DOCSLIB.ORG

This Thesis Has Been Submitted in Fulfilment of the Requirements for a Postgraduate Degree (E.G

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
This Thesis Has Been Submitted in Fulfilment of the Requirements for a Postgraduate Degree (E.G This thesis has been submitted in fulfilment of the requirements for a postgraduate degree (e.g. PhD, MPhil, DClinPsychol) at the University of Edinburgh. Please note the following terms and conditions of use: • This work is protected by copyright and other intellectual property rights, which are retained by the thesis author, unless otherwise stated. • A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. • This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the author. • The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the author. • When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given. Satellite Investigations of Ice-Ocean Interactions in the Amundsen Sea Sector of West Antarctica Malcolm McMillan Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the University of Edinburgh 2012 Declaration I declare that this thesis has been composed solely by myself and that it has not been submitted, either in whole or in part, in any previous application for a degree. Except where otherwise acknowledged, the work presented is entirely my own. Malcolm McMillan January 2012 ii Abstract This thesis analyses satellite-based radar data to improve our understanding of the interactions between the Antarctic Ice Sheet and the ocean in the Amundsen Sea Sector of West Antarctica. Over the last two decades, the European Remote Sensing (ERS) Satellites have provided extensive observations of the marine and cryospheric environments of this region. Here I use this data record to develop new datasets and methods for studying the nature and drivers of ongoing change in this sector. Firstly, I develop a new bathymetric map of the Amundsen Sea, which serves to provide improved boundary conditions for models of (1) ocean heat transfer to the ice sheet margin, and (2) past ice sheet behaviour and extent. This new map augments sparse ship-based depth soundings with dense gravity data acquired from ERS altimetry and achieves an RMS depth accuracy of 120 meters. An evaluation of this technique indicates that the inclusion of gravity data improves the depth accuracy by up to 17 % and reveals glaciologically-important features in regions devoid of ship surveys. Secondly, I use ERS synthetic aperture radar observations of the tidal motion of ice shelves to assess the accuracy of tide models in the Amundsen Sea. Tide models contribute to simulations of ocean circulation and are used to remove unwanted signals from estimates of ice shelf flow velocities. The quality of tide models directly affects the accuracy of such estimates yet, due to a lack of in situ records, tide model accuracy in this region is poorly constrained. Here I use two methods to determine that tide model accuracy in the Amundsen Sea is of the order of 10 cm. Finally, I develop a method to iii map 2-d ice shelf flow velocity from stacked conventional and multiple aperture radar interferograms. Estimates of ice shelf flow provide detail of catchment stability, and the processes driving glaciological change in the Amundsen Sea. However, velocity estimates can be contaminated by ocean tide and atmospheric pressure signals. I minimise these signals by stacking interferograms, a process which synthesises a longer observation period, and enhances long-period (flow) displacement signals, relative to rapidly-varying (tide and atmospheric pressure) ones. This avoids the reliance upon model predictions of tide and atmospheric pressure, which can be uncertain in remote regions. Ice loss from Amundsen Sea glaciers forms the largest component of Antarctica’s total contribution to sea level, yet because present models cannot adequately characterise the processes driving this system, future glacier evolution is uncertain. Observations and models implicate the ocean as the driver of glaciological change in this region and have focussed attention on improving our understanding of the nature of ice-ocean interactions in the Amundsen Sea. This thesis contributes datasets and methods that will aid historical reconstructions, current monitoring and future modelling of these processes. iv Acknowledgements This work was funded by the UK Natural Environment Research Council’s National Centre for Earth Observation, through a Centre for Polar Observation and Modelling PhD studentship. I thank my supervisors, Andy Shepherd and Pete Nienow, for all their help and advice during the past three years. I am grateful to Anthony Newton for acting as my advisor throughout this time. I thank my examiners, Adrian Luckman and Martin Siegert, for their time and effort in reading and examining my thesis. Thanks also go to my office mates, for their humour and friendship, and in particular to those who have shared an enthusiasm for discussing all things ice- related - Kate, Steve, Eero, Ian, Noel, Aud and Tom. Finally, thanks to my parents and to Anna for all their help and support. v Contents Declaration ii Abstract iii Acknowledgements v Contents vi List of Tables x List of Figures xi 1 Introduction 1 1.1 Aim .................................. 1 1.2 Motivation............................... 1 1.3 Objectives............................... 5 2 The Amundsen Sea Sector of the WAIS 7 2.1 PhysicalSetting............................ 7 2.2 Observations of Ice Sheet Change in the Satellite Era . .... 12 2.2.1 ThinningofGroundedIce . 12 2.2.2 Thinning of Ice Shelves . 16 2.2.3 GroundingLineRetreat . 17 2.2.4 IceAcceleration. .. .. 17 2.2.5 A Glimpse of WAIS Instability? . 18 2.3 Post-LGM History of the Amundsen Sea Sector of the WAIS . 21 2.3.1 Ice Sheet Behaviour Inferred from Sea Floor Morphology. 21 2.3.2 Timing of Deglaciation in the Amundsen Sea . 23 2.4 The Coupled Ice-Ocean System . 26 2.4.1 Amundsen Sea Oceanography . 27 2.4.2 Ocean Circulation and Melting in the Ice Shelf Cavity . 31 2.4.3 Tidal Influence on Ice Shelf Dynamics . 35 2.5 Spatial and Temporal Variability in the Amundsen Sea . ... 37 2.5.1 Causes of Temporal Glaciological Variability . .. 38 2.5.2 Causes of Spatial Glaciological Variability . .. 39 2.6 Summary of Current Understanding . 40 vi 3 Review of Methods 43 3.1 Bathymetric Prediction from Sparse Ship Surveys and Marine GravityData ............................. 43 3.2 Tide Model Validation in Antarctic Waters . 47 3.2.1 Validating Tide Models with Interferometric Synthetic ApertureRadar........................ 48 3.3 Satellite-based Methods for Mapping Ice Shelf Flow . .... 53 3.3.1 Mapping Ice Shelf Flow with Synthetic Aperture RadarFeatureTracking . 54 3.3.2 Mapping Ice Shelf Flow with Interferometric SyntheticApertureRadar . 56 3.3.3 Comparison of SAR Techniques for Mapping IceShelfFlow......................... 58 3.4 Summary ............................... 59 4 Amundsen Sea Bathymetry from Marine Gravity Data 60 4.1 Abstract................................ 61 4.2 Introduction.............................. 61 4.3 DataandMethod........................... 63 4.4 Results and Model Assessment . 68 4.5 Conclusions .............................. 76 5 Tide Model Accuracy in the Amundsen Sea 78 5.1 Abstract................................ 79 5.2 Introduction.............................. 79 5.3 TheoreticalBackground . 82 5.3.1 Single-DifferenceApproach. 84 5.3.2 Double-DifferenceApproach . 85 5.4 StudyArea .............................. 86 5.5 Data.................................. 87 5.5.1 Interferometric Synthetic Aperture Radar . 87 5.5.2 TideModels.......................... 89 5.5.3 Meteorological Model Reanalysis . 90 5.6 Methods................................ 91 5.6.1 Single-Difference Technique . 91 5.6.2 Double-Difference Technique . 100 5.6.3 TideModelEvaluation . 100 5.7 Error Assessment of Single-Difference and Double-Difference Meth- ods................................... 101 5.7.1 TopographicError . 103 5.7.2 FlatEarthCorrectionError . 105 5.7.3 IceFlowError......................... 107 5.7.4 AtmosphericPressureError . 109 5.7.5 AtmosphericDistortions . 110 vii 5.7.6 CoherenceError. 111 5.7.7 PhaseUnwrappingError . 112 5.7.8 CombinedError. .. .. 112 5.8 Results................................. 113 5.8.1 Observations of Ice Shelf Flow Displacement . 113 5.8.2 Observations of Ice Shelf Tidal Displacement . 114 5.8.3 TideModelEvaluation . 115 5.9 Discussion ............................... 117 5.9.1 ComparisonofMethods ofObservation . 117 5.9.2 ComparisonofTideModels . 121 5.9.3 Assessment of Inverse Barometer Correction . 125 5.9.4 ComparisontoPreviousWork . 126 5.10Conclusions .............................. 126 6 Mapping Ice Shelf Flow with InSAR Stacking 128 6.1 Abstract................................ 129 6.2 Introduction.............................. 129 6.3 StudyArea .............................. 132 6.4 Data.................................. 133 6.4.1 SyntheticApertureRadar . 133 6.4.2 TideModel .......................... 135 6.4.3 Surface Level Atmospheric Pressure . 136 6.5 Methods................................ 137 6.5.1 Conventional InSAR Stacking . 137 6.5.2 Modelling Tide and IBE Error . 141 6.5.3 Isolating Flow Displacement Using Model Predictions . 141 6.5.4 Multiple Aperture InSAR Stacking . 142 6.6 Results................................. 143 6.6.1 StackedVelocityMap. 143 6.6.2 ErrorAssessment . 144 6.7 Discussion ............................... 155 6.7.1 Comparison of Velocity Predictions
Load more

Recommended publications
  • 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]
  • 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]
  • 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]
  • New Gravity-Derived Bathymetry for the Thwaites, Crosson and Dotson Ice Shelves Revealing Two Ice Shelf Populations Tom A
    https://doi.org/10.5194/tc-2019-294 Preprint. Discussion started: 10 January 2020 c Author(s) 2020. CC BY 4.0 License. New gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves revealing two ice shelf populations Tom A. Jordan1, David Porter2, Kirsty Tinto2, Romain Millan3, Atsuhiro Muto4, Kelly Hogan1, Robert D. Larter1, Alastair G.C. Graham5, John D. Paden6 5 1 British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK 2 Lamont Doherty Earth Observatory 3 Institut des Géosciences de l’Environnement, Université Grenoble Alpes, CNRS, 38000 Grenoble, France 4 Dept. of Earth and Environmental Science, Temple University, Philadelphia, PA 19122, USA 5 College of Marine Science, University of South Florida, St Petersburg, FL 33701, USA. 10 6 Center for Remote Sensing of Ice Sheets (CReSIS), The University of Kansas, Kansas 66045, USA Correspondence to: Tom A. Jordan ([email protected]) Abstract. Ice shelves play a critical role in the long-term stability of ice sheets through their buttressing effect. The underlying bathymetry and cavity thickness are key inputs for modelling future ice sheet evolution. However, direct observation of sub- ice shelf bathymetry is time consuming, logistically risky, and in some areas simply not possible. Here we use airborne gravity 15 anomaly data to provide new estimates of sub-ice shelf bathymetry outboard of the rapidly changing West Antarctic Thwaites Glacier, and beneath the adjacent Dotson and Crosson Ice Shelves. This region is of especial interest as the low-lying inland reverse slope of the Thwaites glacier system makes it vulnerable to marine ice sheet instability, with rapid grounding-line retreat observed since 1993 suggesting this process may be underway.
    [Show full text]
  • Committed Near-Future Retreat of Smith, Pope, and Kohler Glaciers
    Manuscript prepared for The Cryosphere with version 2015/04/24 7.83 Copernicus papers of the LATEX class copernicus.cls. Date: 4 November 2015 Committed near-future retreat of Smith, Pope, and Kohler Glaciers :::::::over :::::the:::::::next:::::30 ::::::::years: inferred by transient model calibration Daniel Goldberg1, Patrick Heimbach2, Ian Joughin3, and Ben Smith3 1Univ. of Edinburgh, School of GeoSciences, Edinburgh, United Kingdom 2University of Texas, Institute for Computational Engineering and Sciences / Institute for Geophysics, Austin, Texas, USA 3Applied Physics Laboratory, University of Washington, Seattle, USA Correspondence to: D N Goldberg ([email protected]) Abstract. A glacial flow model of Smith, Pope and Kohler Glaciers has been is::calibrated by means of inverse control::::::methods against time-varying, annualy resolved observations of ice height and velocities, covering the period 2002 to 2011. The inversion – termed “transient calibration” – pro- duces an optimal set of time-mean, spatially varying parameters together with a time-evolving state 5 that accounts for the transient nature of observations and the model dynamics. Serving as an opti- mal initial condition, the estimated state for 2011 is used, with no additional forcing, for predicting grounded ice volume loss and grounding line retreat over the ensuing 30 years. The transiently cal- ibrated model predicts a near-steady loss of grounded ice volume of approximately 21 km3/a over this period, as well as loss of 33 km2/a grounded area. We contrast this prediction with one obtained 10 following a commonly used “snapshot” or steady-state inversion, which does not consider time de- pendence and assumes all observations to be contemporaneous.
    [Show full text]
  • A Science Review and Outlook for Research on the Instability of Antarctica’S Thwaites Glacier in the 21St Century
    https://ntrs.nasa.gov/search.jsp?R=20180006980 2019-08-31T17:55:13+00:00Z 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.
    [Show full text]