(A) Ice speed of the Antarctic Ice Sheet derived from multisensor data for the time period 2014–2016 (11) with 18 subregions A–K (black thin lines) delineated from surface slope and ice flow direction data (SI Appendix, Fig. S3). (B) Change in flow speed from the time period 2007–2008 to 2014–2015 color-coded from blue (deceleration) to red (acceleration). Grey areas have no data. (C) Basin names for subregions and ocean temperature at 310-m depth from the Southern Ocean State Estimate (SOSE) (12) color-coded from cold (blue) to warm (red). White areas in the ocean are shallower than 310 m depth. (D) Bed topography between 0 and 1,100 m depth, with SLE of each basin in centimeters of SLE (1, 13). (E) Change in grounding line ice discharge, D, for 1979–2017 for the 18 major subregions in billions of tons per year with percentage change in speed color-coded from red (acceleration) to blue (deceleration) and circle radius proportional to change. (F) Total change in mass of major basins color-coded from blue (gain) to red (loss) for 1979–2017 with circle radius proportional to the absolute mass balance. Graphic: Rignot, et al., 2019 / PNAS
(A) Ice speed of the Antarctic Ice Sheet derived from multisensor data for the time period 2014–2016 (11) with 18 subregions A–K (black thin lines) delineated from surface slope and ice flow direction data (SI Appendix, Fig. S3). (B) Change in flow speed from the time period 2007–2008 to 2014–2015 color-coded from blue (deceleration) to red (acceleration). Grey areas have no data. (C) Basin names for subregions and ocean temperature at 310-m depth from the Southern Ocean State Estimate (SOSE) (12) color-coded from cold (blue) to warm (red). White areas in the ocean are shallower than 310 m depth. (D) Bed topography between 0 and 1,100 m depth, with SLE of each basin in centimeters of SLE (1, 13). (E) Change in grounding line ice discharge, D, for 1979–2017 for the 18 major subregions in billions of tons per year with percentage change in speed color-coded from red (acceleration) to blue (deceleration) and circle radius proportional to change. (F) Total change in mass of major basins color-coded from blue (gain) to red (loss) for 1979–2017 with circle radius proportional to the absolute mass balance. Graphic: Rignot, et al., 2019 / PNAS

IRVINE, California, 14 January 2019 (UCI) – Antarctica experienced a sixfold increase in yearly ice mass loss between 1979 and 2017, according to a study published today in  Proceedings of the National Academy of Sciences.

Glaciologists from the University of California, Irvine, NASA’s Jet Propulsion Laboratory and the Netherlands’ Utrecht University additionally found that the accelerated melting caused global sea levels to rise more than half an inch during that time.

“That’s just the tip of the iceberg, so to speak,” said lead author Eric Rignot, Donald Bren Professor and chair of Earth system science at UCI. “As the Antarctic ice sheet continues to melt away, we expect multi-meter sea level rise from Antarctica in the coming centuries.”

For this study, Rignot and his collaborators conducted what he called the longest-ever assessment of remaining Antarctic ice mass. Spanning four decades, the project was also geographically comprehensive; the research team examined 18 regions encompassing 176 basins, as well as surrounding islands.

Techniques used to estimate ice sheet balance included a comparison of snowfall accumulation in interior basins with ice discharge by glaciers at their grounding lines, where ice begins to float in the ocean and detach from the bed. Data was derived from fairly high-resolution aerial photographs taken from a distance of about 350 meters via NASA’s Operation IceBridge; satellite radar interferometry from multiple space agencies; and the ongoing Landsat satellite imagery series, begun in the early 1970s.

The team was able to discern that between 1979 and 1990, Antarctica shed an average of 40 gigatons of ice mass annually. (A gigaton is 1 billion tons.) From 2009 to 2017, about 252 gigatons per year were lost.

The pace of melting rose dramatically over the four-decade period. From 1979 to 2001, it was an average of 48 gigatons annually per decade. The rate jumped 280 percent to 134 gigatons for 2001 to 2017.

Rignot said that one of the key findings of the project is the contribution East Antarctica has made to the total ice mass loss picture in recent decades.

Ice mass balance of Antarctica using the component method (SMB, on grounded ice minus ice discharge, D, at the grounding line) for (A) 1979–1990, (B) 1989–2000, (C) 1999–2009, and (D) 2009–2017. The size of the circle is proportional to the absolute magnitude of the anomaly in D (dD = SMB1979−2008 − D) or SMB (dSMB = SMB − SMB1979−2008). The color of the circle indicates loss in dD (dark red) or dSMB (light red) versus gain in dD (dark blue) or dSMB (light blue) in billions of tons (1012 kg) per year. Dark color refers to dD; light color refers to dSMB. Plots show totals for Antarctica, Antarctic Peninsula, West Antarctica, and East Antarctica. Background is the total mass balance spread into the drainage basins color-coded from red (loss) to blue (gain). Graphic: Rignot, et al., 2019 / PNAS
Ice mass balance of Antarctica using the component method (SMB, on grounded ice minus ice discharge, D, at the grounding line) for (A) 1979–1990, (B) 1989–2000, (C) 1999–2009, and (D) 2009–2017. The size of the circle is proportional to the absolute magnitude of the anomaly in D (dD = SMB1979−2008 − D) or SMB (dSMB = SMB − SMB1979−2008). The color of the circle indicates loss in dD (dark red) or dSMB (light red) versus gain in dD (dark blue) or dSMB (light blue) in billions of tons (1012 kg) per year. Dark color refers to dD; light color refers to dSMB. Plots show totals for Antarctica, Antarctic Peninsula, West Antarctica, and East Antarctica. Background is the total mass balance spread into the drainage basins color-coded from red (loss) to blue (gain). Graphic: Rignot, et al., 2019 / PNAS

“The Wilkes Land sector of East Antarctica has, overall, always been an important participant in the mass loss, even as far back as the 1980s, as our research has shown,” he said. “This region is probably more sensitive to climate [change] than has traditionally been assumed, and that’s important to know, because it holds even more ice than West Antarctica and the Antarctic Peninsula together.”

He added that the sectors losing the most ice mass are adjacent to warm ocean water.

“As climate warming and ozone depletion send more ocean heat toward those sectors, they will continue to contribute to sea level rise from Antarctica in decades to come,” said Rignot, who’s also a senior project scientist at JPL.

Co-authors of this study are Jeremie Mouginot, UCI associate researcher in Earth system science; Bernd Scheuchl, UCI associate project scientist in Earth system science; Mathieu Morlighem, UCI associate professor of Earth system science; and Michiel van den Broeke and Jan M. “Melchior” van Wessem of the Netherlands’ Utrecht University. Funding and support were provided by NASA’s cryospheric sciences and Measures programs, the Netherlands Organization for Scientific Research’s polar program and the Netherlands Earth System Science Centre.

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UCI/JPL: Antarctica losing six times more ice mass annually now than 40 years ago

Time series of cumulative anomalies in SMB (blue), ice discharge (D, red), and total mass (M, purple) with error bars in billions of tons for (A) West Antarctica, (B) East Antarctica; (C) Antarctic Peninsula), and (D) Antarctica, with mean mass loss in billions of tons per year and an acceleration in billions of tons per year per decade for the time period 1979 to 2017. The balance discharge is SMB1979−2008. Note that the total mass change, M = SMB − D, does not depend on SMB1979−2008. Graphic: Rignot, et al., 2019 / PNAS
Time series of cumulative anomalies in SMB (blue), ice discharge (D, red), and total mass (M, purple) with error bars in billions of tons for (A) West Antarctica, (B) East Antarctica; (C) Antarctic Peninsula), and (D) Antarctica, with mean mass loss in billions of tons per year and an acceleration in billions of tons per year per decade for the time period 1979 to 2017. The balance discharge is SMB1979−2008. Note that the total mass change, M = SMB − D, does not depend on SMB1979−2008. Graphic: Rignot, et al., 2019 / PNAS

ABSTRACT: We use updated drainage inventory, ice thickness, and ice velocity data to calculate the grounding line ice discharge of 176 basins draining the Antarctic Ice Sheet from 1979 to 2017. We compare the results with a surface mass balance model to deduce the ice sheet mass balance. The total mass loss increased from 40 ± 9 Gt/y in 1979–1990 to 50 ± 14 Gt/y in 1989–2000, 166 ± 18 Gt/y in 1999–2009, and 252 ± 26 Gt/y in 2009–2017. In 2009–2017, the mass loss was dominated by the Amundsen/Bellingshausen Sea sectors, in West Antarctica (159 ± 8 Gt/y), Wilkes Land, in East Antarctica (51 ± 13 Gt/y), and West and Northeast Peninsula (42 ± 5 Gt/y). The contribution to sea-level rise from Antarctica averaged 3.6 ± 0.5 mm per decade with a cumulative 14.0 ± 2.0 mm since 1979, including 6.9 ± 0.6 mm from West Antarctica, 4.4 ± 0.9 mm from East Antarctica, and 2.5 ± 0.4 mm from the Peninsula (i.e., East Antarctica is a major participant in the mass loss). During the entire period, the mass loss concentrated in areas closest to warm, salty, subsurface, circumpolar deep water (CDW), that is, consistent with enhanced polar westerlies pushing CDW toward Antarctica to melt its floating ice shelves, destabilize the glaciers, and raise sea level.SIGNIFICANCE: We evaluate the state of the mass balance of the Antarctic Ice Sheet over the last four decades using a comprehensive, precise satellite record and output products from a regional atmospheric climate model to document its impact on sea-level rise. The mass loss is dominated by enhanced glacier flow in areas closest to warm, salty, subsurface circumpolar deep water, including East Antarctica, which has been a major contributor over the entire period. The same sectors are likely to dominate sea-level rise from Antarctica in decades to come as enhanced polar westerlies push more circumpolar deep water toward the glaciers.

Four decades of Antarctic Ice Sheet mass balance from 1979–2017