Ocean-driven thinning enhances iceberg calving and retreat of Antarctic ice shelves

Abstract

Iceberg calving from all Antarctic ice shelves has never been directly measured, despite playing a crucial role in ice sheet mass balance. Rapid changes to iceberg calving naturally arise from the sporadic detachment of large tabular bergs but can also be triggered by climate forcing. Here we provide a direct empirical estimate of mass loss due to iceberg calving and melting from Antarctic ice shelves. We find that between 2005 and 2011, the total mass loss due to iceberg calving of 755 ± 24 gigatonnes per year (Gt/y) is only half the total loss due to basal melt of 1516 ± 106 Gt/y. However, we observe widespread retreat of ice shelves that are currently thinning. Net mass loss due to iceberg calving for these ice shelves (302 ± 27 Gt/y) is comparable in magnitude to net mass loss due to basal melt (312 ± 14 Gt/y). Moreover, we find that iceberg calving from these decaying ice shelves is dominated by frequent calving events, which are distinct from the less frequent detachment of isolated tabular icebergs associated with ice shelves in neutral or positive mass balance regimes. Our results suggest that thinning associated with ocean-driven increased basal melt can trigger increased iceberg calving, implying that iceberg calving may play an overlooked role in the demise of shrinking ice shelves, and is more sensitive to ocean forcing than expected from steady state calving estimates.

Keywords: Antarctica; basal melt; ice shelf; iceberg calving; mass balance.

Fig. 1.

Spatial distributions of basal melt and iceberg calving. The area of the red circles denotes mass loss due to iceberg calving of 26 basin systems. The dashed lines divide the ocean around Antarctica into five regions: Weddell Sea (60°W–20°E), Indian Ocean (20°E–90°E), Western Pacific Ocean (90°E–160°E), Ross Sea (160°E–130°W), and Bellingshausen/Amundsen Sea (130°W–60°W). Abbreviations of subbasin systems are described in Dataset S1.

Fig. 2.

Antarctic ice shelf advance and retreat between 2005 and 2011. (A) Larsen B and C Ice Shelf; (B) Fimbulisen, Jelbartisen, and Ekströmisen Ice Shelf; (C) Amery Ice Shelf; (D) Totten and Moscow University Ice Shelf; (E) Mertz Glacier Tongue; (F) Ross Ice Shelf; (G) Getz Ice Shelf; and (H) the floating parts of Pine Island and Thwaites Glaciers, and Crosson Ice Shelf.

Fig. 3.

Different calving features. (A) Example of tabular calving from the Fimbulisen Ice Shelf, (B) example of melt pond induced disintegration from the Larsen B ice shelf, and (C) example of crevasse induced disintegration from the Totten glacier. (1) Calving feature on synthetic aperture radar image in 1997 (bright white ponds shown in B image are melt ponds). ENVISAT ASAR image with area calved marked before (2) and after (3) calving. (4) Ice front changes overlaid on Envisat ASAR image in 2011.

Fig. 4.

Annual Antarctic iceberg calving from 2005 to 2011. (A) All ice shelves by calving size; (B) calving by state of mass balance; (C) ice shelves in positive mass balance; and (D) ice shelves in negative mass balance. Horizontal lines in B, C, and D denote steady-state iceberg calving for those ice shelves.