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Qt26f4j9vv.Pdf UC Irvine UC Irvine Previously Published Works Title Recent Antarctic ice mass loss from radar interferometry and regional climate modelling Permalink https://escholarship.org/uc/item/26f4j9vv Journal Nature Geoscience, 1(2) ISSN 1752-0894 Authors Rignot, E Bamber, JL Van Den Broeke, MR et al. Publication Date 2008-02-01 DOI 10.1038/ngeo102 License https://creativecommons.org/licenses/by/4.0/ 4.0 Peer reviewed eScholarship.org Powered by the California Digital Library University of California LETTERS Recent Antarctic ice mass loss from radar interferometry and regional climate modelling ERIC RIGNOT1,2,3*, JONATHAN L. BAMBER4, MICHIEL R. VAN DEN BROEKE5, CURT DAVIS6, YONGHONG LI6, WILLEM JAN VAN DE BERG5 AND ERIK VAN MEIJGAARD7 1University of California Irvine, Earth System Science, Irvine, California 92697, USA 2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA 3Centro de Estudios Cientificos, Arturo Prat 514, Valdivia, Chile 4University of Bristol, Bristol BS8 1SS, UK 5Institute for Marine and Atmospheric Research (IMAU), Utrecht University, 3584 CC Utrecht, The Netherlands 6University of Missouri-Columbia, Columbia, Missouri 65211, USA 7Royal Netherlands Meteorological Institute (KNMI), 3732 GK De Bilt, The Netherlands *e-mail: [email protected] Published online: 13 January 2008; doi:10.1038/ngeo102 Large uncertainties remain in the current and future between 1992 and 2006 by the European Earth Remote Sensing contribution to sea level rise from Antarctica. Climate warming (ERS-1 and 2), the Canadian Radarsat-1 and the Japanese Advanced may increase snowfall in the continent’s interior1–3, but enhance Land Observing satellites. Our map covers all major outlet glaciers, glacier discharge at the coast where warmer air and ocean ice streams and tributaries of importance for mass flux calculation, temperatures erode the buttressing ice shelves4–11. Here, we use with ice velocity ranging from 100 to 3,500 m yr−1, at a precision satellite interferometric synthetic-aperture radar observations of 5 to 50 m yr−1 (see the Methods section). Short-time variations from 1992 to 2006 covering 85% of Antarctica’s coastline to in velocity, for example, due to ocean tides, are averaged out over estimate the total mass flux into the ocean. We compare the the 24 to 46 day repeat period of our measurements. Velocities mass fluxes from large drainage basin units with interior snow at the grounding line of fast-moving glaciers are assumed to be accumulation calculated from a regional atmospheric climate depth independent, which introduces errors of much less than model for 1980 to 2004. In East Antarctica, small glacier losses in 1% (ref. 3). Wilkes Land and glacier gains at the mouths of the Filchner and Using double-difference interferometry, we mapped glacier Ross ice shelves combine to a near-zero loss of 4 ± 61 Gt yr−1. In grounding lines with a precision of 100 m all around Antarctica, West Antarctica, widespread losses along the Bellingshausen and except for eight glaciers south of 81◦ South where we used Amundsen seas increased the ice sheet loss by 59% in 10 years to the Moderate Resolution Imaging Spectroradiometer (MODIS) reach 132±60 Gt yr−1 in 2006. In the Peninsula, losses increased mosaic13 with a precision of 1 km. Grounding-line thickness is by 140% to reach 60±46 Gt yr−1 in 2006. Losses are concentrated derived from surface elevation assuming ice to be in hydrostatic along narrow channels occupied by outlet glaciers and are caused equilibrium with sea water (see the Methods section). In selected by ongoing and past glacier acceleration. Changes in glacier flow parts of West Antarctica, we have direct measurements of ice therefore have a significant, if not dominant impact on ice sheet thickness with a precision of 10 m instead (see Supplementary mass balance. Information, Table S1). For surface elevation, we use a new digital The mass balance of Antarctica is determined from the elevation model (DEM) combining precise laser altimeter data difference between two competing processes of ice discharge into from the Ice Cloud and land Elevation Satellite from 2003–2004, the ocean by glaciers and ice streams and accumulation of snowfall ERS-1/2 radar altimeter data from 1994 corrected for temporal in the vast interior, which are two large numbers affected by changes in between1,14 and the new GGM02 geoid15. Comparison significant uncertainties2,12. Estimates of ice discharge have been of the DEM with independent laser altimeter data at the grounding sporadic in nature owing to the limited availability of ice velocity line of West Antarctica indicates a vertical precision in elevation and thickness data at the grounding line of Antarctica, as well of 0.15 ± 4 m. Surface elevation above mean sea level is then as precise knowledge of the grounding-line positions. Similarly, converted into solid-ice surface elevation after applying a firn depth estimates of snowfall have been affected by uncertainties associated correction16. We estimate the random error in inferred thickness with the interpolation of sparse in situ data of varying quality and to range from 80 to 120 m when accounting for uncertainties in temporal coverage over the entire continent. grounding-line position, surface elevation, firn depth correction Here, we present a nearly complete map of surface velocities and geoid height. For verification, at the grounding line of Pine along the periphery of Antarctica (Fig. 1) obtained from Island Bay glaciers, our thickness values are within 14 ± 60 m interferometric synthetic-aperture radar (InSAR) data collected of direct thickness measurements10 ranging from 420 to 1,460 m. 106 nature geoscience VOL 1 FEBRUARY 2008 www.nature.com/naturegeoscience © 2008 Nature Publishing Group LETTERS –10 0 10 –20 20 –30 30 JEL A K' A' Indian EKS 40 –40 Ocean AST Antarctic RIL JUT 50 Peninsula –50 VES RAG LAB –66 STA –60 –68 COA Weddell Sea SHI RAY ROB 60 I" –70 WIL SLE –72 K BAI J" –74 SCY B –70 J 70 FLE ENG –76 I REC RYM ORV –78 –80 C LID EVA –80 –82 LAM 80 BER SUP AME H' –84 Bellingshausen Sea FER CAR MOL VIS –86 FOU East Antarctica RUT INS –88 –90 PHI –90 ABB PIG 90 West Antarctica E' WHI MER DEN COS TWG KAM BEA NIM –100 H 100 HSK BIN C' BUD G BYR MAC TOT 110 –110 ECH Amundsen Sea SUL MUL GET HUL MOS LAN 120 –120 F' E DAV FRO Ross Sea DIB 130 –130 NIN MER +10 Gt yr –1 REN COO D –10 Gt yr –1 Indian 140 –140 Ocean D' –150 150 200 km 0 0.01 0.1 1 2 3 km yr –1 –160 160 –170 180 170 Figure 1 Ice velocity of Antarctica colour coded on a logarithmic scale and overlaid on a MODIS mosaic13. Circles denote mass loss (red) or gain (blue) of large basins in gigatonnes per year. Drainage basins are black lines extending from the grounding-line flux gates. Letters A–K0 indicate large basins20. Ice velocities for Siple Coast ice streams and Ronne Ice Shelf are from refs 22,23. See Supplementary Information for acronyms and the Methods section for velocity precision. Solid-ice fluxes are then calculated combining vector ice velocity for 1981–1989. Older maps yield accumulation levels 3 times lower, and ice thickness, with a precision that is glacier dependent and which imply a local mass balance 20 times more negative and high ranges from 2 to 15% (see the Supplementary Information). The rates of glacier thinning that are not observed2. The RACMO2/ANT end points of the selected flux gates define the extent of the glacier accumulation values yield comparable losses for Pine Island and drainage basins determined from the DEM. Individual drainage Thwaites glaciers, which is consistent with the similarity of their basins are grouped into large units labelled A to K0. thinning rates2; other maps yield twice more thinning for Thwaites. Snowfall accumulation is from the RACMO2/ANT regional Finally, the model does not mix data from different time periods atmospheric climate model, at 55 km resolution, averaged for and fully incorporates temporal changes in snowfall between 1980 1980–2004 (refs 17–19). Lateral forcings are taken from European and 2004. A statistical analysis of absolute errors (see the Methods Center for Medium-Range Weather Forecasting reanalyses section) yields an uncertainty in accumulation varying from 10% (ERA-40) for the period 1980–2002, supplemented with European in dry, large basins to 30% in wet, small coastal basins. Center for Medium-Range Weather Forecasting operational Ice flux and snowfall are compared for each glacier, for large analyses after August 2002. Comparisons with 1,900 independent basins A–K0, and for the Peninsula, East and West Antarctica. To field data show excellent agreement (R = 0.82) with the model18. include non-surveyed areas, we apply a scaling factor on the mass The model predicts higher coastal precipitation and wetter fluxes of each large basin A–K0 based on the percentage surveyed conditions in West Antarctica and the western Peninsula17 than area versus total area to cover 100% of Antarctica (Table 1). In East older maps obtained by interpolating limited field data using Antarctica, we obtain a near-zero mass balance of −4±61 Gt yr−1. meteorological variables20 or satellite passive microwave data21. The J00K Filchner22 and E0E Ross sectors are gaining mass, but this Few reliable in situ coastal accumulation data exist for comparison, is compensated by the mass loss in Wilkes Land (basin CE) from but in the high-accumulation sector of the Getz Ice Shelf (basin the Philippi, Denman, Totten, Moscow University Ice Shelf, Cook F0G), the model predicts precipitation levels consistent with a Ice Shelf and David glaciers.
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