Nearshore sea ice shield Antarctic ice shelves from the damaging impact of ocean waves

The Larsen ice shelves extend along the east coast of the Antarctic Peninsula over the northwest part of the Weddell Sea. From north to south, these segments are called the Larsen A, B, C, and D, bordered by Filchner–Ronne Ice Shelf south of the Weddell Sea. In 1995, the Larsen A ice shelf completely disintegrated, followed by a partial break-up of the Larsen B in 2002. The Larsen C ice shelf, the largest in the region and the fourth-largest ice shelf in Antarctica, has already shown a sign of break-up process starting around 2016 and 2017. The break-up of Larsen A and B ice shelves has been attributed to regional atmospheric warming and ocean-driven basal melting. In a new study published in Nature Geoscience, a team of scientists from UK and New Zealand showed that about 85% of the ice-shelf perimeter along the eastern Antarctic Peninsula (EAP) underwent uninterrupted advance between the early 2000s and 2019, reversing the observed retreat in the two previous decades. The advance is attributed to reduced exposure to damaging ocean waves, enhanced ice-shelf buttressing (mechanical effect of an ice shelf on the state of stress at the grounding line), and others. The study showed that these were enabled by increased nearshore sea ice driven by a Weddell Sea-wide intensification of cyclonic surface winds around 2002. An important implication of this finding is that nearshore sea ice plays a critical role in either preventing or accelerating the final rifting and calving of large Antarctic ice shelves.

Fig. 4 in Christie et al. (2022). Schematic diagrams showing the key atmospheric and sea ice processes controlling the (in)stability of the eastern Antarctic Peninsula’s ice shelves through time. The signs following IPO, MLJ, and SAM refer to the states of the Interdecadal Pacific Oscillation, Mid-Latitude Jet and Southern Annular Mode relative to each epoch, respectively. Histograms indicate the probability of ocean wave-induced ice-shelf frontal damage. Note that, unlike the EAP’s other ice shelves, Ronne Ice Shelf is immune to the influence of damaging ocean waves given its thickness.

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