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Antarctic ice-shelf advance driven by anomalous atmospheric and sea-ice circulation

Nature Geoscience volume 15, pages 356–362 (2022)Cite this article

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Abstract

The disintegration of the eastern Antarctic Peninsula’s Larsen A and B ice shelves has been attributed to atmosphere and ocean warming, and increased mass losses from the glaciers once restrained by these ice shelves have increased Antarctica’s total contribution to sea-level rise. Abrupt recessions in ice-shelf frontal position presaged the break-up of Larsen A and B, yet, in the ~20 years since these events, documented knowledge of frontal change along the entire ~1,400-km-long eastern Antarctic Peninsula is limited. Here, we show that 85% of the seaward ice-shelf perimeter fringing this coastline underwent uninterrupted advance between the early 2000s and 2019, in contrast to the two previous decades. We attribute this advance to enhanced ocean-wave dampening, ice-shelf buttressing and the absence of sea-surface slope-induced gravitational ice-shelf flow. These phenomena were, in turn, enabled by increased near-shore sea ice driven by a Weddell Sea-wide intensification of cyclonic surface winds around 2002. Collectively, our observations demonstrate that sea-ice change can either safeguard from, or set in motion, the final rifting and calving of even large Antarctic ice shelves.

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Fig. 1: Ice-shelf front and grounding-line migration in the eastern Antarctic Peninsula south of Cape Longing.
Fig. 2: Areal evolution of the eastern Antarctic Peninsula’s ice shelves, 1961–2019.
Fig. 3: Sea ice concentration and surface-wind conditions over the Weddell Sea sector.
Fig. 4: Schematic diagrams showing the key atmospheric and sea ice processes controlling the (in)stability of the eastern Antarctic Peninsula’s ice shelves through time.

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Data availability

All satellite and climate reanalysis datasets utilized in this study are publicly available and can be obtained from the data repositories detailed in the Methods. The CATS2008a tidal model is available at: https://www.usap-dc.org/view/dataset/601235, and the ice front and 2019 grounding line location files generated in this study are available at https://doi.org/10.17863/CAM.54490 (ref. 81) and https://doi.org/10.17863/CAM.54489 (ref. 82), respectively. Supplementary Data 1 contains a list of all satellite images used in the production of our ice front and grounding line datasets, and Supplementary Data 2 contains the ice-shelf areal extent values used in the production of Fig. 2.

Code availability

The MATLAB codes developed for this study are available upon request to the corresponding author.

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Acknowledgements

We thank A. Cook, T. Haran, J. Ferrigno and J. Wuite for making their historical ice-shelf frontal positions publicly available, D. Floricioiu for providing access to the DLR/ESA AIS CCI GLL product and NASA, USGS, ESA, the EU Copernicus programme, NSIDC, ECMWF, NOAA, G. Marshall and A. Fraser for making all other satellite and climate data utilized in this study available free of charge. This work was funded by the Flotilla Foundation and Marine Archaeology Consultants Switzerland (F.D.W.C., T.J.B., C.L.B., A.M. and J.A.D.) and with the financial assistance (F.D.W.C. and J.A.D.) of the Prince Albert II of Monaco Foundation.

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  1. Christine L. Batchelor

    Present address: School of Geography, Politics and Sociology, University of Newcastle, Newcastle, UK

Authors and Affiliations

  1. Scott Polar Research Institute, University of Cambridge, Cambridge, UK

    Frazer D. W. Christie, Toby J. Benham, Christine L. Batchelor, Aleksandr Montelli & Julian A. Dowdeswell

  2. Gateway Antarctica, University of Canterbury, Christchurch, New Zealand

    Wolfgang Rack

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Contributions

F.D.W.C. devised the study and carried out all acquisition, processing and interpretation of the observational and climate reanalysis datasets referred to in the text. T.J.B., W.R., C.L.B. and A.M. assisted F.D.W.C. with the initial acquisition and processing of the Sentinel-1A/B data. F.D.W.C. wrote the manuscript, and each co-author contributed comments on the text and figures.

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Extended data

Extended Data Fig. 1 Grounding-line migration along Larsen C Ice Shelf.

a, Change in grounding line location (GLL) between 1994-6, 2016-7 and 2019 as determined from satellite radar-based techniques (Methods). Following Fig. 1, symbols denoting recent (2016/7-2019) GLL change are also shown, as well as the position of the 2019 ice front (maroon) and ice surface velocity contours83 (100 m yr−1 increments) over grounded ice. b-j, spatial extent of GLL change across the regions labelled in a, superimposed over recent ice surface velocity magnitudes83. JP1-3 denote unnamed glaciers 1–3 draining from Jason Peninsula; CP1-2, unnamed glaciers 1-2 draining from Churchill Peninsula; At, Atlee; Be, Bevin; An, Anderson; Sl, Sleipnir; Aa, Aagaard; Go, Gould; Ba, Balch; Al, Alberts; Br, Breitfus; Cu, Cumpston; QF, Quartermain-Fricker; Fl, Flint; De, Demorest; Ma, Matthes; Ch, Chamberlain; Re, Renaud; Le, Lewis; Ah, Ahlmann; BG, Bill’s Gulch; Da, Daspit; Me, Mercator; Ap, Aphrodite; Pa, Pan and Cr, Cronus glaciers. HK1-2 denotes the unnamed glaciers flowing from Hollick-Kenyon Peninsula. In e and f, white asterisks denote no change since the mid−1990s in lieu of 2016/7 GLL coverage.

Extended Data Fig. 2 Grounding-line migration along Larsen D, New Bedford, Wright and Keller ice shelves’ fastest-flowing glaciers.

a, Change in grounding line location (GLL) between 1994-6, 2016-7 and 2019 as determined from satellite radar-based techniques (Methods). Following Fig. 1, symbols denoting recent (2016/7-2019) GLL change proximal to Larsen C Ice Shelf (LC) are also shown, as well as the position of the 2019 ice front (maroon) and ice surface velocity contours83 (100 m yr-1 increments) over grounded ice. b-j, spatial extent of GLL change across the regions labelled in a, superimposed over recent ice surface velocity magnitudes83. Ca denotes Casey Glacier; Lu, Lurabee; An, Anthony; Cr, Croom; Cl, Clifford; Ma, Matheson; Ya, Yates; Da, Dana; Mu, Murrish; So, Soto; Ha, Haley; Cli, Cline; Ra, Rankin; Gr, Gruening; Ru, Runcorn; Mr, Maury; Fe, Fenton; Mo, Mosby; MH, Meinardus-Haines and Wa, Waverly glaciers. K denotes the unnamed glacier draining to Keller Inlet. All other abbreviations are the same as in Fig. 1.

Extended Data Fig. 3 Recent changes in EAP ice-surface flow.

a, Landsat 8-derived velocity change between 2016 and 2018 over the Antarctic Peninsula region. Black lines delineate the ice drainage basins detailed in a recent study84. The 2018 ice front position is also shown. To minimise erroneous data coverage over ice divides and other regions of complex topography, data are masked (dark grey) where Verror exceeded 30 m yr-1 in either 2016 or 2018 (or both). Black box indicates the detail shown in c and d. b, Landsat 8-derived Verror. In c and d, HGE denotes Hektoria, Green and Evans; C, Crane; F, Flask and L, Leppard glaciers. Note the continued dynamic acceleration of Flask and Leppard glaciers following the disintegration of Larsen B Ice Shelf in 2002, and the lack of any similar grounded ice-flow acceleration upstream of Larsen C Ice Shelf following the calving of iceberg A-68 (Fig. 1).

Extended Data Fig. 4 Wider climatic conditions over the Weddell Sea Sector.

a and b, Monthly changes in the Interdecadal Pacific Oscillation (IPO) and Southern Annular Mode (SAM), respectively (Methods). Data have been smoothed using a 20-year running mean to emphasise multi-decadal variability. Following Fig. 2, blue (pink) shading denotes the approximate timing of relatively cool (warm) climatic conditions over the Antarctic Peninsula as deduced from (a). c and d, annual-averaged 10 m wind anomalies over the Antarctic Peninsula Ice Sheet for the periods (c) January 1982 to December 2002 and (d) January 2003 to December 2019, respectively, relative to all months on record (1979–2019). Note the abrupt reversal in wind direction over most EAP ice shelves (except Ronne) between the two periods, indicative of reduced foehn wind-driven ice-shelf surface melting, calving and coastal sea-ice evacuation through time (see main text and Supplementary Discussion 3 for further information).

Extended Data Fig. 5 Austral summertime sea-ice conditions over the Weddell Sea Sector.

a and b, Mean passive microwave-derived sea-ice concentration anomalies for all complete austral summertime (DJF) cycles between 2003 and 2019 and 1982 and 2002, respectively, relative to all earlier, complete summertime cycles on record (1980–2019). Black asterisk denotes the approximate location of iceberg A-23a (lightly grounded at this location since 2000); light grey shading, no data. In both panels, dashed boxes indicate sea-ice averaging regions used in the production of Fig. 2 and Extended Data Figs. 9 and 10. Figure highlights the importance of summer sea ice variability in dominating the annual-averaged observations presented in Fig. 3.

Extended Data Fig. 6 Landfast sea ice conditions in the eastern Antarctic Peninsula.

a, Mean extended wintertime (April to October) landfast sea ice occurrence offshore of the EAP, 2002–2017. 100% occurrence denotes permanent landfast sea-ice presence over the observational record during these months. G denotes Gipps Ice Rise. b, Linear trend in extended wintertime landfast sea ice occurrence. Red denotes increased sea ice occurrence through time. Cyan stippling indicates statistically significant trends (p < .1) over the 18-year observational window, as determined from a two-tailed Pearson’s Linear Correlation Coefficient test. Inset shows detail around Gipps Ice Rise, including near the rift that formed iceberg A-68 (dark grey line; see main text and Supplementary Discussion for further information).

Extended Data Fig. 7 EAP ‘open ocean years’, 1979–2019.

a,c,e,g, Monthly mean sea-ice minima observed during the ‘open ocean years’ indicated in Fig. 2. Grey shading denotes <15% sea-ice concentration. Note that means overestimate sub-monthly sea ice extent and concentration, especially near the ice edge. b,d,f,h, ERA5-derived timeseries showing corresponding ocean wave conditions (median peak period and significant height of combined wind waves and swell; see Methods) offshore of the Larsen A, B, C (panels b,d,h) and New Bedford, Wright, Keller and Ronne ice shelves (panel f). Median values were calculated from all cells in the red boxes shown in panels a,c,e,g, when ocean waves were incident upon the ice shelves. Times when waves were not incident are masked. Boxplots show the statistical distribution of observed wave conditions, with outliers (>1.5 times the interquartile range) marked as crosses.

Extended Data Fig. 8 Sea-surface slope conditions prior to ice-shelf frontal recession.

a,c,e,g, Mean HYCOM-derived sea-surface slope anomalies offshore of the Larsen B (LBIS), Larsen D (LDIS) and Ronne ice shelves prior to the collapse of Larsen B (a) and the calving of icebergs A-69 (c), A-70/71 (e), and A-76 (g). Temporal averaging window and baseline periods are indicated top right, the latter of which corresponds to mean sea-surface slope during the month of calving (October 2020 for e given the calving of A-70/71 in early November 2020). Black and cyan lines indicate pre- and post-recession location of the ice shelves, respectively. Dark grey denotes no data. b,d,f,h, timeseries showing mean sea-surface slopes in the days and weeks prior to collapse (b) or calving (d,f,h), as averaged over the red dashed boxes shown in a,c,e,g. Vertical red lines denote the onset of collapse/calving; pink shading, periods of intense slopes following either exceptionally strong winds on the already open ocean (b) or observed, pronounced coastal sea-ice evacuation (d,f,h; cf. Supplementary Videos 2–4). Horizontal grey lines indicate mean slope over the baseline periods shown in a,c,e,g. Relative change in ice-shelf frontal strain, Ɛ, corresponding to variations in slope are also shown (right-hand axes).

Extended Data Fig. 9 Larsen A coastal sea-ice variability.

a, Timeseries showing monthly sea ice concentration (SIC) between 1979 and 1986 when a calving event of uncertain timing occurred (cf. Figure 2). Values represent the average of all cells contained in the red dashed box shown in b. Red lines denote times in which highly anomalous (>2σ), wind-driven coastal sea-ice losses would have rapidly de-buttressed Larsen A’s ice front, prompted enhanced gravitational ice-shelf flow due to increased (oceanward-down) sea-surface slopes and likely initiated calving. Pink shading shows ‘open ocean conditions’ as in Fig. 2. b and c, mean wind (vector) and SIC (raster) anomalies during the times indicated by the red lines in a (1981/2 and 1984, respectively). Note the anomalous offshore direction of winds over Larsen A in both panels. d, map showing the extent of the calving event between 1979 and 1986. Grey lines denote all earlier (1947–1978) observed ice frontal positions5.

Extended Data Fig. 10 Larsen D coastal sea-ice variability.

a, Timeseries showing monthly sea ice concentration (SIC) between 1990 and 1993 when a calving event of uncertain timing occurred (cf. Figure 2). Values represent the average of all cells contained in the red dashed box shown in b. Red lines denote times in which highly anomalous (>2σ), wind-driven coastal sea-ice losses would have rapidly de-buttressed Larsen D’s ice front, prompted enhanced gravitational ice-shelf flow due to increased (oceanward-down) sea-surface slopes and likely initiated calving. In c and d, the position of the ice front as observed on 24th January 1995 is also shown, revealing further retreat of the coastline after January 1993 in response to the observed coastal sea-ice loss shown in a and b and/or the related calving event between December 1992 and January 1993 (d). No other satellite imagery exists between these times. HI denotes Hearst Island; EI, Ewing Island; DI, Dolleman Island; SI, Steele Island.

Supplementary information

Supplementary Information

Supplementary Discussions 1–4, Fig. 1 and references.

Supplementary Data 1

Satellite imagery utilized in this study.

Supplementary Data 2

Ice-shelf areal extent values.

Supplementary Video 1

Time-lapse animation showing the recent calving of iceberg A-68 from Larsen C Ice Shelf, 2017, as observed by Sentinel-1A/B (single (HH) polarization). The black box delimits the region of landfast sea ice (red shading) subject to complete mechanical failure/disintegration ~3 weeks prior to A-68’s calving. Note the synchronous timing between the disintegration of this landfast sea ice and the reactivation of the rift that instigated A-68’s calving.

Supplementary Video 2

Time-lapse animation showing the recent calving of iceberg A-69 from Larsen D Ice Shelf, 2020, as observed by Sentinel-1A/B (dual polarization (HHHV)). The blue box corresponds to the sea-slope averaging region used in the production of Extended Data Fig. 9. Red shading denotes areas of the coastline fringed by landfast sea ice.

Supplementary Video 3

Time-lapse animation showing the recent calving of icebergs A-70 and A-71 from Larsen D Ice Shelf, 2020, as observed by Sentinel-1A/B (single (HH) polarization). The blue box corresponds to the sea-slope averaging region used in the production of Extended Data Fig. 9. The red line tracks the migration of a relatively young, thin band of sea ice from the Ronne Polynya through the averaging box prior to and during the calving of A-70 and A-71.

Supplementary Video 4

Time-lapse animation showing the recent calving of iceberg A-76 from Ronne Ice Shelf, 2021, as observed by Sentinel-1A/B (single (HH) polarization). The blue box corresponds to the sea-slope averaging region used in the production of Extended Data Fig. 9. The red line tracks the limits of the Ronne Polynya in the weeks surrounding A-76’s calving.

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Christie, F.D.W., Benham, T.J., Batchelor, C.L. et al. Antarctic ice-shelf advance driven by anomalous atmospheric and sea-ice circulation. Nat. Geosci. 15, 356–362 (2022). https://doi.org/10.1038/s41561-022-00938-x

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