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Rapid Thinning of Pine Island Glacier in the Early Holocene J Rapid Thinning of Pine Island Glacier in the Early Holocene J. S. Johnson et al. Science 343, 999 (2014); DOI: 10.1126/science.1247385 This copy is for your personal, non-commercial use only. If you wish to distribute this article to others, you can order high-quality copies for your colleagues, clients, or customers by clicking here. Permission to republish or repurpose articles or portions of articles can be obtained by following the guidelines here. The following resources related to this article are available online at www.sciencemag.org (this information is current as of February 27, 2014 ): Updated information and services, including high-resolution figures, can be found in the online version of this article at: on February 27, 2014 http://www.sciencemag.org/content/343/6174/999.full.html Supporting Online Material can be found at: http://www.sciencemag.org/content/suppl/2014/02/19/science.1247385.DC1.html This article cites 38 articles, 8 of which can be accessed free: http://www.sciencemag.org/content/343/6174/999.full.html#ref-list-1 This article appears in the following subject collections: Oceanography www.sciencemag.org http://www.sciencemag.org/cgi/collection/oceans Downloaded from Science (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. Copyright 2014 by the American Association for the Advancement of Science; all rights reserved. The title Science is a registered trademark of AAAS. REPORTS 34. J. A. Forrest, J. Mattsson, Phys. Rev. E Stat. Phys. and Engineering Research Council of Canada, for financial Figs. S1 and S2 Plasmas Fluids Relat. Interdiscip. Topics 61, R53–R56 support. We also thank O. Bäumchen for interesting Database S1 (2000). discussions. References (35, 36) Acknowledgments: The authors acknowledge the École Supplementary Materials Normale Supérieure of Paris, the Fondation Langlois, the www.sciencemag.org/content/343/6174/994/suppl/DC1 19 August 2013; accepted 3 February 2014 Chaire Total–ESPCI ParisTech, as well as the Natural Sciences Materials and Methods 10.1126/science.1244845 is considerable uncertainty associated with mod- Rapid Thinning of Pine Island Glacier el projections of the future evolution of PIG and hence the rate and timing of future ice loss (15). in the Early Holocene The geological record provides evidence of styles and rates of past ice sheet change that can pro- vide constraints on the bounds of possible fu- J. S. Johnson,1*† M. J. Bentley,2,1† J. A. Smith,1 R. C. Finkel,3,4 D. H. Rood,3,5‡ K. Gohl,6 16 7 1 8,9 ture change ( ). In the PIG region, the existing G. Balco, R. D. Larter, J. M. Schaefer geological record consists largely of marine ge- ological data describing grounding line retreat Pine Island Glacier, a major outlet of the West Antarctic Ice Sheet, has been undergoing rapid across the continental shelf (17–21). In contrast, thinning and retreat for the past two decades. We demonstrate, using glacial-geological and little is known about the terrestrial thinning geochronological data, that Pine Island Glacier (PIG) also experienced rapid thinning during the 10 early Holocene, around 8000 years ago. Cosmogenic Be concentrations in glacially transported 1British Antarctic Survey, Natural Environment Research Council, rocks show that this thinning was sustained for decades to centuries at an average rate of more High Cross, Madingley Road, Cambridge CB3 0ET, UK. 2Depart- than 100 centimeters per year, which is comparable with contemporary thinning rates. The most ment of Geography, Durham University, South Road, Durham 3 likely mechanism was a reduction in ice shelf buttressing. Our findings reveal that PIG has DH1 3LE, UK. Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Post Office Box 808 L-397, experienced rapid thinning at least once in the past and that, once set in motion, rapid ice sheet Livermore, CA 94550, USA. 4Earth and Planetary Science De- changes in this region can persist for centuries. partment, University of California, Berkeley, CA 94720, USA. 5Earth Research Institute, University of California, Santa Barbara, 6 ce mass loss from the Pine Island–Thwaites PIG grounding line from 1.2 to 6 m year−1 be- CA 93106, USA. Alfred Wegener Institute Helmholtz–Centre for Polar and Marine Research, Am Alten Hafen 26, 27568 sector dominates the contemporary contribu- tween 2002 and 2007 (4, 9). In addition, thinning 7 Bremerhaven, Germany. Berkeley Geochronology Center, 2455 Ition to sea level from the West Antarctic Ice has been detected 150 km upstream of the ground- Ridge Road, Berkeley, CA 94709, USA. 8Lamont-Doherty Earth Sheet (WAIS) (1, 2). Pine Island Glacier (PIG) ing line (10). The pattern of change is best ex- Observatory (LDEO), Columbia University, Route 9W, Palisades, (Fig. 1A) in particular is currently experiencing con- plained by a dynamic response to increased influx NY 10964, USA. 9Department of Earth and Environmental siderable acceleration, thinning, and retreat (3–6). of warm water to the cavity under the ice shelf at Sciences, Columbia University, New York, NY 10027, USA. This has raised concerns over how much ice will the glacier front (11–14). However, the record *Corresponding author. E-mail: [email protected] — †These authors contributed equally to this work. be lost to the ocean before the ice stream stabi- of change and our understanding of dynamic ‡Present address: Scottish Universities Environmental Research lizes (5–8). Satellite altimetry measurements show changes—over longer time scales of centuries Centre, Rankine Avenue, Scottish Enterprise Technology Park, an increase in rates of thinning of ice close to the to millennia is still limited. Consequently, there East Kilbride G75 0QF, UK. A B 102°W 101°W 100°W 99°W 98°W 110° W 105°W 100° W 95° W 2 03015 50 500 km 75 0 Maish Nunatak S 73° S ' HUDSON Amundsen Sea 0 3 ° Embayment 4 Mt Moses 7 Pine B PS75/214-1 Island Bay PINE Evans ISLAND Knoll 75° S m yr-1 BAY 1000 MOUNTAINS 300 Pine Island Glacier Pine Island 200 250 0 100 200 km ice shelf 150 Glacier S ° 5 100 500 7 50 Fig. 1. Location of study area. (A) Map of the Amundsen Sea Embayment, Pine Island showing location of the study area. The grounded ice sheet is shown in dark gray, 10 Glacier and ice shelves are shown in light gray. (Inset) The location within Antarctica. The box 0 shows the area covered by (B). (B) Map of Pine Island Bay, showing flow velocities (31) of Pine Island Glacier and the unnamed outlet glacier flowing through the andthecrestofthesub–ice shelf ridge (7) is indicated by the dashed white line. The Hudson Mountains, overlaid on Landsat Image Mosaic of Antarctica imagery (gray yellow circle indicates marine sediment core site PS75/214-1, which constrains scale). Contours are in meters. The grounding line is indicated by the solid black line, grounding line retreat (before 11.7 T 0.7 ka) from Pine Island Bay (21). www.sciencemag.org SCIENCE VOL 343 28 FEBRUARY 2014 999 REPORTS history of PIG (22) or how the ice stream evolved undertaken on 12 erratics collected between 0 only be explained by ice-sheet thinning that was through the Holocene to the onset of present-day and 142 m above the present ice surface on the sufficiently rapid to expose the samples instanta- thinning. two nunataks (fig. S3). Details of chemical pro- neously with respect to the precision of their ex- Here, we report detailed glacial-geological cedures, isotopic data, and age calculations are posure ages. evidence from the Hudson Mountains (Fig. 1B) given in (23) and tables S1 to S3. All but one In order to determine the thinning rate at our for rapid thinning in the PIG system ~8 thousand sample—whose anomalously old exposure age sites, we fitted separate linear age-elevation mod- years ago (ka). We studied two nunataks, Mount (~15,800 years) (table S2) we attribute to rework- els to the data from each nunatak (23). Less than Moses and Maish Nunatak, located close to the ing of a previously exposed cobble—yielded 20 km upstream of the modern grounding line, northern margin of PIG within 50 km of its early Holocene 10Be ages, in a narrow time in- modeled thinning rates that best fit the exposure present grounding line (Fig. 1B). An unnamed terval from 6.0 T 0.2 to 8.1 T 0.3 ka (Fig. 2, A, B, age data are 112 and 167 cm year−1 (Fig.2D).Our outlet glacier flows through the Hudson Moun- and C). At Maish Nunatak, exposure ages at all uncertainty analysis shows that these cannot be tains and feeds into Pine Island Glacier ice shelf elevations—a range of 100 m—are indistinguish- distinguished from contemporary thinning rates (Fig. 1B). In common with many of the ice shelf– able. At Mount Moses, the three highest samples (fig. S1). The early Holocene thinning rates are tributary glaciers along the Amundsen Sea coast, yielded exposure ages that are not only indistin- thus sufficiently high that they imply ice-dynamic the outlet glacier is presently thinning rapidly (at guishable over an elevation range of 60 m but are change rather than thinning resulting from changes a rate of 80 to 150 cm year−1)(fig.S1)(4). At also indistinguishable from the ages at Maish in accumulation and ablation. We infer that pre- times when the PIG grounding line was beyond Nunatak. By “indistinguishable,” we mean that vious rapid thinning of the PIG system must have Evans Knoll (~45 km seaward of its current we cannot reject the hypothesis that the scatter been sustained for several decades, and possibly position) (Fig.
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