DOCSLIB.ORG

Understanding Antarctic Ice-Stream Flow Using Ice-Flow Models and Geophysical

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Understanding Antarctic Ice-Stream Flow Using Ice-Flow Models and Geophysical Understanding Antarctic ice-stream flow using ice-flow models and geophysical observations David A Lilien A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2019 Reading Committee: Ian Joughin, Chair Knut Christianson Benjamin Smith Program Authorized to Offer Degree: Department of Earth and Space Sciences ©Copyright 2019 David A Lilien University of Washington Abstract Understanding Antarctic ice-stream flow using ice-flow models and geophysical observations David A Lilien Chair of the supervisory committee: Dr. Ian R Joughin Department of Earth and Space Sciences Ice streams are the primary pathway by which Antarctic ice is evacuated to the ocean. Because the Antarctic ice sheets lose mass primarily through oceanic melt and calving, ice-stream dynamics exert a primary control on the mass balance of the ice sheets. Thus, changes in melt rates at the ice-sheet margins, or in accumulation in the ice-sheet interiors, affect ice-sheet mass balance on timescales modulated by the response time of the ice streams. Even abrupt changes in melt at the margins can cause ice-stream speedup and resultant thinning lasting millennia, so understanding the upstream propagation of marginally forced changes across timescales is key for understanding the ice sheets’ ongoing contribution to sea-level rise. This dissertation is comprised of three studies that use observations and models to understand changes to Antarctic ice-stream dynamics on timescales from decades to millennia. The first chapter synthesizes remotely sensed observations of Smith, Pope, and Kohler glaciers in West Antarctica to investigate the causes and extent of their retreat. These glaciers have displayed some of the largest measured grounding-line retreat, most rapid thinning, and largest speedup amongst Antarctic ice streams. This retreat has drawn interest in their stability both in its own right and as a harbinger of future changes to larger neighboring ice streams. In this study, recent melt rates were determined using flux divergence estimates derived from observations of ice thickness and surface velocity. Out-of-balance melt at the beginning of the study period indicates that the imbalance of this system predates the beginning of satellite velocity observations in 1996. Throughout much of 1996-2010, there was both greater melt over the ice shelves than flux across the grounding line, implying loss of floating ice and elevated melt forcing, and greater grounding-line flux than accumulation, implying adjustment of the grounded ice in response to the ongoing imbalance. The grounding line position of Kohler glacier, and a large melt channel that is unlikely to be a steady-state feature, suggest that the perturbation to this system began on Kohler glacier sometime around the 1970s. Viscosity of the ice shelves, inferred using a numerical model, indicates that weakening of the Crosson ice shelf was necessary to allow the observed speedup, though it is unable to determine whether the weakening was a cause or effect of the ongoing retreat. The second chapter uses a suite of numerical model simulations to determine the dominant drivers of the recent retreat of Smith, Pope, and Kohler glaciers, and extends those simulations that best match observations to evaluate likely future retreat. Similar to the findings of previous studies, the distribution of sub-shelf melt is found to be the primary control on the rate of grounding-line retreat, while the shelf-averaged melt rate exerts a secondary control. The model simulations indicate that, despite ongoing imbalance, the grounding-line position in 1996 was not inherently unstable, but rather elevated melt at the grounding line was required to cause the observed retreat. A weakening of the ice-shelf margins was found to hasten the onset of grounding-line retreat and led to greater speedup. However, without increases in melt beyond 1996 levels, marginal weakening was insufficient to initiate grounding-line retreat. All simulations that capture the observed retreat continue to lose mass until at least 2100, suggesting that ice in this basin may contribute over 8 mm to global mean sea level by 2100. The magnitude of thinning deep in the catchment suggests that the retreat of Kohler and Smith glacier may hasten the destabilization of the neighboring Thwaites glacier catchment. The third chapter uses the timescale of the recently drilled South Pole Ice Core (SPICEcore) and nearby geophysical observations to infer the history of ice flow near the South Pole during the last 10,000 years. The South Pole is located 180 km from the nearest ice divide and drains from the East Antarctic plateau through Academy glacier/Foundation ice stream. As a result, ice flow near the South Pole is potentially affected by the dynamics of these ice streams, and so the history of ice flow in this region has the potential to inform understanding of how marginally forced changes affect the ice-sheet interior. Because the South Pole is far from an ice divide, the accumulation record in SPICEcore incorporates both spatial variations in accumulation upstream and temporal variations in regional accumulation. Comparison between the SPICEcore accumulation record, derived by correcting measured layer thicknesses for thinning, with an accumulation record derived from new GPS and radar measurements upstream, yields insight into past ice flow and accumulation. When ice speeds are modeled as increasing by 15% since 10 ka, the upstream accumulation explains 77% of the variance in the SPICEcore-derived accumulation (vs. 22% without speedup). This correlation is only expected if the ice-flow direction and spatial pattern of accumulation were stable throughout the Holocene. The 15% speedup in turn suggests a slight (3-4%) steepening or thickening of the ice-sheet interior and provides a new constraint on the evolution of the East Antarctic Ice Sheet following the glacial termination. Table of Contents Table of Contents i List of Figures iv List of Tables vi Acknowledgements vii Chapter 1 Introduction................................................................................................................. 1 1.1 Motivation ............................................................................................................................. 1 1.2 Changes to the Antarctic ice sheets ...................................................................................... 2 1.3 Organization .......................................................................................................................... 4 Chapter 2 Changes in flow of Crosson and Dotson Ice Shelves, West Antarctica in response to elevated melt 9 2.1 Introduction ......................................................................................................................... 10 2.1.1 Study Area .................................................................................................................... 12 2.2 Data ..................................................................................................................................... 14 2.2.1 Velocity ........................................................................................................................ 14 2.2.2 Surface elevations ........................................................................................................ 15 2.2.3 Ice-bottom Elevations .................................................................................................. 16 2.2.4 Ice-front positions ........................................................................................................ 18 2.3 Methods............................................................................................................................... 18 i 2.3.1 Flux and melt calculation ............................................................................................ 18 2.3.2 Modeling ...................................................................................................................... 20 2.3.3 Stress Changes ............................................................................................................. 22 2.4 Results ................................................................................................................................. 23 2.4.1 Flux and Melt ............................................................................................................... 23 2.4.2 Buttressing ................................................................................................................... 25 2.4.3 Modeled Weakening ..................................................................................................... 26 2.5 Discussion ........................................................................................................................... 27 2.5.1 Causes of Dotson’s imbalance ..................................................................................... 28 2.5.2 Causes of Crosson’s speedup....................................................................................... 34 2.5.3 Comparison to previous melt estimates ....................................................................... 36 2.6 Summary ............................................................................................................................. 38 Chapter 3 Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler glaciers 47 3.1 Introduction
Load more

Recommended publications
  • Improved Estimation of the Mass Balance of Glaciers Draining Into the Amundsen Sea Sector of West Antarctica from the CECS/NASA 2002 Campaign
    Annals of Glaciology 39 2004 231 Improved estimation of the mass balance of glaciers draining into the Amundsen Sea sector of West Antarctica from the CECS/NASA 2002 campaign Eric RIGNOT,1 Robert H. THOMAS,2 Pannir KANAGARATNAM,3 Gino CASASSA,4 Earl FREDERICK,5 Sivaprasad GOGINENI,3 William KRABILL,5 Andre`s RIVERA,4 Robert RUSSELL,5 John SONNTAG,5 Robert SWIFT,5 James YUNGEL5 1Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, USA E-mail: [email protected] 2EG&G Services, NASA Wallops Flight Facility, Building N-159, Wallops Island, VA 23337, USA 3The University of Kansas, 2291 Irving Hill Road, Lawrence, KS 66045-2969, USA 4Centro de Estudios Cientifı´cos, Avenida Arturo Prat 514, Casilla 1469, Valdivia, Chile 5NASA Wallops Flight Facility, Wallops Island, VA 23337, USA ABSTRACT. In November–December 2002, a joint airborne experiment by Centro de Estudios Cientifı´cos and NASA flew over the Antarctic ice sheet to collect laser altimetry and radio-echo sounding data over glaciers flowing into the Amundsen Sea. A P-3 aircraft on loan from the Chilean Navy made four flights over Pine Island, Thwaites, Pope, Smith and Kohler glaciers, with each flight yielding 1.5–2 hours of data. The thickness measurements reveal that these glaciers flow into deep troughs, which extend far inland, implying a high potential for rapid retreat. Interferometric synthetic aperture radar data (InSAR) and satellite altimetry data from the European Remote-sensing Satellites (ERS-1/-2) show rapid grounding-line retreat and ice thinning of these glaciers.
    [Show full text]
  • I!Ij 1)11 U.S
    u... I C) C) co 1 USGS 0.. science for a changing world co :::2: Prepared in cooperation with the Scott Polar Research Institute, University of Cambridge, United Kingdom Coastal-change and glaciological map of the (I) ::E Bakutis Coast area, Antarctica: 1972-2002 ;::+' ::::r ::J c:r OJ ::J By Charles Swithinbank, RichardS. Williams, Jr. , Jane G. Ferrigno, OJ"" ::J 0.. Kevin M. Foley, and Christine E. Rosanova a :;:,­..... CD ~ (I) I ("') a Geologic Investigations Series Map I- 2600- F (2d ed.) OJ ~ OJ '!; :;:,­ OJ ::J <0 co OJ ::J a_ <0 OJ n c; · a <0 n OJ 3 OJ "'C S, ..... :;:,­ CD a:r OJ ""a. (I) ("') a OJ .....(I) OJ <n OJ n OJ co .....,...... ~ C) .....,0 ~ b 0 C) b C) C) T....., Landsat Multispectral Scanner (MSS) image of Ma rtin and Bea r Peninsulas and Dotson Ice Shelf, Bakutis Coast, CT> C) An tarctica. Path 6, Row 11 3, acquired 30 December 1972. ? "T1 'N 0.. co 0.. 2003 ISBN 0-607-94827-2 U.S. Department of the Interior 0 Printed on rec ycl ed paper U.S. Geological Survey 9 11~ !1~~~,11~1!1! I!IJ 1)11 U.S. DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP I-2600-F (2d ed.) U.S. GEOLOGICAL SURVEY COASTAL-CHANGE AND GLACIOLOGICAL MAP OF THE BAKUTIS COAST AREA, ANTARCTICA: 1972-2002 . By Charles Swithinbank, 1 RichardS. Williams, Jr.,2 Jane G. Ferrigno,3 Kevin M. Foley, 3 and Christine E. Rosanova4 INTRODUCTION areas Landsat 7 Enhanced Thematic Mapper Plus (ETM+)), RADARSAT images, and other data where available, to compare Background changes over a 20- to 25- or 30-year time interval (or longer Changes in the area and volume of polar ice sheets are intri­ where data were available, as in the Antarctic Peninsula).
    [Show full text]
  • First Exposure Ages from the Amundsen Sea Embayment, West Antarctica: the Late Quaternary Context for Recent Thinning of Pine Island, Smith, and Pope Glaciers
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Electronic Publication Information Center First exposure ages from the Amundsen Sea Embayment, West Antarctica: The Late Quaternary context for recent thinning of Pine Island, Smith, and Pope Glaciers Joanne S. Johnson British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK Michael J. Bentley Department of Geography, Durham University, South Road, Durham DH1 3LE, UK and British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK Karsten Gohl Alfred-Wegener-Institut für Polar- und Meeresforschung, Postfach 120161, D-27515 Bremerhaven, Germany ABSTRACT Dramatic changes (acceleration, thinning, and grounding-line retreat of major ice streams) in the Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS) have been observed dur- ing the past two decades, but the millennial-scale context for these changes is not yet known. We present the fi rst surface exposure ages recording thinning of Pine Island, Smith, and Pope Glaciers, which all drain into the Amundsen Sea. From these we infer progressive thinning of Pine Island Glacier at an average rate of 3.8 ± 0.3 cm yr–1 for at least the past 4.7 k.y., and of Smith and Pope Glaciers at 2.3 ± 0.2 cm yr–1 over the past 14.5 k.y. These rates are more than an order of magnitude lower than the ~1.6 m yr–1 recorded by satellite altimetry for Pine Island Glacier in the period 1992–1996. Similarly low long-term rates (2.5–9 cm yr–1 since 10 ka) have been reported farther west in the Ford Ranges, Marie Byrd Land, but in that area, the same rates of thinning continue to the present day.
    [Show full text]
  • Glacial Retreat in the Amundsen Sea Sector, West Antarctica E first Cosmogenic Evidence from Central Pine Island Bay and the Kohler Range
    Quaternary Science Reviews 98 (2014) 166e173 Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev Glacial retreat in the Amundsen Sea sector, West Antarctica e first cosmogenic evidence from central Pine Island Bay and the Kohler Range * Julia Lindow a, , Marion Castex a, Hella Wittmann b, Joanne S. Johnson c, Frank Lisker a, Karsten Gohl d, Cornelia Spiegel a a Department of Geosciences, University of Bremen, Bremen, Germany b Helmholtz-Centre Potsdam e German Research Centre for Geosciences (GFZ), Potsdam, Germany c British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK d Alfred Wegener Institute, Helmholtz-Centre for Polar and Marine Research (AWI), Bremerhaven, Germany article info abstract Article history: The Amundsen Sea Embayment of West Antarctica hosts one of the most rapidly changing sectors of the Received 14 February 2014 West Antarctic Ice Sheet. With the fastest-flowing ice streams in Antarctica, the region around Pine Is- Received in revised form land Bay is characterized by rapid ice-sheet thinning and grounding-line retreat. Published surface- 13 May 2014 exposure data are limited to a few isolated nunataks making it difficult to assess the long-term degla- Accepted 15 May 2014 cial history of the area. To address this, we correlate existing records of lateral ice-stream retreat from Available online 4 July 2014 marine sediment cores with onshore glacial thinning in two key areas of eastern Marie Byrd Land: the Kohler Range and Pine Island Bay. Our 10Be surface-exposure ages are the first from the isolated Kohler Keywords: Surface exposure dating Range and show that the nunataks there became ice-free between 8.6 and 12.6 ka.
    [Show full text]
  • The Last Glaciation of Bear Peninsula, Central Amundsen Sea
    Quaternary Science Reviews 178 (2017) 77e88 Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev The last glaciation of Bear Peninsula, central Amundsen Sea Embayment of Antarctica: Constraints on timing and duration revealed by in situ cosmogenic 14Cand10Be dating * Joanne S. Johnson a, , James A. Smith a, Joerg M. Schaefer b, Nicolas E. Young b, Brent M. Goehring c, Claus-Dieter Hillenbrand a, Jennifer L. Lamp b, Robert C. Finkel d, Karsten Gohl e a British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK b Lamont-Doherty Earth Observatory, Columbia University, Route 9W, Palisades, New York NY 10964, USA c Department of Earth & Environmental Sciences, Tulane University, New Orleans, LA 70118, USA d Lawrence Livermore National Laboratory, Center for Accelerator Mass Spectrometry, 7000 East Avenue Avenue, Livermore, CA 94550-9234, USA e Alfred Wegener Institute for Polar and Marine Research, Postfach 120161, D-27515 Bremerhaven, Germany article info abstract Article history: Ice streams in the Pine Island-Thwaites region of West Antarctica currently dominate contributions to sea Received 6 April 2017 level rise from the Antarctic ice sheet. Predictions of future ice-mass loss from this area rely on physical Received in revised form models that are validated with geological constraints on past extent, thickness and timing of ice cover. 18 October 2017 However, terrestrial records of ice sheet history from the region remain sparse, resulting in significant Accepted 1 November 2017 model uncertainties. We report glacial-geological evidence for the duration and timing of the last glaciation of Hunt Bluff, in the central Amundsen Sea Embayment.
    [Show full text]
  • Grounding Line Retreat of Pope, Smith, and Kohler Glaciers, West
    Geophysical Research Letters RESEARCH LETTER Grounding line retreat of Pope, Smith, and Kohler Glaciers, 10.1002/2016GL069287 West Antarctica, measured with Sentinel-1a radar Key Points: interferometry data • Sentinel-1 is a breakthrough mission for systematic, widespread, 1 1 1,2 1 2 continued, grounding line mapping B. Scheuchl , J. Mouginot , E. Rignot , M. Morlighem , and A. Khazendar in Antarctica • Pope, Smith, and Kohler Glaciers 1Department of Earth System Science, University of California, Irvine, CA, USA, 2Jet Propulsion Laboratory, California are undergoing major changes. Institute of Technology, Pasadena, California, USA The Grounding line of Smith Glacier continues to retreat at 2 km/yr • Crosson and Dotson Ice Shelves lost many pinning points, which Abstract We employ Sentinel-1a C band satellite radar interferometry data in Terrain Observation with significantly threatens their stability Progressive Scans mode to map the grounding line and ice velocity of Pope, Smith, and Kohler glaciers, in in years to come West Antarctica, for the years 2014–2016 and compare the results with those obtained using Earth Remote Sensing Satellites (ERS-1/2) in 1992, 1996, and 2011. We observe an ongoing, rapid grounding line retreat Supporting Information: of Smith at 2 km/yr (40 km since 1996), an 11 km retreat of Pope (0.5 km/yr), and a 2 km readvance of • Supporting Information S1 Kohler since 2011. The variability in glacier retreat is consistent with the distribution of basal slopes, i.e., fast along retrograde beds and slow along prograde beds. We find that several pinning points holding Correspondence to: Dotson and Crosson ice shelves disappeared since 1996 due to ice shelf thinning, which signal the ongoing B.
    [Show full text]
  • Major Increase in West Antarctic Glacial Loss
    Antarctic Science News posted on 27/3/2014 compiled by Dr. Alvarinho J. Luis Major increase in West Antarctic glacial loss Six massive glaciers in West Antarctica are moving faster than they did 40 years ago, causing more ice to discharge into the ocean and global sea level to rise, according to new research. The amount of ice draining collectively from those half-dozen glaciers increased by 77 % from 1973 to 2013. Pine Island Glacier, the most active of the studied glaciers, has accelerated by 75% in 40 years, according to the research published in GRL. Thwaites Glacier, the widest glacier, started to accelerate in 2006, following a decade of stability. The study is the first to look at the ice coming off the six most active West Antarctic glaciers over such an extended time period. Almost 10 % of the world's sea-level rise per year comes from just these six glaciers. The researchers found was a sustained increase in ice discharge -- which has a significant impact on sea level rise. The researchers studied the Pine Island, Thwaites, Haynes, Smith, Pope and Kohler glaciers, all of which discharge ice into a vast bay known as the Amundsen Sea Embayment in West Antarctica. The amount of ice released by these six glaciers each year is comparable to the amount of ice draining from the entire Greenland Ice Sheet annually, Mouginot said. If melted completely, the glaciers' disappearance would raise sea levels another 1.2 meters , according to co-author and UC-Irvine Professor Eric Rignot. The decades of increasing speeds and ice loss are "a strong indication of a major, long-term leakage of ice into the ocean from that sector of Antarctica," noted Rignot.
    [Show full text]
  • In This Issue
    October 1997 Volume XXXII—Number 2 In this issue... Interim head of the Office of Polar Programs appointed Highlights of the 1997–1998 research season Sea-ice conditions force Cape Roberts drill team to withdraw early Teachers at the Poles U.S. Antarctic Program news RADARSAT: Making a digital mosaic of Antarctica Science notebook: News from For the first time in 160 days, the sun begins to rise over McMurdo Station, Antarctica and beyond Antarctica, on 19 August 1997. Though austral spring is still a month away, the sun's return means resumption of flights to and from the base—and the end of Current Antarctic Literature high- isolation for the 154 Americans who spent the winter at the station. Within days lights of the sunrise, 60 new staff members as well as fresh food, newspapers, and mail were delivered to McMurdo. The rising sun also marks the beginning of a 1997–1998 austral summer field new field season on the southernmost continent. season begins early Glaciological delineation of the dynamic coastline of Antarctica The National Science Foundation (NSF) provides awards for research and edu- Antarctica and sea-level change cation in the sciences and engineering. The awardee is wholly responsible for the conduct of such research and preparation of the results for publication. The Foundation awards of funds for Foundation, therefore, does not assume responsibility for the research findings antarctic projects, 1 October or their interpretation. 1996 through 31 January 1997 The Foundation welcomes proposals from all qualified scientists and engi- neers and strongly encourages women, minorities, and persons with disabili- ties to compete fully in any of the research- and education-related programs described here.
    [Show full text]
  • Sustained Increase in Ice Discharge from the Amundsen Sea 10.1002/2013GL059069 Embayment, West Antarctica, from 1973 to 2013
    UC San Diego UC San Diego Previously Published Works Title Dissipative selection of low-frequency modes in a reduced-gravity basin Permalink https://escholarship.org/uc/item/52c3s1t5 Journal Journal of Physical Oceanography, 31(1) ISSN 0022-3670 Authors Cessi, P Primeau, F Publication Date 2001 DOI 10.1175/1520-0485(2001)031<0127:DSOLFM>2.0.CO;2 License https://creativecommons.org/licenses/by/4.0/ 4.0 Peer reviewed eScholarship.org Powered by the California Digital Library University of California GeophysicalResearchLetters RESEARCH LETTER Sustained increase in ice discharge from the Amundsen Sea 10.1002/2013GL059069 Embayment, West Antarctica, from 1973 to 2013 Key Points: J. Mouginot1, E. Rignot1,2, and B. Scheuchl1 • Sustained ASE mass flux increase: 77% since 1973 1Department of Earth System Science, University of California, Irvine, California, USA, 2Jet Propulsion Laboratory, • Thwaites accelerated by 33% during California Institute of Technology, Pasadena, California, USA the last 6 years • Speed changes are pervasive and rapid: major implications for ice flow modeling Abstract We combine measurements of ice velocity from Landsat feature tracking and satellite radar interferometry, and ice thickness from existing compilations to document 41 years of mass flux from the Amundsen Sea Embayment (ASE) of West Antarctica. The total ice discharge has increased by 77% since Supporting Information: • Readme 1973. Half of the increase occurred between 2003 and 2009. Grounding-line ice speeds of Pine Island Glacier • Table S1 stabilized between 2009 and 2013, following a decade of rapid acceleration, but that acceleration reached • Table S2 far inland and occurred at a rate faster than predicted by advective processes.
    [Show full text]
  • Widespread, Rapid Grounding Line Retreat of Pine Island, Thwaites, Smith, and Kohler Glaciers, West Antarctica, from 1992 To
    GeophysicalResearchLetters RESEARCH LETTER Widespread, rapid grounding line retreat of Pine Island, 10.1002/2014GL060140 Thwaites, Smith, and Kohler glaciers, West Antarctica, Key Points: from 1992 to 2011 • Fast grounding line retreat of the 1,2 1 1 2 1 entire Amundsen Sea sector of E. Rignot , J. Mouginot , M. Morlighem , H. Seroussi , and B. Scheuchl West Antarctica 1 2 • Observations are a signature of Department of Earth System Science, University of California, Irvine, California, USA, Jet Propulsion Laboratory, a marine ice sheet instability California Institute of Technology, Pasadena, California, USA in Antarctica • This sector of Antarctica will remain the largest contributor to sea Abstract We measure the grounding line retreat of glaciers draining the Amundsen Sea sector of level rise West Antarctica using Earth Remote Sensing (ERS-1/2) satellite radar interferometry from 1992 to 2011. Pine Island Glacier retreated 31 km at its center, with most retreat in 2005–2009 when the glacier ungrounded Supporting Information: from its ice plain. Thwaites Glacier retreated 14 km along its fast flow core and 1 to 9 km along the sides. • Readme • Figure S1 Haynes Glacier retreated 10 km along its flanks. Smith/Kohler glaciers retreated the most, 35 km along its ice • Figure S2–S6 plain, and its ice shelf pinning points are vanishing. These rapid retreats proceed along regions of retrograde • Figure S7 bed elevation mapped at a high spatial resolution using a mass conservation technique that removes • Figure S8 • Figure S9 residual ambiguities from prior mappings. Upstream of the 2011 grounding line positions, we find no major • Figure S10 bed obstacle that would prevent the glaciers from further retreat and draw down the entire basin.
    [Show full text]
  • Accelerated Glacier Melting in West Antar Melting in West Antarctica
    News date: 25h October, 2016 compiled by Dr. Alvarinho J. Luis Accelerated glacier melting in West Antarctica documented Study findings will help improve predictions about global sea level rise Summary: Two new studies have found the fastest ongoing rates of glacier retreat ever observed in West Antarctica and offer an unprecedented look at ice melting on the floating undersides of glaciers. The results highlight how the interaction between ocean conditions and the bedrock beneath a glacier can influence the frozen mass, helping scientists better predict future Antarctica ice loss and global sea level rise. Two new studies by researchers at the Univ. of California and NASA have found the fastest ongoing rates of glacier retreat ever observed in West Antarctica and offer an unprecedented look at ice melting on the floating undersides of glaciers. The results highlight how the interaction between ocean conditions and the bedrock beneath a glacier can influence the frozen mass, helping scientists better predict future Antarctica ice loss and global sea level rise. The studies examined three neighboring glaciers that are melting and retreating at different rates. The Smith, Pope and Kohler glaciers flow into the Dotson and Crosson ice shelves in the Amundsen Sea embayment in West Antarctica, the part of the continent with the largest decline in ice (see Figure). The primary question is how the Amundsen Sea sector of West Antarctica will contribute to sea level rise in the future, particularly following observations of massive changes in the area over the last two decades. Using satellite data, Scientists continue to measure the evolution of the grounding line of these glaciers, which helps determine their stability and how much mass the glacier is gaining or losing.
    [Show full text]
  • How Much, How Fast?
    How Much, How Fast ?: A Science Review and Outlook for Research on the Instability of Antarctica’s Thwaites Glacier in the 21st century TA Scambos, RE Bell, RB Alley, S Anandakrishnan, DH Bromwich, K Brunt, K Christianson, T Creyts, SB Das, R DeConto, P Dutrieux, HA Fricker, D Holland, J MacGregor, B Medley, JP Nicolas, D Pollard, MR Siegfried, AM Smith, EJ Steig, LD Trusel, DG Vaughan, P Yager Abstract Constraining how much and how fast the West Antarctic Ice Sheet (WAIS) will change in the coming decades has recently been identified as the highest priority in Antarctic research (National Academies, 2015). Here we review recent research on WAIS and outline further scientific objectives for the area now identified as the most likely to undergo near-term significant change: Thwaites Glacier and the adjacent Amundsen Sea. Multiple lines of evidence point to an ongoing rapid loss of ice in this region in response to changing atmospheric and oceanic conditions. Models of the ice sheet’s dynamic behavior indicate a potential for greatly accelerated ice loss as ocean-driven melting at the Thwaites Glacier grounding zone and nearby areas leads to thinning, faster flow, and retreat. A complete retreat of the Thwaites Glacier basin would raise global sea level by more than three meters by entraining ice from adjacent catchments. This scenario could occur over the next few centuries, and faster ice loss could occur through processes omitted from most ice flow models such as hydrofracture and ice cliff failure, which have been observed in recent rapid ice retreats elsewhere. Increased basal melt at the grounding zone and increased potential for hydrofracture due to enhanced surface melt could initiate a more rapid collapse of Thwaites Glacier within the next few decades.
    [Show full text]