DOCSLIB.ORG

Towards Ice-Core-Based Synoptic Reconstructions of West Antarctic Climate with Artificial Neural Networks

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Towards Ice-Core-Based Synoptic Reconstructions of West Antarctic Climate with Artificial Neural Networks INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 25: 581–610 (2005) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.1143 TOWARDS ICE-CORE-BASED SYNOPTIC RECONSTRUCTIONS OF WEST ANTARCTIC CLIMATE WITH ARTIFICIAL NEURAL NETWORKS DAVID B. REUSCH,a,* BRUCE C. HEWITSONb and RICHARD B. ALLEYa a Department of Geosciences and EMS Environment Institute, The Pennsylvania State University, University Park, PA 16802 USA b Department of Environmental and Geographical Sciences, University of Cape Town, Private Bag, Rondebosch 7701, South Africa Received 9 March 2004 Revised 22 August 2004 Accepted 12 November 2004 ABSTRACT Ice cores have, in recent decades, produced a wealth of palaeoclimatic insights over widely ranging temporal and spatial scales. Nonetheless, interpretation of ice-core-based climate proxies is still problematic due to a variety of issues unrelated to the quality of the ice-core data. Instead, many of these problems are related to our poor understanding of key transfer functions that link the atmosphere to the ice. This study uses two tools from the field of artificial neural networks (ANNs) to investigate the relationship between the atmosphere and surface records of climate in West Antarctica. The first, self-organizing maps (SOMs), provides an unsupervised classification of variables from the mid- troposphere (700 hPa temperature, geopotential height and specific humidity) into groups of similar synoptic patterns. An SOM-based climatology at annual resolution (to match ice-core data) has been developed for the period 1979–93 based on the European Centre for Medium-Range Weather Forecasts (ECMWF) 15-year reanalysis (ERA-15) dataset. This analysis produced a robust mapping of years to annual-average synoptic conditions as generalized atmospheric patterns or states. Feed-forward ANNs, our second ANN-based tool, were then used to upscale from surface data to the SOM-based classifications, thereby relating the surface sampling of the atmosphere to the large-scale circulation of the mid-troposphere. Two recorders of surface climate were used in this step: automatic weather stations (AWSs) and ice cores. Six AWS sites provided 15 years of near-surface temperature and pressure data. Four ice-core sites provided 40 years of annual accumulation and major ion chemistry. Although the ANN training methodology was properly designed and followed standard principles, limited training data and noise in the ice-core data reduced the effectiveness of the upscaling predictions. Despite these shortcomings, which might be expected to preclude successful analyses, we find that the combined techniques do allow ice-core reconstruction of annual-average synoptic conditions with some skill. We thus consider the ANN-based approach to upscaling to be a useful tool, but one that would benefit from additional training data. Copyright 2005 Royal Meteorological Society. KEY WORDS: ice cores; synoptic reconstruction; artificial neural networks; self-organizing maps; West Antarctica 1. INTRODUCTION This work seeks to use ice-core proxy datasets to reconstruct 40 years (1954–93) of West Antarctic annual climate as seen in the mid-tropospheric circulation using the well-known but poorly understood link between the atmosphere and ice cores. Ice-core proxy data is calibrated to atmospheric circulation data for the period 1979–93 and then used to predict the latter for the period 1954–78. As an additional test of our method, automatic weather station (AWS) data are also used for a limited reconstruction in the 1979–93 period. As described in further detail in the following sections, our approach to this problem consists of four steps. 1. Simplify the atmosphere: self-organizing maps (SOMs) extract patterns of variability by doing a classification into generalized states. These patterns are useful both for studying the recent atmosphere and as components of the subsequent reconstruction. * Correspondence to: David B. Reusch, Department of Geosciences and EMS Environmental Institute, The Pennsylvania State University, University Park, PA 16802, USA; e-mail: [email protected] Copyright 2005 Royal Meteorological Society 582 D. B. REUSCH, B. C. HEWITSON AND R. B. ALLEY 2. Link ice-core proxy and AWS datasets to the atmosphere: a feed-forward artificial neural network (FF ANN) is trained to predict the patterns from (1) using either ice-core or AWS data. This step calibrates the upscaling tool. 3. Reconstruct earlier climate: ice-core data outside the calibration period are used with the trained FF ANN to predict the associated atmospheric patterns for the rest of the ice-core period. Given sufficient confidence in these predictions, they would be used to develop a full time series of reconstructed climate. 4. Evaluate the methodology: confidence in a climate reconstruction is tied to the data and steps involved in creating it. We thus evaluate the reliability of the SOM-based analysis and FF ANN-based upscaling steps and comment on issues associated with the ice-core data that reduce skill in the upscaling step. 1.1. Ice cores and climate Decades of research have shown ice cores to be extremely valuable records of the Earth’s climate from subannual to millenial time scales and beyond (e.g. Wolff and Peel, 1985; Legrand et al., 1988; Mayewski et al., 1988, 1997; Zielinski et al., 1994; White et al., 1999). As with marine sediment cores, tree rings and other climate proxies, interpretation of the ice-core record of palaeoclimate is not always straightforward. In many cases, although the data are of unquestionably high quality and temporal resolution, our poor knowledge of the relevant transfer functions can greatly reduce the value of the record. This is a recognized problem (Waddington, 1996) and, although process studies and field work have helped greatly in some areas 18 (e.g. in improving our understanding of how δ Oice records temperature), there are still many gaps in the knowledge we need to understand the proxy records fully. This is particularly true in the Antarctic, where direct observational data for the atmosphere are hard to obtain and, when available, tend to be relatively short (by climatological standards) and spatially limited. Ice cores record many different aspects of the climate system, sometimes in multiple ways. Each proxy captures one or more climate features in a way that will likely differ in both space and time to varying 18 degrees. For example, the relationship between δ Oice and temperature can be different at different places 18 and times (Alley and Cuffey, 2001; Jouzel et al., 2003) as other influences on δ Oice vary in their relative effect. Furthermore, many proxies are only captured during precipitation events. This can lead to biases in the proxy when precipitation is seasonally variable. For example, if wet deposition is the dominant capture process for a chemical species and snow only falls during the summer, then the ice-core record for that species will be biased towards a picture of the summer atmosphere. Unfortunately, the subannual character of precipitation is typically not very well known at West Antarctic ice-core sites, and we are often forced to assume that snow falls uniformly throughout the year. Subannual sampling is still possible, and indeed necessary to reconstruct annual cycles of chemical species, but it must be remembered that these data are projected onto an underlying assumption about uniform snowfall. Thus, unless detailed subannual process data are available (e.g. Kreutz et al., 1999), we are limited to studies of ice-core proxies at annual resolution. High-resolution meteorological data (reanalysis and/or observational) provide a means to study relationships between ice-core proxies and the atmosphere over subannual intervals, but we remain limited to annual (or possibly semiannual)-resolution climate reconstructions from the proxies. 1.2. The meteorological record and reanalysis datasets The best meteorological datasets in the Antarctic are typically from two areas: the coastal stations, such as McMurdo, Mawson and Halley Bay, and the two long-term interior plateau stations, South Pole and Vostok (Figure 1). Records from elsewhere in the Antarctic interior are limited, with few exceptions, to AWSs and short-term data collection during traverses and ice-core drilling operations (e.g. Siple Dome). The latter often only represent the summer field season (when the sites are occupied). AWSs provide year-round data, apart from instrument problems, but only measure the near-surface environment in a limited manner. The AWS network, nonetheless, provides an invaluable sampling of the West Antarctic atmosphere. The shortage of direct observational data has, in turn, increased the importance and utility of numerical forecast/data assimilation/analysis products for Antarctic climate research. The two most widely used datasets of this type are from the National Centers for Environmental Prediction–National Center for Atmospheric Copyright 2005 Royal Meteorological Society Int. J. Climatol. 25: 581–610 (2005) ICE-CORE-BASED SYNOPTIC RECONSTRUCTIONS 583 Figure 1. Site map showing AWS (solid circles) and ice-core sites (squares) of this study, and other sites (open circles) and regions mentioned in the text. CWA (central West Antarctica) collectively describes four ice core sites (A, B, C, D) published in Reusch et al. (1999) Research (NCEP–NCAR) in the USA and the European Centre for Medium-Range Weather Forecasts (ECMWF) in the UK. Both forecast models have problems in the Antarctic (e.g. Bromwich et al., 1995; Genthon and Braun, 1995; Cullather et al., 1997) and the shortage of observations tends to produce analyses that resemble the forecast more than in areas with more available observations. Nonetheless, despite their shortcomings (e.g. Marshall, 2002; Bromwich and Fogt, 2004), these products are still much better options than having only the observational data. ECMWF and NCEP–NCAR have each produced so-called reanalysis versions of their model predictions (Kalnay et al., 1996; ECMWF, 2000; Kistler et al., 2001). A reanalysis uses one version of the forecast model for the duration of the study period and thus removes changes to the model as a source of changes in the forecasts.
Load more

Recommended publications
  • The Antarctic Coastal Current in the Bellingshausen Sea
    The Cryosphere, 15, 4179–4199, 2021 https://doi.org/10.5194/tc-15-4179-2021 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. The Antarctic Coastal Current in the Bellingshausen Sea Ryan Schubert1, Andrew F. Thompson3, Kevin Speer1, Lena Schulze Chretien4, and Yana Bebieva1,2 1Geophysical Fluid Dynamics Institute, Florida State University, Tallahassee, Florida 32306, USA 2Department of Scientific Computing, Florida State University, Tallahassee, Florida 32306, USA 3Environmental Science and Engineering, California Institute of Technology, Pasadena, CA 91125, USA 4Department of Biology and Marine Science, Marine Science Research Institute, Jacksonville University, Jacksonville, Florida, USA Correspondence: Ryan Schubert ([email protected]) Received: 4 February 2021 – Discussion started: 19 February 2021 Revised: 20 July 2021 – Accepted: 21 July 2021 – Published: 1 September 2021 Abstract. The ice shelves of the West Antarctic Ice Sheet 1 Introduction experience basal melting induced by underlying warm, salty Circumpolar Deep Water. Basal meltwater, along with runoff from ice sheets, supplies fresh buoyant water to a circula- The Antarctic continental slope in West Antarctica, spanning tion feature near the coast, the Antarctic Coastal Current the West Antarctic Peninsula (WAP) to the western Amund- (AACC). The formation, structure, and coherence of the sen Sea, is characterized by a shoaling of the subsurface tem- AACC has been well documented along the West Antarc- perature maximum, which allows warm, salty Circumpolar tic Peninsula (WAP). Observations from instrumented seals Deep Water (CDW) greater access to the continental shelf. collected in the Bellingshausen Sea offer extensive hydro- This leads to an increase in the oceanic heat content over the graphic coverage throughout the year, providing evidence of shelf in this region compared to other Antarctic shelf seas the continuation of the westward flowing AACC from the (Schmidtko et al., 2014).
    [Show full text]
  • Federal Register/Vol. 86, No. 147/Wednesday, August 4, 2021
    Federal Register / Vol. 86, No. 147 / Wednesday, August 4, 2021 / Proposed Rules 41917 Bureau at (202) 418–0530 (VOICE), (202) Community Channel No. (1) Electronically: Go to the Federal 418–0432 (TTY). eRulemaking Portal: http:// This document does not contain www.regulations.gov. In the Search box, information collection requirements ***** enter FWS–HQ–ES–2021–0043, which subject to the Paperwork Reduction Act is the docket number for this of 1995, Public Law 104–13. In addition, NEVADA rulemaking. Then, click on the Search therefore, it does not contain any button. On the resulting page, in the proposed information collection burden ***** Search panel on the left side of the ‘‘for small business concerns with fewer Henderson ............................ 24 screen, under the Document Type than 25 employees,’’ pursuant to the heading, check the Proposed Rule box to Small Business Paperwork Relief Act of ***** locate this document. You may submit 2002, Public Law 107–198, see 44 U.S.C. a comment by clicking on ‘‘Comment.’’ 3506(c)(4). Provisions of the Regulatory [FR Doc. 2021–16589 Filed 8–3–21; 8:45 am] (2) By hard copy: Submit by U.S. mail Flexibility Act of 1980, 5 U.S.C. 601– BILLING CODE 6712–01–P to: Public Comments Processing, Attn: 612, do not apply to this proceeding. FWS–HQ–ES–2021–0043, U.S. Fish and Members of the public should note Wildlife Service, MS: PRB/3W, 5275 that all ex parte contacts are prohibited DEPARTMENT OF THE INTERIOR Leesburg Pike, Falls Church, VA 22041– from the time a Notice of Proposed 3803.
    [Show full text]
  • Variability in Cenozoic Sedimentation Along the Continental Rise of the Bellingshausen Sea, West Antarctica ⁎ Carsten Scheuer A, , Karsten Gohl A, Robert D
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Electronic Publication Information Center Marine Geology 227 (2006) 279–298 www.elsevier.com/locate/margeo Variability in Cenozoic sedimentation along the continental rise of the Bellingshausen Sea, West Antarctica ⁎ Carsten Scheuer a, , Karsten Gohl a, Robert D. Larter b, Michele Rebesco c, Gleb Udintsev d a Alfred Wegener Institute for Polar and Marine Research (AWI), Postfach 120161, D-27515, Bremerhaven, Germany b British Antarctic Survey (BAS), High Cross, Madingley Road, Cambridge CB3 OET, UK c Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Borgo Grotta Gigante 42/C, 34010 Sconico (TS), Italy d Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19, Kosygin Str, 117975 Moscow, Russia Received 29 September 2004; received in revised form 16 December 2005; accepted 21 December 2005 Abstract Seismic reflection profiles, bathymetric and magnetic data collected along and across the continental margin of the Bellingshausen Sea provide new constraints and interpretations of the oceanic basement structure and Cenozoic glacial history of West Antarctica. Evidence for tectonic boundaries that lie perpendicular to the margin has been identified on the basis of one previously unpublished along-slope multichannel seismic reflection profile. By combining several magnetic data sets, we determined basement ages and verified the positions of possible fracture zones, enabling us to improve previous tectonic and stratigraphic models. We establish three main sediment units on the basis of one seismic along-slope profile and by correlation to the continental shelf via one cross-slope profile. We interpret a lowermost unit, Be3 (older then 9.6 Ma), as representing a long period of slow accumulation of mainly turbiditic sediments.
    [Show full text]
  • Ice Core Records of 20Th Century Sea Ice Decline in the Bellingshausen Sea, Geophysical Research Letters, Submitted
    R. Röthlisberger and N. Abram Abram, N., McConnell, J.R., Thomas, E.R., Mulvaney, R. and Aristarain, A.J., 2008: Ice core records of 20th century sea ice decline in the Bellingshausen Sea, Geophysical Research Letters, submitted. Abram, N., Mulvaney, R., Wolff, E.W. and Mudelsee, M., 2007: Ice core records as sea ice proxies: an evaluation from the Weddell Sea region of Antarctica, Journal of Geophysical Research, 112: D15101, doi:15110.11029/12006JD008139. Castebrunet, H., Genthon, C. and Martinerie, P., 2006: Sulfur cycle at Last Glacial Maximum: Model results versus Antarctic ice core data, Geophysical Research Letters, 33: L22711, doi:10.1029/2006GL027681. Crosta, X., Sturm, A., Armand, L. and Pichon, J.J., 2004: Late Quaternary sea ice history in the Indian sector of the Southern Ocean as recorded by diatom assemblages, Marine Micropaleontology, 50: 209-223. Curran, M.A.J. and Jones, G.B., 2000: Dimethyl sulfide in the Southern Ocean: Seasonality and flux, Journal of Geophysical Research, 105: 20451-20459. Curran, M.A.J., van Ommen, T.D., Morgan, V.I., Phillips, K.L. and Palmer, A.S., 2003: Ice core evidence for Antarctic sea ice decline since the 1950s, Science, 302: 1203-1206. Foster, A.F.M., Curran, M.A.J., Smith, B.T., van Ommen, T.D. and Morgan, V.I., 2006: Covariation of sea ice and methanesulphonic acid in Wilhelm II Land, East Antarctica, Annals of Glaciology, 44: 429-432. Fundel, F., Fischer, H., Weller, R., Traufetter, F., Oerter, H. and Miller, H., 2006: Influence of large-scale teleconnection patterns on methane sulfonate ice core records in Dronning Maud Land, Journal of Geophysical Research, 111: (D04103), doi:10.1029/2005JD005872.
    [Show full text]
  • C:\Users\Francisco\Onedrive
    Observations by the Editor Obs. 1: Methods: The methods are not always clearly described. In particular, in section 3.3, the Fourier transform procedure does not make sense. The IFFT is usually used to convert from the frequency domain to the space domain, not the other way around. The expression "The signal obtained from each step of the FFT decomposition" does not mean anything to me, and the statement that "By studying the progression of these variations, the frequency of the second mode showed the highest frequency where the Sdev reaches an equilibrium" needs to be rewritten, as it does not correspond to anything I understand about signal processing. Response: Sections 3 and 4 were rewritten and reformulated accordingly and the focus of the analysis was modified. With these changes we aim to emphasize that the analysis using FFT aimed to extract low frequency oscillations from a noisy signal obtained from the isotope record. The filtered signal was then compared with meteorological data retrieved from re-analysis data using a linear regression analysis. The linear regression model was fitted to the whole data set and in this way the signal was transformed from the space domain (depth) to the time domain (age). Thereafter temperature, accumulation rate and environmental conditions trends were reconstructed. Obs. 2: I think what is going on is that the authors looked at the FFT spectrum of the signal and decided what parts of it were meaningful, then edited out the higher-frequency, less meaningful portion and used the IFFT to produce a filtered signal containing only low-frequency information.
    [Show full text]
  • Glacier Change Along West Antarctica's Marie Byrd Land Sector
    Glacier change along West Antarctica’s Marie Byrd Land Sector and links to inter-decadal atmosphere-ocean variability Frazer D.W. Christie1, Robert G. Bingham1, Noel Gourmelen1, Eric J. Steig2, Rosie R. Bisset1, Hamish D. Pritchard3, Kate Snow1 and Simon F.B. Tett1 5 1School of GeoSciences, University of Edinburgh, Edinburgh, UK 2Department of Earth & Space Sciences, University of Washington, Seattle, USA 3British Antarctic Survey, Cambridge, UK Correspondence to: Frazer D.W. Christie ([email protected]) Abstract. Over the past 20 years satellite remote sensing has captured significant downwasting of glaciers that drain the West 10 Antarctic Ice Sheet into the ocean, particularly across the Amundsen Sea Sector. Along the neighbouring Marie Byrd Land Sector, situated west of Thwaites Glacier to Ross Ice Shelf, glaciological change has been only sparsely monitored. Here, we use optical satellite imagery to track grounding-line migration along the Marie Byrd Land Sector between 2003 and 2015, and compare observed changes with ICESat and CryoSat-2-derived surface elevation and thickness change records. During the observational period, 33% of the grounding line underwent retreat, with no significant advance recorded over the remainder 15 of the ~2200 km long coastline. The greatest retreat rates were observed along the 650-km-long Getz Ice Shelf, further west of which only minor retreat occurred. The relative glaciological stability west of Getz Ice Shelf can be attributed to a divergence of the Antarctic Circumpolar Current from the continental-shelf break at 135° W, coincident with a transition in the morphology of the continental shelf. Along Getz Ice Shelf, grounding-line retreat reduced by 68% during the CryoSat-2 era relative to earlier observations.
    [Show full text]
  • Rampant Lion Project Afghanistan 2006, 2008 Rampant Lion Project Afghanistan 2006, 2008
    Airborne Gravimetry at the U.S. Naval Research Lab 1980-Present Mary Flather Peters Early History of NRL Airborne Program – Pre Kinematic GPS 1979 Preliminary Design of System First test of Early Prototype off Carolina Coast Jun-80 Loran C Nav RMS ~ 20 mGal 8 Flights Incorporation of GPS Nav and test off Wallops Island, VA Jun-81 RMS < 6 mGal 2 Flights 12 Flights, no Dec-83 Piggy Back Gravity on Airborne Magnetics Study East of Brazil ground truth Blind Test over Eastern NC for DMA Apr-84 Incorporation of Pressure Altimetry RMS 2.5 mGal 4 Flights 15 Flights, Data May-84 Piggy Back Gravity on Airborne Study of the Angola Basin not reduced 12 Flights, no Feb-86 NSF Funded Study of the Antarctic Margin, Airborne Gravity over Ice ground truth Eastern Seaboard Test for NSWC RMS Jun-86 Difference with NSWC Shipboard Data < 4 mGal 6 Flights Feb-87 NSF Study of Antarctic Margin Average Mis-tie 2.2 mGal 10 Flights Sep-87 NSWC Inteferometric GPS Test 6 Flights Oct-87 NSF Study of Antarctic Margin 9 Flights 1988-1989 Gravimeter, Altimeter and Computer upgrades Nov-89 NSWC/ NRL Interferometric GPS/INS tests 6 Flights Norwegian-Greenland Sea and Eurasia Basin Aeromag Profiles (1973-76) Canada and Eurasia Basin Aeromag Profiles (1972-83) P3-B (heavy) -154589 in Spitsbergen -1999 P3-A -149674, NRL Flt Sup. Det. 2nd P-3 Antarctic Geophysical Surveys Airborne Gravity, Magnetics and Surface Topo – P3, L&R − * 1985 – Rio Grande, Argentina – Weddell Sea (East of Ant Peninsula) − * 1986 – Punta Arenas, Chile – Weddell Sea (East of Ant Peninsula) − * 1987 – Punta Arenas, Chile – Bellingshausen Sea (West of Ant Peninsula) Airborne Gravity, Topo Lidar, Ice Thickness Radar, Magnetics – Twin Otter, BGM ⁻ * 1991-1992 Central West Antarctic 9 NSF Study of Antarctic Margin Average Mis-tie 2.2 mGal Kinematic GPS Era Greenland Aerogeophysics Project 1991, 1992 Greenland Gravity Canada and Eurasia Basin Aerograv/mag Tracks (1992-99) Arctic Aerograv Rampant Lion Project Afghanistan 2006, 2008 Rampant Lion Project Afghanistan 2006, 2008 Rampant Lion Project Afghanistan 2006, 2008 .
    [Show full text]
  • The Larsen Ice Shelf System, Antarctica
    22–25 Sept. GSA 2019 Annual Meeting & Exposition VOL. 29, NO. 8 | AUGUST 2019 The Larsen Ice Shelf System, Antarctica (LARISSA): Polar Systems Bound Together, Changing Fast The Larsen Ice Shelf System, Antarctica (LARISSA): Polar Systems Bound Together, Changing Fast Julia S. Wellner, University of Houston, Dept. of Earth and Atmospheric Sciences, Science & Research Building 1, 3507 Cullen Blvd., Room 214, Houston, Texas 77204-5008, USA; Ted Scambos, Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado 80303, USA; Eugene W. Domack*, College of Marine Science, University of South Florida, 140 7th Avenue South, St. Petersburg, Florida 33701-1567, USA; Maria Vernet, Scripps Institution of Oceanography, University of California San Diego, 8622 Kennel Way, La Jolla, California 92037, USA; Amy Leventer, Colgate University, 421 Ho Science Center, 13 Oak Drive, Hamilton, New York 13346, USA; Greg Balco, Berkeley Geochronology Center, 2455 Ridge Road, Berkeley , California 94709, USA; Stefanie Brachfeld, Montclair State University, 1 Normal Avenue, Montclair, New Jersey 07043, USA; Mattias R. Cape, University of Washington, School of Oceanography, Box 357940, Seattle, Washington 98195, USA; Bruce Huber, Lamont-Doherty Earth Observatory, Columbia University, 61 US-9W, Palisades, New York 10964, USA; Scott Ishman, Southern Illinois University, 1263 Lincoln Drive, Carbondale, Illinois 62901, USA; Michael L. McCormick, Hamilton College, 198 College Hill Road, Clinton, New York 13323, USA; Ellen Mosley-Thompson, Dept. of Geography, Ohio State University, 1036 Derby Hall, 154 North Oval Mall, Columbus, Ohio 43210, USA; Erin C. Pettit#, University of Alaska Fairbanks, Dept. of Geosciences, 900 Yukon Drive, Fairbanks, Alaska 99775, USA; Craig R.
    [Show full text]
  • Southern Elephant Seal Movements and Antarctic Sea Ice H
    Antarctic Science 12 (If:3-15 (2000) 0 British Antarctic Survey Printed in the United Kingdom Southern elephant seal movements and Antarctic sea ice H. BORNEMANN1*, M. KREYSCHER', S. RAMDOHRl, T. MARTINZ,A. CARLINP, 1. SELLMANN' and J. PLoTZI 'Alfied- Wegener-lnstitutfir Polar- und Meeresforschung, Postfach 12 01 61, 0-27515 Bremerhaven, Germany 21nstitutfir Meereskunde, Diisternbrooker Weg 20,D-24105 Kiel, Germany 3Departamento de Ciencias Bioldgicas, Instituto Antcirtico Argentino, Cerrito 1248, 1010 Buenos Aires, Argentina 4Dienstleistungfur Wissenschaft und Forschung, Am Bremerhavener Innovations- und Griinderzentrum, Stresemannstrasse 46, 0-27568 Bremerhaven, Germany *[email protected] Abstract: Weaned pups and post-moult female elephant seals (Mirounga leonina) were fitted with satellite transmitters at King George Island (South Shetland Islands) between December 1996 and February 1997. Of the nine adult females tracked for more than two months, three stayed in a localized area between the South Shetland Islands and the South Orkney Islands. The other six females travelled south-west along the coast of the Antarctic Peninsula up to the Bellingshausen Sea. Two of them then moved north-east and hauled out on South Georgia in October. One female was last located north of the South Shetland Islands in March 1998. In total, eight females were again sighted on King George Island and six of the transmitters removed. The tracks of the weaners contrasted with those of the adults. In January, five juveniles left King George Island for the Pacific sector spending about four weeks in the open sea west of the De Gerlache Seamounts. Three of them returned to the tip of the Antarctic Peninsula in June, of which one was last located on the Patagonian Shelf in November 1997.
    [Show full text]
  • Iii. Diatom Phytoplankton Studies in the Southern Pacific Ocean, Composition and Correlation to the Antarctic Convergence and Its Paleoecological Significance
    III. DIATOM PHYTOPLANKTON STUDIES IN THE SOUTHERN PACIFIC OCEAN, COMPOSITION AND CORRELATION TO THE ANTARCTIC CONVERGENCE AND ITS PALEOECOLOGICAL SIGNIFICANCE Juliane Fenner, Hans-Joachim Schrader, and Harry Wienigk, Geologisch-Palaontologisches Institut and Museum der Universitat Kiel, D-23 Kiel, Federal Republic of Germany INTRODUCTION during the Antarctic summer. Although most chloro- phyll data have been obtained from material collected During Leg 35 of D/V Glomar Challenger from during the Antarctic spring, summer, and autumn, Callao, Peru to Ushuaia, Argentina, 2 February to 30 Bunt (1961) and El-Sayed (1966b) made their observa- March 1974, surface water samples (4 m water depth) tions also during the winter. were collected in the southern part of the East Pacific Ocean, off the coast of Chile and in the Bellingshausen OCEANOGRAPHY OF THE SOUTHEAST Sea. The study is supplementary to the investigation PACIFIC OCEAN done on fossil diatoms of the sediment cores recovered The Southern Ocean (Deacon, 1963; The Oxford during the leg (see Schrader, this volume). Atlas, 1963) is governed by the Westwind Drift result- Figures 1, 2, and 3, and Table 1 show the position of ing in the clockwise Antarctic Circumpolar Current the stations at which plankton collections and which has volocities up to 25 cm/sec~1 (Neumann and simultaneous surface water temperature measurements Pierson, 1966, cited in Gordon, 1971a) where west were made. winds are at a maximum (at about 50° S latitude) with The object of the study was to determine: (1) patterns
    [Show full text]
  • An Improved Bathymetry Compilation for the Bellingshausen Sea, Antarctica, to Inform Ice-Sheet and Ocean Models
    The Cryosphere, 5, 95–106, 2011 www.the-cryosphere.net/5/95/2011/ The Cryosphere doi:10.5194/tc-5-95-2011 © Author(s) 2011. CC Attribution 3.0 License. An improved bathymetry compilation for the Bellingshausen Sea, Antarctica, to inform ice-sheet and ocean models A. G. C. Graham1, F. O. Nitsche2, and R. D. Larter1 1Ice Sheets programme, British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK 2Lamont Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, New York, 10964, USA Received: 30 September 2010 – Published in The Cryosphere Discuss.: 15 October 2010 Revised: 14 January 2011 – Accepted: 3 February 2011 – Published: 16 February 2011 Abstract. The southern Bellingshausen Sea (SBS) is a ning and acceleration of the WAIS, measure changes to its rapidly-changing part of West Antarctica, where oceanic and glaciers and ice shelves at ocean margins, and estimate the atmospheric warming has led to the recent basal melting impacts of future changes on the environment (including sea and break-up of the Wilkins ice shelf, the dynamic thin- level), with implications for society as a whole (e.g. Over- ning of fringing glaciers, and sea-ice reduction. Accurate peck and Weiss, 2009). sea-floor morphology is vital for understanding the contin- A concerted focus of West Antarctic studies is on the ued effects of each process upon changes within Antarc- southern Bellingshausen Sea (SBS), fed by ice draining tica’s ice sheets. Here we present a new bathymetric grid for the WAIS as well as the adjoining Antarctic Pensinusla the SBS compiled from shipborne multibeam echo-sounder, Ice Sheet, where major changes are already taking place spot-sounding and sub-ice measurements.
    [Show full text]
  • Variability of the Southern Boundary in the Bellingshausen Sea, Southern Ocean
    Variability of the Southern Boundary in the Bellingshausen Sea, Southern Ocean Ria Oelerich Co-Authors: Karen J. Heywood Gillian M. Damerell Andrew F. Thompson E-Mail: [email protected] Introduction - The Bellingshausen Sea is located between the West Antarctic Peninsula and the Amundsen Sea - The Antarctic Slope Front that rings the continental slope of Antarctica supports a westward current whose structure and variability influences exchange processes close to Antarctica such as the transport of warm Circumpolar Deep Water onto the shelf (Thompson et al., 2018) - This water mass is responsible for the transport of heat across the shelf and therefore the basal melting of ice shelves - Due to the lack of observations it is still unclear if the Antarctic Slope Front exists in the Bellingshausen Sea or if there are other structures close to the shelf break such as the Southern Boundary of the Antarctic Circumpolar Current moderating the transport of warm water onto the shelf. - Therefore observations of cross-slope sections in the Bellingshausen Sea from 2007 and 2019 are used in comparison with NEMO 1/12 ° Reanalysis data (GLOBAL_REANALYSIS_PHY_001_030) from 2000 to 2018 to investigate: - Current structures - Distance of the Southern Boundary to the shelf break - Seasonal and interannual variability of the Southern Boundary Area of Interest Figure 1: a) Map of observed cross-slope CTD sections from 2007 (blue) and 2019 (red) along with LADCP / SADCP quivers averaged over the top 500 m. The black contours show the 500 and 750 a) m isobath based on the IBCSO data set (Arndt et al., 2013). The bold and the dashed white contour mark the Southern 5 Antarctic Cirumpolar Front (SACCF) and the Southern Boundary (SB) of the ACC defined by Orsi et al.
    [Show full text]