1
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Park T, Nakayama Y, Nam S. Amundsen Sea circulation controls bottom upwelling and Antarctic Pine Island and Thwaites ice shelf melting. Nat Commun 2024; 15:2946. [PMID: 38605000 PMCID: PMC11009355 DOI: 10.1038/s41467-024-47084-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Accepted: 03/15/2024] [Indexed: 04/13/2024] Open
Abstract
The Pine Island and Thwaites Ice Shelves (PIIS/TIS) in the Amundsen Sea are melting rapidly and impacting global sea levels. The thermocline depth (TD) variability, the interface between cold Winter Water and warm modified Circumpolar Deep Water (mCDW), at the PIIS/TIS front strongly correlates with basal melt rates, but the drivers of its interannual variability remain uncertain. Here, using an ocean model, we propose that the strength of the eastern Amundsen Sea on-shelf circulation primarily controls TD variability and consequent PIIS/TIS melt rates. The TD variability occurs because the on-shelf circulation meanders following the submarine glacial trough, creating vertical velocity through bottom Ekman dynamics. We suggest that a strong or weak ocean circulation, possibly linked to remote winds in the Bellingshausen Sea, generates corresponding changes in bottom Ekman convergence, which modulates mCDW upwelling and TD variability. We show that interannual variability of off-shelf zonal winds has a minor effect on ocean heat intrusion into PIIS/TIS cavities, contrary to the widely accepted concept.
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Affiliation(s)
- Taewook Park
- Division of Ocean and Atmosphere Sciences, Korea Polar Research Institute, Incheon, 21990, Republic of Korea.
| | - Yoshihiro Nakayama
- Institute of Low Temperature Science, Hokkaido University, Sapporo, 060-0819, Japan.
| | - SungHyun Nam
- School of Earth and Environmental Sciences/Research Institute of Oceanography, Seoul National University, Gwanak-gu, Seoul, 08826, Republic of Korea
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2
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Miles BWJ, Bingham RG. Progressive unanchoring of Antarctic ice shelves since 1973. Nature 2024; 626:785-791. [PMID: 38383628 PMCID: PMC10881387 DOI: 10.1038/s41586-024-07049-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Accepted: 01/09/2024] [Indexed: 02/23/2024]
Abstract
Mass loss of the Antarctic Ice Sheet has been driven primarily by the thinning of the floating ice shelves that fringe the ice sheet1, reducing their buttressing potential and causing land ice to accelerate into the ocean2. Observations of ice-shelf thickness change by satellite altimetry stretch back only to 1992 (refs. 1,3-5) and previous information about thinning remains unquantified. However, extending the record of ice-shelf thickness change is possible by proxy, by measuring the change in area of the surface expression of pinning points-local bathymetric highs on which ice shelves are anchored6. Here we measure pinning-point change over three epochs spanning the periods 1973-1989, 1989-2000 and 2000-2022, and thus by proxy infer changes to ice-shelf thickness back to 1973-1989. We show that only small localized pockets of ice shelves were thinning between 1973 and 1989, located primarily in the Amundsen Sea Embayment and the Wilkes Land coastline. Ice-shelf thinning spreads rapidly into the 1990s and 2000s and is best characterized by the proportion of pinning points reducing in extent. Only 15% of pinning points reduced from 1973 to 1989, before increasing to 25% from 1989 to 2000 and 37% from 2000 to 2022. A continuation of this trend would further reduce the buttressing potential of ice shelves, enhancing ice discharge and accelerating the contribution of Antarctica to sea-level rise.
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3
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Davison BJ, Hogg AE, Gourmelen N, Jakob L, Wuite J, Nagler T, Greene CA, Andreasen J, Engdahl ME. Annual mass budget of Antarctic ice shelves from 1997 to 2021. SCIENCE ADVANCES 2023; 9:eadi0186. [PMID: 37824617 DOI: 10.1126/sciadv.adi0186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Accepted: 09/07/2023] [Indexed: 10/14/2023]
Abstract
Antarctic ice shelves moderate the contribution of the Antarctic Ice Sheet to global sea level rise; however, ice shelf health remains poorly constrained. Here, we present the annual mass budget of all Antarctic ice shelves from 1997 to 2021. Out of 162 ice shelves, 71 lost mass, 29 gained mass, and 62 did not change mass significantly. Of the shelves that lost mass, 68 had statistically significant negative mass trends, 48 lost more than 30% of their initial mass, and basal melting was the dominant contributor to that mass loss at a majority (68%). At many ice shelves, mass losses due to basal melting or iceberg calving were significantly positively correlated with grounding line discharge anomalies; however, the strength and form of this relationship varied substantially between ice shelves. Our results illustrate the utility of partitioning high-resolution ice shelf mass balance observations into its components to quantify the contributors to ice shelf mass change and the response of grounded ice.
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Affiliation(s)
| | - Anna E Hogg
- School of Earth and Environment, University of Leeds, Leeds, UK
| | - Noel Gourmelen
- School of Geosciences, University of Edinburgh, Edinburgh, UK
- Earthwave, Codebase, Office L2, 3 Lady Lawson St, Edinburgh, UK
| | - Livia Jakob
- Earthwave, Codebase, Office L2, 3 Lady Lawson St, Edinburgh, UK
| | - Jan Wuite
- ENVEO IT GmbH, Innsbruck 6020, Austria
| | | | - Chad A Greene
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - Julia Andreasen
- Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN, USA
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4
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Davison BJ, Hogg AE, Rigby R, Veldhuijsen S, van Wessem JM, van den Broeke MR, Holland PR, Selley HL, Dutrieux P. Sea level rise from West Antarctic mass loss significantly modified by large snowfall anomalies. Nat Commun 2023; 14:1479. [PMID: 36932070 PMCID: PMC10023770 DOI: 10.1038/s41467-023-36990-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Accepted: 02/27/2023] [Indexed: 03/18/2023] Open
Abstract
Mass loss from the West Antarctic Ice Sheet is dominated by glaciers draining into the Amundsen Sea Embayment (ASE), yet the impact of anomalous precipitation on the mass balance of the ASE is poorly known. Here we present a 25-year (1996-2021) record of ASE input-output mass balance and evaluate how two periods of anomalous precipitation affected its sea level contribution. Since 1996, the ASE has lost 3331 ± 424 Gt ice, contributing 9.2 ± 1.2 mm to global sea level. Overall, surface mass balance anomalies contributed little (7.7%) to total mass loss; however, two anomalous precipitation events had larger, albeit short-lived, impacts on rates of mass change. During 2009-2013, persistently low snowfall led to an additional 51 ± 4 Gt yr-1 mass loss in those years (contributing positively to the total loss of 195 ± 4 Gt yr-1). Contrastingly, extreme precipitation in the winters of 2019 and 2020 decreased mass loss by 60 ± 16 Gt yr-1 during those years (contributing negatively to the total loss of 107 ± 15 Gt yr-1). These results emphasise the important impact of extreme snowfall variability on the short-term sea level contribution from West Antarctica.
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Affiliation(s)
| | - Anna E Hogg
- School of Earth and Environment, University of Leeds, Leeds, UK
| | - Richard Rigby
- School of Earth and Environment, University of Leeds, Leeds, UK
| | - Sanne Veldhuijsen
- Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, the Netherlands
| | - Jan Melchior van Wessem
- Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, the Netherlands
| | - Michiel R van den Broeke
- Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, the Netherlands
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5
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Christie FDW, Steig EJ, Gourmelen N, Tett SFB, Bingham RG. Inter-decadal climate variability induces differential ice response along Pacific-facing West Antarctica. Nat Commun 2023; 14:93. [PMID: 36646677 PMCID: PMC9842681 DOI: 10.1038/s41467-022-35471-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Accepted: 12/05/2022] [Indexed: 01/18/2023] Open
Abstract
West Antarctica has experienced dramatic ice losses contributing to global sea-level rise in recent decades, particularly from Pine Island and Thwaites glaciers. Although these ice losses manifest an ongoing Marine Ice Sheet Instability, projections of their future rate are confounded by limited observations along West Antarctica's coastal perimeter with respect to how the pace of retreat can be modulated by variations in climate forcing. Here, we derive a comprehensive, 12-year record of glacier retreat around West Antarctica's Pacific-facing margin and compare this dataset to contemporaneous estimates of ice flow, mass loss, the state of the Southern Ocean and the atmosphere. Between 2003 and 2015, rates of glacier retreat and acceleration were extensive along the Bellingshausen Sea coastline, but slowed along the Amundsen Sea. We attribute this to an interdecadal suppression of westerly winds in the Amundsen Sea, which reduced warm water inflow to the Amundsen Sea Embayment. Our results provide direct observations that the pace, magnitude and extent of ice destabilization around West Antarctica vary by location, with the Amundsen Sea response most sensitive to interdecadal atmosphere-ocean variability. Thus, model projections accounting for regionally resolved ice-ocean-atmosphere interactions will be important for predicting accurately the short-term evolution of the Antarctic Ice Sheet.
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Affiliation(s)
- Frazer D. W. Christie
- grid.5335.00000000121885934Scott Polar Research Institute, University of Cambridge, Cambridge, CB2 1ER UK ,grid.4305.20000 0004 1936 7988School of GeoSciences, University of Edinburgh, Edinburgh, EH8 9XP UK
| | - Eric J. Steig
- grid.34477.330000000122986657Department of Earth & Space Sciences, University of Washington, Seattle, WA 98195-1310 USA
| | - Noel Gourmelen
- grid.4305.20000 0004 1936 7988School of GeoSciences, University of Edinburgh, Edinburgh, EH8 9XP UK
| | - Simon F. B. Tett
- grid.4305.20000 0004 1936 7988School of GeoSciences, University of Edinburgh, Edinburgh, EH8 9XP UK
| | - Robert G. Bingham
- grid.4305.20000 0004 1936 7988School of GeoSciences, University of Edinburgh, Edinburgh, EH8 9XP UK
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6
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Yadav J, Kumar A, Srivastava A, Mohan R. Sea ice variability and trends in the Indian Ocean sector of Antarctica: Interaction with ENSO and SAM. ENVIRONMENTAL RESEARCH 2022; 212:113481. [PMID: 35588776 DOI: 10.1016/j.envres.2022.113481] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2021] [Revised: 04/01/2022] [Accepted: 04/24/2022] [Indexed: 06/15/2023]
Abstract
Antarctic sea ice variability is primarily associated with ocean-atmospheric forcing driven by anomalous conditions over the tropical regions of the Pacific and Indian Oceans. The ice-ocean-atmosphere dynamics in the Indian Ocean Sector (IOS) of Antarctica have been studied using monthly satellite and reanalysis observations over four decades (1979-2019). In this study, we revealed that the annual sea ice extent (SIE) in the IOS increases at a rate of 0.7 ± 0.9% decade-1, with a maximum increase in austral summer (5.9 ± 3.7% decade-1). The wavelet approach was used to determine the variability in IOS sea ice caused by the El Niño/Southern Oscillation (ENSO) and southern annular mode (SAM). The SIE has a significant association with both indices during the summer and autumn. In comparison to ENSO, the sea ice variability associated with SAM is typically seasonal in nature and lacks distinct patterns. The wavelet coherence analysis revealed a relatively weak relationship between ENSO and SAM but a highly significant coherence between climatic indices and SIE. We observed that sea ice in the IOS is influenced significantly by climatic oscillations during their negative SAM/El Niño or positive SAM/La Niña phases. Furthermore, the study demonstrated a substantial impact of climatic disturbances in determining the sea ice variability in the IOS.
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Affiliation(s)
- Juhi Yadav
- National Centre for Polar and Ocean Research, Ministry of Earth Sciences (Govt. of India), Goa, India; Department of Marine Geology, Mangalore University, Mangalore, 574 199, India
| | - Avinash Kumar
- National Centre for Polar and Ocean Research, Ministry of Earth Sciences (Govt. of India), Goa, India.
| | | | - Rahul Mohan
- National Centre for Polar and Ocean Research, Ministry of Earth Sciences (Govt. of India), Goa, India
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7
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Flexas MM, Thompson AF, Schodlok MP, Zhang H, Speer K. Antarctic Peninsula warming triggers enhanced basal melt rates throughout West Antarctica. SCIENCE ADVANCES 2022; 8:eabj9134. [PMID: 35960791 PMCID: PMC9374342 DOI: 10.1126/sciadv.abj9134] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Accepted: 06/30/2022] [Indexed: 06/15/2023]
Abstract
The observed acceleration of ice shelf basal melt rates throughout West Antarctica could destabilize continental ice sheets and markedly increase global sea level. Explanations for decadal-scale melt intensification have focused on processes local to shelf seas surrounding the ice shelves. A suite of process-based model experiments, guided by CMIP6 forcing scenarios, show that freshwater forcing from the Antarctic Peninsula, propagated between marginal seas by a coastal boundary current, causes enhanced melting throughout West Antarctica. The freshwater anomaly stratifies the ocean in front of the ice shelves and modifies vertical and lateral heat fluxes, enhancing heat transport into ice shelf cavities and increasing basal melt. Increased glacial runoff at the Antarctic Peninsula, one of the first signatures of a warming climate in Antarctica, emerges as a key trigger for increased ice shelf melt rates in the Amundsen and Bellingshausen Seas.
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Affiliation(s)
- M. Mar Flexas
- Environmental Science and Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Andrew F. Thompson
- Environmental Science and Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Michael P. Schodlok
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Hong Zhang
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Kevin Speer
- Geophysical Fluid Dynamics Institute and Department of Scientific Computing, Florida State University, Tallahassee, FL 32306, USA
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8
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Miles BWJ, Stokes CR, Jamieson SSR, Jordan JR, Gudmundsson GH, Jenkins A. High spatial and temporal variability in Antarctic ice discharge linked to ice shelf buttressing and bed geometry. Sci Rep 2022; 12:10968. [PMID: 35768612 PMCID: PMC9243100 DOI: 10.1038/s41598-022-13517-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Accepted: 05/25/2022] [Indexed: 11/09/2022] Open
Abstract
Antarctica's contribution to global mean sea level rise has been driven by an increase in ice discharge into the oceans. The rate of change and the mechanisms that drive variability in ice discharge are therefore important to consider in the context of projected future warming. Here, we report observations of both decadal trends and inter-annual variability in ice discharge across the Antarctic Ice Sheet at a variety of spatial scales that range from large drainage basins to individual outlet glacier catchments. Overall, we find a 37 ± 11 Gt year-1 increase in discharge between 1999 and 2010, but a much smaller increase of 4 ± 8 Gt year-1 between 2010 and 2018. Furthermore, comparisons reveal that neighbouring outlet glaciers can behave synchronously, but others show opposing trends, despite their close proximity. We link this spatial and temporal variability to changes in ice shelf buttressing and the modulating effect of local glacier geometry.
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Affiliation(s)
- Bertie W J Miles
- School of Geosciences, Edinburgh University, Edinburgh, EH8 9XP, UK. .,Department of Geography, Durham University, Durham, DH1 3LE, UK.
| | - Chris R Stokes
- Department of Geography, Durham University, Durham, DH1 3LE, UK
| | | | - Jim R Jordan
- Department of Geography and Environmental Sciences, Northumbria University, Newcastle upon Tyne, NE1 8ST, UK.,Laboratoire de Glaciologie, Université Libre de Bruxelles, Brussels, Belgium
| | - G Hilmar Gudmundsson
- Department of Geography and Environmental Sciences, Northumbria University, Newcastle upon Tyne, NE1 8ST, UK
| | - Adrian Jenkins
- Department of Geography and Environmental Sciences, Northumbria University, Newcastle upon Tyne, NE1 8ST, UK
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9
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LIMA LUCIANAS, PEZZI LUCIANOP, MATA MAURÍCIOM, SANTINI MARCELOF, CARVALHO JONAST, SUTIL UESLEIADRIANO, CABRERA MYLENEJ, ROSA ELIANAB, RODRIGUES CELINAC, VEGA XIMENAA. Glacial meltwater input to the ocean around the Antarctic Peninsula: forcings and consequences. AN ACAD BRAS CIENC 2022; 94:e20210811. [DOI: 10.1590/0001-3765202220210811] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Accepted: 01/21/2022] [Indexed: 11/21/2022] Open
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10
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Decadal-scale onset and termination of Antarctic ice-mass loss during the last deglaciation. Nat Commun 2021; 12:6683. [PMID: 34795275 PMCID: PMC8602255 DOI: 10.1038/s41467-021-27053-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Accepted: 11/02/2021] [Indexed: 11/25/2022] Open
Abstract
Emerging ice-sheet modeling suggests once initiated, retreat of the Antarctic Ice Sheet (AIS) can continue for centuries. Unfortunately, the short observational record cannot resolve the tipping points, rate of change, and timescale of responses. Iceberg-rafted debris data from Iceberg Alley identify eight retreat phases after the Last Glacial Maximum that each destabilized the AIS within a decade, contributing to global sea-level rise for centuries to a millennium, which subsequently re-stabilized equally rapidly. This dynamic response of the AIS is supported by (i) a West Antarctic blue ice record of ice-elevation drawdown >600 m during three such retreat events related to globally recognized deglacial meltwater pulses, (ii) step-wise retreat up to 400 km across the Ross Sea shelf, (iii) independent ice sheet modeling, and (iv) tipping point analysis. Our findings are consistent with a growing body of evidence suggesting the recent acceleration of AIS mass loss may mark the beginning of a prolonged period of ice sheet retreat and substantial global sea level rise.
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11
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Agrelo M, Daura-Jorge FG, Rowntree VJ, Sironi M, Hammond PS, Ingram SN, Marón CF, Vilches FO, Seger J, Payne R, Simões-Lopes PC. Ocean warming threatens southern right whale population recovery. SCIENCE ADVANCES 2021; 7:eabh2823. [PMID: 34652948 PMCID: PMC8519561 DOI: 10.1126/sciadv.abh2823] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Whales contribute to marine ecosystem functioning, and they may play a role in mitigating climate change and supporting the Antarctic krill (Euphausia superba) population, a keystone prey species that sustains the entire Southern Ocean (SO) ecosystem. By analyzing a five-decade (1971–2017) data series of individual southern right whales (SRWs; Eubalaena australis) photo-identified at Península Valdés, Argentina, we found a marked increase in whale mortality rates following El Niño events. By modeling how the population responds to changes in the frequency and intensity of El Niño events, we found that such events are likely to impede SRW population recovery and could even cause population decline. Such outcomes have the potential to disrupt food-web interactions in the SO, weakening that ecosystem’s contribution to the mitigation of climate change at a global scale.
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Affiliation(s)
- Macarena Agrelo
- Laboratório de Mamíferos Aquáticos, Programa de Pós-graduação em Ecologia, Departamento de Ecologia e Zoologia, Universidade Federal de Santa Catarina, Florianópolis, SC, Brazil
- Instituto de Conservación de Ballenas, O'Higgins 4380, Ciudad Autónoma de Buenos Aires 1429, Argentina
| | - Fábio G Daura-Jorge
- Laboratório de Mamíferos Aquáticos, Programa de Pós-graduação em Ecologia, Departamento de Ecologia e Zoologia, Universidade Federal de Santa Catarina, Florianópolis, SC, Brazil
| | - Victoria J Rowntree
- Ocean Alliance, 32 Horton Street, Gloucester, MA 01930, USA
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA
| | - Mariano Sironi
- Instituto de Conservación de Ballenas, O'Higgins 4380, Ciudad Autónoma de Buenos Aires 1429, Argentina
- Facultad de Ciencias Exactas, Físicas y Naturales (FCEFyN), Universidad Nacional de Córdoba, Córdoba 5000, Argentina
| | - Philip S Hammond
- Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, St Andrews, Fife KY16 8LB, Scotland, UK
| | - Simon N Ingram
- School of Biological and Marine Sciences, University of Plymouth, Plymouth PL4 8AA, UK
| | - Carina F Marón
- Instituto de Conservación de Ballenas, O'Higgins 4380, Ciudad Autónoma de Buenos Aires 1429, Argentina
- Facultad de Ciencias Exactas, Físicas y Naturales (FCEFyN), Universidad Nacional de Córdoba, Córdoba 5000, Argentina
| | - Florencia O Vilches
- Instituto de Conservación de Ballenas, O'Higgins 4380, Ciudad Autónoma de Buenos Aires 1429, Argentina
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA 95064, USA
| | - Jon Seger
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA
| | - Roger Payne
- Ocean Alliance, 32 Horton Street, Gloucester, MA 01930, USA
| | - Paulo C Simões-Lopes
- Laboratório de Mamíferos Aquáticos, Programa de Pós-graduação em Ecologia, Departamento de Ecologia e Zoologia, Universidade Federal de Santa Catarina, Florianópolis, SC, Brazil
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12
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Complex Principal Component Analysis of Antarctic Ice Sheet Mass Balance. REMOTE SENSING 2021. [DOI: 10.3390/rs13030480] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Ice sheet changes of the Antarctic are the result of interactions among the ocean, atmosphere, and ice sheet. Studying the ice sheet mass variations helps us to understand the possible reasons for these changes. We used 164 months of Gravity Recovery and Climate Experiment (GRACE) satellite time-varying solutions to study the principal components (PCs) of the Antarctic ice sheet mass change and their time-frequency variation. This assessment was based on complex principal component analysis (CPCA) and the wavelet amplitude-period spectrum (WAPS) method to study the PCs and their time-frequency information. The CPCA results revealed the PCs that affect the ice sheet balance, and the wavelet analysis exposed the time-frequency variation of the quasi-periodic signal in each component. The results show that the first PC, which has a linear term and low-frequency signals with periods greater than five years, dominates the variation trend of ice sheet in the Antarctic. The ratio of its variance to the total variance shows that the first PC explains 83.73% of the mass change in the ice sheet. Similar low-frequency signals are also found in the meridional wind at 700 hPa in the South Pacific and the sea surface temperature anomaly (SSTA) in the equatorial Pacific, with the correlation between the low-frequency periodic signal of SSTA in the equatorial Pacific and the first PC of the ice sheet mass change in Antarctica found to be 0.73. The phase signals in the mass change of West Antarctica indicate the upstream propagation of mass loss information over time from the ocean–ice interface to the southward upslope, which mainly reflects ocean-driven factors such as enhanced ice–ocean interaction and the intrusion of warm saline water into the cavities under ice shelves associated with ice sheets which sit on retrograde slopes. Meanwhile, the phase signals in the mass change of East Antarctica indicate the downstream propagation of mass increase information from the South Pole toward Dronning Maud Land, which mainly reflects atmospheric factors such as precipitation accumulation.
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13
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Kim BH, Seo KW, Eom J, Chen J, Wilson CR. Antarctic ice mass variations from 1979 to 2017 driven by anomalous precipitation accumulation. Sci Rep 2020; 10:20366. [PMID: 33230242 PMCID: PMC7683593 DOI: 10.1038/s41598-020-77403-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 10/28/2020] [Indexed: 11/09/2022] Open
Abstract
Antarctic ice mass balance is determined by precipitation and ice discharge, and understanding their relative contributions to contemporary Antarctic ice mass change is important to project future ice mass loss and resulting sea level rise. There has been evidence that anomalous precipitation affects Antarctic ice mass loss estimates, and thus the precipitation contribution should be understood and considered in future projections. In this study, we revisit changes in Antarctic ice mass over recent decades and examine precipitation contributions over this period. We show that accumulated (time-integrated) precipitation explains most inter-annual anomalies of Antarctic ice mass change during the GRACE period (2003–2017). From 1979 to 2017, accumulated Antarctic precipitation contributes to significant ice mass loss acceleration in the Pacific sector and deceleration in the Atlantic-Indian Sectors, forming a bi-polar spatial pattern. Principal component analysis reveals that such a bi-polar pattern is likely modulated by the Southern Annular Mode (SAM). We also find that recent ice mass loss acceleration in 2007 is related to a variation in precipitation accumulation. Overall ice discharge has accelerated at a steady rate since 1992, but has not seen a recent abrupt increase.
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Affiliation(s)
- Byeong-Hoon Kim
- Division of Glacial Environment Research, Korea Polar Research Institute, Incheon, 21190, Republic of Korea.,Department of Earth Science Education, Seoul National University, Seoul, 08826, Republic of Korea
| | - Ki-Weon Seo
- Department of Earth Science Education, Seoul National University, Seoul, 08826, Republic of Korea.
| | - Jooyoung Eom
- Department of Earth Science Education, Kyungpook National University, Daegu, 41556, Republic of Korea
| | - Jianli Chen
- Center for Space Research, University of Texas at Austin, Austin, TX, 78759, USA
| | - Clark R Wilson
- Center for Space Research, University of Texas at Austin, Austin, TX, 78759, USA.,Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, 78712, USA
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14
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Abstract
Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are among the fastest changing outlet glaciers in Antarctica. Yet, projecting the future of these glaciers remains a major uncertainty for sea level rise. Here we use satellite imagery to show the development of damage areas with crevasses and open fractures on Pine Island and Thwaites ice shelves. These damage areas are first signs of their structural weakening as they precondition these ice shelves for disintegration. Model results that include the damage mechanism highlight the importance of damage for ice shelf stability, grounding line retreat, and future sea level contributions from Antarctica. Moreover, they underline the need for incorporating damage processes in models to improve sea level rise projections. Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are among the fastest changing outlet glaciers in West Antarctica with large consequences for global sea level. Yet, assessing how much and how fast both glaciers will weaken if these changes continue remains a major uncertainty as many of the processes that control their ice shelf weakening and grounding line retreat are not well understood. Here, we combine multisource satellite imagery with modeling to uncover the rapid development of damage areas in the shear zones of Pine Island and Thwaites ice shelves. These damage areas consist of highly crevassed areas and open fractures and are first signs that the shear zones of both ice shelves have structurally weakened over the past decade. Idealized model results reveal moreover that the damage initiates a feedback process where initial ice shelf weakening triggers the development of damage in their shear zones, which results in further speedup, shearing, and weakening, hence promoting additional damage development. This damage feedback potentially preconditions these ice shelves for disintegration and enhances grounding line retreat. The results of this study suggest that damage feedback processes are key to future ice shelf stability, grounding line retreat, and sea level contributions from Antarctica. Moreover, they underline the need for incorporating these feedback processes, which are currently not accounted for in most ice sheet models, to improve sea level rise projections.
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15
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Adusumilli S, Fricker HA, Medley B, Padman L, Siegfried MR. Interannual variations in meltwater input to the Southern Ocean from Antarctic ice shelves. NATURE GEOSCIENCE 2020; 13:616-620. [PMID: 32952606 PMCID: PMC7500482 DOI: 10.1038/s41561-020-0616-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2019] [Accepted: 06/19/2020] [Indexed: 05/27/2023]
Abstract
Ocean-driven basal melting of Antarctica's floating ice shelves accounts for about half of their mass loss in steady-state, where gains in ice shelf mass are balanced by losses. Ice shelf thickness changes driven by varying basal melt rates modulate mass loss from the grounded ice sheet and its contribution to sea level, and the changing meltwater fluxes influence climate processes in the Southern Ocean. Existing continent-wide melt rate datasets have no temporal variability, introducing uncertainties in sea level and climate projections. Here, we combine surface height data from satellite radar altimeters with satellite-derived ice velocities and a new model of firn-layer evolution to generate a high-resolution map of time-averaged (2010-2018) basal melt rates, and time series (1994-2018) of meltwater fluxes for most ice shelves. Total basal meltwater flux in 1994 (1090±150 Gt/yr) was not significantly different from the steady-state value (1100±60 Gt/yr), but increased to 1570±140 Gt/yr in 2009, followed by a decline to 1160±150 Gt/yr in 2018. For the four largest "cold-water" ice shelves we partition meltwater fluxes into deep and shallow sources to reveal distinct signatures of temporal variability, providing insights into climate forcing of basal melting and the impact of this melting on the Southern Ocean.
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Affiliation(s)
- Susheel Adusumilli
- Scripps Institution of Oceanography, University of California San Diego, CA, USA
| | - Helen Amanda Fricker
- Scripps Institution of Oceanography, University of California San Diego, CA, USA
| | - Brooke Medley
- Cryospheric Science Laboratory, NASA Goddard Space Flight Center, MD, USA
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16
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Holland DM, Nicholls KW, Basinski A. The Southern Ocean and its interaction with the Antarctic Ice Sheet. Science 2020; 367:1326-1330. [PMID: 32193320 DOI: 10.1126/science.aaz5491] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The Southern Ocean exerts a major influence on the mass balance of the Antarctic Ice Sheet, either indirectly, by its influence on air temperatures and winds, or directly, mostly through its effects on ice shelves. How much melting the ocean causes depends on the temperature of the water, which in turn is controlled by the combination of the thermal structure of the surrounding ocean and local ocean circulation, which in turn is determined largely by winds and bathymetry. As climate warms and atmospheric circulation changes, there will be follow-on changes in the ocean circulation and temperature. These consequences will affect the pace of mass loss of the Antarctic Ice Sheet.
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Affiliation(s)
- David M Holland
- Department of Mathematics, New York University, New York, NY 10012, USA. .,New York University Abu Dhabi Institute, Abu Dhabi, United Arab Emirates
| | | | - Aurora Basinski
- Department of Mathematics, New York University, New York, NY 10012, USA.,New York University Abu Dhabi Institute, Abu Dhabi, United Arab Emirates
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17
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Castagno P, Capozzi V, DiTullio GR, Falco P, Fusco G, Rintoul SR, Spezie G, Budillon G. Rebound of shelf water salinity in the Ross Sea. Nat Commun 2019; 10:5441. [PMID: 31784513 PMCID: PMC6884573 DOI: 10.1038/s41467-019-13083-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Accepted: 10/15/2019] [Indexed: 11/09/2022] Open
Abstract
Antarctic Bottom Water (AABW) supplies the lower limb of the global overturning circulation and ventilates the abyssal ocean. In recent decades, AABW has warmed, freshened and reduced in volume. Ross Sea Bottom Water (RSBW), the second largest source of AABW, has experienced the largest freshening. Here we use 23 years of summer measurements to document temporal variability in the salinity of the Ross Sea High Salinity Shelf Water (HSSW), a precursor to RSBW. HSSW salinity decreased between 1995 and 2014, consistent with freshening observed between 1958 and 2008. However, HSSW salinity rebounded sharply after 2014, with values in 2018 similar to those observed in the mid-late 1990s. Near-synchronous interannual fluctuations in salinity observed at five locations on the continental shelf suggest that upstream preconditioning and large-scale forcing influence HSSW salinity. The rate, magnitude and duration of the recent salinity increase are unusual in the context of the (sparse) observational record. Ross Sea Bottom Water, a major source of Antarctic Bottom Water, has experienced significant freshening in recent decades. Here the authors use 23 years of summer measurements to document temporal variability in the salinity of the Ross Sea High Salinity Shelf Water (HSSW) and found that HSSW salinity decreased between 1995 and 2014 and rebounded sharply after 2014.
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Affiliation(s)
- Pasquale Castagno
- Dipartimento di Scienze e Tecnologie, Università degli Studi di Napoli "Parthenope", Centro Direzionale, Isola C4, 80143, Napoli, Italy.
| | - Vincenzo Capozzi
- Dipartimento di Scienze e Tecnologie, Università degli Studi di Napoli "Parthenope", Centro Direzionale, Isola C4, 80143, Napoli, Italy
| | - Giacomo R DiTullio
- Grice Marine Laboratory, University of Charleston, 205 Fort Johnson Road, Charleston, SC, 29412, USA
| | - Pierpaolo Falco
- Dipartimento di Scienze e Tecnologie, Università degli Studi di Napoli "Parthenope", Centro Direzionale, Isola C4, 80143, Napoli, Italy
| | - Giannetta Fusco
- Dipartimento di Scienze e Tecnologie, Università degli Studi di Napoli "Parthenope", Centro Direzionale, Isola C4, 80143, Napoli, Italy
| | - Stephen R Rintoul
- CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia.,Centre for Southern Hemisphere Oceans Research, Hobart, Tasmania, Australia.,Australian Antarctic Program Partnership, Hobart, Tasmania, Australia
| | - Giancarlo Spezie
- Dipartimento di Scienze e Tecnologie, Università degli Studi di Napoli "Parthenope", Centro Direzionale, Isola C4, 80143, Napoli, Italy
| | - Giorgio Budillon
- Dipartimento di Scienze e Tecnologie, Università degli Studi di Napoli "Parthenope", Centro Direzionale, Isola C4, 80143, Napoli, Italy
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18
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Kennicutt MC, Bromwich D, Liggett D, Njåstad B, Peck L, Rintoul SR, Ritz C, Siegert MJ, Aitken A, Brooks CM, Cassano J, Chaturvedi S, Chen D, Dodds K, Golledge NR, Le Bohec C, Leppe M, Murray A, Nath PC, Raphael MN, Rogan-Finnemore M, Schroeder DM, Talley L, Travouillon T, Vaughan DG, Wang L, Weatherwax AT, Yang H, Chown SL. Sustained Antarctic Research: A 21st Century Imperative. ACTA ACUST UNITED AC 2019. [DOI: 10.1016/j.oneear.2019.08.014] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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19
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Marine ice sheet instability amplifies and skews uncertainty in projections of future sea-level rise. Proc Natl Acad Sci U S A 2019; 116:14887-14892. [PMID: 31285345 PMCID: PMC6660720 DOI: 10.1073/pnas.1904822116] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The potential for collapse of the Antarctic ice sheet remains the largest single source of uncertainty in projections of future sea-level rise. This uncertainty comes from an imperfect understanding of ice sheet processes and the internal variability of climate forcing of ice sheets. Using a mathematical technique from statistical physics and large ensembles of state-of-the-art ice sheet simulations, we show that collapse of ice sheets widens the range of possible scenarios for future sea-level rise. We also find that the collapse of marine ice sheets makes worst-case scenarios of rapid sea-level rise more likely in future projections. Sea-level rise may accelerate significantly if marine ice sheets become unstable. If such instability occurs, there would be considerable uncertainty in future sea-level rise projections due to imperfectly modeled ice sheet processes and unpredictable climate variability. In this study, we use mathematical and computational approaches to identify the ice sheet processes that drive uncertainty in sea-level projections. Using stochastic perturbation theory from statistical physics as a tool, we show mathematically that the marine ice sheet instability greatly amplifies and skews uncertainty in sea-level projections with worst-case scenarios of rapid sea-level rise being more likely than best-case scenarios of slower sea-level rise. We also perform large ensemble simulations with a state-of-the-art ice sheet model of Thwaites Glacier, a marine-terminating glacier in West Antarctica that is thought to be unstable. These ensemble simulations indicate that the uncertainty solely related to internal climate variability can be a large fraction of the total ice loss expected from Thwaites Glacier. We conclude that internal climate variability alone can be responsible for significant uncertainty in projections of sea-level rise and that large ensembles are a necessary tool for quantifying the upper bounds of this uncertainty.
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20
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Gwyther DE, O'Kane TJ, Galton-Fenzi BK, Monselesan DP, Greenbaum JS. Intrinsic processes drive variability in basal melting of the Totten Glacier Ice Shelf. Nat Commun 2018; 9:3141. [PMID: 30087352 PMCID: PMC6081466 DOI: 10.1038/s41467-018-05618-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 07/19/2018] [Indexed: 11/29/2022] Open
Abstract
Over the period 2003–2008, the Totten Ice Shelf (TIS) was shown to be rapidly thinning, likely due to basal melting. However, a recent study using a longer time series found high interannual variability present in TIS surface elevation without any apparent trend. Here we show that low-frequency intrinsic ocean variability potentially accounts for a large fraction of the variability in the basal melting of TIS. Specifically, numerical ocean model simulations show that up to 44% of the modelled variability in basal melting in the 1–5 year timescale (and up to 21% in the 5–10 year timescale) is intrinsic, with a similar response to the full climate forcing. We identify the important role of intrinsic ocean variability in setting the observed interannual variation in TIS surface thickness and velocity. Our results further demonstrate the need to account for intrinsic ocean processes in the detection and attribution of change. Low frequency intrinsic ocean variability has an unknown impact on Antarctic ice shelves, yet can arise even in the absence of varying climate forcing. Here, the authors show that this variability significantly affects modelled basal melting under the Totten Ice Shelf, with implications for the attribution of change.
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Affiliation(s)
- David E Gwyther
- Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, TAS, 7001, Australia.
| | | | - Benjamin K Galton-Fenzi
- Australian Antarctic Division, Kingston, TAS, 7050, Australia.,Antarctic Climate & Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, TAS, 7001, Australia
| | | | - Jamin S Greenbaum
- Institute for Geophysics, University of Texas at Austin, Austin, TX, 78758, USA
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21
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Shepherd A, Fricker HA, Farrell SL. Trends and connections across the Antarctic cryosphere. Nature 2018; 558:223-232. [DOI: 10.1038/s41586-018-0171-6] [Citation(s) in RCA: 101] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Accepted: 03/21/2018] [Indexed: 11/09/2022]
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22
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Abstract
We present two narratives on the future of Antarctica and the Southern Ocean, from the perspective of an observer looking back from 2070. In the first scenario, greenhouse gas emissions remained unchecked, the climate continued to warm, and the policy response was ineffective; this had large ramifications in Antarctica and the Southern Ocean, with worldwide impacts. In the second scenario, ambitious action was taken to limit greenhouse gas emissions and to establish policies that reduced anthropogenic pressure on the environment, slowing the rate of change in Antarctica. Choices made in the next decade will determine what trajectory is realized.
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