Widespread increase in discharge from West Antarctic Peninsula glaciers since 2018

Abstract. Many glaciers on the Antarctic Peninsula have retreated and accelerated in recent decades. Here we show that there was a widespread, quasi-synchronous and sustained increase in grounding line discharge from glaciers on the west coast of the Antarctic Peninsula since 2018. Overall, west Antarctic Peninsula discharge trends increased by over a factor of three, from 0.5 Gt/y/decade during 2017 to 2020 up to 1.6 Gt/y/decade in the years following, leading to a grounding line discharge increase of 7 Gt/y (7.4 %) since 2017. The acceleration in discharge was concentrated at glaciers connected to deep, cross-shelf troughs hosting warm ocean waters, and the acceleration occurred during a period of anomalously high subsurface water temperatures on the continental shelf. Given that many of the affected glaciers have retreated over the past several decades in response to ocean warming, thereby highlighting their sensitivity to ocean forcing, we argue that the recent period of anomalously warm water was likely a key driver of the observed acceleration. However, the acceleration also occurred during a time of anomalously high atmospheric temperatures and glacier surface runoff, which could have contributed to speed-up by directly increasing basal water pressure and, by invigorating near-glacier circulation, increasing submarine melt rates. The spatial pattern of glacier acceleration therefore provides an indication of glaciers that are exposed to warm ocean water at depth and/or have active surface-to-bed hydrological connections. Both atmospheric and ocean temperatures in this region and its surroundings are likely to increase further in the coming decades, suggesting that discharge increases may continue and become more widespread.