. This same process is

likely a key factor in generating the seasonal signal in the anion record because chloride ions arc

moderately mobile in the presence of liquid water, especially when the amount of snowmclt surpasses

levels of 10-20% of an annual layer (equivalent to 20-40% melt in core; Tarussov, 1992). Hence, it can be

assumed that the annual signature in Cl' that remains weak, yet visible, throughout the 315 m core is

actually a by-product (and thereby a "secondary" feature) of the preferential rcfrcczing of meltwater in

wintertime layers. It must then be considered at least partly coincidental that the pit data indicate that the

original anion values arc also highest in the (late) wintertime. Furthermore, it can thereby be suggested

that the melt influence may veiy well be responsible for the overall synchroncity of the three annually-

varying parameters (as seen in Fig. 4.5). The secondary nature of the annual signature in Cl' also means

that the peak values in any given year almost certainly do not reflect environmental conditions in that

same calendar year, but rather represent an integration of conditions over a period of several years, and

perhaps as long as a decade during the periods with the warmest summers.

In Fig. 4.6. deterioration of the annual signal (years indicated by small triangles) in each

parameter is seen moving from right to left, representing zones of GB97C1 with an average of 20%. 50%.

80% meltwater ice. respectively. To illustrate potential changes in layer-counting ability' among the three

climate phases, Fig. 4.6 also includes one set of three age-dated sections for each time period, oriented

top-to-bottom. By comparison, it can be seen that confident layer counting is hindered when melt layers

coalesce into multi-annual zones of superimposed ice. as depicted by the '80% ice' zones that fortunately

occur only infrequently in the Graham Bell ice core (six or eight episodes as viewable in Fig. 3.2). In

addition to the "clipping" of the melt record along the 100% boundary, isotopic variability is noticeably

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80% Melt 50% Melt 20% Melt -12 -12 £ -16 O -20 7jC -24 100 - 100 100 - p 8 0 -

£ 40 - £ 40 20 -

2 -

r r j m w | r t » i f i i i i | i m r | II I I | M I I [ I fWVrf, 55 56 57 58 59 60 69 70 71 72 73 100 101 102 103 104 105

2 -16 S -16

-20 O -20 “ VC -24 - 1 > 14 c -24 -

100 100 - P 80 4 4 60 - 60 - £ 40

20 - 20 -

*m | i i i i | i ii i f n n [ Ft i »]t p 154 155 156 157 158 159 172 173 174 175 176 136 137 138 139 140

£ -16

100 - p 80

£ 40 -

Fig. 4.6 Annual signal in GB97C1 as a function of melt % (as indicated) for separate 5-m intervals during 19th-20th century (top), Little Ice Age (middle), and Medieval Warm Period (bottom). 55

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. diminished. The chloride record, already established to be generated by a secondary process, seems less

affected by increasing meltwater infiltration although the regularity of peaks is often superior in unusually

low-melt zones (e.g.. in the 261-266 m zone and at 98.5-101.5 m as seen previously in Fig. 4.1b).

Application of the melt stratigraphy for dating may actually be most effective in the -50% range where

maximum variability between high and low melt exists. In very low melt regions, ambiguity from thick

generally melt-free zones is possible, essentially subject again to ''clipping1' on the low side. Although

Fig. 4.6 reveals the great difficulty in elucidating individual years in each record, it also illustrates the

power in the iterative cross-correlation approach that has eliminated those isolated oscillations in one

profile not supported by the others. The numerous time horizons provided by the high-rcsolution

sampling regulated the sensitivity of the layer determination, i.e.. determining the degree to which minor

peaks and valleys were ignored in the final counting.

4.1.3 Final time scale determination

The age dating of the Graham Bell deep ice core was meticulously accomplished via the multi-

parameter annual layer determination, using the chloride. 5I!,0. and melt percent records to cross-check

the counting. Only on rare occasions (such as the prolonged cold period of the 1830s (Fig. 4.1b) when

meltwater percolation was limited) did minimum Cf values appear to have been largely undisturbed. Not

surprisingly, this period also exhibited unusually strong and well-preserved oscillations in <5uO. Because

these Cf maxima are perfectly aligned with the isotope minima, it again reinforces the notion that anion

concentrations are highest in winter snowfall even before the melt influence. The anomalously low

summertime levels (-5-10 ppb) of Cl' seen in the 1830s are indeed very unusual when compared to the

core as a whole. Whereas low values (and strong primary seasonality) may commonly persist through

several "cool" summers, it is only when an extended period of limited summertime melting occurs that

these layers can remain free from influence long enough to be permanently archived in an unaltered stale.

As an example, the extremely low C f values that were present in GB94C1 (Fig. 4.2) at 4.6-5.8 m depth

(1988-89) were eventually "erased” by infiltration from above, presumably (as suggested above) during the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. late summer months of 1995, a full seven years later. Throughout most of the core, dust peaks are

episodic and more random (as in Fig. 4.2b), though still generally related to the ice stratigraphy.

Therefore, particle counts do not provide a means for confirming the dating. Several unusual orange-

brown dust layers appear in the ice core (discussed in Section 6.5). though insoluble particles are

generally few and even the more concentrated layers usually remain invisible to the naked eye.

The GB97C1 dating for the recent past (last 50 years) is sufficiently reliable, given very regular

peaks in Cf back to 1980. and the identification of the well-known nuclear test horizon of 1963-64

(mainly from testing by the Soviet Union in the Arctic during 1961-62) in the tritium (3H) profile shown

in Fig. 4.7. Tritium was determined by liquid scintillation counting (Oeschgcr et al., 1979; Schottcrer. et

al.. 1977) on water samples combined from aliquots leftover from the 1C analysis. Total p-radioactivity

was determined at BPRC by the author from separate samples (see Fig. 3.6) using a Tennelcc LB-loot)

Series low-level beta counter following ion-cxhange filtration (Pinglot and Pourchet. 1979). The

analogous profile (Fig. 4.7b) of total P-radioactivity (including both 90Sr and 13 Cs fallout) shows a sharp

peak of unprecedented magnitude at 29.5 m depth, or approximately six years earlier than the tritium

event. This finding indicates the degree to which the radioactive material (apparently migrating in

conjunction with soluble anions, as inferred from the remarkable similarity of the two records. Fig. 4.7b

and c) must have travelled vertically in the fim layer. Limited beta measurements on GB97C2 (Fig. 4.7b

inset) also denoted the strong event at a similar depth (stratigraphically equivalent), although the peak

magnitude here was far less even with the finer sampling. Hence, it must be concluded that the

concentration of radioactive material in this layer (which is seen to lie exactly at a major stratigraphic

boundary) is highly variable and the extreme value seen in GB97C1 should not be taken to reflect the true

amount of fallout during deposition. This "trapping" effect by sharp stratigraphic boundaries between

major coherent ice/bubbly ice layers is a feature that is seen throughout the ice core for multiple

parameters.

Identification of the tritium horizon in both 1997 cores presented the opportunity' of calibrating

the initial GB97C1 layer-counting by chloride and density/melt. Because the original counting placed the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Depth (m) -1994 GrahamBell (FJL) Fig. 4.7 Depth-based profiles of beta-radioactivity for GB94CI (left) and GB97CI (right), compared also withGB97C1 compared also (right), and GB97CI (left) beta-radioactivityforprofilesGB94CI of Depth-based 4.7 Fig. 25 20 15 10 Total p-radioactivity p-radioactivity Total 1994 Core1 0 200 400 600 400 200 0 chloride and chloride tritium records. (dis/hr/kg) Z Q £ o> O) h-

tritium peak in the year 1960, it was determined that two identified annual peaks (those Cl' peaks marked

by asterisks in Fig. 4.2) should no longer be counted, as these events were small and not supported

strongly by the other records. Hence, in Fig. 4.8, which compares the radionuclide profiles from Graham

Bell with real-time measurements of tritium in precipitation (IAEA. 1969). the tritium peak is situated at

-1962, only 1-2 years earlier than what would be expected in unaltered snow. Because the peak values in

GB97C1 are muted (i.e., 500 T.U. as compared to expected peak values of 700-800 T.U.). this minor

temporal offset may not be incompatible given the nature of the vertically-percolating mcltwatcr.

However, while trace elements can potentially be subject to enhanced migration, it is not likely that the ice

exhibiting elevated tritium (incorporated as part of the water molecule) could have effectively descended

more than a small distance relative to ice showing background levels, and therefore 1-2 years of lead time

was deemed compliant.

Evidence for limited percolation effects on the tritium record exists also in the region just below

the major reference horizon, i.e.. the 1958-59 secondary maximum from "pre-moratorium" U.S. testing in

the Pacific (Carter and Moghissi, 1977). This event appears in the IAEA Ottawa record shown, as well as

in many Greenland ice cores (Koide and Goldberg. 1985; Mosley-Thompson et al.. 2001). The nature of

the GB97C1 profile suggests that a large enough fraction of the snow accumulation from the peak tritium

years (either 1958-59 or 1963-64. or both) was mobilized downward to the same layer displaying high

concentrations of both chloride and beta-emitting fallout, to create this additional peak in the profile that

does not correspond to an actual atmospheric signal. Elsewhere, smaller horizons at both the initial onset

of large-scale testing (in 1952) and a 1972 response from either French testing in Polynesia or Chinese

tests at Lop Nor (40°N, 90°E) (Koide and Goldberg. 1985) that is recorded in Svalbard (but not Ottawa)

appear less influenced by percolation. Their stratigraphic positions indicated that the adjusted layer-

counting did not contain any errors of >2 years, and so no further dating adjustments were made.

Signatures of known volcanic eruptions, whether identified through preserved tephra or acid-

sulfate deposition, are invaluable tools for calibrating ice core histories (Hammer. 1980; Bradley and

Jones. 1992) and despite complications from high background sea-salt sulfate and percolation effects.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

Decay- Corrected (78°N, (78°N, 15°E) to July, to July, 1998 Isfjord, Svalbard

Decay- Corrected to July, to 1998 July, (45°N, 76°W) Ottawa, Ottawa, Canada

^ 6 3 ^ 6 4 ) '57('S&-'5Q) ierc. £®rc? ''}'61-'62 GB97C1 GB97C1 dates 1997 Core 1997 1 Graham Graham Bell (reference dates) *53 (’52) 1st rise 1st (’52) *53 0 200 400 600 0 200 400 600 800 0 200 400 600 800

800

400

0 1997 Core 1997 1 Graham Bell Graham “ Sr & 137Cs and 3H in Graham Bell (FJL) ice cores cores ice (FJL) Bell Graham in 3H and data) (IAEA precipitation in Tritium (decay-corrected to time ofthe ice core measurements) front two IAEA northern hemisphere sites. p 0 0 2000 4000 6000

Total p-radioactivity (dis/hr/kg) (dis/hr/kg) p-radioactivity Total (T.U.) 3H (T.U.) 3H (T.U.) 3H Fig. 4.K Fig. 4.K Time-based profiles ofbcta-radioactivity and tritium from Graham Bell ice cores, compared to near real-time tritium records 1995 1985 1990 1970 1965 1980 1960 1955 1950 2000 »

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. were detectable in Windy Dome ice. The dramatic 1783 fissure eruption of the Lakagigar (aka Laki)

volcanic district in Iceland (Bcminghausen. 1964; Thorarinsson. 1969; Thordarson et al., 1996) is a well-

documented event in ice cores from numerous sites in Greenland (Hammer. 1984; Zielinski, et al.. 1994).

A very strong signal in acidic S04: from this eruption was identified at a depth of 123.1 meters in

GB97C1 that yielded a firm timc-scalc origin for dating the lower majority of the record. As indicated in

Section 3.2.1. individual samples from the Laki event were bottled and refrozen for later cation analysis.

As shown in Fig. 4.9 (central values given in Table 4.1). S04:' alone is present in elevated quantities and

pH calculations of each sample yielded a minimum value of 3.7. confirming the high acidity of the event.

Even for large eruptions (VEI of 6 and above) that involved intense stratospheric charging of sulfuric

acid, the residence time for this aerosol is usually only about two years. Hence, it is unusual that the Laki

event (a VEI-4 fissure eruption) produces a signature of elevated sulfuric acid levels in the form of three

individual maxima over at least two years in the GB97C1 record (Fig. 4.9). However, it should be noted

that 10 individual eruptions occurred along the 17-milc fissure over a five month period between June and

November. 1783. Yet because over 60% of the total volume of ejecta was released in the first 1.5 months

(Thordarson et al.. 1996). and because Greenland ice cores generally reveal one uniform acid-sulfatc peak

(Hammer. 1984; Moslev-Thompson et al.. 2001). the GB97C1 Laki signature was considered to be

unusual.

It might have been assumed that any percolation that occurred in the years following the Laki

eruption would have tended to move material downward and perhaps create a "trailing off effect towards

deeper ice. However, the apparently abrupt onset of S04: from a flat baseline to extraordinarily high

levels (-10 ppm) suggests instead that the anions had truly been mobilized to some extent, but then very'

distinctly rcdeposited at the base of a thick bubble-free ice layer acting, as described above, as a

stratigraphic "trap" for migrating sulfate ions. In fact, a pair of chloride peaks coexisting with the low er

two Laki sulfate maxima, counted originally as two separate years, were reconsidered to represent only

one accumulation year based on the lack of support from isotopic and stratigraphic evidence. Hence, it

has been assumed that the peak has migrated one year from its original position in the year 1783 (at

Cl- (ppm) nss-SOf (ppm) 8'8° <%°) 0.8 Fig. 4.9 GB97C1 data for 124.3 - 125.5 m pertinent to the Laki 1783 eruption. Years shown shown Years eruption. 1783 Laki the to pertinent m 125.5 - 124.3 for data GB97C1 4.9 Fig. - determined jointly by stable isotopes, chloride, and melt layers, and were adjusted adjusted were and layers, melt and chloride, isotopes, stable by jointly determined as shown. as slightly to place the largest sulfate between the March 1782 and March 1783 horizons, horizons, 1783 March and 1782 March the between sulfate largest the place to slightly 2. 124.6 124.4 Melt Stratigraphy: Solid (Meltwater-lce), Stippled (Bubbly Ice) (Bubbly Stippled (Meltwater-lce), Solid ' K S a n n J B a & M GB97C1 Depth (m) Depth GB97C1

2. 125.0 124.8 mm 62 125.2 too small to view to small too background values values background 125.4 Top Depth Melt Cl n o 3 SO,: Na" N K f K" Mg:* Ca:* Calc. in Core (m): Percent: (ppb): (ppb): (ppb): (ppb): (ppb): (ppb): (ppb): (ppb): pH. 124.964 100 173.4 29.9 230 112.1 62.1 5.8 16.7 17.8 5.71 124.996 100 247.5 32.9 314 133.1 50.9 4.7 18.0 23.4 5.40 125.028 100 689.7 67.3 1271 346.5 40.4 15.7 57.0 50.9 4.65 125.060 100 645.5 86.8 3051 229.5 37.2 8.0 35.6 41.3 4.18 125.092 100 745.1 134.9 9703 180.6 76.7 9.6 34.1 44.3 3.68 125.124 30 107.0 58.9 7935 108.1 62.1 9.2 15.2 31.1 3.80 125.155 0 96.6 38.4 5091 164.5 51.0 10.3 22.3 51.2 4.02 125.186 0 112.5 36.5 1095 83.2 31.7 4.0 48.7 16.6 4.78 125.217 40 120.1 28.0 39.6 46.8 48.3 2.2 8.9 15.9 5.81

Tabic 4.1 GB97CI Laki eruption results.

124.55 m) to 1782 due to percolation, it is recognized that the entire zone of enhanced acid-sulfaic front

Laki may have migrated downward more than this single year, but there remains no direct evidence of any

potentially enhanced sinking. Also, the counting of years between 1783 and other nearby volcanic

horizons both above and below appears quite robust in this particularly cold and well-preserved interval.

Additional volcanic signatures recognized both from major eruptions in the tropics, as well as

smaller eruptions in the high northern latitudes (e.g.. Iceland), further refined the layer-counted age scale

and imparted high confidence in the continuity of the ice archive and the accuracy of the dating. In some

cases, eruptions were detected primarily by unusually-strong wintertime isotopic depletion (producing

among the lowest 5,!(0 values in the entire core), as was the case for both 1835 (Coseguina) and 1815

(Tambora). Because these eruptions follow'ed the Laki event by merely a few decades and took place

during the coldest (best preservation) period, high probability of correct identification was inferred. Given

that the strong isotopic depletions exhibited in GB97C1 ice appear to occur during the wintertime, this

finding supports the argument of Kodera (1994) that stratospheric processes can create tropospheric

cooling from volcanic aerosols even during polar night (consider also Kelly et al., 1984).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. More often, volcanic eruptions were detectable via unusuallv-high sulfate amounts not mirrored

by other species, particularly chloride. Accordingly, potential eruption signatures were generally

identified in the non-seasalt (nss) SO.!2 profile, employing the chloride values to exclude the scasalt

component of sulfate given the known abundances of the two anions in ocean water (Broccker and Peng.

1982). The S042', nss-S042'. and 6lB0 profiles, excerpted from the complete GB97C1 record across 2-m

intervals surrounding each identified eruption, are shown in Fig. 4.10. Because of differential migration

of ions during meltwatcr percolation, the relative positions of peaks of chloride and sulfate can change

significantly and lead to negative nss-S042' values in many cases. Most notably, an apparent elevated

sulfate level following the Coseguina eruption actually results in a strongly negative anomaly in the nss-

componenl. Here, it appears that unusually-fine firn grains that would have formed in the cold winter

following the large eruption created a particularly effective stratigraphic trap that captured enormous

quantities of migrating chloride ions (see Fig. 4.1: peak concentration - 10.6 ppm) in addition to the

elevated sulfate, making any identification of a true acid-sulfatc anomaly impossible. Also hindering

attempts to identify Icelandic eruptions by calculated pH was the lack of fluoride measurements, a species

which may have been responsible (as HF) for significant portions of the total acidity (DeAngclis and

Legrand. 1994).

Other eruptions (Simkin et al., 1981) identified with differing degrees of confidence included

1883 (Krakatau). 1755 (Katla), 1730-36 (Lanzarote). 1600 (Huaynaputina). 1362 (Oraefajokull). and

1259 (unknown, perhaps El Chichon: Tilling et al., 1984: Palais et al.. 1992). Of these, only the potential

Huaynaputina event was not noted in the process of sampling and analyzing the core on a daily basis. As

can be seen from the comparison of S042 and nss-S042' records, the anomaly suggested to represent this

eruption is relatively small (in true concentration) compared to a zone of very high sulfate (but also

chloride) just below. Again, it might be deduced that the known large-scale cooling effect of this eruption

(deSilva and Zielinski. 1998) created another strong ion trap (though no strong evidence is deduced from

the isotopic profile). Nevertheless, the identification of this eruption was not considered absolute, and

hence the dating was not altered to place the event at the expected time. 1601-02. In fact, high sulfate

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Krakatau (1883) Coseguina (1835) Tambora (1815)

: oo £ . f \ 80 j

P a a to - k V fl

O 0.5 - W b 00 0 . 0 - 0.0 e •0.5 -0.5 -0.5 1.5 -

1.0 - 0.5 - 1y ^ W n r ^ r nlV~^ 8 o.o 0.0 T | I I I I 72.5 73.0 73.5 74.0 74.5 99.0 99.5 100.0 100.5 101.0 109.0 109.5 110.0 110.5 111.0 Laki (1783) Katla (1755) Lanzarota (1733) to U)

8 I b o . o -

: E a Q. 1 o to 124.0 124.5 125.0 125.5 126.0 135.5 136.0 136.5 137.0 137.5 144.5 14S.0 145.5 146.0 146.5 Huaynaputina (1600) Oraefajokull (1362) Unknown (1258) -12 *<> <£. -16 P -20 To -24 J > a a a a a a o to (j> o.o H CO -0.5 •0.5

8 0.0 bJL, - hn-Vl I i i i t i 193.0 193.5 194.0 194.5 195.0 274.0 274.5 275.0 275.5 276.0 304.0 304.5 306.0 305.5 306.0 Depth (m) Depth (m) Depth (m)

Fig. 4.10 Graham Bell (FJL) Core 1 (1997) • Identification of nine volcanic horizons in 8u O and/or SO.,2*. Annual dating shown for S>aO by small triangles, determined by Cl* and melt records when necessary, e.g. MWP < 1450. ^

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. values from Greenland cores (deSilva and Zielinski, 1998) from this time period have also not been

absolutely tied to the VEI-6 eruption of Huaynaputina. but considered possibly due to input from other

smaller eruptions in the northern latitudes instead. Perhaps coincidentally, the layer-counting in the

G1SP2 core places the two-year nss-SO.f' anomaly in 1603-04, precisely matching the layer-counted date

of 1603 for the anomaly at 194.0 m in GB97C1. Similarly, an attempt to identify the large 1641 Ml.

Parker. Phillippines eruption (Delfin Jr. et al., 1997) was prevented by the existence of separate signatures

in each parameter at similar depths, i.e., a sharp l80-depletion at 178.5 m (1648-1649) vs. a minor sulfate

anomaly at 181.2 m (1640). Neither was considered to be indicative of Parker 1641 with any certainty.

The two eruptions identified in the lowest portion of the core (275-315 m) arc particularly

important for guiding the age-dating of GB97C1. which otherwise would be open-ended and greatly

uncertain. Conspicuous nss-SOf' anomalies at 275.1 m and 305.0 m were assigned to the Oraefajokull.

Iceland (VEI 6) eruption of 1362 (seen also in Greenland ice: Palais et al.. 1991) and the unknown

eruption of 1258 (historically unrecorded, but identified as tropical by way of ice core signatures from both

polar regions: Palais et al.. 1992). respectively. Of the 7.772 samples from GB97C1 (excluding the Laki

eruption) that were derived from the prc-1900 portion of the ice core (62.9 - 314.8 m). i.e.. before sulfate

values were heavily influenced by anthropogenic emissions, only 15 (or 0.2%) yielded nss-SOr

concentrations of more than 0.5 ppm. In fact, these two anomalies are the only two large events (nss-

S04: > 0.5 ppm) in the lowest 80 m of the core. Tentative layer-counting concurrent with IC analysis

suggested the higher event to be an Oraefajokull signal even before the lower horizon was reached, and

layer-counting in between the two easily conformed to a total of 103 years. Note that no significant delay

between eruptions in Iceland and GB97C1 response was expected (in contrast to low-latilude events), so

designated anomalies carry the same year designation as the eruptions themselves. Given this degree of

support from a comprehensive and well-spaced volcanic history, the accuracy of the three-parameter layer-

counted age scale (shown graphically, with horizons indicated, in Fig. 4.11) is suggested to be within the

time window over which the ice cap actually archives many of the signals, i.e.. the active percolation

window for anions estimated currently at 7 years.

Age (yrs. BP) 800 700 600 400 500 300 200 Fig. 4.11 Final layer-counted GB97C1 age/depth relationship, indicating location and dates dates and location indicating relationship, age/depth GB97C1 layer-counted Final 4.11 Fig. 0 0 1 0 of identified horizons. identified of Tritium1962 Tambora 1816 Tambora Krakatau 1884 Krakatau Katla 1755 Katla 100 1836 >*Coseguina Laki1782 67 Depth (m) Depth 150 Lanzarote 1733 Lanzarote Oraefajokull 1362 Oraefajokull 200 Huaynaputina 1603 Huaynaputina Unknown/ El Chichon? 1259 ElChichon? 250 300 Finalization of the GB97C1 timescale resulted from a reconciliation of the dated horizons with

the cumulative layer counting, which began with counting Cl' peaks, and later incorporated both melt

percent and 5180, when all data became available. Horizons considered to be established (with

reservations, as noted) arc listed in Table 4.2.

1980 - Confident layer-counting (18.0 m) 1962 - Tritium peak (27.0 m) 1884 - Krakatau (73.4m) 1836 - post-Coseguina cold event (99.9 m) 1816 - post-Tambora cold event (110.0 m) 1782 - Laki eruption (125.1 m) 1755 - Katla eruption (136.4 m)* 1733 - Lanzarotc eruptions (145.4 m)* 1603 - Huaynaputina eruption (194.0 m)** 1362 - Oraefajokull eruption (275.1 m) 1259 - Unknown (El Chichon?) eruption (305.0 m)

* The Katla (1755) and Lanzarote (1733) eruption signatures are given 'absolute' designation only because of the proximity to the Laki event, and reasonably high layer-counting confidence in between. Additionally, the Lanzarote eruption continued over several years and cannot be prescribed to a single year.

** Dating was not altered to fix Huaynaputina horizon at 1601-02 (as in Greenland) because association of the small nss-sulfatc anomaly at 194 m with that particular eruption seemed tenuous, and perhaps coincidental. Hence, the 1603 age is as determined by the best layer-counting possible from the GB97C1 core itself.

Table 4.2 List of horizons identified in the GB97C1 record.

Annual layers between each of these horizons were adjusted iteratively in order to provide the

necessary number of counted years. As a general rule, the layer boundaries "best" defined were chosen in

areas in which more years were originally counted than required. These boundaries were usually strongly

defined in at least two of the three annual markers, and those only distinct in one of the three records were

normally the ones removed. During the GB97C1 core cutting/analysis phase, annual layers in Cl' were

counted sequentially as results were generated, and the Laki 1783 eruption was expected at a depth of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. approximately 115 m. In actuality, the event was discovered 10 m deeper into the core, suggesting an

error of about 10% in counting with no known horizons for guidance.

4.1.4 Time scale verification

An intial survey of GB97C1 10Bc and 36C1 completed by J. Beer (Synal et a l 1987) confirmed

the layer-counted timescale to within several decades, by matching to the secular variations in cosmogenic

flux as determined from tree-rings (Stuiver et al., 1998) and other well-dated ice cores (Beer et al., 1984:

Raisbeck et al., 1987). Fifteen ice samples, each representing about 7-8 years of snow accumulation, were

extracted from GB97C1 from between 143 m and the bottom, covering about 500 years of the ice archive

from the Medieval Warm Period and the Little Ice Age. Depth ranges for extracting these samples were

selected judiciously to make certain that differences in chloride, melt, and dust concentrations (that could

reveal potential melt influence) were minimized (Table 4.2). Subsequent comparison of the cosmogenic

results to these three core parameters did not reveal any significant relationships, suggesting that the

fluctuations were indicative of production rate changes in the free atmosphere.

Because the late Holocenc is punctuated by a scries of regular solar minima (commonly known as

Wolf. Sporer. and Maunder) that governed cosmogenic activity in the upper atmosphere, it was possible to

match the two GB97C1 profiles to the IntCal AHC (Stuiver et al.. 1998) decadally-rcsolved curve as

shown in Fig. 4.12. Here it can be seen that the succession of three L1A minima is well-defined in the

Graham Bell ice core, although the layer-countcd/volcano-guided ages for GB97C1 display an offset

(lead) of 50 and 70 years for 36C1 and I0Be, respectively. Roughly 20 years of the apparent lead can be

explained by the longer mixing time of radiocarbon within the global CO? budget, as seen between

Greenland ice core 10Be and the IntCal profile over this period (J. Beer, personal communication). An

additional decade might be explained by the downward migration of trace elements in the upper fim zone

of Windy Dome, as documented in p-radioactivity for the 1963-64 bomb horizon (Section 4.1.3). The

remainder of the offset might have been due to the non-continuous sampling of the ice core and random

measurement errors. The slight offset of the two cosmogenic nuclides (respective to one another) within

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. X o> « E o o 4-4 o 1.0 0.8 0.6 - r - - 0.4 0.8 0.6 Intcal Intcal curve C (Stuiver) GB97C1 GB97C1 (,0Be) (“GB97C1 Cl) 1998). Actual layer-counted age scales el al., 0.4 ka BP (1950) 0.2 for both GB97CI profiles shilled to show maximum correlation; and by 50 years years 70 for for36CI >0Be. 0 .0 - -20 Fig. 4.12 records GB97C1 compared and |0Be to 3f’CI Intcal (Stuvier, AI4C Q.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Depth range Average Avg. c r Avg. dust 36C1 Error 10Be Error Layer- in core (m): melt conc. conc. (atoms/g) (%): (atoms/g) (%): counted percent: (ppb): (per ml) (x I05): (x 105): median (x 104): age: 143.50-146.54 32.6 552 1.18 .600 12.7 10.14 4.2 1735 167.80-170.66 47.5 697 1.70 .781 11.5 13.94 3.2 1675 182.66-185.68 53.3 719 2.67 .703 12.1 14.39 4.6 1633 188.84-191.56 44.8 709 1.51 .888 12.1 17.45 4.2 1614 200.62-203.68 35.1 867 2.28 .413 20.6 15.22 4.6 1579 211.52-214.56 35.8 598 3.13 .530 15.0 11.35 4.6 1547 224.67-227.40 41.0 707 0.87 .623 15.0 16.71 6.1 1509 237.53-240.11 36.0 1023 1.86 .875 12.0 14.95 4.5 1469 249.05-252.09 46.2 1085 1.82 .695 12.9 20.12 5.6 1439 261.97-264.58 24.9 644 1.88 .749 14.3 16.19 5.6 1402 273.69-276.64 51.6 1123 1.12 .480 21.0 17.78 9.2 1364 285.82-288.66 51.4 733 1.13 .524 15.5 11.12 8.5 1321 291.24-294.12 41.2 1347 1.33 .696 14.8 13.38 8.0 1303 302.29-305.01 48.0 652 1.39 .779 12.7 17.42 4.8 1265 312.72-314.81 32.2 897 3.10 .662 14.2 15.70 6.5 1230

Tabic 4.3 GB97C1 cosmogenic isotope results.

the GB97C1 ice core itself warrants future study, and might also be due to post-depositional processes.

However, the important feature of the cosmogenic profiles produced in this study is that the matching as

shown indicates no cumulative dating error from top (1750) to bottom (1225). because the apparent shift

is consistent throughout this period. Hence, given very strong age control (fixed confidently on Laki

1782-3 to within a year or two) for the late 18th century by multiple eruption events, the cosmogenic

analysis supports the layer-counted timescale as originally produced with 1259 and 1362 as authenticated

volcanic horizons.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.2 Creation of Windy Dome time series

Once the three-parameter cross-checked layer counting was finalized, the individual boundary

depths were averaged to produce a single layer-thickness profile for use in reconstructing accumulation on

the Windy Dome summit. In Fig. 4.5, it was shown that over the length of the core, the relationship

between the three annual markers shows on average no significant offset in timing. Calculating the

analogous distributions over shorter intervals, representing separately the MWP. LIA. and 20th century,

did not distinguish any obvious pattern over time, although the spread of sample-ofTset values from the

LIA most simulated a normal distribution compared to the warmer phases of the record. This result

would tend to agree with the perception stated earlier that confidence in annual dating (especially for

6‘*0) was enhanced during the LIA. Unlike the accumulation reconstruction, annual averages were

determined for anions, melt percent, and 5,!*0 based on their respective timcscales. for the purpose of

having each value represent a designated annual oscillation (from peak-to-peak or trough-to-trough).

Nitrate and sulfate averages employed the chloride-based layer counting. Annual averages for

microparticles were determined from the mean timcscale based on the other three records, the same as for

accumulation. In the creation of these averages, each measurement was weighted according to its sample

size relative to the thickness of the annual layer, in terms of ice equivalent. Decadal averages were

determined as a simple arithmetic mean of the ten years included within, with the uppermost 'decade'

representing only 1990-97 (inclusive), and continuing in form downcore (1980-89. etc.). Because each

annual layer has been assumed to represent the period from March 1st of the previous year to Feb 28th of

the year designated, a ten-month offest from tme calendar years is inherently imposed upon the decadal

record. This error is assumed to be insignificant due to the uncertainty in the annual dating and the

nature of the vertical mixing in the ice itself.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.3 Time/depth modeling and accumulation reconstruction

4.3.1 Annual layer thickness modifications

The process of reconstructing the annual accumulation values involves converting the true annual

layer depths to an ice-equivalent depth (IED) scale (via the measured densities discussed in Section 3 . 1.

and shown in Fig. 4.2) and then essentially "unthinning" each individual layer according to a simple

model formula. To correct layer depths, each sample interval from the analysis was multiplied by its

measured density and then divided by 0.92 g cm 3, the maximum density of glacial ice found in deep cores

from the dry snow zones of Antarctica (Paterson. 1994). At a depth of 24.78 m (20.32 m IED). the core

ice was considered fully-densificd and hence no further density corrections were made below this point.

For each accumulation year (Mar.-Feb.). the average IED layer thicknesses based on all three layer-

counting techniques (chloride. 6lsO, and melt startigraphy) were used. This approach removed much of

the subannual variance in the positions of identified maxima (or minima) for each parameter, likely due to

post-depositional processes that could have influenced each record differently.

4.3.2 Flow modeling

The flow model used to rcconstuct accumulations was a two-parameter steady-state function that

equates an average annual surface accumulation ( b . IED) with the sum of the annual vertical displacement

of all layers below (Thompson et al.. 1990). The formula that relates age (in years before present, or yrs.

BP) to depth in core is given by.

T (yrs. BP) = h/bp [(1 - z/h)'p - 11 (Eq. 4.3.1),

where h is the IED thickness of the glacier, p is the thinning parameter, and z is the center depth (IED) of

the layer in question. From the steady-state approximation (b constant), the relationship above can be

equated for two well-dated horizons at times T\ and 7?, yielding the relationship,

Tz [(1 - zl/hyp - 11 = r, [(1 - :zlh) p - 11 (Eq. 4.3.2),

where z x and zz are the IED depths of the two chosen horizons. The thinning parameter, p. is then

uniquely solvable, as is b now from Eq. 4.3.1 (using either horizon). If the accumulation rate is truly

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. steady-state (or nearly so) and the two chosen horizons bracket a large portion (mainly in time) of the ice

core record, then the determination of p and b becomes nearly independent of the exact choice of

horizons. For GB97C1. it made the most sense to use the definitive Laki horizon (1782-3) and the 1259

sulfate anomaly from the unknown eruption (both presumed to be accurate to within a single year). These

two horizons not only represent the points of minimum dating error, but also are spaced at convenient

places in the depth-based record, including very near the core bottom such that little effective

extrapolation would be required. Because the GB97CI core was incomplete, the precise value of h

remained unknown, although the estimate of 500 m (495.5 m ice equivalent) used in the reconstruction

was deemed very reasonable given the sounding-based thickness map (see Fig. 3.1b) generated by

Macherct et al. (1998). Modify ing this thickness estimate by 10% (to 550 m) only altered reconstructed

accumulation values by 1.0-1.5%. so the results were largely unaffected by this uncertainty.

4.3.3 Accumulation reconstructions

Using the expressions and horizons identified in the preceding sections, individual accumulation

values (a) were then determined for all years back to 1225 A.D. The correction to each buried annual

layer involves only the thinning parameter, p. and the depth of the layer with respect to the total ice

thickness.

a (IED) =/(I-:/h (Eq. 4.3.3).

Alternatively, one may think of this process as determining the degree of deviation of the thickness of

each annual layer from the model curve of layer thicknesses, given by.

U (IED) = b (1 - z/h r "> (Eq. 4.3.4).

Hence, both parameters (b and p) are actually implicit in the reconstruction. Eq. 4.3.3 can then be

rewritten as.

a (IED) = b (I Umodti) (Eq. 4.3.5).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Although it is not explicitly defined as such, the average accumulation over the period between the surface

and 7V (in this case, 1259) is identical to b (0.64 m ice eq.). The model parameters that govern this

reconstruction are:

(T\, Z\) = (215 yrs. BP, 119.98 m IED) - 1782/3 A.D. Laki eruption (T;, z2) = (738 yrs. BP, 300.48 m IED) * 1259 A.D. unknown eruption resulting in the following output values: b = 0.6444 m ice eq., p = 0.06173.

Compared to intrinsic ice core records such as trace chemistry, accumulation reconstructions are

the most susceptible to dating errors. Not only arc these records limited (by definition) to no better than

annual resolution, accumulation rates arc also twicc-dcpendcnt upon the layer-counted time scale

employed. Whereas dating errors only influence the position of relative highs and lows of other

parameters, both the position in time and the magnitude itself of any given accumulation event is

determined by the time scale and the accuracy’ of the counted years therein. Consequently, the detection of

multiple identifiable horizons becomes more critical for the GB97C1 accumulation record. With two

volcanic horizons in the bottom section of the core (supported by cosmogenic evidence) and other 18th

and 19th century horizons surrounding the Laki event, confidence in the layer counting to within a range

of a single decade can be upheld throughout the record. In this situation, although any given

accumulation value may be subject to significant argument as to its accuracy, the true accumulation

history is quite likely to be faithfully represented by the actual decadal- to ccntury-scalc variability’ as

shown in Fig. 4.13. Hence, there may truly be several years of error propagation in either direction at

positions further removed from definitive horizons, but the errors must eventually cancel out bv the time

the next lower horizon is approached. Nevertheless, it is useful to consider a more prudent accumulation

reconstruction for a core like GB97C1 with such concerns over meltwater influence. For this reason, an

interval-based accumulation reconstruction is also depicted in Fig. 4.13 (thick superimposed line). Even

with this limitation, the major features of the fully-resolved accumulation record are evident, including the

decrease from high values late in the MWP to sustained low values in the 17th and 18th centuries, as well

as the temporary interruption in accumulation growth during the mid-20th century when increases in melt

activity likely counteracted the expected enhanced precipitation due to wanning.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 4.13 Graham Bell (1997) Core 1 accumulation profile (in m water equivalent), reconstructed from two-parameter model with with model two-parameter from reconstructed equivalent), water m (in profile 1accumulation Core (1997) Bell Graham 4.13 Fig. Reconstructed Accumulation (meters w.e.) 0.2 0.4 0.4 0.6 0.8 1.0 1.2 00 90 80 70 60 50 40 1300 1400 1500 1600 1700 1800 1900 2000

Laki and the 1259 (unknown) eruptions as chosen liorizoiis chosen as eruptions 1259(unknown) the and Laki 1 T ----- 1 ----- 1 ----- 1 ----- 1 ----- b=0.644 m, p=.0617; h = 500 m (495.5 ice eq.) ice (495.5 m 500 = h p=.0617; m, b=0.644 Model (1782 & 1259 pinning points): points): pinning &1259 (1782 Model 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- Year (A.D.) Year 1 ----- 1 5-sample running mean (1-3-4-3-1) runningmean 5-sample ----- Individualvalues 1 ----- 1 ----- Average accumulation between horizons between accumulation Average 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- 1 ----- I 1 ----- I 1 ----- T 1 CHAPTER 5

CALIBRATION AND APPLICATION OF THE GB97C1 6l80

AND MELT RECORDS AS PALEOTHERMOMETERS

5.1 Historical temperature records in the Eurasian Arctic sector

The earliest continuous temperature measurements in the Eurasian High Arctic began in the

second decade of the 20th century at the Isfjord Radio station (Hcssclbcrg and Johannessen. 1958) on

West Spitsbergen. The first several years ( ca . 1912-1920) of the Isfjord Radio data point to a remarkable

warming, primarily during the winter months, that in the end proved to be a crucial piece of real-time

evidence to relate ice core proxy records to documented environmental change. Previous to. or concurrent

with, the installation of the meteorological station at Isfjord Radio, several Russian Arctic stations also

began recording temperatures continuously, including Karmakuly. Kanin Nos. and Vaygach in the

Novaya Zemlya sector, and Dikson Island further east. Wintertime temperature changes were seen in

these locations as well, though the warming was much less prominent. Records from the north coast of

Norway that continue back in time as far as 1840 (in the case of Vardo) show only a modest warming over

the 1915-1925 period. Thereby, it is suggested that the phenomenal warming witnessed at Isfjord Radio

represents a regional enhancement of the Little Ice Age termination limited to the northern Barents Sea

margin. The continuity of the ice core results (to be shown in Chapter 8) from eastern Svalbard to

Severnaya Zemlya (including GB97C1 in Franz Josef Land) supports this hypothesis.

Table 5.1 lists all of the locations for which monthly-averaged temperature data were compiled

for the development of a regional climate history and thereby the calibration of isotope data as

paleotemperatures. Data from individual sites within seven sub-regions (Fig 5.1) were examined to

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Site Latitude Loncitude WMO Station # Yrs. of Coveraee Alert (AL) 82.5°N 62.33°W 7108200 1951-91 Myggbukta (MG) 73.5°N 21.6°W 433001 1932-39, 1946-50 Danmarkshavn (DN) 76.77°N 18.67°W 432000 1953-93 Nord (ND) 81.6°N 16.67°W 431000 1952-72, 1982-87 Reykjavik (RK.) 64.13°N 21.9aW 403000 1903-91 Akureyri (AK) 65.68°N 18.08°W 406300 1882-1993 Teigarhom (TG) 64.7°N 14.7°W 409602 1884-1970 Dalatangi (DA) 65.27°N 13.58°W 409700 1981-90 Jan Mayan (JM) 70.93°N 8.67°W 100100 1921-93 Thorshavn (TH) 62.02 °N 6.77°W 601100 1882-1925, 1931-93 Akraberg (AG) 61.4°N 6.67°W 600900 1981-90 Isfjord Radio (IS) 78.07°N 13.63°E 100500 1912-40, 1947-76 Barenlsburg (BA) 78.07°N 14.22°E 2010700 1981-90 Lufthavn (LU) 78.25 °N 15.47°E 100800 1977-93 Bjornoya (BJ) 74.52 DN 19.02°E 102800 1951-93 liopen (HP) 76.5°N 25.07°E 106200 1981-90 Victoria (VC) 80.17°N 36.88°E 1959-92 Tromso (TR) 69.68°N 18.92°E 102500 1856-80, 1920-1993 Fruholmen (FR) 71.P N 24.0°E 105500 1981-90 Gjesvar (GJ) 71.P N 25.4°E 106602 1878-1926 Sletnes (SL) 71.08°N 28.23°E 107800 1899-1940 Varde (VR) 70.37°N 31.PE 109800 1840-1993 Murmansk (MR) 68.97°N 33.05°E 2211300 1919-93 Kanin Nos (KN) 68.65^ 43.3°E 2216500 1916-93 Vaygach (VG) 70.4aN 58.85°E 2302206 1914-50 Karmakuly (KY) 72.38°N 52.73 °E 2074400 1897-1950 (WW gaps), 1981-90 Menshikova (A/.V) 70.72 °N 57.623 E 2302201 1981-90 Bolvanskiv (BO) 70.45 °N 59.07°E 2302202 1981-90 Belyy Nos (BE) 69.48°N 60.33°E 2302203 1981-90 Amderma (AM) 69.77°N 61.68°E 2302200 1981-90 Nagurskaya (NG) 80.88°N 47.50°E 1952-91 B. Tikhaya (TK) 80.33°N 52.88°E 102800 1929-59 Rudolf (RU) 81.88CN 57.88°E 1937-42, 1947-92 Heisa (HS) 80.62 °N 58.05 °E 2004600 1957-93 Gavan (GV') 76.18°N 63.57°E 2035700 1981-90 MareSale (XLA) 69.72°N 66.82°E 2303200 1981-90 Kharasovoy (KH) 71.4°N 67.73°E 2303201 1981-90 Zhelanya (ZH) 76.95 °N 68.58°E 2035300 1931-60, 1981-90 Popov (PV) 73.33=N 70.03 aE 2066700 1981-90 Tambey (TM) 71.48°N 71.82°E 2066701 1981-90 Vize (VZ) 79.5°N 76.98°E 2006900 1951-93 Uyedineniya (UY) 77.5°N 82.23°E 2027400 1961-90 Dikson (DK) 73.50°N 80.4 °E 2067400 1916-93 Sopochanaya (SO) 71,9°N 82.72 °E 2067403 1981-90 Sterlegovas (ST) 75.4°N 88.78 °E 2027403 1981-90 Golomyanniy (GO) 79.55°N 90.623E 2008700 1981-90 O. Russkaya (RS) 77.18°N 96.58°E 2029204 1981-90 Bolshevik (BK) 78.23 °N 103.12°E 2029205 1981-90 Federova (FD) 77.72 °N 104.28°E 2029200 1932-93 Andreya (AN) 76.8°N 110.833E 2029208 1981-90 Pronchishch (PR) 75.53°N 113.25aE 2150402 1981-90

Table 5.1 Names and locations of sites in the North Atlantic/Eurasian Arctic region from which temperature data were compiled for creating spatial correlation maps (including those in italics) and a single representative temperature history (including only those in boldface) for the Barents Sea region.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SZWLYA 60 W CAN/GR

NZMLYA ZH

40°W SVALBARD BJ CRUSSIA

N OR WAY GJ l L 6 TR

20°E

Fig. 5. 1 Sites and sub-regions used in the determination of a composite temperature record for the Eurasian Arctic from 1840-1993.

CAN/GR AL ND DK Alert (AL) 1.0 Nord (ND) .08 1.0 SVALBARD Danmarkshavn (DN) .01* .21* 1.0 I IS VC BJ Isfjord (IS) .00 .51 .13*! 1.0 Victoria (VC) .10* .37* ,40V .87* 1.0 NORWAY Bjornoya (BJ) .01 .41 .11* .90 .66* 1.0 TR VR MR Tromso (TR) .00 .11 .02* .36 .38* 41 II 1.0 Vardo (VR) .01 .14 .04* .44 .43* .50 .74 1.0 FRJSFLD Murmansk (MR) .00 .09 .04* .32 .37* .35 .75 .92 1.0 | NG RU HS Nagurskaya (NG) .00 .40 .10* .71* .78* .66 .15 .18 .13 | 1.0 Rudolf (RU) .01 1 .30 .12* .52 .52* .53 .07 .08 .06 i .93 1.0 CRUSSIA • O) Heisa (HS) .01* .21* o .56* .70* .53* .24* .23* .17*' .88* .86* 1.0 KN KY VG Kanin Nos (KN) .00 .09 .02* .26 .27* .22 .37 .72 .73 .15 .08 .15*1 1.0 Karmakuly (KY) .63 1.0 I NZMLYA Vaygach (VG) — I — .62 .87 I 1.0 VZ UY Vise (VZ) .02 .16 .01* .34 .43* .31 .12 .10 .12 .70 .70 .64* .16 1.0 ____ , SZMLYA Uyedineniya (UY) .02* .03* .05* .13* .21* .11* .05* .12* .08* .29* .27* .36* .21* .77* 1.0 I DK FD — I — Dikson (DK) .05 .02 .01’ .04 .00* .04 .06 .09 .12 .22 .19 .08* .35 .52 .57* I I 1.0 : Federova (FD) .04 .04 .02* .08 .16* .14 .10 .10 .10 .37 .42 .34* .25 — | — .62 .59*1 .66 I 1.0

Fig. 5.2 Correlation matrix - r2 values for annual average temperatures over a period of 30 years, nominally 1951-1980 (in some cases, 1947-1976). Asterisk denotes those correlations based on data overlap of less than 25 years. Italic type denotes those correlations based on the time period 1920-1950. Values in boldface are correlations greater than 0.4 (0.5 for under 25 year overlap). Highlighted individual boxes indicate correlations within a particular subregion.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. determine the level of agreement between records that would justify consolidating records. In the process,

a correlation matrix involving all of the sites with overlapping long records (30 years in most cases) was

constructed (Fig. 5.2) to illustrate those areas that show greater covariance of annual temperatures,

especially in relation to sites in Franz Josef Land. Only the records from northeastern Greenland and

Ellesmere Island showed poor internal correlation, and because these records also correlated poorly with

those from the Eurasian Arctic they were not incorporated into the final composite history but arc still

shown for sake of comparison.

5.2 Spatial correlation of temperatures and generation of a representative temperature history for Franz

Josef Land

In Fig. 5.2. the 30-ycar cross-correlations involving Franz Josef Land show a predictable pattern,

with r values over 0.80 within the archipelago itself, and consistently over 0.50 with Svalbard sites

(highlighted) and decreasing to insignificant values at more extreme distances. Using additional sets of

correlation statistics from 20th century data, correlation maps were constructed to delineate the pattern of

similarity to conditions in Franz Josef Land on both an annual (Fig. 5.3) and seasonal (Fig. 5.4) basis.

Because of differences in the time periods that stations were occupied, the annual correlations were

calculated for two different 30-vear periods and then both values (when available) were considered while

manually producing contour lines. For the seasonal maps, monthly data were available for a large number

of stations for the decade of the 1980s, and because data for each month were utilized individually, the

number of monthly means used for the correlations was also about 30.

The outline of significant annual correlation (estimated by the r=0.4 contour) in Fig. 5.3 points

strongly toward both the west and south and to a lesser degree east, but is greatly limited toward the

Scandinavian coast. Some uncertainty in the contouring resulted from potentially spurious values

suggested by great differences in correlation between the two time periods, e.g., at Jan Mayen where no

measurable correlation was observed in the years before I960. However, the overall annual pattern can

readily be imagined as a combination of the two dissimilar patterns depicted in the pair of correlation

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. O.10/.01 20° E Annual (1961-90)/(1931-60)

Fig. S.3 Spatial correlation map of annual air temperatures with the Franz Josef Land composite record for two separate 30 yr. periods, when applicable: 1961-90 and 1931-60.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 9 . .11

Greenland

40 °W

s „ » \

Faeroe Is. Jan. sea ice margin o.OO 20°E (50% conc.) derived <>oo from SMMR and SSM/I DJF (1981-90) data (1978-87) (29 months)

0 3 . 02°

Greenland

July sea ice margin Faeroe Is c (50% conc.) derived 20°E from SMMR and SSM/I data (1978-87) JJA (1981-90) (30 months)

Fig. 5.4 Spatial correlation maps of air temperatures (winter-DJF, summer-JJA) with Krenkel Station, Ostrov Heisa (FJL) temperatures for 1981-90 (individual monthly averages).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. maps in Fig. S.4. separately considering winter (DJF) and summer (JJA) data for a mere 10-year period.

The area of conformity to FJL conditions in wintertime is far greater and extends greatly toward the

Norwegian Sea in the W-SW octant, and to a similar degree toward Severnaya Zemlya to the east. In

contrast, the restricted region of high summertime correlation persists only a modest distance toward

Svalbard in the west, but more significantly southward into the Kara Sea. Superimposed upon the

seasonal correlation maps is the average position of the sea ice margin in the months of January and July,

respectively, as determined from satellite (i.e.. SSMR and SSM/I) measurements (Gloersen et al.. 1992).

While the maximum sea ice margin appears to have little influence on the widespread similarity of air

temperatures during polar night, it is apparent that the position of the minimum sea ice boundary must

largely shape the spatial uniformity of air temperatures in the region. In Fig. 4.3. sea level temperatures

at Ostrov Vizc were seen to be stabilized near the melting point for much of the summer, as any excess

heat into the system (whether advcctivc via ocean/air transport, or radiative) would mainly provide the

latent heat necessary for melting additional sea ice. Hence, only when the sea ice margin retreated a

substantive distance from a given location could atmospheric temperatures be expected to rise

significantly above 0°C. The alignment of the summertime correlation pattern precisely along the sea ice

boundary strongly suggests a linkage between the ice margin position and the incidence of unusual

warming in the region.

During the period over which most of these correlations were determined (1931-90). most of the

variance in the temperature histories was year-to-year variability about a steady mean. One common

exception is that the records from the northern Barents Sea locations tend to show a moderately large

cooling during the decade 1955-1965 not seen clearly in the coastal records from the European mainland.

This isolated signature is a major reason why correlations are consistently lower between FJL and sites in

north coastal Norway, and indeed a pattern of north Barents enhancement was recognized by Rodewald

(1977) as reproduced in Fig. 5.5. Extreme wintertime temperature changes of up to 5°C were experienced

at locations in and around Franz Josef Land, set up by an anomalous transpolar surface flow emanating

from the north coast of Alaska. The westward-propagating pattern of cold anomalies mimics that of the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RUSSIA N o r t h P a c

North A t l a n t i c v p c i a n -(195 AT (1961- AT RUSSIA FrM1 North Pacific Ocaan

winter montlis (DJFM)-70 vs. of 1951-60 1961 overthe Norih Atlantic and north polar regions (afterRodcwald, 1977). AP (1961- AP v-(195T-6fi CANADA. Fig. Fig. 5.5 Mean cliangc in a) surface atmosplieric pressure (mb), and b) surface atmospheric temperature (°C), during the four

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. annual and DJF correlation maps and must be a manifestation of a concomitant southward shift of the

polar front. For the eastern half of the Arctic region, this kidney-shaped pattern of enhanced temperature

response appears to be similar for both the (relatively) moderate cooling of the 1960s and also the

remarkable warming of the 1920s. The limited area of this unusual feature indicates that any ice core

parameter from GB97C1 particularly sensitive to wintertime conditions is likely only applicable to the

north Barents/Kara seas and not to large-scale or hemispheric environmental change. Futhcrmorc. any

future techniques to stack palcohistories into single Arctic or hemispheric time series should properly

weight (in a spatial sense) annual or wintertime proxies from GB97C1 accordingly.

Following the sub-region designations outlined in Fig. 5.1. seven composite temperature histories

were generated by relating all records to reflect mean conditions at a single location (those highlighted by

boldface type in Figs. S. I - 5.3) that produced the most overlap with the other sites within that particular

sub-region. Rescaling each individual record to that of the reference location was accomplished v ia

simple mean differencing and variance calibration (according to the ratio of standard deviations) for the

entire interval of overlap presented. Once the rescaled temperature records were summed for each sub

region. anomalies were regenerated using the common period 1951-80 as basis for the climatology, and

then the final seven histories (those shown in Fig. 5.6) were produced by rescaling back to the mean Franz

Josef Land statistics, i.e.. the climatology of the station at Rudolf Island. Hence, the seven profiles mimic

the conditions at Rudolf Island, but yet depict variability in the regions from where they were each

produced, the purpose being to extend the genuinely Arctic history (limited to less than 100 years) with

longer records from locations nearby. While the poorer correlations with these southern sites introduces

some concern about inclusion in the composite, in the end the rough similarities adequately fulfilled the

intentions of the process, especially considering the decadal-mixing in the ice core record itself.

Furthermore, the intent of including the Norway data was to establish the climate stability of the 19th

century before the greater part of the Eurasian Arctic had been explored. The analogous series of

subregion histories for the DJF quarter (Fig. 5.7) illustrate the extraordinary magnitude of the change at

Isfjord Radio as compared to the corresponding shifts at the more southerly sites available at the time. In

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ep (C Tm. °) ep (°C) Temp. (°C) Temp. (°C) Temp. -12 -18 - -9 - -15 - -18 - - -9 Tromso/Vardo/Gjesvar/Stelnes/Murmansk Kanin Nos/Vaygach/Karmakuly Dikson/Federova Bjonwya/lsfjord/Lutthavn/Victoria VizeVUyedineniya/Zhelaniya Rudolfa/Heisa/NagurskayafTikhaya Year (A.D.) Danmarkshavn/Aleft/Nord mean conditions at RudolfIsland, 1951>80) _i 2000 1990 1980 1970 1960 1950 1940 1930 1920 1910 1900 1890 1880 1870 1860 1850 1840 -9 - -9 - -9 - -9 - Fig. Fig. 5.6 Annual average temperatures for Eurasian Arctic by sub-region (all available records combined and scaled to match -18 - -15 - -15 - Q. © © -15 - 0 Q. a .0) -15.0) -

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ep (C Tm. °) ep (°C) Temp. (°C) Temp. (°C) Temp. -10 -15 -20 -30 -25 -15 -20 -25 -30 -35 Nos/Vaygach/Karmakuly Kanin Tromso/Vardo/Gjesvar/Stelnes/Murniansk Dikson/Federova Bjornoya/lsfjord/Luflhavn/Victoria Rudolfa/Heisa/Nagurskaya/Tikhaya Vize/Uyedineniya/Zhelaniya Year (A.D.) Danmarkshavn/Alert/Nord mean conditions at RudolfIsland,-80). 1951 Fig. Fig. 5.7 DJF average temperatures for Eurasian Arctic by sub-region (all available records combined and scaled to match 2000 1990 1980 1970 1960 1950 1940 1930 1920 1910 1900 1890 1880 1870 1860 1850 1840 1 -25 1 0 ~ -2 0 -I I- -30 -= o -15 0 0 -4

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. conjunction with the melt record (a JJA-temperature proxy), the analogous JJA quarter temperature series

(Fig. 5.8) will be utilized to estimate winter temperature changes at the Windy Dome site over the length

of the core (Section 5.5).

In summary, the degree of warming beginning in the second decade of the 20th century

diminished greatly toward the southern margin of the Barents/Kara sea perimeter, so for the final

temperature reconstruction the southern three sub-regions were modified to simulate the Isfjord Radio

warming. For the coastal Norwegian summary record (NORWAY), adjustments to each annual value

were made via a three-stage modeling of the differences in absolute "Rudolf-calibrated" temperature (Fig.

5.9). employing two linear regression formulae to only include the trend components (that mimic, in an

inverted sense, the actual temperature profiles: sec Fig. 5.11). The temperature rescaling for the early-

period (1840-1917) was fixed at the value determined by the second regression line at the time of initial

warming above the 19th century mean which occurs at 1917. Similar modifications were made to the

Severnaya Zemlya (SZEMLYA) and Coastal Russia (CRUSSIA) records, to produce when ultimately

assembled in final form (Figs. 5.10. 5.11a). a history that quite likely represents both the interannual

variability (of the 20th century) and the magnitude of the abrupt wanning of the 1915-25 period along

(only) the northern Barents margin. The stability of the first half of the record (initially based entirely on

data from the north coast of Norway), up to and including the first two decades when higher Arctic

records begin, implies that no significant regional climate change occurred over this period. This

observation suggested a posteriori that no alteration of the fixed adjustment of early Norway temperatures

(according to 19th century Svalbard trends that could only be largely speculative) was tenable, and

furthermore that the stepwise jump exhibited in air temperatures between the 19th and 20th centuries

could provide a valid methodology- for 6lsO-T calibration for GB97C1. Finally, because of the excellent

correlation between the SVALBARD and FRSJSFLD composites (as seen in Fig. 5.6) within the 20th

century, supported also by the response pattern to the 1960s cooling (Fig. 5.5), it has been assumed that

the rescaling to the Svalbard trend was equivalent to the same for Franz Josef Land, if data had actually-

been collected there at that early time.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ep (C Tm. °) ep (°C) Temp. (°C) Temp. (°C) Temp. -2 -2 -2 - - - Kanin Nos/Vaygach/Karmakuly Biomoya/lsfjord/LufthavnA/ictoria Dikson/Federova Tromso/Vardo/Gjesvar/Stelne s/Murmansk Tromso/Vardo/Gjesvar/Stelne Rudolfa/Heisa/Nagurskaya/Tikhaya Vize/Uyedineniya/Zhelaniya Year (A.D.) Danmarkshavn/Alert/Nord mean conditions at RudolfIsland, 1951-8(1). Fig. Fig. 5,8 JJA average temperatures for Eurasian Arctic by sub-region (all available records combined and scaled to match - 2000 1990 1980 1970 1960 1950 1940 1930 1920 1910 1900 1890 1880 1870 1860 1850 1840 -2 CL I— I— -2 -

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 of the permission with Reproduced Fig. 5.9 Difference in annual average temperatures between Svalbard and Norway (both scaled (both Norway and Svalbard between temperatures average annual in Difference 5.9 Fig. Temperature Difference (Norway - Svalbard) °C -2 3 - -3 to match mean conditions at Rudolf Island. 1951-80); subtraction to Norway temperatures: temperatures: Norway to subtraction 1951-80); Island. Rudolf at conditions mean match to - 2000 continued by 1912-1940 regression (solid) line to 1917 (r~ = 0.57), and set constant (dashed) (dashed) constant set and 1937. 0.57), to (r~= 1917 back to (dashed) line (solid) extrapolated regression .04) = 1912-1940 (r: by 1947-1993 from continued line regression to according rm 97bc ni 1840. until back 1917 from ♦ ♦ 1980 1960 ♦ ♦ Year (A.D.) Year ♦ ♦ 1940 1920 1900 Temp. (°C) Temp. (°C) Temp. (°C) Temp. (°C) 1 - -15 -12 1 - -15 -12 1 - -15 -12 1 - -18 -12 9 - -9 9 - -9 9 - -9 - - 00 90 90 90 90 90 90 90 90 90 90 80 80 80 80 80 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 - - Fig. 5.10 Annual average temperatures (adjusted to Svalbard trend, as indicated) for Eurasian Arctic by sub-region sub-region by Arctic Eurasian for indicated) as trend, Svalbard to (adjusted temperatures average Annual 5.10 Fig. -I alaalbercrscmie n cldl ac encniin tRdl sad 1951-80). Island, Rudolf at conditions mean match lo scaled and combined records available (all Danmarkshavn/Aleit/Nord Year (A.D.) Year Vize/Uyedineniya/Zhelaniya Rudolfa/Heisa/Nagurskaya/Tikhaya Bjocnoya/lstjord/Lutthavn/Victoria Adjusted to Svalbard trend (1917-1993) trend Svalbard to Adjusted Dikson/Federova Adjusted to Svalbard trend (1917-1993) trend Svalbard to Adjusted Tromso/Vardo/Gjesvar/Sletne s/Murmansk Adjusted to Svalbard trend (1917-1993) trend Svalbard to Adjusted Kanin Nos/Vaygach/Karmakuly Kanin -15 - - -9 - -21

Temp. (°C) Temp. (°C) Temp. (°C) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. without prohibited reproduction Further owner. copyright of the permission with Reproduced

Fig. 5.11 Comparison of: a. Eurasian Arctic composite temperatures (scaled to Rudolf Island. FJL FJL Island. Rudolf to (scaled temperatures composite Arctic Eurasian a. of: Comparison 5.11 Fig. Composite (Rudolfa) Temperature - 6 180 ( % o ) Adjusted to Svalbard trend (°C) -10 -14 -14 -12 -16 -16 -20 -18 -15 -15 -22 -16 -16 -17 -17 -18 -18 -19 -19 -21 -20 -8

n dutdt vladted n .Gaa el(97 oe iOfr 1840-1993. for 1SisO Core (1997) Bell Graham b. and trend) Svalbard to adjusted and

00 90 90 90 90 90 80 80 1840 1860 1880 1900 1920 1940 1960 1980 2000 1—I—T 1920-1993 ave. = -12.70°C = ave. 1920-1993 1840-1899 ave. = -16.43°C -16.43°C = ave. 1840-1899 1920-1993 ave. = -16.75%0 -16.75%0 = ave. 1920-1993 1840-1899 ave. = -18.81%o -18.81%o = ave. 1840-1899

______* * ** * 19th-20th diff. = 3.73°C = diff. 19th-20th analogous tothose in5.9 Fig. 9h2t if =2.06%o diff. 19th-20th • •« •« * • . ____ • ■ * V * * t * * regressionlines Year (A.D.) Year 92 I I 4 Franz Josef LandFranz CoastalRussia Zemlya Novaya Norway Svalbard Severnaya Zemlya Severnaya

5.3 Calibration of GB97C1 6uO as a paJeothcrmometer

The use of stable isotopes in precipitation, whether based on oxygen-18 or deuterium, for

paleolhermometry applications is based upon a long history of sample collection and interpretation of

relation to weather and climate (Dansgaard et al.. 1973; Sonntag et al., 1983; Johnsen et al., 1989). At

high latitudes, such as Franz Josef Land, the 6lsO values in snowfall can faithfully be expected to follow

previously established relationships (with respect to surface temperatures) for the Arctic as a whole

(Johnsen et al.. 1989; Jouzcl et al.. 1997), the only remaining concern being the redistribution of values

by both percolation (mixing) and post-depositional (solid-liquid) fractionation (Amason. 1969; Lehmann

and Siegenthalcr. 1991). While both of these phenomena have been clearly witnessed at Graham Bell, in

the absence of significant net removal of meltwatcr from the Windy Dome summit (as suggested by results

in Sections 5.4.1 and 7.4). mean isotopic values on a decadal scale have not been altered greatly.

However, the preferable method of calibrating ice core 6l!lO to annually-averaged air temperatures from a

neighboring station was not possible for GB97C1 due both to the lack of precise core dating (to within one

year) and the post-depositional alteration already noted.

However, the remarkably similar step feature in both the GB97C1 8li!0 profile and the

Barents/Kara composite temperature history (Fig. 5.11) provides the means to propose a feasible

calibration for the entire record, and is given particular credibility according to the extremely large

magnitude of the shift. Hence, the means for the calibration was then manifested over a range of more

than 2 per mil on the 5'*0 scale, or roughly one-third the magnitude of the glacial-interglacial shifts seen

in many ice cores from around the world (Thompson et al.. 1998). Consistent with studies involving

concurrent 8I!<0 and surface temperature (T,) measurements made throughout the Arctic region

(Dansgaard et al.. 1973; Johnsen et al., 1989). a consistent linear relationship was established normally

written in the form of the standard paleothermometry equation,

51!,O(0 = oT,(r) + P (%o) (Eq. 5.3.1)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. where a and P are time-independent coefficients representative of the isotope and temperature data

generated over a particular time interval, t. Dansgaard's initial North Atlantic/Greenland data collection,

gathered over a wide temperature range of -5° to -50°C, generated the following equation.

6 !!,O(0 = 0.69Ts(f) - 13.6 (%o) (Eq. 5.3.2)

Subsequent studies produced similar slopes (a values) of 0.62-0.67 for annual data over short time spans,

but calibration studies over longer periods (Jouzel et al.. 1997). from centuries to millennia, indicate

lesser slope values, down to values of 0.33 for the last glacial-interglacial transition in central Greenland

(Cuffey et al.. 1995). Intermediate values of 0.5-0.6 have been found to be applicable to records that span

the most recent climatic oscillation including the Little Ice Age. Calibration of oxygen isotopes via

borehole temperature modelling for a central Greenland ice core (GISP2 site) yielded the optimal result

(Cuffey et al.. 1994).

6lsO(f) = 0.53T,(r) - 18.8 (%o) (Eq. 5.3.3)

for a length of core that spanned 1340 years (649-1989 A.D.). An analogous calibration for GB97C1 was

deemed unfeasible based on the effects of latent heat release on englacial temperatures on VVindv Dome.

Instead, the most sensible approach for GB97C1 calibration proved to be a simple "two-sample ratio"

provided by the step function. Through comparison of the respective mean values of GB97C1 51!lO and

temperatures from the composite history (Fig. 5.11). for long periods (60-75 years) before and after the

abrupt rise, the following palcothcrmometry equation is generated.

6l!fO(/) = 0.55T,(/) - 8.1 (%o) (Eq. 5.3.4)

The mean temperatures for both periods (1840-1899 and 1920-1993) from the composite history,

calibrated to conditions at Rudolf Island station near sea level, were reduced by 3°C (equivalent to 509 m

of elevation change with a lapse rate of 0.6°C/100 m). to approximate actual conditions at the Windy

Dome summit. The resultant time series of paleotemperatures derived from the GB97C1 oxygen isotope

measurements is depicted in Fig. 5.12a.

The GB97C1 slope value of 0.55 agrees well with the GISP2 results, and although that study was

based on a much longer time window (1,340 years compared to 160 years), it involved similar isotopic

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. -1 0

to <1) o «> " 2 0

annual values 5SRM (1-3-4-3-1) i 1------1------1------1-1------1-1------1-1------1-1------r 2000 1900 1800 1700 1600 1500 1400 1300 Year (A.D.)

Fig. 5.12 Comparison of temperature proxy reconstructions from Graham Bell (1997) Core 1. a. 518O-annual temperatures, and b. melt-proxy summer temperatures.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. variations in the l-2%o range. As shown by Boyle (1997), the 6lsO-T intercept (or P value) is dependent

upon the initial equilibrium temperature for the moisture source with more negative values for warmer

evaporation conditions. The large discrepancy in P values between the calibration for GB97C1 and that of

the companion GISP2 core likely indicates a more northern source for moisture for Franz Josef Land.

Johnsen et al. (1989) suggested a latitude range of 35-40°N for the bulk of moisture reaching Greenland

and initial equilibrium temperatures in the 20-25°C range. In contrast, the resultant P value of -8. l%o for

GB97C1 corresponds to a mean source temperature in the vicinity of 5°C. conditions that currently exist

in the region near Iceland (65-70°N) in the Norwegian Sea. in the absence of a more indisputable

calibration scheme, a more accurate assessment of the source location seems unlikely. The higher latitude

suggested for Franz Josef Land source moisture compared to Greenland might reflect water-recycling

activity along the North Atlantic storm track. Specifically, stable isotopic signatures in water vapor would

be largely lost whenever the bulk of the cloud moisture was rc-rcleascd back into the open ocean to then

be replaced by newly-generated water vapor in the extensive convergence zone along the Atlantic-

Norwcgian Sea track. In this situation, only the last evaporation stage would be recorded in isotopic

parameters such as the paleothcrmometry intercept value and d-cxcess values.

The calibration methodology just described for GB97C1 circumvents the apparent offset in the

timing of the abrupt warming that occurred in the early 20th century by not incorporating values from the

20-year period between 1900 and 1920 in the determination of the two coefficients. The roughly 10-ycar

lead time between the initial rise in Graham Bell 61!lO and the subsequent strong temperature shift cannot

be explained convincingly, due in part to the uncertainty of the precise dating in this region of core (no

Katmai (1912) eruption signature was distinguishable). But given that dating accuracy' improves greatly

just a few decades earlier with a sequence of eruption events as guide, it is more likely that the lead time

in the isotopic record either reflects actual timc-trangressive behavior or else a large persistent vertical

migration of meltwater. Solid-liquid fractionation (described in Section 5.4.1). if in a state of "secular

equilibrium." could only act to confuse signals between a given layer and those just below and would not

lead to additional sinking of this abrupt climate signature. If the timescale were truly correct and the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. entire 10-year lead then attributed solely to percolation effects, it would indicate that (at this particular

time in history) a far larger amount of water-mass migration of accumulated ice had occurred, in contrast

to the percolation of mainly trace materials described earlier. Of course, this hypothetical water-migration

pulse would necessarily have had to pass through numerous annual layers while leaving the seasonal

oscillations generally intact, which would be counterintuitive given the trends in Fig. 4.6. Furthermore,

the magnitude of seasonal oscillations in §imO actually increases somewhat in the period between 1900

and 1920, even in this zone of high melt percentage.

Without further evidence, the validity of these conjectures must be consider unresolved, as must

the suggestion of a truly time-lransgrcssive warming front. However, several studies have pointed out that

the warming did appear to propagate from the Eurasian Arctic toward lower latitudes (Rogers. 1985. Fu et

al.. 1999). and evidence exists also that glaciers began to recede in Svalbard even before the abrupt 1919

warming (Hessclbcrg and Johanncsscn. 1958). This concept will be rcadresscd in Section 9.1 in

conjunction with a ncwly-rcvcalcd proxy record of North Atlantic variability that lends additional support

to the -1909 onset of winter warming in GB97C1. Because the stcp-function in ice core 6I!<0 itself has

been used as a time horizon for Eurasian Arctic cores (Watanabe et al.. 2001). it is important to determine

exactly when this event occurred at each location within the Barents/Kara region.

5.4 Application of the GB97C1 melt percent record as a summer temperature proxy

Whereas the stable isotopic record from Graham Bell Island primarily reflects wintertime

temperature due to its much greater variability over both short and long periods, the presence of

infiltration ice only reflects the maximum temperatures occurring in the late summer. In previous studies,

ice core-melt records have been successfully related to summer climate and seasonal ice cover in

neighboring seas (Koemer. 1977: Koemer and Fisher. 1990; Kameda et al.. 1995). The latent heat

required to melt accumulated snow provides the physical link by which a simple parameter such as melt

percent can be so powerful in reconstructing summer temperatures, as long as the glacier conditions have

not radically changed over time. On Windy Dome, the facies change to superimposed ice has been rare

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and only temporary, so the method was considered to be valid. In addition, the large englacial

temperature changes (bottoming out at -11.4°C) obviously did not prevent seasonal warming or the

surface layers to the melting point, as clear ice layers arc present throughout the core. Hence, "clipping"

of the record on either the high or low side has been minimal.

Based on empirical data (cited in Tarussov. 1992). the Krenke-Khodakov equation relates the

meltwater produced during a given summer. .-I (mm), to the mean June-August temperature Tu ,\ (°C). as:

A = {Tuk + 9.5)3 (Eq. 5.4.1).

This cubic expression relating snowmelt to temperature was further developed (Tarussov, 1992) for use in

reconstructing a summer temperature curve from the 1987 Austfonna ice core melt record (Arkhipov.

1999). Several model approximations were made in the derivation of the final transfer function. First,

wetting of surface snow/firn grains during First exposure to percolating meltwater causes an initial

densification (observable by the first-year rise from -0.40 to -0.52 g cm'3 as in Fig. 4.2) that is equivalent

to 9% of the original accumulation layer. Fully-infiltrated clear ice layers, however, only require a total of

50% meltwater infiltration to fill all the available pore volume, so that the total mcltwater-icc content is

determined by:

.1 = (0.41 * \l + 0.09)*6 (Eq. 5.4.2).

where M is the annual density-corrected melt percent and b is the reconstructed accumulation (mm w.e.)

for that year. By substitution, the summer proxy temperature is related to the melt and accumulation

estimates according to the following expression:

Tjm = [(0.41*A/ + 0.09)*Z>)1,3 - 9.5 (Eq. 5.4.3)

The lower profile in Fig. 5.12 represents a smoothed version of the annual JJA-temperature proxy

determined from GB97C1 by annual dating. The temperature range reflected in the profile (-2.5 to -5.5

°C) agrees well with a sea level temperature near 0°C and a summertime lapse rate of ~0.6°C/100 m (or

~3.0°C adiabatic cooling).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.4.1 Post-depositional influences on the GB97C1 melt percent record

The major concern in applying the melt-proxy formulae for temperature reconstructions is the

possibility of meltwater runoff from the Windy Dome summit. To examine this issue, average

reconstructed accumulations were determined for successive 5% intervals of M between 0-100% (Fig.

5.13a). which detected a roughly linear relationship indicating lower accumulation values at higher

meltwater concentrations. Instead of indicating true runoff, however, the linear nature of the trend points

to a simple "dilution" phenomenon, given that an equal quantity of meltwater will create higher melt

percent in a thinner layer, in agreement with Eq. 5.4.2. Dividing the GB97C1 history into the three

climatic periods (Fig. 5.13b) produced similar linear trends for the majority of the record, but also a

noticeably different relationship for the last 150 years, with a sharp decrease in accumulation when melt

percentages surpassed 85%. Therefore, it is suspected that the four or five extended periods of multi-year

clear ice formation during the 20th century did indeed lead to some limited net runoff and potential loss of

information about summer warmth, as well as potentially the reduction of some chemical fluxes (e..?..

Mg:\ SO f). However, dating within these ice layers was often challenging and hence this result is

largely uncertain. In any case, the record "clipping" cither by extended periods of no melt, or thick layers

of superimposed ice. is remarkably low for Windy Dome due to the fortuitous nature of the core

containing just over 50% melt. Finally, the problem of net transfer of meltwater from one layer to the

next in the Tjja determination is partly counteracted by an assumption that addition of meltwater from

subsequent years above will compensate for this loss, and that the average over any five- to ten-year period

is not likely to be greatly altered by vertical redistribution alone.

The formation of meltwater from deposited snow and ice has an additional circumstance that

leads to more restructuring of the final archived signal in a core from such a glacier. Just as >!*0

fractionates between liquid and vapor phases of water (Majoube, 1971), the phase change between solid

ice and meltwater also leads to isotopic separation. Lehmann and Siegenthaler (1991) determined the ice-

water fractionation factor (a) to be 1.0291 for oxygen-18 and 1.212 for deuterium. Hence, meltwater

Recon. Accumulation (H20 eq.) Recon. Accumulation (H20 eq.) Fig. 5.13 Relationship between melt percent and reconstructed accumulation for for accumulation reconstructed and percent melt between Relationship 5.13 Fig. 0.8 0.7 0.6 . - 0.5 0.8 0.7 0.7 0.6 0.5 0.5 0.4 -

1 2 3 4 5 6 7 8 9 100 90 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 100 90 80 70 60 50 40 30 20 10 0 GB97C1 for a. all years, and b. separated into three climatic periods. climatic three into separated b. and years, all a. for GB97C1 1 1 1 1 1 1 1 1 | T | 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 H a v 1225-1450 "Medieval Warm Period' "MedievalWarm 1225-1450 v - 1451-1850 "Little 1451-1850 Ice Age" 1851-1997 "20th century"1851-1997 Annual Melt Percent Melt Annual A Annual Melt Percent Melt Annual o 100 1225-1997 (Allyears) 1225-1997 V

r20.63 = b regression: linear = 0.70-0.001 = 9M

formed initially will be ~3%o depleted relative to the remaining fim/ice, a smaller effect than the liqmd-

vapor change where differences can be more than 10%o. depending upon the temperature during

evaporation and kinetic factors. Amason (1969) first documented the influence of post-depositional

fractionation on isotopic composition in glaciers in Iceland, where great quantities of meltwatcr-loss

caused 5D values to rise significantly. However, with only minor amounts of meltwater loss in GB97C1,

the ice-water fractionation phenomenon can only cause reorganization of the detailed signal over limited

time windows. The influence of fractionation at the annual scale can be witnessed in Figs. 4.2 and 4.6 by

the chaotic nature of the annual oscillations in 6lsO. In some cases, it is obvious that percolation mixing

has smoothed out the annual variations, but in other places, ice-water fractionation has actually enhanced

the annual signature. Given the in-phase relationship between meltwater ice and depleted 81!lO (Fig. 4.5).

which is still likely to be largely due to the enhanced capture of percolating meltwater by tightly-packed

wintertime ice grains, it can also be argued that dear ice layers reflect a portion of meltwater depleted by

fractionation. Also, the large disparity between 6,sO values in years 1987-1989 among the various 1994

short cores (Fig. 2.3) may also be partially due to differential fractionation between the sites. Noting the

higher density/mcll content in ZA94CI within the accumulation years 1986-88 and 1991 (i.e.. March

1985-Feb. 1988 and March 1990-Feb. 1991) relative to the GB94C1 core (Fig. 2.4b). it can be seen how

these layers may have depleted by infiltration with the intermediate two years of accumulation being a

source for the lower ice layers and thereby enriched in the process.

Because of the melt percent estimates that were made on every GB97C1 sample prepared for

6lxO analysis, the influence of fractionation could easily be determined. Fig. 5.14 shows the frequency

distribution of melt percent estimates, and Fig. 5.15 illustrates the average 51!fO value at each 10%

interval of melt percent, with the anomalous recent past separated from the remainder of the GB97C1

record. Here, it is seen clearly that ice-water fractionation is manifested in the ice core record, as high as

0.90%o separation (roughly one-third of the maximum possible) over the last 100 years. While this

relationship seems to mimic the alignment of melt and 5IS0 of Fig. 4.5, seasonal variations are not likely

to govern this result, partly because the character of the melt record is reflected mostly by thick ice layers

101

(% o ) 2000

6180 1000 Count Fig. 5.15 Relationship of 8I1!0 vs. melt (infiltration ice) percent for GB97C1, in 10% increments increments 10% in GB97C1, for percent ice) (infiltration melt 8I1!0 vs. of Relationship 5.15 Fig. -16 -18 -17 -19 -20 0 Fig. 5.14 Distribution of samples cut from GB97C1 according to estimated to according GB97C1 from cut samples of Distribution 5.14 Fig. (total 9,029 samples). Shift values due to solid/liquid fractionation given at right for for right at given fractionation solid/liquid to periods. due time values Shift different samples). 9,029 (total 1 2 3 4 5 6 7 8 9 100 90 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 100 90 80 70 60 50 40 30 20 10 0 W eighted Averages Averages eighted W melt (infiltration ice) percent, in 10% increments (total 9,029 samples). 9,029 (total increments 10% in percent, ice) (infiltration melt -18.61%o -18.92%o 16.53%o I ~1 20th century 20th ~1LIA / MWP I I I Melt Percent Melt 102 Percent Melt All— - v - MWP / LIA / MWP - v - - W eighted Averages eighted W a — 20th century century 20th a ples sam -19.34%o 0.41 %o -19.02%o 4 — 0.90%o 0.42%o Shift that cross annual boundaries. Also, with the level of interannual isotopic variability exceeding the

seasonal oscillations in many parts of the core, it is understandable that the overall average values here

(determined at each melt %) expose other processes instead. Indeed, the fact that the 5I!tO difference

between the <50% and >50% melt segments increases during the period with the smallest annual signal

(demonstrated quantitatively in Section 7.2) proves that the modest seasonality is not dominating this

relationship. The planned d-exccss study of GB97C1 will also incorporate a test to determine if ice-water

fractionation has a detectable influence on this parameter as well. Because the ratio between the

respective a values for the two elements (7.3) differs from that of the Meteoric Water Line ( 8 .0 . given as

Sl!,0 = 8 * 8 D + 10%o (d-cxcess)), melt fractionation can also yield signatures in d-cxcess. Again, long

term averages of d-exccss should not show any signs of this influence, apart from the few zones affected

by some net meltwater loss from the summit.

5.5 Multi-proxy method for estimating DJF temperatures from GB97C1

With a pair of GB97Cl-bascd proxy records responding independently to annual and summer

(JJA) temperature variations, it then became possible to combine these histories to estimate winter (DJF)

temperatures by calibrating against the meteorological data (from Section 5.2) once more. Using the

monthly temperature values for Franz Josef Land, quarterly averages were determined for both Dccembcr-

February and June-August, 1930 to 1993 inclusive. Simply by averaging the DJF and JJA composites

together, a fairly accurate estimate of the average temperature for that calendar year (including all but the

initial December value, which represents the end of the previous year) is generated. For the FRZJSFLD

composite, a correlation of 0.61 (r. 1930-1993) was found between actual annual temperatures and the

DJF-JJA mean used as proxy, with only a 1.68°C offset (proxy warmer) between the long-term means.

Because this history' does not include the large transition of the early 20th century, the same test was done

with the four-station SVALBARD composite (calibrated to Bjomaya climatology). Over the longer.

WWII-intemipted period (1912-1940. 1947-1993), the analogous DJF-JJA means correlated to the actual

annual temperatures for Svalbard with a r of 0.76. and 0.85 for the earlier period alone when

103

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. temperatures were rising steadily (particularly during winter). Here, the offset between the proxy

estimates and the annual means was only 0.39°C, with again the proxy values being slightly warmer.

However, the important test of this DJF-proxy method was to determine if the correlation was stable

across the 1915-1925 transition itself, something that could only be assessed via the Svalbard data.

Examination of the time series of departures of the proxy values from the annual means uncovered no

qualitative difference in the ability of the method to simulate the 12-month data. No appreciable trend

was observed even when crossing the abrupt climate transition, and the correlation between temperatures

and the proxy departures was nil ( r = 0.002). Hence, simple of the DJF and JJA temperatures averages

(accounting just for mean differences) proved to be a satisfactory predictor of annual temperature

variations for these two archipelagos.

With the 6l!<0 calibrated as an annual temperature recorder, and the melt percent applied as a

JJA-predictor (in conjunction with reconstructed accumulation rates), it was then possible to rearrange the

relationship developed above to generate DJF estimates (TDjp) for the 772-ycar GB97C1 history. For

FRZLSFLD. the offset in means was simply added to the calibrated 5I!<0 temperature (5“‘0-7’annl. using

the a and (3 values as discussed in Section 5.3. and then subtracting an additional 3°C for 500 m

elevation), and then the quantity was doubled before subtracting the melt-proxy JJA estimates as follows:

7W = (8lsO - 7 W + 1.68 °C)*2 - r„A (Eq. 5.5. 1)

Of course, because the natural variance in the wintertime temperatures is so much larger, the 7Djf

estimates produced reflect the isotope-derived contribution much more than the melt-proxied results. In

fact, the only appreciable difference in the nature of the TD!F history from the isotopic-tcmperature profile

itself is the magnitude of the step change between the recent past and previous centuries. Duplicating the

early Svalbard data itself, average DJF temperatures in Franz Josef Land appear to have abruptly warmed

by a remarkable 8.3°C following 1910 relative to the previous -700 year mean, and 9.4°C relative to the

150-year period from 1760-1909. The DJF multi-proxy reconstruction generated in this fashion, was

decadally-reaveraged and is shown in Fig. 9.1.

104

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 6

INTERPRETATION OF GB97C1 ION CHEMISTRY AND MICROPARTICLE RECORDS

6 .1 Overv iew of the soluble chemistry records

Although numerous common features exist in the anion chemistry records from Graham Bell's

Windy Dome, there are also certain constituents that display unique characteristics and point to separate

governing mechanisms. When examining the (approximately) 1-m averages (by core section/tube) and

the resultant pH values in Fig. 6 .1. the dominant feature is the marked change at ~57 m. coincident with

the step function in the isotopic record and corresponding to a date of about 1910. However, identification

of a Medieval Warm Period (MWP) signature in the ion chemistry record is less distinct, only perceptible

in the major sea-salt parameters Na* and Cl", and to a lesser degree, K* and NFLT. Other species, like

Ca2~, Mg:\ SOf' (Laki notwithstanding), and NOV display almost perfectly stable concentrations

throughout the first 600 years of record (as seen in the analogous time-based version in Fig. 6.2). with

evidence for rising values beginning around 1850 for all but N 0 3 which shows elevated values only after

1930. Employing the sodium record as a proxy for the true sea-salt aerosol component, so-called "pre

industrial" background concentrations of each ion were determined, partitioning each into sea-salt (ss)

and non-sca-salt (nss) components. Only the nitrogen-containing species lack an oceanic source, instead

being derived in nature from terrestrial biologic processes and in the case of nitrate, various

photochemical atmospheric reactions particularly in the presence of O 3 (Liang et al.. 1998). It is quickly

established that sea-salt is the dominant component to the total aerosol flux (Fig. 6.3) being incorporated

into the ice on Graham Bell Island, with anywhere from 50% to 93% of the total of each of the non-

nitrogen-containing ions being ss-derived. The potential loss of magnesium ions from the ice archive.

105

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 1 1 1 1 1 1 1 1 1 .1 1 1 1 1 1 I 1 _ L 1 1 1 __1_ 1 1 1 -J------J__L__1__L-. & s 8 - £ S - l z

a 8 - Q . _ a

o ’ 8 - z - -L w CO E P _ co a. — | r- wa.

w o A / i L Sa. ' S —i c l r § - i* -1- J k j

1 2 - i S 8 J

K* (ppb) K* V j i r r f ) ) C 50 150 100

E s 5 Y ^ V ji r M U J 1

E~ a. a ______

♦ z 4 4 w f V f U l 4 ^ 4 T3 aj ■e w - V > .£ j W i I

Fig. 6.1 1-meter averaged values (by tube) of all major ionic species from Graham Bell (1997) Core 1. and calculated pH values. Anion values based on detailed samples, cation values from 1-m survey samples. 106

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 16 ppb (17 ppb) ss (17 ppb) 34 ppb (55 ppb) ss (55 ppb) 51 51 ppb (810 ppb) (810ss ppb) 874 ppb 451 ppb (ss) U | r # / U \ j l tion) ^jxnirJVrHjlflAA f 138 ppb (-Laki) (114 ppb) ss (114 ppb) U 4 —I—i—i—I I —i—r—j—i—I—r —I—i—i—I t l I—i—i—I—i 1 pre-1800 averages 107 Year (A.D.) r —i—I—I—I—i—p-T—i—i 1 I I ’ 1 —i—I—I—I—i—p-T—i—i r —I 1900 1800 1700 1600 1500 1400 1300 1 1 ss (17 ppb)

t—i—i t—i—i i I—i—i ll ll contribu seasalt (expected ‘ ‘ . 1 1 . 49 ppb ' timescale. Anion values are based on detailed measurements, whereas cationvalues are based _! _! j 25 ppb 1800) meanconcentration and the contribution from sea-salt (ss) based on Na" concentration. “(flw on the 1-m survey samples. Values indicated attop right represent the pre-industrial (1225-

1 3 0 0 2 0 0 0 0 50 50 1.0 1.5 0.0 0.5 50 1.0 0.0 0.5 150 1 0 0 1 0 0 1 0 0 1 0 0 200 200 300 1 0 0

y (uidd)jo (uidd)+bn Fig. 6.2 1-m averagedvalues ofeight major ions measured in GB97C1, shown on the layer-counted (qdd)/HN (qdd).EON (uidd) .^QS (qdd) +z6w (qdd) (qdd) Reproduced with permission theof copyright owner. Further reproduction prohibited without permission. PRE-INDUSTRIAL LAST 30 YEARS f^eq .-1 r “ “ HCOj I I I H + H* + 40 C az Caz Mgz Mgz --3 0 ILL n h ;

20 Na Na

- - 10

- L 0 ANIONSCATIONS ANIONS CATIONS

Fig. 6.3 Mean ionic composition of GB97C1 ice over the pre-industrial period 1225-1800. and last 30 years (1968-1997): pH and bicarbonate ion concentration determined by simultaneous solution assuming ionic balance with minor constituents (bromide, organic acids) negligible.

leading to slightly lower concentrations than would be expected from a ss-source. will be discussed in the

following section.

A more thorough examination of the increased acidification of 20th century snowfall is possible

from the profiles depicted in Fig. 6.4. GB97C1 pH values (determined by ion-balance calculation) become

progressively lower (more acidic) toward the present in the depth range 30-60 m. in concert with recent

additions of H-SO 4 and HNO3 to the environment from anthropogenic sources. However, instead of a

smooth, persistent trend toward more acidic values, a number of regular oscillations in the total acidity arc

easily recognizable, including an exaggerated waveform in the uppermost active layer. The lack of a

108

S 0 42 (ppm) nss-S042' (peq I'1) Calc. pH 6.5 6.5 Fig. 6.4 Average sulfate, nss-sulfate, and calculated pH values (bold line, 1-2-1 filter) from filter) 1-2-1 line, (bold values pH calculated and nss-sulfate, sulfate, Average 6.4 Fig. 6.0 5.0 5.5 4.5 4.5 0.9 0.9 0.6 0.0 0.3 1.2 20 25 10 15 0 5 5

A t f i l J V I\j L j \ I ;V 1 [ ] 2 4 6 8 10 2 140 120 100 80 60 40 20 0 stacked percolation cells (see text) roughly 13.5 years in length. in years 13.5 roughly text) (see cells percolation stacked 1783 eruption (125 m). The number designations on the pH profile indicate perceived perceived indicate profile pH the on designations number The m). (125 eruption 1783 GB97C1 (top 150 m), showing onset of anthropogenic influence (~70 m), and the Laki Laki the and m), (~70 influence anthropogenic of onset showing m), 150 (top GB97C1 1 —i —i —i —i —i —i —i —i —i —i —i —i —i r | i— i— i— |— i— i— i— |— i— i— i— [— i— i— i— |— i— i— i— |— i— i— i— |— i— i— —

2 3 2 1

U \ f s M 5 4 VV “V I 109 Depth (m) Depth

Laki 1783 surface (Tube 1) pH value reflecting true (primary) snow acidity for current precipitation (assumed to be

~5.2) may be due to -30 cm of lost surface snow during the drill initialization, and thereby partial

representation in the first meter-long section of core by the previous year's (post-melt) accumulation.

Also, because the first meter consisted largely of low-dcnsity material yet to undergo major diagcnesis.

this might indicate that the extremely high values of many chemical species in this delicate meter of core

have been influenced by infiltration/fractionation by mcltwater from the thermal-drilling operation itself

and hence do not reflect true values. Older layers just below the surface, however, arc also characterized

by higher values (near pre-industrial levels) primarily because the nss-S04:* concentrations arc noticeably

diminished, arguing for the downward leaching of acidic material. Continued evolution of these top

layers would likely have occurred in the following years, leading to values of -5.4 similar to the peak of

the oscillation just below, and -5.2 for average pH under current conditions.

As will be continually supported throughout the remainder of this discussion on the chemistry

record from Graham Bell, the unusual waveforms existing in the pH profile arc thought to represent a

stacking of successive "percolation cells" that involve especially coherent boundaries (i.e.. cells arc

underlain by a "stratigraphic trap") that isolate each new accumulating zone (with open vertical exchange)

from an older one that abuptly becomes closed off once a certain depth is reached. With only limited

detailed analysis of cations on which to rely, decreased variability and measurement error make it difficult

to perceive the continuation of these cells into older ice from the Little Ice Age. although the inference is

that they do persist throughout the entire length in some form. To gauge a rough periodicity of

percolation cell formation, each oscillation in pH is numbered sequentially in Fig. 6.4 from the surface to

the Laki horizon yielding a mean thickness of-13.5 accumulation years per cell.

Methanesulfonate (MSA) is often utilized as an indicator of marine biological activity in the

surface ocean (Saigne and Legrand. 1987; Legrand et al.. 1991; Whung et al.. 1994), with unusually high

concentrations and strong seasonality in the Arctic due to the common presence of the particular

dimethylsulfide (DMS)-producing species of plankton (e.g.. dinoflagellates. coccoliths) that bloom only

when polar night terminates. DMS oxidizes by separate pathways to both MSA' and SO*"' (by way of

110

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SO;), and hence the ratio of the two aerosol products is expected to be constant when considering only this

biogenic source. For this reason, the GB97C1 record was examined to elucidate the relationship of MSA'

to the nss-component of SO.f' and to then establish the source of the recent increase in acid sulfate.

Although measurements were attempted on both fluoride and MSA' for the 289 1-m integrated samples by

the gradient IC method, complications from other species with similar retention made quantification

difllcult. and hence these records are not shown. However, with judicious elimination of suspect values, a

flat baseline of MSA' values from 60 to 315 m depth is found (similar to SOf itself) with an average

concentration of ~12 ppb. Detailed measurements of MSA' on the upper section of core (discussed

below), however, were robust and indicated larger fluctuations with the highest meter-averaged value of

27 ppb (-7-8 m depth) but also periods of very low concentration (1-2 ppb) and thereby an overall

decrease toward the present. Hence, the nss-SOf'/MSA' weight ratio that distinguishes anthropogenic

nss-sulfate from other potential sources easily signals the upward trend in sulfate as a response to fossil

fuel burning. For the cold pre-industrial LIA period (118-228 m. 1500-1800 A.D.). a ratio of 2.5 is

obtained, within the range of natural values (i.e.. 2-6) cited for high latitude regions (Prospcro et al..

1995). In contrast, near-surface ratios of these two ions range between 40 and 60. far greater than that

found in any natural aerosol source, with low-latitude "clean air" aerosols only having a maximum weight

ratio around 20.

Pollutant sources of NO}' and SOj2' are expected to be from central and northern Europe,

primarily in wintertime due both to higher fossil fuel consumption and also more favorable circulation

patterns, though the existence of occasional trans-polar transport of pollutants from Asia or North

America has been seen in Iceland (Prospero et al.. 1995). Transport of fossil fuel by-products from North

America via the North Atlantic, however, has been considered minimal (Rahn. 1981: Carlson. 1981) due

to continual rainout dilution within the persistent low-pressure systems in the path toward Franz Josef

Land. While indications are that pollution injections into the Eurasian Arctic are infrequent but highly

concentrated, the nature of the ice archive at Graham Bell is such that any high variability in NCV and

nss-SQr' profiles would not represent this primary signature.

I l l

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.2 Basis of interpretation of ion chemistry records according to conservation in GB97C1 ice

Soluble chemistry constituents in ice core archives reflect contributions from many sources, not

only marine (sea-salt, marine biogenic) and terrestrial (dust, land plants/animals) but also input from

anthropogenic activity (fossil fuel burning, agriculture) and atmospheric phenomena (lightning-induced

chemical reaction). The use of chemical profiles as proxy climate histories is predicated on the

establishment of each ion as a conservative species in the core taken as a whole. While it is undeniable

that even moderately mobile ions arc transported vertically to deeper layers (in some cases by much more

than a single year's accumulation), if no appreciable amount of meltwater is lost from the system these

species might yet provide useful primary information averaged over longer time windows. The suspicion

that true loss of mass from the summit site on Windy Dome is rare (based on the analysis presented in

Section 5.4.1) docs not guarantee that soluble ions are not preferentially lost via effective leaching by just

small amounts of meltwater. Consideration of the conservative nature of the major ions was undertaken

by examining the ratios of the three ions largely believed to be primarily sea-salt derived, i.e.. sodium,

chloride, and magnesium. Contributions from windblown dust are likely very small (Keene et al.. 1986)

in such a remote polar site with very little exposed land in the vicinity and following a long track of open

ocean (or sea ice) from moisture source to deposition site. Indeed, insoluble dust concentrations arc very

low to the point of rarely producing visible layers.

Detailed cation measurements were made on samples that were retained from the original flrn-

sampling procedure, representing approximately the top 25 meters of the GB97C1 core. In the process,

the opportunity was taken to simultaneously re-evaluate these 361 samples for anions, utilizing a gradient

procedure that also measured fast-eluting minor anions such as fluoride and methancsulfonate (MSA ).

Bromide, an additional ion present in small quantities (2.8 ppb mean concentration expected) due to the

abundant sea-salt presence, was detectable but not distinguishable from chloride using this method. Other

organic acid ions such as formate and acetate were also detectable, but once in liquid form rapid exchange

with the open atmosphere precluded quantifiable results. The lower seven profiles of Fig. 6.5 depict a

common recent history, seemingly differing only by the degree to which each ion is influenced by leaching

112

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Q. ' Q. 200 - - V— fijbijJlJLA _1i! _U j ■O Q. ■= /I _ 0 'Iilji—*. JLHnnJf yi -.An . . Ji JL i~ Ji l J U . . J i .a -- Q. Q.

(5 ^ . .. __ J*rVWiWJkjAK 4_ E 3Q. cU o O h J I P V A a ^ a ______m J U m , S' Q. Q.

V A V 1!

Q. Q.

f ' V.JO#A j v \ I W V ^ v a ____ £3 Q. Q. -i lln n CO O Aj J E Q. 3

♦ CD z ■ V l L i ^ v l\hk- E Q. 3 u j ■O Q.

Xz f w - r " i---1---1---r r -i----T---- 1---- 1---- r----1---- r T “ "j ' I “ T T I '| T ■ i i 1

Fig. 6.5 Detailed profiles of all major (and two minor) soluble species in the upper 25 meters of GB97C1, ordered by the apparent degree of percolation influence, from ammonium (minimum, bottom) to MSA (maximum, top); K' and F indeterminate. 113

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and redeposition at lower depths. (Note however, that decadal- to century-scale variations, which would

be seen only as subtle differences here, are not being considered at the moment.) The zone between 13.0

and 18.S m in particular has been heavily leached by meltwater that can be seen manifested in the visual

stratigraphy as a 4-m thick clear ice layer (17.5-21.5 m: see Fig. 3.3) spread evenly across the point at

which concentrations rebound (at -19 m). From the relative appearances of these profiles, the elution

sequence of MSA' > SOf > (NCff - Mg2' - Ca2*) > (Na' - Cl ) > NH.r can be suggested, with F and K'

indeterminate due to their uniqueness (see discussion below). This sequence agrees well with other

studies (Davies et al.. 1982: Brimblccombe et al.. 1987; Bales et al.. 1989; Cragin et al.. 1993: Eichlcr et

al.. 2001) that have indicated sulfate ion as particularly mobile, nitrate somewhat less so. and ammonium

and chloride as more tightly contained in ice grains.

While anion measurements were done at very high resolution (3-4 cm) throughout the core, only

the integrated samples representing -1-m core sections were analyzed for the two cations (Na'. Mg2')

expected to primarily indicate the sea-salt component. Hence, the determination of the ratio properties

(i.e.. slope, intercept, temporal stability) of ion pairs was necessarily done only on that scale. Fig. 6.6a

depicts the linear relationship between the two dominant sea-salt ions culled from the cation survey

analysis that closely mirrors the line produced by pure sea-salt aerosol. Although the chloride values used

in this slope determination were averages from the fine-sampling analysis, the 1-m integrated

measurements produced nearly identical results. Hence, the slight scatter away from the regression line is

believed to be due either to post-depositional influence or else minor secondary sources of cither ion.

Support for the former explanation is provided by the profile in Fig. 6.6b, which shows the Cf/Na'

equivalent ratio over the length of the core. While it can only remain speculation, the apparent similarity

between the ratio and the solution pH (shown superimposed in Fig. 6.6b) suggests that the periodic

enrichments of chloride relative to sodium are more likely to be due to preferential (albeit subtle)

mobilization of sodium in this glacier. Most evident is the lone Na'-enriched zone occurring just below

the base of the large ice layer at 21.5 m. whereas ice within the 4-m ice layer itself is strongly Cl -

enriched. The slight enrichment of chloride over sodium in GB97C1 as a whole may be due to

114

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 0 0 (1225-1997) 80 - Cl‘ = 0.81 + 1.21 *Na r2 = 0.985 Cl' = 0.0 + 1.16*Na+ ecr 60 - (U

o 40 -

20 -

0 20 40 60 80 Na+ (neq/l)

Cl'/Na

o cb &

sea-salt Calculated pH

“i—i—i—|—i—i—i—i—|—i—;—i—i—|—i—m —i—|—i—i—i—i—|—i—i—i—i—|—r 50 100 150 200 250 300 Core Depth (m)

Fig. 6.6 a. Plot of sodium vs. chloride in GB97C1 by 1-m tube core sections; by single measurement (Na*). average of individual samples (Cf), compared to the relationship from pure sea-salt aerosol: b. the O'/Na* ratio (in equivalents) by meter in the ice core, compared with calculated pH values (both 5SRM, 1-3-4-3-1).

115

Na* (fieq/l) Na* (neq/l) Fig. 6.7 Plot of magnesium vs. sodium in GB97C1 by 1-m tube core sections; by single by sections; core tube 1-m by GB97C1 in sodium vs. magnesium of Plot 6.7 Fig. 0 - 60 80 0 - 40 0 8 20 0 - 60 0 - 40 20 - - zone, zone, measurement from combined samples, for a. high-melt zones (top) and b. low-melt low-melt b. and (top) zones high-melt a. for samples, combined from measurement Avg. eq. ratio (Na*/Mg2*)= ratio eq. Avg. .7 48 wihe) # (weighted) 4.87 5.27; 4.22; 4.16 (weighted) 4.16 4.22; (Na*/Mg2*)= ratio eq. Avg. Na* = 0.0 + 4.41 *Mg2*4.41 + 0.0 = Na* Na* = 1.39 + 3.79*Mg2* + 1.39 = Na* (1500-1850) • i.e., • m * * LIA (bottom). LIA r2 = 0.77 r20.77 = R • • < r B 9 .1. 1 . * Mg2*(neq/l) Mg2*(neq/l) 116 * 10 10 top 7 values (circles): (circles): values 7 top r20.67 = 4.05*Mg2* + 0.58 = Na* without Regression (1225-1500, 1850-1997) 1850-1997) (1225-1500, r20.56 = Na* = 0.0 +4.41 *Mg2* +4.41 0.0 = Na* 3.51*Mg2*+ 6.53 = Na* HIGH MELT HIGH LOW MELT LOW 15 15 a. 20 20 preferential scavenging of sodium aerosol during transport following the reaction of NaCl particles with

sulfuric acid (Legrand et al.. 1996).

Unlike the NaVCl' relationship, the NaVMg2' ratios (Fig. 6.7) are highly-dcpendent upon melt

influences, with the plot of values corresponding to the warm (summertime) phases of the record (i.e.. the

MWP and last 150 years) showing large deviations from linearity and a significantly non-zero intercept.

From the scatter of values in Fig. 6.7a. it can be seen that a large number of values do fall close to the line

for pure sea-salt composition, but that many others are skewed more toward higher relative values of Na'.

influencing both the slope and intercept. While the shallower slope produced by the high-melt regions of

the core might seem to indicate anomalously high values of Mg2', actually the true weighted average of

NaTMg2' ratios indicates just the opposite, i.e., that overall there is about a 10% average loss of Mg2'

assuming that both ions were solely derived from sea-salt aerosol. In contrast, the lower melt zone of core

deposited during the Little Ice Age (chosen as 1500-1850 A.D. for Fig. 6.7b) shows much less deviation

from the sea-salt line, with a roughly even scatter of values above and below the line, perhaps suggesting

relative movement of the two ions respective to one another, but no major loss of cither. The slope and

intercept values of the regression line are also closer to those of sea-salt aerosol, and become even more

compliant after eliminating the highest values that appear Mg2'-deficient. The weighted average of the

Na'/Mg2' in this zone (4.16) is also closer to the sea-salt value (4.41). and if the assumption of no loss of

magnesium is made, could indicate a small source of nss-sodium to the ice cap and thereby the suggestion

of a somewhat greater than 10% loss of Mg2' during the warmer periods.

Along similar lines, an estimate of SO.*2' loss can be made for the earlier of these two high-melt

zones, coincident with the Medieval Warm Period (1225-1500 A.D.). Whereas the total sulfate record

shows a flat baseline for all pre-industrial times, the rise in NaCl toward deeper depths translates into a

decrease in the calculated nss-component of SO.f\ Assuming that no change in the other nss-sources of

sulfate (mineral dust. DMS) occurred, a reduction from an average value of 35 ppb in the L1A to 8.9 ppb

in the MWP is indicated due to leaching out of the system. Against a background of 132 ppb ss-SCL2

determined solely for the MWP, this quantity would translate to a reduction in total sulfate by -16.5%.

117

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Additionally, this amount of mass loss from the pre-industrial period taken as a whole would revise the

SO f' average value up to ~ 150 ppb instead of 138 ppb. the ss-portion remaining unchanged of course.

While this analysis is more problematic given assumptions about two other potential sources that might

have had climatological influences, the estimate does appear consistent with the value of 10% derived for

magnesium, an ion that appeared just slightly less mobile in the upper portion of core as shown in Fig.

6.5. Another issue to consider is the deposition mechanism of these aerosols, in that increased

accumulation during the MWP (Fig. 4.13) could have yielded similar flux values for both periods without

any loss for the period before 1500. However, the high accumulation on Windy Dome would seem to

determine that the ion budget (including nss-SOf) was deposited primarily by wet deposition (Davidson.

1989) such that the relative reduction of sulfate in the early part of the record is not by "dilution."

Therefore, with the major components of ss-aerosol showing elevated concentrations during the MWP

without any regard to accumulation, the suggestion is that sulfate concentrations were affected in some

different way.

6.3 Interpretation of the SO f' and N03' profiles as an anthropogenic pollution recorder

Considering the dramatic rise of both anthropogenic H 2SO4 and HNOj in the GB97C1 core, the

overall appearance and magnitude of the recent trends can be compared with similar reconstructions from

other Northern Hemisphere sites. Some difficulty in assessing slopes and sustained levels is presented by

the oscillatory nature of the two acid components generated through intra-cell percolation activity.

However, utilizing the very simplest methodology, i.e.. linear regression, acceptable estimates of the 20th

century rise can be made. Choosing a regression in the time domain from 1900-1997 yields a base level at

the outset very similar to the 1850-1900 average of nss-SO^"’ o f-1.5 peq/1 (-70 ppb). and defines from

this point a rise to -7.5 peq/1 (-350 ppb) by the end of the record. Beginning somewhat later due to its

independent response to polluting sources (Benkovitz et al.. 1996), an analogous linear approximation

(1930-1997) for nitrate increase rendered a factor of three increase, from stable values of -50 ppb up to

-150 ppb by 1997. Results from Core 20D obtained in 1984 from southern Greenland (Mayewski et al..

118

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1986; 1990) revealed increases from 22-30 to 84 ppb (about 3-fold) for nss-S042' and ~55 to 115 ppb for

NOj' (about 2-fold). Given the 13-year offset in the time of extraction of these two cores, the respective

rates of increase are in fair agreement. Steeper rates of increase in anthropogenic sulfuric acid input were

suggested for a location (Schwikowski et al., 1999) where it is likely that similar European-derived

aerosols are captured as for Windy Dome. For Colie Gnifctti in the Swiss Alps. levels over 10 times those

of the pre-industrial background were determined. Interestingly, reconstituting the total nss-SO r fraction

from this core to match the same parameter as defined in GB97C1. produces nearly identical percentage

increases at exactly twice the concentration, i.e., a rise from ~3 peq/1 to ~15 p.cq/1. However, a sizeable

portion (~l. 5-2.0 peq/l) of the nss-component here is believed to be derived from the Sahara Desert and so

this influence, that dilutes the apparent rise to only a factor of five, would not be expected to be important

at the latitude of Franz Josef Land. On the other hand. DMS-exhalation from the ocean is considered a

negligible source for nss-S042' at Colle Gnifetti. whereas it might contribute as much as 35 ppb (0.73

peq/l) of the total sulfate amount for GB97C1. Because the dust-dilution is larger for Colle Gnifetti than

the DMS-dilution is for GB97C1. the possible loss of additional nss-S042' due to runoff of ion-enriched

mcltwaters. like that suggested for the MWP, may indeed have attenuated the signal of anthropogenic

increase in Graham Beil ice by some amount if indeed the two sites experienced similar inputs of

pollution.

6.4 Other aspects of the GB97C1 chemistry record

The history of ammonium (NFLO concentrations in the GB97C1 core shows a similar two- to

three-fold increase in levels over the past two centuries due to independent anthropogenic factors.

Gaseous ammonia emission in Europe more than doubled from 2.2 Mt in 1870 to 4.7 Mt in 1980. the

majority of the increase occuring since 1930 (Asman and Drukker, 1988). The sources of ammonia have

been identified as livestock waste products and fertilizer manufacture and use, the latter beginning on a

large scale only after World War II. In agreement with the timing of this development, NHT levels in

Windy Dome ice rise from an established baseline of ~25 ppb linearly to ~70 ppb by 1997. However, an

119

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. earlier baseline shift is evident that is not mirrored by noticeable changes in any other soluble compound.

Between 75 and 95 m depth, representing the 50-year period between 1820 and 1870, ammonium

concentrations rose by roughly two-thirds from 16 to 26 ppb. This phenomenon was not observed in the

core from Colle Gnifetti in Switzerland (Doscher et al., 1996), but these authors point out that enhanced

NH3-NHT conversion is possible in the presence of sulfuric acid. Indeed. Asman and Drukker (1988)

suggest that the upper limit of this acid-catalyzation effect would have already been reached by the year

1900 and perhaps even by 1870. It follows then that the initial rise in NHT may not have been due to

increasing agricultural activity but rather a synergistic effect from the appearance of large-scale coal-

burning. This should be considered even though the onset of nss-SO.f does not become apparent in the

GB97C1 record until somewhat later, perhaps due to some acid sulfate-leaching (delaying the initial pH

drop) recognizing that ammonium is particularly immobile in the ice and could not be expected to have

migrated into older ice. In GB97C1, the pre-industrial average concentrations of ammonium arc less than

half of those in the Swiss core (-16 ppb compared to 35-40 ppb), so the possibility exists that VVindv

Dome was more sensitive to these changes due to lower background levels as well.

Fluoride salts have unusual properties in ice (flouride itself being termed a "structure making"

ion) and also create an electric charge separation between the solid and liquid phases during freezing of

dilute ionic solutions, termed the Workman-Reynolds effect (Hobbs, 1974: p. 606-614). Maximum

freezing potential of fluoride salts occurs at concentrations on the order of 10'5 M, whereas NaCl causes

maximum potentials between 10"3 and lO”1 M (Hobbs. 1974; p. 608). For the uppermost 25 m of GB97CI.

where K~ and F ions are uniquely coupled, the total ionic concentration is -0.8 x 10'5 M. and given some

degree of fractionation between phases, the ionic content of percolating meltwater would be several times

higher. However, while this concentration lies precisely at the point where KF produces maximum

potential differences. NaF has similar properties and no relationship between these two ionic species is

seen in Fig. 6.5. For comparison. F is affiliated with the Ca~* ion in central Greenland ice (DeAngelis

and Legrand. 1994), though this is attributed to a gas-phase reaction between HF and CaC03 dust. While

the nature of the potassium-fluoride relationship in GB97C1 cannot be further addressed without more

120

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. data from other parts of the core, there is an expectation based on these earlier studies that this

phenomenon might be understood with more research.

Fluoride concentrations are very sporadic in the recent ice within GB97C1, with 238 (66%) of

361 samples showing less than 2 ppb F, but then 25 (7%) samples containing concentrations greater than

20 ppb. Mean concentration (not including the first core section which is very enriched) is ~7.5 ppb. only

a small portion of which is likely attributable to sea-salt aerosol (0.08 ppb if equivalent to seawater),

although F can be prcfentially incorporated into aerosols at the ocean/atmosphere interface (Carpenter.

1969). The fluoride levels in the recent past most probably reflect coal and fuel oil consumption, but also

may include some amount from eruptions and/or degassing from Iceland volcanoes. Both sources would

contribute fluoride as HF. and from studies of gaseous emissions (Cadle. 1980) coal burning would

produce a sulfate : fluoride weight ratio of 12 : 0.18 (or 66.7 : 1). Given the present nss-S04:' : F ratio of

350 : 7.5 (47 : I) in GB97C1, this suggests that little HF is scavenged before reaching Franz Josef Land

unlike in Greenland cores (DeAngclis and Legrand. 1994) or that Iceland is indeed a major additional

source. If fluoride did prove to be essentially a primary signature in the Windy Dome record, the spikes at

17.5 m (1981) and 23.0 m (1971) could reflect eruption signatures from Hekla in Iceland during 1980 and

1970. respectively.

The possibility of employing GB97C1 MSA* results as a regional spring/summer sea ice proxy

(as has been attempted for Svalbard by O'Dwyer et al ., 2000) was considered, but not deemed feasible in

the end. This conclusion resulted from the suspicion that not only is this ion particularly mobile in the

presence of melt (see Fig. 6.5). but also is likely to have suffered some amount of mass loss, perhaps more

than the mean 10% suggested for Mg:~ during high-melt periods (and yet significantly higher on an

episodic basis). Indeed, the levels of MSA' in GB97C1 were reduced in the near-surface layers (~8.5 ppb)

as compared to deeper ice (~12 ppb). a decline found during a time when sea ice has continued to retreat

(as inferred from the majority of observations and reconstructions). Although the Lomonosovfonna

(1997) ice coring site, where the MSA' study was based, is a higher location with less average melting

(estimated at 25%; Pohjola et al., 2002), similar percolation properties likely exist there. This inference is

121

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. made because although periods of meltwater formation may truly be somewhat rarer there (due to the

higher elevation), the annual average temperature (and hence ice temperatures at depth) are much warmer

(-2.5°C) and water may effectively percolate more freely. Windy Dome, even under current conditions,

has a much sharper negative gradient in the upper 10 m during late summer due to its stable ice

temperature at depth near -6°C. which will retard vertical motion. Also, higher accumulation (by -50%)

on Graham Bell would also counteract deeper penetration of meltwater, temporally-speaking. These

competing influences may indeed lead to a similar ion migration flux for these two glaciers.

The apparent high mobility of MSA' places into question the inference that this tracer can be

utilized as a primary proxy signature for sea ice and climate from Eurasian Arctic glaciers. However, the

nature of the link between this parameter and regional sea ice conditions suggests that secondary

processes may be creating an artificial signal, via a true snowmelt-SST connection (as produced by

Koerner. 1977; Kocmer and Fisher, 1990). The roughly 16-year cycles seen in the 76-year history

produced by O'Dwyer et al. (2000) are not too dissimilar to the 13.5-year cycles seen in the pH record

from GB97C1. previously suggested to be the average cell-lhickness in GB97C1 over the last two

centuries. Furthermore, it may be possible to relate high MSA' zones in GB97C1 at 8m (-1990). 12-13 m

(-1985). and between 19 and 24 m (1969-1978) to three similar events in the Lomonosovfonna '97 record

(Fig. 2a in O'Dwyer et al., 2000), ignoring the extreme surface-snow peak that (as in GB97C1) likely

represents a pre-melt signature. Even more intriguing is that the appearance of oscillations in the

Svalbard record suggest the same “stacked percolation cell" phenomenon, with concentrations often

ramping up toward higher values at deeper depths where the base of each cell is located (and where

extreme values commonly exist). The suggestion is then that the proxy usage of the Lomonosovfonna

MSA' record might not be based erroneously either in time (i.e., dating) or by its sensitivity to climate, but

rather may just be reflecting different mechanisms than were presented. The question remains whether

the formation and thickness of percolation cells in the ice is predominantly glaciological (site-specific) or

climatological (regionally homogeneous) in essence. There are enough differences between the surface

conditions (e.g., temperature, melt, snowfall) of these two sites to suggest that if the most mobile of the

122

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ions (including also S04:‘ and Mg2") did continually coincide throughout their respective lengths

(correlated independently in time), then the dimatological mechanism would be supported. In addition,

the proposal of a mode of Arctic/North Atlantic variability at similar intervals, i.e., 15-20 years (Mysak.

1995). would further argue that the initial distribution and concentration of melt layers respond to

dimatological forces, even as the meltwater (and soluble constituents therein) continually modifies the

nature of these same melt zones as time passes.

6.5 Characteristics of the history of dust deposition and size distribution in GB97C1

Very few dust layers are visible in GB97C1, and those that were detected occurred mainly in the

lower third of the core. Layers were seen differently by the two observers (Table 6.1), although three of

the seven potentially visible layers were detected by both researchers. The disparity' in detection may have

been due to the difference between natural and artificial illumination, viewing a "wet" vs. "dry" core

surface, and any alteration of the core and/or core surface characteristics following transport from the

field. The most easily discerned dust event in the core was the yellow-brown layer at -185.5 m. and

although it only produced the eleventh-highest dust concentration (>2 fim size fraction), it resulted in an

extremely large "instantaneous" concentration upon removing the dilution effect of the remainder of the

sample. (Dust concentration of the "clear" ice surrounding the identified layer was assumed to be

equivalent to an average of the two samples immediately above and below the dust event itself.) Other

layers are broader but more diffuse, including the 2.5 cm layer at 228 m depth that also yields very high

concentrations especially in the coarser fractions. Despite the fact that the very thin layer that exists at

-211.5 m depth yields the highest "instantaneous" dust concentration within the core, this layer is still

difficult to discern as a dust event because it lies precisely along a sharp contrast between bubbly and clear

ice. In general, the dust layers did not occur in a particular orientation with respect to the melt

stratigraphy, and so this layer was an exception.

123

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Layer Thickness (mm) Dust Concentration Avg. Approx. Dust Cone, (per ml) xlO4 Grain within layer* ml'1 xl0J Depth Year Arkhipov KAH >0.63 p.m >2 p.m Size (pm) >0.63 pm >2 (im (m) (A.D.) (Field) (Lab) 185.47 1627 3 mm 3 mm 29.0 4.7 7.2 290 47 204.76 1570 ------22 mm 48.4 13.8 6.6 65 20 211.54 1551 ------1 mm 76.4 8.7 6.2 2234 259 227.93 1501 ------25 mm 90.9 34.3 7.9 109 41 279.63 1347 8 mm 4 mm 38.2 1.7 6.6 16 7 280.16** 1345 1 mm ------18.4 4.8 7.3 ** ** 302.79 1267 24 mm 11 mm 22.7 7.1 6.5 39 12 Core Avg. 1.6 0.13 4.8

* Sample size is approximately 3 cm ** Dust concentration peak was spread across two adjacent samples, making uncertain the position of the thin, highly concentrated layer no longer visible. Average of two sample values used.

Table 6.1 Visible Dust Stratigraphy from GB97C1

Fig. 6.8 shows the relationship between the average grain size (AGS. as defined in Section 3.2.2)

and the dust concentration (small fraction) of each sample, plotted as the base-10 logarithm. All of the

visible layers lie above 5.3 (-200.000 particles per ml) on the logiodust axis, and to the right of 5.9 on the

AGS axis, suggesting that the condition of visibility requires both a high concentration of material and a

coarser distribution. Three layers (approx. 104.2. 137.9. and 149.2 m depth) with greater than 200.000

counts per ml were not visible, possibly because the particles were too fine. The concentrated coarse

layers detected in the analysis at 97.1 m (1841). 202.1 m (1577). and 260.1 m (1407) (marked by x's in

Fig. 6.8) were not perceptable to either observer, perhaps because the material in these layers lacked the

necessary degree of coloration to be seen.

Periods of lower dust deposition are in many cases affiliated with periods of higher melt percent

(Fig. 6.9). and hence the possibility that the larger-scale variability in the dust record is largely a post-

depositional signature is posed. Accordingly, simple ratios between the colder/dustier LLA (1450-1850

A.D.) and the wamer periods both before and after, yielded nearly identical 15% LIA shifts in both melt

124

log10Dust (>0.63 pm) (per ml) 6 - 5 Fig. 6.8 Plot of logl0(dust concentration) vs. average grain size (AGS) in Graham Bell Bell Graham in (AGS) size grain average vs. concentration) logl0(dust of Plot 6.8 Fig. - (1997) Core 1 (all samples), with region including visible layers indicated. layers visible including region with samples), 1 (all Core (1997) * - • • ■- •* • • Average Grain Size (|im) Size Grain Average r e f r v - v • > : 8 6 4 125 visible Layers 10 12 Average Grain Size -16 6 - 3 . 5180 spline200 -log10dust spline200 -1 7

-18 O O (% o ) CO - 1 9 -co O) -20

-21 100 -

80 -

60 -

40 -

20 -

0 -

o o

range for instrumental bias correction

2000 1900 1800 1700 1600 1500 1400 1300 Year (A.D.)

Fig. 6.9 Annual melt percent vs. microparticle concentration (corrected for instrument bias) and average grain size (AGS) (all 5SRM, 1-3-4-3-1) in Graham Bell Core 1 (1997). Superimposed on the AGS curve are the trends of GB97C1 5lsO and dust concentration (inverted) both produced by spline functions with stiffness 200.

126

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. percent and dust concentration. Specifically, mean dust counts of 14.6, 17.3, and 13.4 (xlO3) per ml (for

1850-1997, 1450-1850, and 1225-1450 A.D., respectively), appear in concert with respective melt

averages of 61%, 52%, and 59%. The very high values in the surface snow/fim (mirrored by the

uncontaminated pit samples) and the lack of an annual signal even in the coldest of periods (as in Fig.

4.1b) further suggest that any dimatological interpretation of the dust concentration profiles from

GB97C1 is problematic.

The average grain size (Fig. 6.9, top), however, is qualitatively different and exhibits a profile

with some bulk similarities to the isotopic variations, which respond generally to wintertime temperatures.

Yet when compensating for the skewed distribution inherent in dust concentrations by taking the base-10

logarithm of each annual value, the analogous smoothed profile of this parameter (also superimposed in

Fig. 6.9. top) also shows some gross similarity to the AGS trends. In fact, one might argue that the AGS

record reflects some proportion of both of these influences. If the fining of particles during the LI A docs

have dimatological significance, a potential mechanism might be the decreased duration of exposed land

on the non-glaciatcd portion of Graham Bell Island to the northeast of Windy Dome (Fig. 3.1) that might

be a local source of coarser dust. Of course, the cooler summers implied by reduced melting in the core

(and determined separately from the use of 8I80 as temperature proxy) could also be argued to have led to

shorter times of exposed land. So while it remains difficult to say whether the proposed influence of melt

percolation on dust concentration also influences the size distribution, there is some limited support for a

dimatological interpretation of the grain size parameter. The provenance of the dust found in GB97C1

cannot be determined without further study of the composition and morphology of the particles

themselves. However, studies have shown that large quantities of fine dust can be transported large

distances to the Arctic (Welch et al., 1991; Franzen et al.. 1994), and the possibility that some of the dust

deposited on Windy Dome originates in the Sahara Desert is supported by the latter study of an unusual

yellow-snow event in northern Fennoscandia during March, 1991. The rare visible layers in the GB97C1

core, in fact, might represent these unusual long-distance transport events from low latitudes.

127

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 7

SPECTRAL PROPERTIES OF THE GB97C1 TIME SERIES

AND COMPARISON TO OTHER PALEOHISTORIES

7.1 Spectral analysis of the GB97C1 melt, chemistry, and isotope records

To evaluate the periodic nature of the records from the deep Graham Bell ice core, a common

spectral technique designed specifically for noisy time series that relate to typically chaotic atmospheric

phenomena was employed. Singular Spectrum Analysis (SSA) is a method by which individual

oscillatory principal components (PCs) arc modelled by empirical orthogonal functions (EOFs) that reflect

the waveform as it is realized in the actual dataset submitted. The SSA Toolkit was developed by Vautard

et al. (1992) and subsequently adapted for use in the MathWorks(©) Matlab 6.1 commercial software

program by Eric Breitenberger of the Geophysical Institute, University of Alaska. Fairbanks.

Reconstructed Components (RCs) are complete time series generated by the SSA Toolkit that represent

any chosen individual or pair of PCs. Choosing a proper window length (M) requires an iterative

approach, optimizing the tradeoff between improved resolution and overly strict frequency tolerance

experienced with increasing window size. In general practice, M values no greater than 20% of the length

of the time series are used. Because only those oscillatoiy components with periods shorter than the

window length could be represented by a PC pair (comparable to a sine-cosine pair in traditional Fourier

analysis, and roughly equal in eigenvalue), M values were usually at least as large as the longest period of

interest, when possible. Following extraction of the significant RC pairs, mean periodicities were

determined by the maximum entropy method (MEM) component of the SSA Toolkit, and scaled variances

were determined for each pair from the eigenvalue spectrum.

128

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. With 772 years of continuous measurements of most parameters, the Graham Bell records

required little pre-processing before evaluating by SSA. Annual averages of 5**0 only required

normalization and detrending by use of stiff spline functions, as shown. To more closely approximate a

true normal distribution of values, base-10 logarithms of the chloride concentrations (in ppb) were

introduced instead of the original data. Melt percent data contain a peculiar binary-type distribution (as

seen in Fig. 5.14) and so the JJA-tcmpcrature proxy record (that showed a roughly normal distribution of

values) was chosen for spcctal analysis instead. For estimation of the annual signal strength and analysis

of individual climate periods, data from GB97C1 were "gridded" on a consistent bimonthly basis (i.e.. six

values per accumulation year) by a technique described in more detail by Henderson et al. (1999). This

time step interval was chosen due to the loss of true monthly resolution for the earlier centuries (Fig. 3.5).

The three climatic periods were defined here as the years 1225-1525 (MWP). 1500-1800 (LIA). and 1775-

1997 A.D. (19th-20th centuries), the overlap intended to counteract aliasing in the analysis, and the

extended length of the modem period necessary for applying suitable window lengths.

The output from the SSA analysis for the GB97C1 annual 5l!lO time scries is shown in Fig. 7.1.

with the sum of the ten significant RCs shown atop the raw data (with subtracted trend shown), followed

by the five individual RC pairs in order of variance represented in the total detrended signal. While all of

the spectral power displayed is of the interdecadal variety’, the possibility that higher frequency signals

may be lost by migration and fractionation effects is noted. The greatest variance (13.6%) is represented

by a waveform with a mean periodicity of -74 years and expressed most strongly during the warm climate

phases. Amongst the separate analyses for each climate phase (Figs. 7.2-7.4) this oscillation is manifested

somewhat differently, showing a reduced mean period (68 years) during the MWP (Fig. 7.4) and

becoming undecipherable during the shorter modem period (Fig. 7.2). Over much of the last 500 years,

the isotopic history of GB97C1 is dominated by periodicity in the 20-35 year band, represented by the

third-largest spectral component (23.1 year mean period) of the annual analysis covering all 772 years.

Whereas the 23-year cycle displays a persistent magnitude throughout the last 225 years, it is redefined as

separate components at both higher (16.0 years) and lower (32.5 years) frequencies during the LIA (Fig.

129

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RC1-10 36.6% var

Raw values/spline (dark line)

13.6% var

0.0 - RC12 (74 yrs.) 6.6% var.

RC34 (15.2 yrs.) 6.2% var

0.0 - RC56 (23.1 yrs.) 5.3% var.

RC78 (45 yrs.) 4.9% var

0.0 - RC910 (31.8 yrs.)

2000 1900 1800 1700 1600 1500 1400 1300 Year (A.D.)

Fig. 7.1 SSA reconstructed components representing the first 10 eigenvectors for the annual 8lsO. M=95. Detrended with spline (stiflhess=200) as shown atop raw values.

130

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 w o' 1 - £ 0 -

-1 -

-2 -

Raw vaiues/Spline (dark 0.5 -

0.0 - -0.5 - RC12 (1.0 yrs.) 17.2% var

RC34 (23.4 yrs.) 9.0% var. 0.4 ^ 0.0 -E 7.6% var -0.4 - RC56 (32.5yrs. + 4)

RC78 (8.3 yrs.) 0.3 H 0.0 -0.3 H RC9-10 (11.6 yrs.)

RC11-12 (5.3 yrs.) 4.0% var. T 1--- 1---1--- 1---1--- 1--- 1--- 1---1--- 1--- 1--- 1--- 1--- 1--- 1---1--- 1--- 1--- 1---1--- r 2000 1950 1900 1850 1800 Year (A.D.)

Fig. 7.2 SSA reconstructed components representing the first 12 eigenvectors for the bimonthly 51!iO anomalies, M=210, over the period 1775-1997. Detrended with spline (stiffness= 1000) as shown atop raw values.

131

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 to . W * w v V w w

Raw values/Splme (dark line) 16.3% var

RC12 (1.0 yrs.) 6.2% var.

RC34 (32.5 yrs.)

2.1% v ar

RC7 (70 yrs.)

RC8 (15.2 yrs. + 4) 3.5% var

RC9-10 (7.4 yrs.) - i — 1— 1— 1— |— 1— 1— 1— 1— |— 1— 1— 1— 1— |— 1— 1— :— 1— |— 1— r 1800 1750 1700 1650 1600 1550 1500 Year (A.D.)

Fig. 7.3 SSA reconstructed components representing the first 10 eigenvectors for the bimonthly 6lsO anomalies, M=360, over the period 1500-1800. Detrended with spline (stifFness=!000) as shown atop raw values.

132

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 "55 o £

values/Spline (dark line) RC12 (1.0 yrs.) 13.2% var

RC34 (68 yrs.) 11.3% var.

6.3% var

RC56 (17.3 + 19.3 yrs.) 6.3% var.

RC78 (15.6 + 21.0 yrs.) 5.5% var

RC9-10 (9.2 yrs.) 4.0% var.

Fig. 7.4 SSA reconstructed components representing the first 12 eigenvectors for the bimonthly 8I!fO anomalies. M=390. over the period 1225-1525. Detrended with spline (stiffness=1000) as shown atop raw values.

133

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.3). An additional minor component, strongest during the 19th century when record preservation was at

a maximum, has an ENSO-like periodicity of 3.3 years. This waveform follows two more components

(8.3 and 11.6 years) that lie near the frequency band of 9-10 years that Venegas and Mysak (2000; also

Wang and Ikeda. 2001) isolate as the dominant mode of wintertime variability over the last century.

Additionally, their spatial reconstructions indicated that the strongest response for this mode occurred in

sea ice concentrations within the Barents Sea. coupled oppositely to anomalies in the Labrador Sea.

Finally, their 30-50 year signal points to a maximum positive sea ice anomaly in the Greenland and

Barents seas at 1912 and 1971, near the position of isotopic minima in the RC56 interdecadal waveform

as well as the 12-component RC sum (Fig. 7.2).

The SSA results for the detrended logi0CI' anomalies (Fig. 7.5) include significant oscillations in

similar frequency bands, i.e.. decadal (11.7 years), multidccadal (24.5 years), and longer term (40-60

years) variability. The largest amount of variance is also at low frequency, with the three separate

bimonthly analyses (results not shown) redefining this mode at 67 years (I9th-20th centuries). 39 years

(LIA). and 63 years (MWP). The 11.7-vear component displays fairly consistent strength throughout the

772-year history, except for one short interval (1680-1730) intriguingly coincident with the latter portion

of the Maunder solar minimum period. The LIA and MWP SSA analyses also contain 5-year periodicities

representing small portions (~4%) of the total variance. The GB97C1 JJA temperature time series is

mostly represented by three RC pairs (Fig. 7.6) of similar magnitude oscillating at roughly 28.5. 50. and

34 year periods. The 50-year component is most realized in the 14th-16th centuries, whereas in recent

centuries a 12.3-year component has grown to equal significance. An analogous three-phase SSA

deconstruction of the bimonthly-melt % values (not possible with the JJA series, fixed at an annual basis)

shows a leading pair at 13.2 years, close to that determined roughly in the pH record (Fig. 5.4). Whether

this waveform is a climatological or glaciological phenomenon remains unresolved, a question that could

only be answered with more detailed study.

134

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 RC1-8 19.1% var.

0 log10CI (±std)log10CI -1 D oui wall iae/Q nlina friar Ir li n a 'i 2

0 -2 0.4 5.6% var. 0.0 -0.4 RC12 (46 yrs.) 4.7% var 0.4 0.0 0.4 RC34 (57 yrs.) 4.5% var. -0.4 0.2 0.0

- 0.2 -0.4 RC56 (11.7 yrs.) 4.3% var. 7 03 j- 0.0 RC78 (24.5 yrs.) 7 -0.3

2000 1900 1800 1700 1600 1500 1400 1300 Year (A.D.)

Fig. 7.5 SSA reconstructed components representing the first 8 eigenvectors for the annual log10Cr anomalies, M=120. Detrended with spline (stififness=200) as shown atop raw values.

135

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 RC1-8. 23.5% var. 0 -1 Raw anomalies/Spline (dark line)

7.0% var. o I* [\j f\j JJA Temp (std) 0.4 0.0 -0.4 RC12 (28.5 yrs.) 6.4% var

RC34 (50 yrs.) 0.3 5.4% var 0.0 -0.3 RC56 (34 yrs.) 4.7% var

RC78 (12.3 yrs.)

2000 1900 1800 1700 1600 1500 1400 1300 Year (A.D.)

Fig. 7.6 SSA reconstructed components representing the first 8 eigenvectors for the annual JJA temperature anomalies, M=105. Detrended with spline (stiffhess=200) as shown atop raw values.

136

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.2 The strength of the annual signal as determined by spectral analysis for the chemistry and isotope

records

Using the bimonthly SSA analysis from the previous section, it was possible to reconstruct the

magnitude of the annual signal in both the chloride and 5180 time series. Simple differencing between

peak and trough values within each year's seasonal oscillation, as represented by the leading pair (for

8ixO, RC12 in each of Figs. 7.2-7.4) produced a separate time series of annual signal strength. For this

analysis, identical window lengths (210, 360, and 390 respectively) were chosen for the two three-phase

dcconstructions, with the 25-year overlap intervals reconciled by incremental scaling to more strongly

weigh the output away from the "edges." A graphical comparison of the annual signal in CP and <5'*0 is

given in Fig. 7.7. which can also be considered a representation of the quality of each parameter as a

dating tool. As remarked in Section 4.1.2. the isotopic record is somewhat more influenced by changes in

the mcltwater activity in the core, as the annual range drops from a maximum of ~2.3%o in the heart of

the LIA to a minimum of just -1. l%o in the middle of the 20th century. This latter value is small enough

to suggest that the annual S1!lO signature at this point within Windy Dome is effectively removed, and

shows how close the ice cap exists respective to the equilibrium line altitude (ELA) to becoming

undatable. The annual signature in chloride also improves slightly in the colder periods, but because it

already represents a secondary signature involving the migration of ions through the snowpack (unlike

5lxO which is a modified primary signal), the differences are less evident. However, there is also a strong

80-year periodicity evident in the chloride annual signature that is independent of the long waveforms in

the chloride concentrations themselves. However, without knowing very precisely how the annual

oscillations in Cf are produced in the core (via what must be chaotic, multi-year post-dcpositional

processes), it is difficult to evaluate the similarity in period to solar Gleissberg cycles (Garcia and

Mouradian. 1998) as being meaningful or purely coincidental. No consistent phase relationship could be

established between the oscillations in Cl'-annual signal strength and the wavelet-filtered Fennoscandian

summer temperatures reconstructed from tree rings and used as a solar proxy (Ogurtsov et a /., 2002).

137

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1400 1600 1500 1300 as determined by the SSA-filtered component (RC12) Year (A.D.) C l' Annual signal in 8180; 1a - 1.7%o Annual signal 1a in Cl"; ~ 650 ppb 1900 1800 1700 from the bimonthly analyses; spliced together from three separate parts, as depicted in Figs. 7 2-7.4. 2000 Fig. Fig. 7.7 Annual signal strengths in GB97CI and 1.4 1.2 1.0 0.8 0.6 3 (0 0) Q. ro c 3 O) ro C C ■O I c/5 < ui oe

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.3 Comparison of the GB97C1 core result to other paleohistories

7.3.1 Arctic and Northern Hemispheric temperature proxy compilations

For purposes of evaluating recent and ongoing climate changes over a longer-term perspective,

several researchers have compiled well-spaced temperature proxy histories into individual regional or

hemispheric indices covering the last millennium. A comparison of six of these products is included in

Briffa et al. (2001) and shows clearly the three-phase climate pattern with the cold 17th and 19th

centuries separating the MWP from the anomalously warm 20th century . Two of these compilation time

series were selected (Ovcrpcck et al.. 1997; Mann el al.. 1999) and are shown in Fig. 7.8 aligned with the

temperature variations inferred from both GB97C1 melt- and isotopc-paleothermometry. While both of

these large-scale compilation products are suggested to mainly indicate spring and summer temperatures

(April-August), simple visual comparison suggests that each of the Windy Dome proxies shares certain

common features, but not all. Most obvious is the relative warm period between 1750 and 1820. seen

especially in the Arctic compilation (Ovcrpeck et al.. 1997). that is represented by normal melt conditions

in GB97C1 even as the isotopic record suggests the very coldest period in the 772-year history. However,

the summer temperatures in Franz Josef Land are here indicated to be rising sharply around 1850. while

both composite records show cold temperatures abruptly ending ca. 1910-20, just as in the Windy Dome

isotopic record. In fact, this dominant transition induces the isotopic record to more closely resemble

these summertime compilations. Given that Franz Josef Land has already been suggested to have a

tremendous division by season when considering climate changes, it is recognized that the melt-inferred

history has more inherent uncertainty due to its far lesser magnitude of variation. Furthermore, the spatial

pattern of summer temperature anomalies covers much less area and likely responds greatly to the position

of the sea ice margin, a phenomenon that is specific to a limited number of locations. It is also possible

that certain records within the compilation products shown reflect more strongly spring as compared to

summer temperatures, and hence incorporate characteristics of the larger wintertime variability.

139

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. -24 - (Overpeck etal., 1997)

•0 5 > u 0 .9 "c6

0.2 _>> co E o 0.0 c (0

CL - 0.2 - E a) X -0.4 -

2000 1900 1800 1700 1600 1500 1400 1300 Year (A.D.)

Fig. 7.8 Comparison of GB97C1 JJA (melt) and annual (Sl80 ) temperature proxy records, to Arctic summer temperature anomaly time series, compiled from 20 other paleoclimate records, and Northern Hemisphere summer temperatures reconstructed primarily from 12 regional climate indicators (tree-rings, ice cores).

140

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.3.2 Northern Eurasia tree-ring records

Given the limited and partly contradictory relationships suggested between GB97C1 and large-

scale summary paleohistories, it was deemed more appropriate to consider just individual records in those

places most likely to respond to similar climate forcings. For this reason, a transect of tree-ring proxy

records of summer temperature was collected spanning the northern margin of the Eurasian continent at

roughly 70°N latitude (Fig. 7.9). When carefully treated to retain low-frequency signals (Cook et al.,

1995; Esper et al., 2002), tree-ring growth and density profiles can yield valuable information about

climate change. The five temperature-sensitive dendrochronologies selected are shown in Fig. 7.10

aligned in wcst-to-east orientation, and compared to the TJIA reconstruction from GB97C1. A large

degree of sitc-to-site variation is easily seen amongst the six profiles, though the cooler LIA phase

between 1500 and 1800 A.D. is still generally recognizable in most. Most interesting is that the Graham

Bell profile appears to share far more similarity with the tree-ring records from the eastern sector

compared to the western sector. In fact, apart from a single warm event at -1760 that seems to be

common among all of the records, the finer scale oscillations in the Norway and Finland histories arc

completely opposite in phase particularly after 1800. In contrast, the warming shown at both Taimyr and

Chokurdak. Siberia around 1840 (not revealed by the Arctic composite of Overpeck et al.. 1997) is similar

to that which is inferred from Graham Bell ice. Overall, the Salekhard and Chokurdak histories show the

greatest similarity to GB97C1 summer melt, with a LIA-onset betwen 1450 and 1500 A.D.. and

consistently warmer temperatures (Salekhard only) in the centuries before. The Taimyr record includes a

unique extreme cold period around 1300. correlative to a very minor low-melt period in the Windy Dome

record. Another notable event is the extreme warming in the Salekhard record at 1470. opposing in

phase, but within a lengthy warm period in northern Norway. As will be shown in Section 8.2. this time

may represent a period of high melt and glacier retreat in West Spitsbergen.

141

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 1 0 North Pac i f i c Ocean

• •ring S«« U shktvsky S m o f Okhotsk

A Bona- Churchill RUSSIA (United Stetet) Alaska Chokurdak *

C/AN* ADA

Taimyr A

fc Nauk'^'Vavilov Ml tteon nz Gratam

Svatoard

Greenland Lomo’^fc. lan d « t\ Nova Zamlya Spttat^oroan A m u n d s\ Sarand Saa

Lake man RUSSIA

Norway

North /c# corg sites Atlantic Inchnadampf) a frgg-nng 0 sites O c e a n &

S e a l* a 500 1000 km

CQ/te Gnitetti

Fig. 7.9 Map of the Northern Hemisphere, showing locations of important ice core studies, selected tree-ring sites, and one cave site, considered in this study. 142

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Tornetrask (68°N, 20°E)

Lake Inari (69°N, 27°E

Graham Bell (81 °N, 64°E)

Salekhard 68°N, 70°E)

Taimyr (72°N, 102°E)

O) n

Chokurdak (70°N, 147°E) 10'S P

— i------1------1------1------1--1------1--1------1--1------■--1------1------1— 2000 1900 1800 1700 1600 1500 1400 1300 Year (A.D.)

Fig. 7.10 Comparison of summer temperature proxy reconstructions from: a. Sweden (Briffa et al.. 1992), b. Finnish Lapland (Briffa and Schweingruber, 1992), c. Franz Josef Land (this study), d. northern Urals (Briffa et al., 1995), e. central Siberia (Naurzbaev and Vaganov, 1999), and f. northeastern Siberia (Hughes et al., 1999). 143

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.3.3 Sea ice records and historical reconstructions

While one of the primary goals of the Graham Bell ice core project was to validate and

reconstruct a chosen core parameter as a sea ice proxy, this aspect of the research must for the moment

remain undetermined. As indicated in Section 2.3, preliminary relationships suggested between chloride

concentrations and local sea ice variations could not be substantiated with the deep core. Not only was Cl"

determined to be out-of-phase with the annual migration of the sea ice margin across the Barents Sea (Fig.

2.2), the wintertime maxima in all aerosol species (with perhaps the exception of NRO can not be

considered to be primary signatures of depositional flaxes. Furthermore, the profile of either major sea-

salt species (Na~ or Cl") over the length of the core mimics that of the stable isotope history very closely,

especially when plotted as the base-10 logarithm to approximate the same normal distribution of values.

Because the sea ice margin is roughly S00 miles to the southeast during mid-winter, it seems very unlikely

that the position of this margin (that has no apparent influence on the annual signature) would govern

scasalt availability to Windy Dome, even though the reduction of NaCl in the core during the LIA is

strongly indicated. Because a threshold change in polar front position is inferred according to the

extraordinary' enhancement of the 1910-1920 wanning, the suggestion then of differing advection patterns

for aerosol transport follows. A trajectory analysis by Carlson (1981) proposed that pollutant-rich Arctic

haze is more likely to be derived from sources at or north of the polar front based on meteorological

arguments. In particular, adiabatic expansion of air parcels from more southerly locations would

necessitate the rapid development of water vapor saturation and aerosol removal. It is through this

saturation process that the Arctic aerosol flux becomes stratified vertically in the lower troposphere

(Carlson, 1981: Rahn, 1977) with a dry, concentrated aerosol layer aloft commonly at -1.5 km.

In considering the seasalt variations in GB97C1. it appears most likely that the lower

concentrations relate to these advection and stratification phenomena. This concept is supported by the

rejection of a mechanism simply involving residence time, which would work in the opposite direction

(i.e.. increased fluxes in the colder, drier LIA expected). If it is true that the largest concentrations of

seasalt are deposited in situations when the air mass does not fully cross the polar front, then it can be

144

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. imagined that the brief, warm periods occurring with far northward intrusion of wintertime depressions

are key to seasalt deposition on Windy Dome. While these systems have favorable conditions for aerosol

removal, they would only be required to retain the seasalt for a period of roughly two days to reach

icebound Franz Josef Land. The positive excursions in temperature shown in winter for O. Vize (Fig. 4.3)

likely became rare events in the LIA. Therefore, it is postulated here that the perpetual southerly position

of the polar front during this time dictated that aerosols entrained in the open ocean east of Iceland would

have always been required to cross the polar front boundary and thus be depleted following rapid

development of saturated air. Another possibility to consider is the wind-driven cntrainmenl of aerosol

(Blanchard and Woodcock. 1980), in that these encroaching systems from lower latitudes arc often

energetic storms that could produce larger quantities of airborne seasalt particles at the outset.

Dominance of an Arctic easterly flow in wintertime would be both less energetic and also primarily over

pack ice. even though conditions for preservation of entrained seasalt would be favorable.

Fig. 7.11 shows a comparison of two reconstructions of sea ice conditions in the Barents Sea

region along with several potentially sensitive parameters from GB97C1. There is general agreement

between the two sea ice histories that conditions have become increasingly ice-free in the late summer

over the last century. This finding is confirmed as continuing over recent decades via satellite

measurements (Parkinson et al., 1999). However, there are no parameters measured in the ice core that

show this same trend: rather, conditions are suggested to have either been stable or growing slightly

colder since the midpoint of the past century. Summer temperatures from Graham Bell melt have shown

large-scale similarity to similar reconstructions from northern continental Eurasia (as discussed above),

but yet show no obvious relation to the paleolatitude of the August sea ice margin as reconstructed by

Vinje (1997: 1999) from whaling records. While one or two short-lived retreats of the margin to northern

latitudes may possibly be connected to melt events in the ice core, this implication is just as likely to be

coincidental given the large-scale dissimilarity. Therefore, it can only be hypothesized that sea ice

variability cast of 60°E, presumably a more critical longitude for Graham Bell climate, was largely

different than in the vicinity of Svalbard where whaling ships sailed. No observations of sea ice

145

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.0 -

c 0.5-

--16

0 . 0 - --18

--20

Q, -4 - L n _

Sea-ice conc. Latitude of sea-ice margin near FJL between 20° and 45°E

-so

100

o o o o o o o o o o C\j Year (A.D.)

Fig. 7.11 Comparison of three decadally-averaged proxy records from GB97C1 with the history' of August sea ice margin positions as determined by Vinje (1997; 1999), and annual sea ice concentrations from the updated Walsh and Johnson (1979) gridded data set (for 19 grid cells in the Barents Sea between 76°N and 81°N and 33.1°E and 70.0°E.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. conditions could possibly have been made in this region until after 1873 when Franz Josef Land was

discovered. Hence, it might be true that the inability to develop a sea ice proxy method for GB97C1 may

be related more to the lack of suitable observations. Also, since the onset of the satellite era in 1973.

changes in sea ice extent in the Barents Sea have been relatively small compared to those suggested by the

whaling data for centuries past, so calibration of any core parameter from GB97CI would be made

difficult accordingly.

7.3.4 Precipitation history from Scotland

True precipitation reconstructions, independent of temperature, arc rare and valuable for this

reason. An annually-dated cave calcitc structure (i.e.. speleothem) from Inchnadamph. Scotland (58°N.

5°W) was sampled and measured by Proctor et al. (2000). who then calibrated the growth record to local

precipitation data in northern Scotland. This record (Fig. 7.12). when compared to the reconstruction of

accumulation rates in Windy Dome (Section 4.3.3). shows one important common feature. Around 1930.

precipitation dropped sharply about 15% and remained diminished until 1975. With the exception of a

short-lived maximum, accumulation rates were reduced on Graham Bell at this same time, especially low

from 1950 to 1980 coincident with several zones of superimposed ice seen in the core. Similarity between

the two records degrades in previous centuries, in particular a large oscillation in the 17th century that is

very minor in the GB97C1 record. However, the overall structure in each record is higher precipitation in

the warmer periods, with the cave record showing consistently higher rainfall in the MWP between 1100

and 1330 (earlier period not shown). Also, the common linear increase of precipitation/accumulation

from 1750 to 1900 suggests that, at least in the recent past, the two sites are recording similar variations

in supply of moisture along a continuous moisture track beginning in the North Atlantic and continuing

into the Barents Sea.

More importantly, the inference can thusly be made that the high-melt zones of the mid-20th

century do not represent major losses of mass from the Windy Dome summit. It is these unusually low'

accumulation values that are most responsible for the period of reduced summer temperature (TuA)

147

Reconstructed GB97C1 Accum. (m w.e.) Inchnadamph Precipitation (m w.e.) 2.2 2.0 0.8 0.9 0.7 0.7 1.0 1.8 0.6 1.6 0.5 0.5 0.4 0.4 0.3

Fig. 7.12 Comparison o f a. precipitation history from Scotland (Proctor (Proctor Scotland from history precipitation a. f o Comparison 7.12 Fig.

00 90 80 70 60 50 40 1300 1400 1500 1600 1700 1800 1900 2000 from a speleothem record, and b. reconstructed accumulation (5SRM, 1-3-4-3-1) 1-3-4-3-1) (5SRM, equivalent). accumulation water m (both FJL reconstructed Bell, b. and Graham from record, speleothem a from 148 Year (A.D.) Year et al., et 2000) inferred inferred 2000) suggested for 1940-1970 in Fig. 7.10 above. Hence, the recognition of a common feature from a

climatologically-similar location, calibrated through this very same period, steers one away from

concluding that the low accumulation is a spurious result based on a suggestion of significant (>10%)

runoff. Furthermore, it would also suggest that the previous indication of significant mass loss (roughly

10 cm, or -15%) from the summit during those 35 years (post-1850) with greater than 85% melt was

perhaps misleading, and in fact the bulk of the melt derived from these accumulation years may simply

have become incorporated into lower layers.

149

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 8

A PROPOSAL FOR A COMMON EURASIAN ARCTIC

ICE CORE TIME SCALE BASED UPON THE GB97C1 DATING

8.1 The Windy Dome record in the perspective of the history of Eurasian Arctic ice coring

Because GB97CI is the first long Eurasian Arctic ice core record that has been generated with

continuous subannual resolution, it is also the first record that has been annually dated with high

confidence of accuracy (to within a single decade). A useful task was to look back at the collection of

Eurasian ice core records that have been produced over the last 25 years to discover if similarities between

those histories and GB97C1 exist that might warrant time scale revisions by cross-matching. Researchers

working over the years in both Svalbard and Severnaya Zemlya have generated numerous ice core

histories from various glaciers and ice caps (Tables 8.1 and 8.2). However, many of these have been

difficult to interpret given the low resolution and/or poor continuity in the analysis and therefore also

uncertainty in the time scales. In some cases, multiple layer-counting methods were used that were not in

close agreement. In other cases, simple model formulae were employed to yield an approximate age

profile without confirmation on the bottom end. Also, some glaciers in Svalbard that have been cored

(e.g.. Punning et al., 1980) have internal ice temperatures that are very nearly at the melting point for

which vertical transport of seasonal meltwater may be enhanced. However, because the three

archipelagoes in question are all located at nearly the same latitude and all lie in similar positions relative

to the summer sea ice margin (Fig. 2.2), the possibility of broad similarity was considered strong. This

concept was strengthened by the strong correlation between annual or wintertime temperatures between

Franz Josef Land and the neighboring island groups as shown in Figs. 5.3-5.4.

150

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Latitude/ Year Elevation Ice Core BH T(°C) Archipelago Ice Cap, Location Longitude Drilled (m asl) thickness Length Max/Min Neg. grad. Lomonosovfonna, 78-48' N -0.4/-2.8 Svalbard West Spitsbergen 17°30'E 1976 1000 m 220 m 201 m (0-107 m) 78”44' N 11 i t 17-34’ E 1982 1040 m 134.2 m 134.2 m ?/? 78“52' N I I n 17-25' E 1997 1230 m 127 m 122 m -2.5/ ? Haghetta, W. 79°IT N Pos. grad. » Spitsbergen 16°50' E 1987 1200 m 85.6 m 85.6 m -10.4/-9.4 Snatjellafonna, 79-08' N Neg. grad. » W. Spitsbergen 13°18'E 1992 1190 m 83.9 m? 83.9 m -1.3/-2.9 240 m Fritdjof Glacier, 77°50' N (119m Pos. grad. M W. Spitsbergen 14-25' E 1979 380 m 7 analyzed) -0.1/-3.4 Gronljord - 213 m Fritdjof Divide, 77-54' N (201 m Neg. grad. „ W. Spitsbergen 14°15'E 1980 450 m 213 m analyzed) -0.2/-0.4 586 m Amundscnisen, 77-17 N (368 m •I W. Spitsbergen 15°15’ E 1980 700 m 586 m analyzed) ? / ? Asgardfonna, 79-27 N Neg. grad. » W. Spitsbergen 16-43' E 1993 1140 m -200 m 185.3 m -5.0/-7.5 Vestfonna, 79°56’ N Neg. grad. •I Nordauslandet 19-31’ E 1981 580 m 208 m 208 m -0.8/-2.4 79°58' N Neg. grad. t i i t 2!°01'E 1995 600 m 210m 210 m -2.0/-5.0 Austl'onna, 79°50' N « Nordauslandet 24-00' E 1985 750 m -560 m 204.1 m -2.7/ ? 79°51'N Neg. grad. i t .. 24-08' E 1987 750 m 566.7 m 566.7 m -3.4/-8.1 79-50' N Neg. grad. i t .. 24-01'E 1999 750 m -560 m 289.1 m -2.S/-7.5 Franz Josef Windy Dome, 80°47 N Neg. grad. Land Graham Beil Is. 63°32' E 1997 509 m -500 m 314.8 m -5.5/-11.4 Severnaya Akademii Nauk. 80-30' N Neg. grad. Zemlva Komsomolets Is. 94°50' E 1986 810 m -720 m 561 m -9.7M4.7 t t 80-30' N (tilted?) » (continue hole) 94-50' E 1987 810 m -720 m 759.8 m " 80°31'N 1999- Neg. grad. • t » 94°49' E 2001 -800 m 723.9 m 723.9 m 7/-14J Vavilov Dome, 462 m - October 79-20' N 1978/9 (300 m Pos. grad. Revolution Is. 96-00’ E Hole 1 720 m 462 m analyzed) -6.1/-11.6 79°16’N 1979 •• i t 96°22’ E Hole 2 680 m 556.5 m 556.5 m ? / ? 79-12'N Neg. grad. " 96-40' E 1983 720 m 466.2 m 466.2 m -9.1/-10.3 • t 79-27 N « (North Divide) 95-21' E 1988 650 m 461.6 m 461.6 m ? / ?

Table 8.1 Sites, coordinates, and summary information about ice cores obtained in the Eurasian Arctic.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ice Cap, Location Core Accumulation Bottom No. 6‘*0 Avg 6 llfO Avg Melt% Designation Rate (w.e.) Age(est.) samples 20th c./LIA 20th c./LIA Lomonosovfonna, 1976 900- West Spitsbergen 201 mcore 65-82 cm 1100 A.D. 188 -12.9/-14.7 (34%) 1982 (a). 100 m, it 134.2 m core 40-45 cm 1655 A.D. N/A N/A 32%/28% 1997 ® 82 m. it 122 mcore 36-42 cm 1715 A.D. -1,600 -15.8/-16.5 (25%) Hiaghetta, 1987 (w/ hiatus) W. Spitsbergen 85.6 m core 5-20 cm -6.0 ka N/A N/A 7 Snotjellafonna, 1992 (2> 42.5 m. W. Spitsbergen 83.9 m core 48 cm 1925 A.D. N/A N/A •> Fritdjof Glacier, 1979 W. Spitsbergen 119m core •> 7 N/A N/A (-75%) Grontjord - Fritdjof Divide, 1980 1150- W. Spitsbergen 201 m core 70-160 cm 1600 A.D. 296 -10.7/-11.2 (-100%) Amundsenisen, 1980 1000- W. Spitsbergen 368 m core 70-80 cm 1200 A. D. 144 -9.6/-11.5 20%/26% Asgardfonna, 1993 ® 49 m. (49 m core) (estimated) W. Spitsbergen 185.3 m core 31 cm -1860 A.D. -130 -18/-20.5 (-10%) Vestfonna, 1981 500- Nordauslandet 208 m core 35-45 cm 1100 A.D. 69 -14.4/-16.0 62%/57% 1995 " 210m core 34 cm -1240 A.D. -200 -16.7/-18.2 90%/66% Austfonna, 1985 Nordauslandet 204.1 m core 57 cm -1550 A.D. 98 -I6.5/-18.4 84%/58% 1987 " 566.7 m core " -2.6 ka N/A N/A 82%/59% 1999 it 289.1 m core 45-50 cm -1200 A.D. -500 -16.6/-18.7 84%/62% Windv Dome, 1997 Graham Bell Is. 314.8 m core 59 cm 1225 A.D. -9,000 -17.1/-19.3 62%/52% Akademii Nauk, 1986 (converted) Komsomolets Is. 561 mcore 30-40 cm 3.5^4.5 ka 213(8D) -20.9/-22.6 •> 1987 759.8 m core it 10-13 ka 108 -19.5/-22.7 75%/39% 1999-2001 0-15 m. tt 723.9 m core 45 cm 7 7 7 (-50%) Vavilov Dome. (this study) October 1978/9 HI (this study) i® 300 m, Revolution Is. 300 m core 97 cm 1500 A.D. 144 -17.0/-19.5 69%/69 % 1979 H2 (this study) (this studv) it 556.5 m core 79 cm 1.6-1.7 ka 273 -17.1/-19.5 7 1983 (this study) (this study) it 466.2 m core 31 cm 5.0-5.2 ka 140 -18.4/-20.4 52%/42% 1988 (this study) (this study) " (North) 461.6 m core 26 cm 5.0-5.2 ka 225 -17.8/-20.6 69%/93%

Table 8.2 Summary of characteristics of ice cores obtained in the Eurasian Arctic.

152

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Historically, stable isotopes and melt percents have been the most commonly produced records

from Eurasian Arctic ice cores. Nearly all isotopic, chemical, and stratigraphic information from these

cores have been previously tabulated and archived in the data bank titled "Deep Drilling of Glaciers:

Soviet-Russian Projects in the Arctic, 1975-1990" (abbreviated DDGA) by S. Arkhipov (1999), currently

available on the World Wide Web for free download. Approximately ten long records of 5,sO and melt

percent are now available, although for certain cores only one of the two profiles were generated and

presented in the literature. One complication has been that some of the numerical datafiles of older

paleohistories that were produced from the Eurasian Arctic have apparently been lost over the course of

time such that the illustrations in various publications now provide the only source of those records. In

the analysis to follow, some records were regenerated in numerical form through digitization of published

graphs, cither by the author or from those produced by S. Arkhipov which were subsequently standardized

to a 2-m interval.

Ice coring in the Eurasian Arctic began in the mid-1970s on the islands of West Spitsbergen.

Svalbard (Gordiyenko et al.. 1981; Punning et al.. 1980) and October Revolution Island. Severnaya

Zemlya (Korotkevich et al.. 1985; Morcv et al.. 1988) to the west and east of Franz Josef Land,

respectively (Fig. 7.9). Soon thereafter, drilling projects were completed in other locations within these

two archipelagoes, eventually to include both large ice fields in Nordauslandet. Svalbard. Vcstfonna was

drilled to bedrock (208 m) in 1981 (Vaikmae et al.. 1985) and Austfonna first drilled partially (204 m) in

1985 (Arkhipov et al.. 1987) and then to bedrock (567 m) in 1987 (Zagorodnov et al.. 1990), although

isotopic compositions were not reported for this deep core. In most cases, measurements of 5uO and/or

melt percent from these cores were presented at very' coarse resolution, and often times included gaps and

occasionally also conspicuously-outlying data points. As coring continued in the 1980s and into the

1990s, the quality of the analyses gradually improved and duplicate records from various ice caps began to

isolate discrepancies, and also continuity when applicable.

During these later decades, other multinational teams retrieved ice cores from the Eurasian

Arctic. However, cores from Hoghetta (Fujii et al., 1990) and Snofjellafonna (Goto-Azuma et al.. 1995).

153

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. in northern West Spitsbergen, were either too limited in time or lacked complete analysis to be considered

for matching with GB97C1. In contrast, recently-obtained cores from both Austfonna (1999) and

Vcstfonna (1995) in Nordauslandet were appended to the matching effort following the initial chronology

development, given that they represented a concentrated new effort to improve upon the earlier records

from these same locations (Watanabe et al., 2001). Following the same computer-aided manual technique

of digitization, isotope and melt records from these two sites were later reproduced and added to the suite

of ice cores cross-correlated to GB97C1. Unfortunately, the presentation of the Asgardfonna. West

Spitsbergen 185 m core (Uchida et al., 1996) did not include stable isotope analyses, and the additional 49

m core (5'*0 profile shown in Watanabe. 2001) only appears to contain -130 years of record, so these

histories were not considered here.

Ten depth-based oxygen isotope profiles arc depicted in Fig. 8.1, oriented from left to right in

accordance with a longitudinal progression from west to cast. In every case except for GB97C1 (for

which smoothed 1-m averages are shown), the data presented are original raw values (as best as was

known) without any manipulation, other than graphically connecting lines across sample gaps that were

present in some records in order to produce continuous lines that aid in the detection of events and trends.

Several of the cores from Severnaya Zemlva continued past the 400 m depth horizon depicted in Fig. 8.1

(see Table 8.1), but are not shown in their entirety as the deeper portions do not correspond to the window

of time contained in GB97C1. The time perspective of the earlier portions of these longer cores will be

addressed in Section 8.2.1. Akademii Nauk ice cap on the island of Komsomolets. Severnaya Zemlya was

drilled over a period of two years from 1986-87 (Savatyugin and Zagorodnov. 1988: Kotlyakov et al.,

1990), recovering two cores from a nearly identical location. The 1986 core terminated above bedrock at

a depth of 561 m and was analyzed for deuterium isotopes (5D) in two segments (data only available from

the DGGA archive: Arkhipov. 1999) including the depth ranges 9 to 337 m (shown) and 472 to 557 m

(not shown in Fig. 8.1: see Fig. 8.6). In 1987, a team returned to the site and drilled a second core that

continued to bedrock at 760 m depth, although some amount of borehole tilting was presumed to have

occurred, resulting in an artificially-augmented core length (V. Zagorodnov. personal communication).

154

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CM X Oi SEVERNAYA ZEMLYA > (0 > CO goCO > o (0 CM >

CO CM CO > 5 ° 'TV'**! O to CM CO Tf CM N CO CD " - m i CD c o z O CM 2 5 if) CO CO CO o CM CM CO If) 0 CO (X CO 2 - o _J 1 C/3 in co _ CO CD _

CM COI in OI i .w '-S? CM U l o ' ' I 6 o m t 1 r

t© Fig. 8 1 lee core isolopic records from Eurasian Arctic, on depth scale; arranged (left to right) by longitude from west to east. O o O o CO M" (UJ) ijid a a

155

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The second core (AN'87) was analyzed at much lower resolution for 8lsO over its entire length, and so the

two profiles are superimposed on Fig. 8.1 with the 8D converted to equivalent S180 with an assumption of

a d-cxccss value of 15 per mil.

8.2 Isotopic and melt percent matching with GB97C1

In the following sections, a proposal is made for a common agescale for many of the major

Eurasian Arctic ice core records given the assumption that the dating methodology, resolution, and

resultant paleohistory for GB97CI has been superior to all previous attempts. However, it is not assumed

nor expected that the single, integrated chronology generated herein necessarily represents a real-time

reality, though it is expected that the use of multi-parameter annual counting (guided by volcanic horizons

and validated by cosmogcnic flux arguments) has greatly improved the age control over the greater

portion of the past millennium. Furthermore, any spatial variability, potential real lead/lag relationships

between sites (as well as apparent ones due to differential meltwatcr migration), and limited ability to

match sub-decadal features effectively precludes absolute certainty in the time domain. In the final

analysis however, it has been shown following this endeavor that a coherent picture of climate variations

can indeed be obtained for at least the north-central and eastern portion of the Barents/Kara shelf region

that is largely consistent with the annually-dated histories considered previously in Section 7.3.

Via an iterative cross-matching procedure using GB97CI as the central agescale reference, the

new proposed Eurasian Arctic ice core chronology over the 1225-2000 A.D. interval is depicted in Figs.

8.2 (5>80) and 8.3 (melt percent). Included along the bottom of both figures are the ages that were

estimated from the original published records, as well as long-term mean values of the parameters shown.

Depth-age rescaling was accomplished by use of the AnalySeries 1.2 software (Paillard et al.. 1996).

which employs linear interpolation between successive matchpoints chosen by the user linking certain

prominent features that can plausibly be treated as common simultaneous events. In the process, each

depth-based ice core record from the Eurasian Arctic was adjusted to the GB97C1 timescale. The depth-

age points chosen to produce this chronology are given in Tables B.1-B.4 (Appendix). Importantly,

156

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. FRANZ SVALBARD SEVERNAYA' JOSEF (tom ^0 ZEMLYA LAND (dxs=15%o) Amnd '80 Lomo'76 Vest'81 Aust'85 Gr-Fr ‘75 GB '97 AN '86 Vav ‘88 Vav '83 Vav '79H2

8180 (o/oo) 2000

1900

1800

1700

% 1600

1500

-% 1400

(Age Previously 1300 1300 - Published) Year A.D. 17 S180 (o/oo) -11.1 °/oo -11.3 %o -14.2 %o -15.8 %o -18.1 %0 -18.9 %o -22.3 %o -20.1 %o -20.1 o/00 -19.1 o/00

Fig. 8 2 Isotopic records from Eurasian Arctic ice cores presented on proposed common chronology based on GB97C1. SEVERNAYA SVALBARD FRANZ JOSEF ZEMLYA LAND Amnd'8Q Lomo'82 Vest'81 Aust'65 Aust'67 AN '86 Vav ‘88 Vav '83 Vav '78/9H1 GB '97 Melt % 0 30 60 30 60 90 0 30 60 90 60 90 0 30 60 90 .1_1 -1-1. I-.J-1-1-L Li_i_l_i_i_l_i.i-_i_ - 2000 2000 1 ■ ‘ ------

1900 - - 1900

1800

1700 - 1700

600 - 1600

1500 - 1500 (-3.5 ka)

Age Previously lished) 1300 - - 1300 (900-k (-2.1 ka, (1465) (1500) 1100)1 rev. 950) (-2.1 ka) I T rl ' '1 l ' ■ I 0 30 60 30 60 90 0 30 60 90 30 60 90 30 60 90 Melt % 24.1% 31.2% 60.6% 62.1% 62 9% 555% 44.8% 90.8% 44.8% 69.0%

Fig 8.3 Melt percent records from Eurasian Arctic ice cores presented on proposed common chronology based on GBV7CI. because all records showed an enhanced isotopic enrichment in the recent past, it was possible to define a

reliable horizon at -1910 that helped to guide the cross-matching further downcore by considering the

relative depths of this transition.

Melt records were not available from the entire suite of nine cores, although when possible

comparable records from other cores taken from a similar location (those not completely analyzed for

5uO) were included. Because of the far greater similarity in stable isotope records across the region, the

majority of the matching procedure involved the $'hO records alone and the melt records were normally

only consulted for refinement and identification of occasional extreme events. Exceptions included the

Lomonosovfonna 1982 ice core for which no isotope information is available, and because of the

dissimilarity in core length relative to the nearby 1976 core (Table 8.1). the two records could not be

combined. (A complete melt percent history for Lomonosovfonna 1976 is also not available in the

literature.) Similarly, Auslfonna (1987) was not analyzed for stable isotopes, whereas a 1985 core from a

similar location (with no significant depth-deplh offset discernible from a simple mclt-stratigraphy match)

provided both 5l!lO and melt percent, but only for the top 200 m of the 560 m thick ice cap. Hence, the

lower portion of the 1987 melt record from Austfonna was matched to GB97C1 melt percent beginning

from the age-dcpth horizon provided at the end of Austfonna 1985. i.e.. 1580 A.D. at 200 m.

In most cases, the proposed common chronology has resulted in only a modest alteration of the

published timescale. in the range of 200-300 years (one way or the other) at the depth representing the

1225 A.D. horizon determined by the GB97C1 record. Presumed dating offsets of this magnitude are

understandable given the possibility for propagation of errors from unconfirmed layer-counting or models

based on single accumulation estimates. However, the records from Vavilov Dome in Severnaya Zcmlva

were originally assigned timescales that appear to be greatly unrealistic with ages much more than twice

as old as the proposed chronology indicates. Recently, the Vavilov 1988 age/depth relationship was re

evaluated on a glaciological basis (Golubev, 1998) and suggested an accumulation rate that is much closer

to that determined by the GB97C1 matching. The age dating of Akademii Nauk (1986 core) from

Kotlyakov et al. (1990; based alternately on visible stratrigraphy and optical density) deviated only

159

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. slightly from what the cross-matching indicated. Given the great degree of similarity seen among all of

the matched Severnaya Zemlya isotope histories and GB97CI working from the present backwards to

1750. by which time relative accumulation rates are generally established, the older ages previously

estimated for the Vavilov cores simply cannot be substantiated. The poorer quality of the matching in the

earlier centuries of the period of overlap, when climate variability was muted, makes precise age control

questionable for all of the Vavilov sites. However, aspects of the age-depth relationship proposed for these

cores that can be used to infer variations in accumulation (Section 8.3) do support the new chronology of

Vavilov Ice Dome to at least 1225 A.D.

As expected, the quality of the matches between GB97C1 and the other Eurasian Arctic cores is

superior for 6laO as compared to the melt records. While this finding might be partially due to the order

in which the matching was undertaken, a more likely interpretation follows from the episodic nature of

melting (occurring at just one specific time of year) and also the limited correlation of summertime

temperatures over the region (as shown earlier in Fig. 5.4). Also, according to Eq. 5.4.2. melt percentage

values arc partly contingent upon annual accumulation rates and hence these histories incorporate two

potentially independent variables. Indeed, while the stratigraphic transition between LIA and 2(>th

century conditions is mirrored in the large majority of the Eurasian cores (on this chronology), the shift is

in some cases inverted with lower melt percentages indicated for the recent past. In the sites showing

reduced melt for the 20th century, sharp increases in accumulation may have outweighed the expected

increase in seasonal melt: this result might be particularly true in locations that were already (during the

LIA) located in high-pcrcoiation/superimposed ice zones (e.g., Vavilov 1988).

Despite the lesser degree of similarity between the Eurasian Arctic melt records, one high-

resolution palcohistory from Austfonna. Nordausiandet (Arkhipov, 1999 • made available in original

digital form in the DDGA archive) shows remarkable similarity with the analogous record from G97C1

once aligned as shown in Fig. 8.3. Although the Austfonna 1987 record is partly "clipped" on the high

side by sections of superimposed ice in the recent past, a number of compelling common features arc seen

throughout the 770-year history. Included among these are important timelines in the early part of the

160

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. history with high melt zones indicated near the base of the records at 1240 and 1280, as well as low melt

zones at 1400 and 1470. The match is somewhat less supported during the heart of the LIA. suggesting

that there are larger differences in melt percent during periods of lower accumulation, times when there

might also be greater variance between records from different locations.

An unusually strong meltwater layer at - 2 10-230 m depth in the otherwise low-mclt

Amundsenisen 1980 core (Zagorodnov and Samoilov, 1982). dated with low confidence by match to

GB97C1 to 1430-1520. appears to be a potentially important stratigraphic horizon for West Spitsbergen

cores. The Asgardfonna Site 1 (185 m) core (Uchida et al., 1996) shows a similar melt-rich layer at 120-

140 m depth (not presented in terms of melt percent) that is likely coincident. The depth ratio of these

melt horizons (-0.6) matches closely the ratio of the depths of the early 20th century 61!lO transition

between the same two cores. 34 m in Asgardfonna (from Watanabc et al., 2001) compared to 55 m in

Amundsenisen. and thereby supports the hypothesis of simultaneity. Furthermore. Lomonosovfonna

1982. a 134-m core to bedrock, is suggested from the matched chronology' to terminate at this same time

suggesting that particular high elevation site became partially dcglaciated (whereas the nearby 1976 core

seemingly continues to -1000 A.D.).

In comparing the degree of similarity between the GB97C1 SIS0 profile and the other regional

isotopic histories, it can be seen that the three West Spitsbergen cores (Granfjord-Fridtjolbreen 1975.

Amundsenisen 1980. and Lomonosovfonna 1976) do not resemble GB97C1 to the same degree. Hence, it

should be considered that these matches are more speculative (particularly before 1700) and so the time

scales proposed here arc not altogether certain. However, there is evidence here that the three records,

while largely different than the others, share a greater amount of similarity when considering them

separately. In particular, the 19th-20th century transition appears more gradual, also peaking somewhat

later (assuming the match is correct) around 1950, followed by a sharp depletion event to LIA levels not

reproduced in any of the other cores. The position of West Spitsbergen in an area proximal to open water

all year round (and hence influenced more by North Atlantic currents), and its mountainous terrain

creating local orographic effects, suggest potentially large differences in mean climatology. In contrast.

161

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the records from Nordauslandet to the east all fall closely in line with the other eastern records. Both

Austfonna and Vestfonna have similar morphologies to Graham Bell and the Severnaya Zemlya ice caps

(i.e., dome-shaped ice caps on relatively flat, low-lying islands) and are also generally surrounded by a

wide sea ice zone during winter. From these common characteristics, it follows that the central/eastern

Barents and Kara paleotemperature histories show more similarity.

8.2.1 Consideration of the pre-1225 history of ice cores from Severnaya Zemlya

As previously mentioned, several of the Eurasian Arctic ice cores provide records that continued

back into earlier millennia well beyond that of the Graham Bell 1997 315-m ice core. Included among

these cores is the Akademii Nauk 1986 core that reached bedrock at —760 m. and has been presented on

differing timcscales that indicate a bottom age of 9.5 ka (Kotlyakov et al.. 1990) and 12 ka (Klementyev et

al.. 1991). Cross-matching to GB97C1 cannot help to distinguish between these various possibilities, but

the reasonably close agreement between the Kotlyakov et al. (1990) time scale and the GB97Cl-bascd

1225 A.D. horizon supports the general interpretation of a long record. Indeed, nothing from this study

can question the interpretation that the 3 per mil isotopic depletion seen -30 m above the bedrock contact

represents the very end of the Last Glacial Stage, more specifically the Younger-Dryas (YD) stadial

(Mangcrud et al.. 1974) of 11.7-13.0 ka (calendar years). As has been previously noted (Kotlyakov et al..

1990), the gradual isotopic cooling displayed throughout the Holocene (upward from 700 m depth to 100

m depth as shown in Fig. 8.4) resulting in LIA values at or below the level of the suspected YD interval, is

likely an elevation bias casued by the continually-growing ice cap as the climate cooled (Nikolaev et al..

1997).

Although the Vavilov Dome cores, obtained from four different locations on the ice cap. also

extend further back into the past than GB97C1, it can be questioned that glacial stage ice exists in any of

these records, as has been considered by Stievenard et al. (1996) for the Vavilov 1988 core. The map in

Fig. 8.5 shows the locations of the four drilling sites (as best as could be determined from the rough

longitude/latitude positions recorded then) with respect to both the surface and bedrock topography. The

162

5 180 ( % o ) 6 ,8 0 ( % o ) Fig. 8.4 Sevemava Zemiya deep ice cores, after a proposed depth-depth rescaling referenced to referenced rescaling depth-depth proposed a after cores, ice deep Zemiya Sevemava 8.4 Fig. 10 0 30 0 50 0 700 600 500 400 300 200 100 0 Akademii Nauk '86, following stable isotope match with GB97C1 over top 772 years. 772 top over GB97C1 with match isotope stable following '86, Nauk Akademii . 759.8 m (bedrock) m 759.8 . in in Vavilov 78/Y9 (Hole 1) core core 1) (Hole 78/Y9 Vavilov 462 m (top 300 m analyzed) m 300 (top m 462 Akademii Nauk '86787 core core '86787 Nauk Akademii Ak Nauk '86/’87 Depth (m) Depth '86/’87 Nauk Ak n Vavilov '79 (Hole 2) core core 2) (Hole '79 Vavilov 556.5 m (bedrock) m 556.5 163 Vavilov ’83 core core ’83 Vavilov 466.2 m (bedrock) m 466.2 Thin line: line: Thin SD (’86) SD d-excess d-excess 15%o (bedrock) 461.6 m 461.6 core '88 Vavilov Vavilov (North) (North) o o co •22 P •22 16 20

° 2 100°E

Karpinsky Ice Cap 79 30 N Dnll sites !

1978/9 Hi v 1979 H2 1983 Surface contours

1 ^ 2 0 0 Bedrock I Vavilov Ice Dome contours University Ice Cap

October Revolution Is., Severnaya Zemlya, Russia

(after Barkov, et al., 1992)

Fig. 8.5 Map of October Revolution Island, Severnaya Zemlya, including surface and bedrock topography of Vavilov Ice Dome, and locations of ice cores.

164

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. corresponding four isotopic records (incompletely analyzed for Vavilov 1978/79 Hole 1) are illustrated as

they were cross-matched to GB97C1 above the 1225 A.D. horizon, but also depicted here in their entirety

aligned continuously to the Akademii Nauk 5D/5uO depth-based profile. Here it can be seen that some

common features exist just below the GB97C1 termination point, seen in their most exaggerated form in

the Vavilov 1979 Hole 2 core. An isotopic high exists in all four records at an equivalent AN'86 depth of

210 m, followed by a sharp depletion and gradual rise towards a second high at 280-300 m (a double peak

in three of the four records).

Despite the lower quality of the matching among the Severnaya Zemlya records, due partly to the

low resolution and presence of gaps in the analysis, the proposed alignments of Fig. 8.4 can be supported

based not only on the superior matching for -750 years from the top but also given an assessment of

necessary accumulation rates and considering also basal topography. Following ground-based and

airborne surveying (Bogorodskiy et al.. 1980; map, as shown in Fig. 8.5, simplified by Barkov et al..

1992), a subglacial trough was revealed oriented from northeast to southwest toward the marine outlet,

effectively delineating two bedrock highs in the north-central and southeast portions of the Vavilov Ice

Dome. As one might then expect, the cores taken nearest the subglacial highs (Vavilov 1983 and Vavilov

1988) appear to have produced the longest paleohistories. whereas the earlier cores taken from a more

central location on the dome (and in the case of Vavilov 1979 Hole 2, a physically-longer core) actually

contain less time. This result gives support to the idea that early in its history. Vavilov Dome was two

separate ice caps that later coalesced into one larger structure. The shorter histories provided by the cores

taken from above the trough then must dictate significantly larger accumulation rates, in agreement with

what the GB97C1 matching already suggested for these cores. Presuming the published AN'86 ages to be

generally accurate for the latter half of the Holocene (both time scales yield similar results), approximate

bottom ages of 5.0-5.2 ka for Vavilov 1983 and 1988. and just 1.6-1.7 ka for Vavilov 1979 Hole 2. can be

suggested. The bottom age of Vavilov 1978/79 Hole 1 cannot be estimated due to the incomplete isotope

profile.

165

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8.3 Evidence of support from qualitative accumulation reconstructions

From the series of age-depth matchpoints (tabulated in Appendix B) now applied to nearly every

Eurasian Arctic ice core in the process of generating the common chronology, it was then possible to

create very rough profiles of accumulation variations at many of these sites. To produce a real

quantitative accumulation assessment, annual counting would be required, so this endeavor only produced

data in a qualitative sense and will necessarily lack structure at all intermediate positions between

successive matchpoints. However, because accumulation rates were reconstructed on a sample-by-samplc

basis, some artificial structure is apparent in the profiles as shown in Fig. 8.6. To reconstruct

accumulation values, both a Nye model (Dansgaard and Johnsen. 1969) and the two-parameter function

(Section 4.3.2) were generated and the resultant accumulations from the two formulae were averaged. For

each Nye model, the exact surface accumulation value that yielded the proper age at the base of the

GB97C1 matching (either 1223 A.D. or a more recent age if the record terminated above this point) was

used. For the two-parameter model, the depth of the ca. 1910 isotopic transition provided the upper time

horizon (Tl). and a point at or near the end of the matching provided the lower (T2). For those few

Eurasian Arctic ice cores (e.g.. Vcslfonna 1995) that terminated at bedrock with an age of less than 1000

years, either age model type becomes unfeasible and hence accumulations were not validly determined.

Because accumulation reconstructions arc solely derived from the subtle deviations away from the

otherwise smooth age-depth function, even minor mismatches in the cross-dating will yield large errors in

the final accumulation values. Hence, in comparing the results from all the Eurasian Arctic cores (now

excluding West Spitsbergen, for which matching was already problematic), only modest similarities are

noted. In general, most of the cores show elevated values during the most recent 200 year period, with

particularly large variations in the 20th century. All the cores from Severnaya Zemlya show exceptionally

large increases beginning around 1730 and reaching maxima around 1900. Furthermore, even with the

very large variability in average accumulation among the various sites on Vavilov Dome (up to nearly a

factor of four), the long-term trends and even most of the short-lived events are reproduced. The

continuity of these reconstructions, including that of Akademii Nauk. lends strong support to the validity

166

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2000 - 1900 - 1800 - 1700 - 1600 - 1500 - 1400 - 1300 Vav '79H2 Vav 1.05 0.86 0.34 0 3 0 6 Accum. (m ice eq.) 0.43 0.28 0.3 0.6 0.65 0.61 0.51 0.3 0.6 0.3 0.6 0.9 0.0 0.3 0.6 0.5 1.0 1.5 2.0 Vest '81 Aust'99 Aust’87 GB'97 AN'86 Vav'88 Vav'83 Vav’78/9H1 0.43 0.3 0.6 0.9 Fig 8.6 Qualitative accumulation reconstructions for all applicable Eumsian Arctic ice cores based on GB97CI chronology. 1400 - 1300 - 1500 - 1900 1900 - 1800 - 2000 r 1700 - ig ig 1600 -

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of the isotopic cross-matching that taken alone would have been considered unreliable (for at least several

of the Vavilov cores). The Nordauslandet cores produced less uniform results, showing poor

reproducibility between the two longer Austfonna cores. (For matching Austfonna 1987 (melt only) to

GB97C1, Austfonna 1985 5lsO was considered an equivalent and applicable record, given its close

proximity. Hence, the matching strategy was actually comparable to that of Austfonna 1999 back to

-1500 and thereby is not a potential cause of the accumulation differences.) Even with these large

differences, the common occurrence of sharply-decreasing accumulation rates upwards from the base of

the 1225 A.D. horizon is detectable, culminating in a brief period of low accumulation centered at 1330.

These features are also seen consistently in the Severnaya Zemlya cores. Although not entirely obvious, a

similar structure is present in the GB97CI accumulation record itself, as is a high accumulation zone at

about 1550 that appears in some of the other reconstructions.

8.4 Summary of environmental history from the north margin of the Barents/Kara sea (excluding West

Spitsbergen)

Several publications have included averaged or smoothed profiles of §'*0 from recently-obtained

ice cores taken from Vestfonna 1995 and Austfonna 1999 (Watanabe. 1996: Watanabe et al.. 2001).

While not annually-dated, the Austfonna 1999 core (289 m) was analyzed at comparatively high

resolution, and multiple time horizons were sought. In addition to the 1963 nuclear horizon (determined

by tritium at 21.3 m). several volcanic horizons were proposed based on a detailed ECM (conductivity)

profile including the prominent Laki 1783 event. In the presentation of the 6**0 record in time, a Nye

model function based on near-surface accumulation was employed, which did yield consistency with the

Laki identification. Following the development of the Eurasian Arctic chronology detailed above, both of

the newer Nordauslandet cores were also aligned to best match GB97C1 suggesting some dating-error

propagation before 1750. As shown in Fig. 8.7, the match suggests a positive age correction to the Nye

ages of about 115 years, all concentrated in the lower half of the record, corroborating the identification of

Laki but not that of Mt. St. Helens (1482) as suggested in Watanabe et al. (2001). The corresponding

168

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. FRANZ FRANZ mcFF severnaya IOQCC SEVERNAYA NORDAUS- NORDAUSLANDET j u o c r ZEMLYA LANDET LAND ZEMLYA land Vest '95 Aust '99 GB *97 AN’86 Vest '95 Aust '99 Aust '87 GB '97 AN '86

-21 -18 -15 -21 -18 -15 5 180 (%0) 30 60 90 0 30 60 90 Melt % 2000 J i I , ■ X 2000

1900- 1900

1800- 1800

-1700

1600

1500

1400

(Age Previousty 1300

Year Year (A.D.) (AD.) T Tri-|li, ■P“’T -21 -18 -15 -24 -21 30 60 90 30 60 90 0 30 60 -18.0%o -18.3%o -18.9%o -22.3%o 68 .0% 63.9% 62.9% 55.5% 44.8%

Fiy. 8 7 High-quality ice core records from north-central Barents presented on proposed common chronology based on GB97CI Austfonna 1995 melt record shows clear similarities throughout the 770-year history and required no

significant fine-tuning of the original isotopic match. Alignment of the §180 and melt records from

Vestfonna 1995 to mimic the GB97C1 age scale led to an offset of approximately 220 years at the base

from that of the model time scale. From Fig. 8.7, it can be seen that the two newer Nordauslandet cores

show better agreement in 5,!(0 during the latter part of the LIA (1700-1900) relative to the melt percent,

but in the earlier period (1300-1600) there is perhaps more similarity in the melt histories. However, it is

possible that averaging techniques employed by the original authors may be partially responsible for any

perceived differences.

Fig. 8.7 is intended to represent a unified, coherent picture of north-central Barents/Kara climate

over the period 1225-2000. Cores from West Spitsbergen were not included as they appear to show

significant differences in their climate history, but Nordauslandet. Franz Josef Land (via GB97C1). and

Severnaya Zemlya (represented here by Akademii Nauk alone) together illustrate a strongly-tied

climatology. All of the four sites appear to have experienced the same sequence of events in the three-

phase (MWP-LIA-20th century) climate history over the last millennium. Site-to-site variability is

apparent during some intervals, although many of the perceivable differences in the line scale are likely

attributable to varying averaging techniques and minor matching errors. However, given the strong

enhancement of isotopic response to the termination of the LIA (not mirrored in records from northern

Scandinavia), it should be noted that this coherent climate history only applies to this particular region of

the Barents and Kara seas that lies within the boundaries of the seasonally-migrating Arctic sea ice front.

Previously (Sections 5.3 and 5.5) it was demonstrated that 5l!fO trends would mainly represent wintertime

variability because of the far greater standard deviation in temperature during those months. In

agreement with this finding, the area of strong correlation in the instrumental records was larger during

the winter quarter. While one then might be led to conclude that the winter-dominant 6lsO

paleothermomctry might then be more applicable to a larger portion of the Eurasian Arctic and sub-Arctic

regions, this assumption is almost certainly false. In the development of the 5lsO-T calibration (Section

5.2) it was shown that regions just beyond the north-central Barents Sea (northern Scandinavia, north-

170

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. central Siberia, eastern Greenland) Tailed to document a temperature shift anything like the wanning

recorded at Isfjord Radio beginning in 1912. or indeed displayed in these ice core paleohistorics. The

most reasonable conclusion is that this phenomenal warming, witnessed abruptly in the late 1910s just

along the north margin of the Eurasian continental shelf, is tied into positive feedbacks related to the

position of the sea ice margin and the meteorological polar front. In terms of magnitude especially, it

should not be deemed appropriate to closely relate these winter-sensitive climate records to any larger area

of the Arctic basin or to most other parts of Europe and Asia.

171

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER9

CONCLUSIONS

The Windy Dome ice corc-climate study proved to be a highly-successful endeavor, providing not

only several independent palcohistorics of environmental change in the Eurasian Arctic, but also

demonstrating a methodology by which future ice coring programs in these less-than-ideal glaciological

conditions can yield meaningful results and valid interpretations. The 315-meter ice core obtained in

1997 from the summit of Windy Dome. Franz Josef Land was established to contain a continuous 772-

year record of climate variability in the region. High-rcsolution sampling throughout the length of the

core resulted in the detection of important stratigraphic time horizons that guided the layer-counted age

scale. In addition, these records of melt percents, ion concentrations, dust deposition, and stable isotopic

ratios were linked, cither individually or in tandem, to specific controlling mechanisms that in turn could

lead to the core records being utilized as proxies.

Specific findings from the comprehensive ice core retrieval and analytical program, following

two successful field operations to Franz Josef Land, include the following:

1) Of the four ice caps in Franz Josef Land visited during the 1994 reconnaissance, the summit of Windy

Dome. Graham Bell Island was demonstrated to experience the most favorable conditions for signal

preservation. Other sites atop Luna Dome. Alexandra Land and the ice dome covering Hall Island

showed higher amounts of meltwater-ice and Hydrographer Dome on Hayes Island was observed to be in a

negative annual balance even at its highest point. By matching properties of the Hayes record to those of

the other ice cores, the 1994-surface age of Hydrographer Dome was estimated at 1946.

172

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2) Along the west-to-east transect, average 5lsO values drop from -14.4%o on Alexandra Land to -16.8%o

on Graham Bell Island confirming the existence of colder annual temperatures in the east, though

distance-from-sourcc may also play a role in defining mean isotopic ratios via progressive fractionation.

Over the 10-year period of overlap, some common features in the physical and glaciochemical records

suggest some rcgional-scalc continuity, but individual events differed in magnitude and post-dcpositional

effects were experienced to different degrees.

3) The annual signature in the Windy Dome record was determined to be characterized by maximum

concentrations of scasalt aerosol (e.g., Na\ Cl~) during the late winter months of February and March,

generally coincident with more depleted 6lsO values and higher incidence of mcltwatcr ice in the visible

record. This relationship was consistent throughout the core, and although surface pit samples and

unusually low-melt zones in the core show the same tendency, it is suggested that percolation and

rcfrcczing processes lead to the same arrangement in a secondary manner.

4) The original conjecture of a primary linkage between minimum sea ice extent in the Barents Sea and

chloride deposition in Windy Dome ice was not validated by the 1997 deep ice core results. Post-

depositional modification of ionic signatures was easily detected, and due to an apparent warm summer in

1995 a current upper limit of active percolation was estimated at ~7 meters, equivalent to ~8 years of

accumulation. In addition, sea-salt aerosols deposited in Windy Dome ice are suggested to reflect changes

in the characteristics of advecting air masses, considered either horizontally or vertically, as opposed to

the position and distance to the winter sea ice edge.

5) Over the length of the 315 m ice core, the annual signal (and hence the reliability of the dating) varies

as a function of the melt activity, with a mere 15% reduction in melt percent during the colder Little Ice

Age period (-1450*1870 A.D.) being responsible for a -30-40% increase in the amplitude of the seasonal

173

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. oscillation in 5lsO. The warm 20th century ice produces the most difficult record to date accurately, the

annual counting of both 8IaO and chloride being only approximate (cst. 10% error), indicating the need

for firm time horizons to guide layer-counting. The annual signal in chloride is seen to be slightly less

influenced by melt influence, and displays (independently from the concentration values) an 80-year

oscillation that remains unexplained.

6) The elution sequence of ions determined for the uppermost 25 meters was proposed as MSA' > SO f >

(NO,' - Mg2* ~ Ca2*) > (Na* ~ Cl") > NR,* with 1C and F showing an independent affiliation that may

represent a previously unreported process involving the peculiar properties of fluoride species in icc-watcr

mixtures. The nature of the post-depositional reworking of ion concentrations in Windy Dome is

proposed to be represented by a succession of "stacked percolation cells." that become scaled and archived

only at a ccnain critical depth as accumulation continues. While the one-time percolation depth was

estimated at the equivalent of 8 years, the percolation cells revealed in the pH record represent on average

-13.5 years of accumulation, suggesting a more complex multi-annual evolution of the soluble

components. It remains uncertain whether the time interv al of cell formation is climatically-scnsitivc.

although the suggestion is made via a similar ion profile from Svalbard (O'Dwycr et al.. 2000) that the

initial distribution of melt layers (and hence summertime warmth) does govern the emplacement of

"stratigraphic traps" that underlie each cell.

7) Accumulation values show a relationship with melt percent that is generated for the most part by the

"dilution" of meltwater infiltration by thicker winter snowfall layers. Actual meltwater loss (by lateral

transport) from the summit is suggested to occur rarely, only when there is a temporary facies change to

superimposed ice for several consecutive years. During these periods of warmer summers, flaxes of

highly-mobile ions (SO.,2. Mg2*) are reduced by 10-15%. suggesting losses of -5% of the annual

precipitation yield according to a conservative estimate for the ion fractionation ratio of 2-3.

Redistribution of the percolating meltwater into lower layers in the stratigraphic column was also detected

174

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. by a 5lsO contrast of up to 0.90%o due to solid-liquid fractionation and partial physical separation of the

melt from the remaining flm grains.

8) Despite complications from melt influence and high background levels, volcanic eruptions are

detectable in the ice from Windy Dome when core analysis is conducted on a One scale. Most obvious is

the tremendously high acid sulfate levels produced by the Laki eruption of 1783, which were likely

mobilized (and perhaps concentrated) to some degree shortly thereafter. Several other large eruptions

(e.g.. Tambora. Coscguina) that occurred within several decades of the Laki event were detected by

smaller sulfate anomalies or in some cases by strongly depleted S1!,0 values, and led to further time scale

refinement. Two major eruption signatures were detected near the core bottom that were confirmed by

subsequent cosmogcnic analysis to be evidence of the 1362 and 1259 volcanic horizons, and guarantee the

accuracy of the layer-counted age scale to within a single decade down to the bottom age of 1225 A.D.

9) Historical temperature records for the Eurasian high Arctic arc completely absent for the 19th century,

but one important time scries began in 1912 at Isfjord Radio. West Spitsbergen. It was only here that the

tremendous wintertime warming of the first two decades of the 20th century was documented from a

location in the high Eurasian Arctic. Given that the rapid decline in the magnitude of this warming away

from the northern Barents margin closely mirrors (in reverse) the better-resolved pattern of changes that

occurred during the 1960s. the kidney-shaped structure of that cooling event is suggested to represent the

manifestation of a semi-permanent polar front shift that characterized the LIA.

10) On the basis of the preceding analysis of real-time records, a simple two-step isotope-calibration

scheme was applied across the abrupt climate boundary at the termination of the LIA around 1910. The

resulting values for the paleothermometry coefficients (a = 0.55. and p = -8.1%o) are consistent with

5uO-T slopes determined from Greenland ice cores and with a moisture source in the Norwegian Sea east

of Iceland, respectively. Application of this calibration produced a 772-year history of proxied annual

175

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. temperatures that depict a recognizable pattern of climate variations over much of the Northern

Hemisphere, with the exception of the inflated magnitude of the 20th century warming via a threshold

change in polar front position.

11) Summer (June-August) temperatures at Windy Dome were reconstructed by the melt-proxy method of

Tarussov (1992), incorporating the individual annual accumulations instead of using a constant value.

The palcohistory generated thusly compared well with tree-ring based reconstructions from the central

and eastern portion of the Siberian coastline along the 70th parallel, but showed no obvious relationship

with similar records from Fcnnoscandia. Once more, the three-phase climate paradigm of the last

millennium was apparent in the summer temperature reconstruction, but with the onset of a mild 0.5°C

warming occurring at around 1850 as opposed to the tremendous >8°C wintertime warming concentrated

at -1910. The greatly reduced variance of summer temperatures was seen to reflect the limited

temperature range created on an annual basis by the dampening effects of the melting sea ice nearby.

However, the amplification of 20th century wintertime warming at Franz Josef Land means that the

summer temperatures, that currently show limited spatial correlation on an annual basis, actually

demonstrate greater spatial applicability over the longer term.

12) The contribution of anthropogenic pollution to the Arctic is seen dramatically in three soluble

species, with influence first detectable in the nss-sulfate profile at -1890. but perhaps earlier in the

ammonium record at -1840 according to a suspected enhancement of NFLT formation from gaseous

ammonia via acid catalysis. Nitrate levels first showed an unprecedented rise around 1930. and then rose

by roughly a factor of three by 1997. whereas sulfate levels have increased five-fold over the past 100

years. These findings are in line with those determined from other ice cores that also reflect

anthropogenic aerosols that originate in Europe.

176

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13) Generally concurrent with temperature conditions, accumulation rates are higher in warmer climate

exhibiting a steady rise from -0.5 m water equivalent (w.e.) in the late 18th century to a maximum of

-0.7 m w.e. by 1900, followed by highly-fluctuating rates in the uppermost 50 years of record. Whereas

the period from 1950 to 1980 is coeval with several episodes of multi-year meltwater ice layers and

quantifiable losses of certain ions, the recognition of a similar reduction found in precipitation records

from northern Scotland at this time argues against major loss by ablation in Windy Dome.

14) The most significant oscillatory components within three independent Windy Dome time scries

identified by Singular Spectum Analysis denote highest variance at multi-decadal frequencies.

Specifically, periodicity in the winter-sensitive 6lsO record is strongest at -70 years, whereas the summer

temperature record displays a more complex array of waveforms with dominant power at -30 and -50

years. The palcohistory of sea-salt chloride deposition in the core displays significant components at -40

and -60 years, with the lower frequency waveform predominant in wanner times and then effectively

replaced by the 40-ycar component during the colder LIA. Both the summer temperatures and chloride

concentration also have some lesser tendency to oscillate at near-decadal frequencies (-12 years).

15) By placing the improved age control for the Windy Dome ice core in the role of a "Rosetta Stone." the

time scales of Eurasian Arctic ice cores obtained in years past were readdressed and a common chronology

was proposed that aligns recognizable features in 5uO and/or melt percent over the time since 1225 A.D.

The outcome from this procedure highlights a prevailing signature of climate over the past 200 years in

the region from Nordauslandet. Svalbard to Severnaya Zemlya. Taking the best available records from

these three sites (including Windy Dome in the center), isotopic records consistently point to an greatly-

enhanced 20th century warming along the 80th parallel not likely experienced anywhere else on Earth.

Interestingly, ice cores from West Spitsbergen. Svalbard (despite their proximity to the Isfjord Radio

station) appear to depict a slightly different climate history, which might reflect their different

dimatological or glaciological setting.

177

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9.1 Final discussion

In conjunction with the inference made in Section 4.1.1, the nature of the Windy Dome ice core

record is such that a decadal time step is the most appropriate interval over which to present the final

results. However, up to this point, the results have been presented most often at their highest resolution in

order to compare and contrast the fine structure in the various time series as well as the larger scale

variability. For this final look, a summary of six important ice core parameters or proxy records, averaged

dccadally, is given in Fig. 9.1. The three-phase climate structure is clearly evident in a majority of the

parameters, with the Medieval Warm Period (MWP) coming to a close between 1450 and 1500, and the

subsequent Little Ice Age (LIA) terminating between 1870 and 1920, in line with evidence elsewhere

(Grove. 1988). Only the wintertime temperatures (and thereby the annual averages) inferred from

isotopc-paleolhcrmomctry suggest that the MWP was fundamentally different than the last century.

Consequently the supposition can be made that the "threshold" condition of episodic northerly excursions

of the polar front during mid-winter was not reached during the MWP. consistent with the conclusion of

Mann et al. (1999) that the 20th century is "anomalous in the context of at least the past millennium."

The cause of the abrupt climate shift of the early 20th century is still under debate. Hansscn-

Bauer and Forland (1998) have argued that because a purely advcction-drivcn climate model (and hence

circulation patterns) cannot explain the 1920 warming in Svalbard, then sea ice feedbacks must be

partially responsible for the dramatic warming. This hypothesis seems logical given that the wintertime

sea ice margin is local to West Spitsbergen and past reconstructions (Vinje. 1997: 1999) indicate its

movement to the southwest during the colder intervals of previous centuries. However, the dose

similarity in magnitude and evolution of the 20th century wanning between all the cores from

Nordauslandet through Franz Josef Land to Severnaya Zemlya argues against sea ice feedback as a

dominating (direct) cause. Because the significant temperature changes in the region are almost

exclusively a wintertime phenomenon, the three glaciated island sites effectively lie in very different

regimes with respect to the sea ice configuration. Nordauslandet is partially sheltered from the influence

of warm, salty Atlantic water by the presence of West Spitsbergen to the west. However, open water still

178

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. • I ~ 75 _2 9i in F l II riy-L 3 ^ 50 < a. 2.0

E 15 a.Q. 1.0 kn O yVj ^ V 0.5 lAi/ 1 V >< CM 1.0 E 3 x 0.5 - 3 V e V U c. 0.0 x P x -25 9-E§ * -30 T3 (U

Fig. 9.1 Summary of decadal results from the Graham Bell (1997) ice core study, including from top, a. reconstructed accumulation, b. chloride concentration, c. chloride flux, d. DJF- temperatures from mixed proxy records, e. annual temperatures from 51!,0 record, and f. JJA-temperatures from melt/accumulation.

179

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. is found in many years along the north margin of both islands as an eastward extension of Whaler's Bay.

Hence, the ice caps of Nordauslandet exist within perhaps SO miles of the sea ice margin in any given

modem winter. In contrast, even in the current period of retreating sea ice, Graham Bell Island lies 500

miles to the northeast of the sea ice margin and Severnaya Zemlya over 1000 miles distant. Yet the

isotopically-inferred wanning experienced at all these sites is nearly identical (Fig. 8.7), with the

subsequent post-1950 moderate cooling visible as well. This finding indicates that only atmospheric

phenomena could be responsible for such a coherent pattern along a transect that penetrates far into the

wintertime pack ice. Because large-scale temperature patterns indicate only a 0.5-1.0°C cooling for the

Little Ice Age. then the most reasonable conclusion is that LIA winters along the northern Barents/Kara

margin were characterized by very few (if any) episodes of penetrating mid-latitude cyclones (shown in

Fig. 4.3 by short-term warmings of more than 10°C).

The timing of the abrupt isotopic shift ( ca . 1909) inferred from the annual counting of GB97C1

via the three-parameter reconciliation method docs suggest a nearly 10-year lead relative to the warming

witnessed at Isfjord Radio. W. Spitsbergen. Because it seemed less likely that percolation cftects and

misdating (even combined) could yield such a large offset, the possibility of a real time-trangrcssivc event

beginning before the installation of the weather station in Svalbard (1912) should be considered. An

interesting study (Dawson et al.. 2002) detailing North Atlantic variability during the late 19th century

has just come to light that examined reports of gale-force winds from coastal sites in Scotland and Ireland.

Following an initial period of exceptional storminess between 1885 and 1898. a sharp reduction in gale

episodes was discovered just after 1905 in two of the three sites studied. Their interpretation of a

southward shift in the cyclone track in the first decade of the 20th century is supported by the ice core

data. Furthermore, their proposed mechanism of increased sea ice extent along the east coast of

Greenland (regardless of conditions in the Barents Sea) forcing a weakening and repositioning of the

Icelandic Low is also entirely compliant. This expansion of the Greenland anticyclone, in essence

instituting a large teleconnection to the Barents Sea region via the altered storm track, is a phenomenon

that warrants modelling study, and has the potential for creating future abrupt changes in the high

180

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. latitudes of Eurasia if this threshold is again reached. The widespread consistency of the isotopic histories

from Nordauslandet to Severnaya Zemlya over the last two centuries should be taken as convincing

evidence that a wholesale change of this type did actually occur in the large-scale circulation pattern of the

North Atlantic.

To continue, the paradigm established for North Atlantic climate variability of the latter half of

the 20th century, whether defined as the North Atlantic Oscillation (NAO. van Loon and Rogers. 1978) or

the pole-centered Arctic Oscillation (AO; Thompson and Wallace. 1998). is insufficient as a model for the

variability seen in the Eurasian Arctic cores. Even though the pattern of pressure anomalies diagrammed

in Fig. 5.5 for 1960s cooling mimics that of the NAO negative phase, the LIA cooling could not have had

exactly this same stnicturc over the entire Northern Hemisphere. Paleoclimatic reconstructions of

temperature and sea ice extent in the Labrador Sea on Baffin Island. Canada (Grumct et al.. 2001) point

to a colder conditions there for most of the LIA. Because shills in the "classic" NAO lead to anomalies of

opposite sign in the Labrador and Barents seas, then there must have been some other additional influence

that led to cold conditions simultaneously in both locations. The Dawson et al. (2002) study suggests

likewise, given that NAO variability had no relationship to the occurrence of gale-forcc winds over

northwestern Europe before 1910. However. Rogers (1997) has recognized that the NAO-drivcn seesaw

of temperatures in Greenland vs. Europe can be explained by either of two patterns, one of which includes

the extended trough into the Barents Sea (as in Fig. 1.1) and another less common circulation pattern with

a more isolated Icelandic low and more southerly flow over Scandinavia. It may be that the relative

occurrences of these different modes of the NAO could be altered by larger climate variability and be a

factor in the nature of the dissimilarities between the respective patterns of LIA and 1960s cooling. The

lack of continuous 19th century observations in most of the Arctic dictates that high-resolution.

accurately-dated paleorecords are necessary to examine these issues. Hence, the continued improvement

of the methodology in analyzing and dating Eurasian Arctic ice cores from seasonal melt zones is critical.

At present, there are a number of other ice core studies in progress in the Eurasian Arctic that

should continue to refine the developing picture of unusual climate variations in this unique region.

181

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Additionally, there is the prospect of a return to Graham Bell Island at some point in the near future by

those involved in the project described herein to complete a core to bedrock as originally intended.

However, several other locations further to the east provide additional strong candidates for future drilling

projects, that could be expected to correlate closely to the Windy Dome record yet also reveal different

signatures further from the influence of the North Atlantic and the sea ice edge. Among these arc the

small ice dome on Ostrov Bennetta (Bennett Island) in the dc Long archipelago at 76.8°N, 158.0°E (350

masl) and both the Karpinsky (79.6°N, 99.0°E. 965 masl) and University (79.0°N, 99.1°E. 800 masl) ice

caps on October Revolution Island. Severnaya Zemlya. These latter two ice bodies (Fig. 8.5) would likely

produce records akin to the Vavilov cores, yet being somewhat higher they would be stronger candidates

for a high-resolution study with the intention of annual counting and identification of numerous datable

horizons. The very small ice cap on Bennett Island may be a riskier endeavor, but is the only viable

candidate for ice core drilling in a wide longitudinal zone. As such, an ice core from this glacier would

represent an important step toward circum-Arctic coverage and could yield new and different information

about climatc/sea ice variability in an equally-rcmotc region. Furthermore, the lateral extent of the

enhanced warming established for the northern Barents/Kara margin could be determined in a location

that is well beyond the central area of large anomalies as shown in Fig. 5.5.

Finally, the bottom age of Windy Dome is itself an issue of some import to glaciologists and

climatologists who arc debating the nature of Holocene variability in the Eurasian Arctic. The agc-dcpth

relationship for the 315-meter core obtained in 1997 cannot provide an accurate estimate for a bottom age.

especially since the ice thickness is not precisely determined at the summit. However, there is reason to

believe that the most recent episode of total deglaciation of Graham Bell Island occurred at one of two

periods. -10-11 kyr BP (as for Akademii Nauk) or -5 kyr BP (as suggested in Section 8.2.1 for Vavilov

Dome). The strong warming of the Climatic Optimum period between 9 and 7 kyr BP (Duplessv et al..

2001) may well have led to the complete removal of glacier ice throughout Franz Josef Land, with sea

level high and isostatic depression of the land surface still in effect. However, reconstructions of post

glacial rebound (Forman et al.. 1996) indicate only minor uplift for Graham Bell Island during the early

182

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Holocene given that the center of loading for the Barents Sea ice cap during the Weichselian was far to

the southwest. Therefore, out of all islands within Franz Josef Land. Graham Bell Island (or perhaps

Wilczek Land) would be the most likely candidate to still retain ice from the Younger Dryas cold interval,

as apparently exists on Komsomolets Island. Severnaya Zemlya. However, the conjecture of this author,

baseless though it may be, is that Windy Dome will prove to have a mid-Holocene age at its base.

183

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. BIBLIOGRAPHY

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Abdalati. W.. R.C. Bales, and RH. Thomas, Program for Arctic Regional Climate Assessment. Arctic Res. o f the U.S., 12, 38-54. 1998.

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Arkhipov', S.M.. V.N. Mikhalenko. L.G. Thompson, V.S. Zagorodnov, M.G. Kunakhovitch. K.E. Smirnov. A.V. Makarov, and M.P. Kuznetsov. CTpaTHrpacbini nesrrejibiioro caoa jicjiiihkoboio Kynojia BcTpeiibiu ua o. rpeaM-Bejui. 3eMJm fppaima-HocinJia. Materialv Glyatsiol. Issled.. 90. 169-186. 2001. (in Russian)

Fritzsche, D.. F. Wilhems, L.M. Savatyugin, J.F. PingloL H. Mayer, H.-W. Hubberten. and H. Miller. A new deep ice core from Academy of Sciences ice cap, Severnaya Zemlva - first results, Ann. Glaciol.. 35. 2002, in press.

Fujii. Y.. K. Kamiyama. T. Kawamura, T. Kameda. K. Izumi. K. Satow. H. Enomoto. T. Nakamura. J.O. Hagen. Y. Gjcssing, and O. Watnabe, 6000-year climate records in an ice core from the Hoghetta Ice Dome in northern Spitsbergen. Ann. Glaciol.. 14, 85-89. 1990. (also Dowdeswell. J.A.. D.J. Drewry. and J.C. Simoes. Correspondence, J. Glaciol., 36, 353-356, 1990. and Fujii, Y., Correspondence. Y.. J. Glaciol.. 37. 186-189, 1991.)

Glazovskiy, A.F., I.Y. Ignateva. and Y.Ya. Macheret. Bo3Moaatbift Mexamnn pocra JtemuiKoBoro xynojta o. TpeaM-BeJia (3eMiia (Ppatma-HocHcpa) npii ue3iia*iHTeJibUbix noxoaoaaiiHHX. Materialv Glyatsiol. Issled.. 89 , 187-193, 2000. (in Russian)

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Goto-Azuma, K„ S. Kohshima, T. Kameda, S. Takahashi, O. Watanabc, Y. Fujii. and J.O. Hagen, An ice- core chemistry record from Siwfjellafonna, northwestern Spitsbergen, Ann. Glaciol., 21, 213-218. 1995.

Kameda. T.. S. Takahashi, K. Goto-Azuma, S. Kohshima. O. Watanabe, and J.O. Hagen. First report of ice core analyses and borehole temperatures on the highest icefield on western Spitsbergen in 1992. Bull. Glacier Res.. II, 51-61. 1993.

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Zagorodnov. V.S. and I.A. Zotikov, Core drilling at Spitsbergen, in Data o f Glaciological Studies. Chronicle Discussions, No. 40, edited by G.A. Avsyuk. pp. 257-266, OPP-NSF, Amerind. New Delhi. 1988. (English translation)

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Ice core research elsewhere in the Northern Hemisphere:

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North Atlantic-Arctic ocean/atmosphere phenomena:

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206

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX A

1994 FRANZ JOSEF LAND SHORT CORE RESULTS

207

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a. 2 O) in h i i m 1 W 10 15 20

-12 J -15

COO -18 oo V -21 -

I f 9 CO t_ _ co d) 6 o S A /-i ■S3 ° 3 3 X Q ^ w 0 f 3 E 2 OJ o 1 CO II M. L

%Q. 400

0 ° 200 l y 0 4 E _ • co ■ ® • §> ?• ? n 2 O • • , a . j UIAa a / w AA l i * i 0 t 1------1------1 *n1* i■ i i "* i i "| - 1 ------i 1------I 1------i 1------i 1------■ ■■ ^ 1------i 1------i 1------.i1------i— i.—r i , . r .i ■ .» r 10 15 20 Depth (m)

Fig A. 1 Raw data of oxygen isotope ratio, dust concentration, and major anions from GB94C1. Dating of chloride peaks indicated with dots/years.

208

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. -12 -

2 - 1 5 ■ P -1 8-j

^ -21

e y - a- E CO w * § S 6 : A No data (bottled samples)

9- 400 -

6 ° 200

0 o> 01 m co 2 - cn

0 5 10 Depth (m)

Fig. A.2 Raw data of oxy gen isotope ratio and major anions from GB94C2. Dating of chloride peaks indicated with dots/years.

209

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. O m • ° u co • CO • 05 O) CM • £ • O) in o ■o- i f 20 oo CO I - (O 0)

6 - 05 CM

a - 4 0 0 -

O 200 --1

9 -

6 - 3 -

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Depth (m)

Fig. A.3 Raw data of oxygen isotope ratio, dust concentration, and major anions from H94C1. Solid, clear meltwater-ice existed below the super-concentrated dust layer separating a thin snow/fim layer at .65 m from the 'old' ice below. Dating of 5l!tO troughs indicated with dots/vears. Ages uncertain.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. -1 2 - -15 -

e ^ to=*• E (O

600 -

3 400 -

o 200 -

6 -

cn o> m o>ao

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 Depth (m)

Fig A.4 Raw data of oxygen isotope ratio, dust concentration, and major anions from G94C1. Dating of chloride peaks indicated with dots/years.

211

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. -12 - -15 - CO -18 -

-21 -

co i_ 4 — (DO)

■9 300 -

200 - CO

100 -

o 05 05 in 00

0 2 3 41 5 6 7 8 9 Depth (m)

Fig A.5 Raw data of oxygen isotope ratio, dust concentration, and major anions from ZA94C1. Dating of chloride peaks indicated with dots/years.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. -14

H94C1 GB97C1

1945 1940 1935 1930 1925 1920 Year (A.D.)

Fig A.6 Annual averages of oxygen isotopic ratios and sulfate for the 1994 core from Hayes Island, matched to the 1997 Graham Bell Is. core.

213

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX B

DEPTH-DEPTH AND DEPTH-AGE MATCHPOINTS FOR

EURASIAN ARCTIC COMMON CHRONOLOGY

214

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. AN'86 GB97C1 Vest'95 GB97C1 Aust'99 GB97C1 Depth (m) Age BP’97 Depth (m) Age BP’97 Depth (m) Age BP'97 9.5 21.0 0.8 2.0 2.1 0.0 21.2 55.0 14.9 27.0 11.5 13.0 41.1 94.0 38.0 85.0 17.7 25.0 57.1 124.0 43.7 99.0 27.8 43.0 79.0 179.0 51.0 118.0 37.6 67.0 105.1 247.0 61.4 151.0 45.7 85.0 115.0 290.0 71.3 178.0 3T3 104.0 122.9 338.0 91.9 254.0 63.3 123.0 139.0 434.0 97.1 273.0 70.3 139.0 145.0 469.0 103.1 302.0 75.1 151.0 155.0 551.0 106.6 318.0 89.8 176.0 169.1 645.0 114.2 356.0 102.3 204.0 175.1 698.0 120.7 387.0 108.3 220.0 180.7 729.0 125.5 404.0 113.3 235.0 191.5 771.0 128.6 416.0 119.0 251.0 139.3 462.0 126.1 267.0 147.7 485.0 133.4 287.0 153.0 504,0 138.1 300.0 156.8 519.0 147.4 330.0 167.6 564.0 157.3 362.0 171.8 587.0 172.1 414.0 178.6 618.0 180.0 446.0 185.5 646.0 185.2 464.0 194.3 685.0 198.2 513.0 203.4 733.0 207.3 549.0 209.1 755.0 217.1 587.0 224.2 608.0 236.8 655.0 241.0 677.0 256.6 734.0 270.4 771.0

Table B. 1 Depth-time matchpoints used to rescale the Akademii Nauk '86 ice core (and the Vavilov cores by the relationships given in Table B.2 below) and the second generation (1990s) Svalbard 51!,0/melt records to an equivalent Graham Bell (FJL) '97 time scale, to bedrock or 1225 A.D. horizon.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Vavilov Eq. AN'86 Vavilov Eq. AN'86 Vavilov Eq. AN'86 Vavilov Eq. AN'86 '88 Depth Depth (m) 83 Depth Depth (m) '79H2 Depth (m) '79H1 Depth (m) 9.0 9.5 5.0 9.5 11.0 17.0 11.0 17.0 25.0 43.1 26.6 41.1 31.0 21.2 33.0 21.2 35.0 57.1 62.8 79.0 41.0 25.0 41.0 25.0 51.0 76.9 93.2 113.0 71.0 43.1 55.0 34.9 65.0 90.8 126.5 141.1 153.0 75.0 73.0 43.1 85.0 117.0 GB hrzn 177.0 83.0 105.0 57.1 115.0 145.0 217.0 205.1 205.0 105.1 153.0 75.0 149.0 180.7 261.9 235.0 253.0 135.1 185.0 89.0 GB hrzn 300.0 283.0 291.0 153.1 207.0 103.3 181.0 219.1 308.2 297.0 337.0 180.7 261.0 129.1 211.0 260.5 328.2 323.0 GB hrzn 297.0 147.0 239.0 309.5 335.6 329.0 365.0 203.0 275.0 352.5 364.9 382.0 401.0 223.1 309.0 402.0 375.6 402.0 419.0 235.0 331.0 450.0 391.6 440.0 487.0 264.9 383.0 516.5 406.5 476.5 517.0 283.0 431.0 567.5 428.7 524.0 545.0 297.0 459.0 605.0 441.6 553.5 557.0 305.0 465.2 600.0

Tabic B.2 Dcpth-dcpth matchpoints used to rescale Vavilov Dome ice core 8lxO records to equivalent Akademii Nauk '86 depth scale, consistent with individual GB97C1 depth-time matching above 1225 A.D. Graham Bell horizon, as indicated.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Gr-Fr'75 GB97C1 Amnd'80 GB97C1 Lomo'76 GB97C1 Lomo'82 GB97CI Depth (m) Age BP'97 Depth (m) Age BP'97 Depth (m) Age BP'97 Depth (m) Age BP'97 1.0 23.0 5.0 23.0 1.0 23.0 1.0 15.0 27.5 30.9 33.0 45.0 26.0 45.0 15.0 69.0 42.5 35.6 51.0 76.0 47.5 76.0 29.0 116.0 62.5 41.9 63.0 100.0 58.2 100.0 39.0 158.0 79.0 88.0 99.0 171.0 68.6 124.0 57.0 227.0 95.0 139.4 153.0 319.8 80.0 149.0 77.0 295.0 107.0 171.0 181.0 392.3 90.0 171.0 89.0 352.0 150.0 221.0 203.0 447.4 100.0 216.5 109.0 414.0 181.0 288.7 213.0 505.8 112.0 271.0 133.0 518.0 202.5 381.9 229.0 568.0 120.0 336.0 251.0 636.0 125.0 377.0 269.0 714.0 135.0 428.0 284.0 771.0 143.0 459.0 151.0 500.0 156.0 529.0 161.0 568.0 167.0 602.0 171.0 636.0 174.0 680.0 178.0 714.0 184.0 760.0 185.5 771.0

Table B.3 Depth-tinic matchpoints used to rescale West Spitsbergen 6l80/mclt records to equivalent Graham Bell (FJL) '97 time scale, to bedrock or 1225 A.D. horizon.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Vest'81 GB97C1 Aust'85/87 GB97C1 Depth (m) Age BP’97 Depth (m) Age BP'97 1.0 17.0 1.0 10.0 5.0 23.0 9.0 23.5 29.0 89.0 13.0 31.6 51.0 124.0 17.0 40.7 65.0 170.0 41.0 86.9 88.0 247.0 59.0 121.3 99.0 314.0 83.0 162.3 109.0 369.0 89.0 180.0 127.0 511.0 99.0 204.1 139.0 596.0 105.0 219.6 143.0 627.0 117.0 244.8 149.0 674.0 121.0 253.5 155.0 725.0 123.0 257.3 159.0 749.0 135.0 292.6 162.0 767.0 143.0 314.6 149.0 328.2 153.0 336.5 159.0 350.2 167.0 365.7 175.0 382.0 177.0 387.9 188.0 411.0 199.0 439.0 '87 Melt only 211.0 462.0 215.0 481.0 226.0 519.0 234.0 538.0 244.0 557.0 254.0 584.0 266.0 613.0 275.0 634.0 284.0 656.0 288.0 670.0 301.0 701.0 311.0 725.0 319.0 740.0 335.0 771.0

Table B.4 Depth-time matchpoints used to rescale Nordauslandet 8l80/melt records to equivalent Graham Bell (FJL) '97 time scale, to bedrock or 1225 A.D. horizon.

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