Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Ice shelf collapse reduces buttressing and enables grounded glaciers to contribute more rapidly to sea-level rise in a warming climate. The abrupt collapses of the Larsen A (1995) and B (2002) ice shelves on the Antarctic Peninsula (AP) occurred, at least for Larsen B, when long-period ocean swells damaged the calving front and the ice shelf was inundated with melt lakes that led to large-scale hydrofracture cascades. During collapse, field and satellite observations indicate föhn winds were present on both ice shelves. Here we use a regional climate model and machine learning analyses to evaluate the contributory roles of föhn winds and associated melt events prior to and during the collapses for ice shelves on the AP. Föhn winds caused about 25 % <span class="inline-formula">±</span> 3 % of the total annual melt in just 9 d on Larsen A prior to and during collapse and were present during the Larsen B collapse, which helped form extensive melt lakes. At the same time, the off-coast wind direction created by föhn winds helped melt and physically push sea ice away from the ice shelf calving fronts that allowed long-period ocean swells to reach and damage the front, which has been theorized to have ultimately triggered collapse. Collapsed ice shelves experienced enhanced surface melt driven by föhn winds over a large spatial extent and near the calving front, whereas SCAR inlet and the Larsen C ice shelves are affected less by föhn-wind-induced melt and do not experience large-scale melt ponds. These results suggest SCAR inlet and the Larsen C ice shelves may be less likely to experience rapid collapse due to föhn-driven melt so long as surface temperatures and föhn occurrence remain within historical bounds.

Highlights

  • Abstract.‌I‌ce‌‌shelf‌‌collapse‌‌reduces‌‌buttressing‌‌and‌‌enables‌‌glaciers‌‌to‌‌contribute‌‌more‌‌rapidly‌‌to‌‌sea-level‌‌rise‌‌in‌‌a‌‌ warming‌‌climate.‌‌The‌‌abrupt‌‌collapses‌‌of‌‌the‌‌Larsen‌‌A‌‌and‌‌B‌‌ice‌‌shelves‌‌on‌‌the‌‌Antarctic‌‌Peninsula‌‌(AP)‌‌have‌‌been‌‌ attributed‌‌to‌‌increased‌‌surface‌‌melt.‌‌However,‌‌no‌‌studies‌‌examine‌‌the‌‌timing,‌‌magnitude,‌‌and‌‌location‌‌of‌‌surface‌‌melt‌‌ processes‌‌immediately‌‌preceding‌‌these‌‌disintegrations.‌‌Here‌‌we‌‌use‌‌a‌‌regional‌‌climate‌‌model‌‌and‌‌Machine‌‌Learning‌‌ 15 analyses‌‌to‌‌evaluate‌‌the‌‌influence‌‌of‌‌föhn‌‌wind‌‌events‌‌on‌‌the‌‌surface‌‌liquid‌‌water‌‌budget‌‌for‌‌collapsed‌‌and‌‌extant‌‌ice‌‌ shelves.‌‌We‌‌find‌‌föhn‌‌winds‌‌caused‌‌25%‌‌of‌‌the‌‌total‌‌annual‌‌melt‌‌in‌‌just‌‌9‌‌days‌‌on‌‌Larsen‌‌A‌‌which‌‌helped‌‌melt‌‌lakes‌‌surpass‌‌ a‌‌critical‌‌stability‌‌depth‌‌that,‌‌we‌‌suggest,‌‌ultimately‌‌triggered‌‌collapse.‌‌By‌‌contrast,‌‌föhns‌‌appear‌‌to‌‌pre-condition,‌‌not‌‌ trigger,‌‌Larsen‌‌B's‌‌collapse.‌‌AP‌‌extant‌‌ice‌‌shelves‌‌will‌‌remain‌‌less‌‌vulnerable‌‌to‌‌surface-melt-driven‌‌instability‌‌due‌‌to‌‌ weaker‌‌föhn-driven‌‌melt‌‌so‌‌long‌‌as‌‌surface‌‌temperatures‌‌and‌‌föhn‌‌occurrence‌‌remain‌‌within‌‌historical‌‌bounds.‌ ‌

  • 45 meltwater‌‌applies‌‌outward‌‌and‌‌downward‌‌pressure‌‌to‌‌the‌‌walls‌‌and‌‌tip‌‌of‌‌crevasses‌‌that‌‌can‌‌propagate‌‌through‌‌the‌‌ice‌‌shelf‌‌ (Scambos‌‌et‌‌al.,‌‌2003;‌‌Banwell‌‌et‌‌al.,‌‌2013;‌‌Bell‌‌et‌‌al.,‌‌2018).‌‌Melt‌‌lakes‌‌at‌‌critical‌‌water‌‌depths‌‌create‌‌a‌‌fracture‌‌pattern‌‌that‌‌ splits‌‌ice‌‌shelves‌‌into‌‌sections‌‌with‌‌aspect‌‌ratios‌‌that‌‌support‌‌unstable‌‌rollover‌‌and‌‌hydrofracture‌‌cascades‌‌that‌‌begin‌‌when‌‌ melt‌‌lakes‌‌drain‌‌or‌‌calving‌‌occurs‌‌at‌‌the‌‌ice‌‌shelf‌‌terminus‌‌(Banwell‌‌et‌‌al.,‌‌2013;‌‌Robel‌‌et‌‌al.,‌‌2019).‌‌ ‌ Previous‌‌research‌‌acknowledges‌‌enhanced‌‌surface‌‌melt‌‌during‌‌years‌‌of‌‌collapse‌‌and‌‌the‌‌presence‌‌of‌‌föhn‌‌wind‌‌

  • 55 events‌‌on‌‌the‌‌eastern‌‌AP‌‌since‌‌2002‌‌(Vaughan‌‌et‌‌al.,‌‌2003;‌‌Bozkurt‌‌et‌‌al.,‌‌2020).‌‌The‌‌questions,‌‌therefore,‌‌arise:‌‌1)‌‌To‌‌what‌‌ extent‌‌does‌‌föhn-induced‌‌melt‌‌contribute‌‌to‌‌the‌‌surface‌‌melt‌‌budget‌‌on‌‌the‌‌AP?;‌‌2)‌‌Does‌‌the‌‌confluence‌‌of‌‌föhn-induced‌‌ melt‌‌quantity,‌‌spatial‌‌impact,‌‌and‌‌timing‌‌constitute‌‌a‌‌trigger‌‌for‌‌the‌‌collapse‌‌of‌‌the‌‌LAIS‌‌and‌‌LBIS?;‌‌3)‌‌What‌‌are‌‌the‌‌ implications‌‌of‌‌föhn-induced‌‌melt‌‌for‌‌the‌‌remaining‌‌eastern‌‌AP‌‌ice‌‌shelves?‌‌ ‌ To‌‌address‌‌these‌‌questions‌‌we‌‌consider‌‌three‌‌metrics:‌‌Section‌‌3.1‌‌explores‌‌the‌‌total‌‌annual‌‌melt‌‌quantity‌‌and‌‌spatial‌

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Summary

Introduction

Abstract.‌I‌ce‌‌shelf‌‌collapse‌‌reduces‌‌buttressing‌‌and‌‌enables‌‌glaciers‌‌to‌‌contribute‌‌more‌‌rapidly‌‌to‌‌sea-level‌‌rise‌‌in‌‌a‌‌ warming‌‌climate.‌‌The‌‌abrupt‌‌collapses‌‌of‌‌the‌‌Larsen‌‌A‌‌and‌‌B‌‌ice‌‌shelves‌‌on‌‌the‌‌Antarctic‌‌Peninsula‌‌(AP)‌‌have‌‌been‌‌ attributed‌‌to‌‌increased‌‌surface‌‌melt.‌‌However,‌‌no‌‌studies‌‌examine‌‌the‌‌timing,‌‌magnitude,‌‌and‌‌location‌‌of‌‌surface‌‌melt‌‌ processes‌‌immediately‌‌preceding‌‌these‌‌disintegrations.‌‌Here‌‌we‌‌use‌‌a‌‌regional‌‌climate‌‌model‌‌and‌‌Machine‌‌Learning‌‌ 15 analyses‌‌to‌‌evaluate‌‌the‌‌influence‌‌of‌‌föhn‌‌wind‌‌events‌‌on‌‌the‌‌surface‌‌liquid‌‌water‌‌budget‌‌for‌‌collapsed‌‌and‌‌extant‌‌ice‌‌ shelves.‌‌We‌‌find‌‌föhn‌‌winds‌‌caused‌‌25%‌‌of‌‌the‌‌total‌‌annual‌‌melt‌‌in‌‌just‌‌9‌‌days‌‌on‌‌Larsen‌‌A‌‌which‌‌helped‌‌melt‌‌lakes‌‌surpass‌‌ a‌‌critical‌‌stability‌‌depth‌‌that,‌‌we‌‌suggest,‌‌ultimately‌‌triggered‌‌collapse.‌‌By‌‌contrast,‌‌föhns‌‌appear‌‌to‌‌pre-condition,‌‌not‌‌ trigger,‌‌Larsen‌‌B's‌‌collapse.‌‌AP‌‌extant‌‌ice‌‌shelves‌‌will‌‌remain‌‌less‌‌vulnerable‌‌to‌‌surface-melt-driven‌‌instability‌‌due‌‌to‌‌ weaker‌‌föhn-driven‌‌melt‌‌so‌‌long‌‌as‌‌surface‌‌temperatures‌‌and‌‌föhn‌‌occurrence‌‌remain‌‌within‌‌historical‌‌bounds.‌ ‌ 45 meltwater‌‌applies‌‌outward‌‌and‌‌downward‌‌pressure‌‌to‌‌the‌‌walls‌‌and‌‌tip‌‌of‌‌crevasses‌‌that‌‌can‌‌propagate‌‌through‌‌the‌‌ice‌‌shelf‌‌ (Scambos‌‌et‌‌al.,‌‌2003;‌‌Banwell‌‌et‌‌al.,‌‌2013;‌‌Bell‌‌et‌‌al.,‌‌2018).‌‌Melt‌‌lakes‌‌at‌‌critical‌‌water‌‌depths‌‌create‌‌a‌‌fracture‌‌pattern‌‌that‌‌ splits‌‌ice‌‌shelves‌‌into‌‌sections‌‌with‌‌aspect‌‌ratios‌‌that‌‌support‌‌unstable‌‌rollover‌‌and‌‌hydrofracture‌‌cascades‌‌that‌‌begin‌‌when‌‌ melt‌‌lakes‌‌drain‌‌or‌‌calving‌‌occurs‌‌at‌‌the‌‌ice‌‌shelf‌‌terminus‌‌(Banwell‌‌et‌‌al.,‌‌2013;‌‌Robel‌‌et‌‌al.,‌‌2019).‌‌ ‌ Previous‌‌research‌‌acknowledges‌‌enhanced‌‌surface‌‌melt‌‌during‌‌years‌‌of‌‌collapse‌‌and‌‌the‌‌presence‌‌of‌‌föhn‌‌wind‌‌ 55 events‌‌on‌‌the‌‌eastern‌‌AP‌‌since‌‌2002‌‌(Vaughan‌‌et‌‌al.,‌‌2003;‌‌Bozkurt‌‌et‌‌al.,‌‌2020).‌‌The‌‌questions,‌‌therefore,‌‌arise:‌‌1)‌‌To‌‌what‌‌ extent‌‌does‌‌föhn-induced‌‌melt‌‌contribute‌‌to‌‌the‌‌surface‌‌melt‌‌budget‌‌on‌‌the‌‌AP?;‌‌2)‌‌Does‌‌the‌‌confluence‌‌of‌‌föhn-induced‌‌ melt‌‌quantity,‌‌spatial‌‌impact,‌‌and‌‌timing‌‌constitute‌‌a‌‌trigger‌‌for‌‌the‌‌collapse‌‌of‌‌the‌‌LAIS‌‌and‌‌LBIS?;‌‌3)‌‌What‌‌are‌‌the‌‌ implications‌‌of‌‌föhn-induced‌‌melt‌‌for‌‌the‌‌remaining‌‌eastern‌‌AP‌‌ice‌‌shelves?‌‌ ‌ To‌‌address‌‌these‌‌questions‌‌we‌‌consider‌‌three‌‌metrics:‌‌Section‌‌3.1‌‌explores‌‌the‌‌total‌‌annual‌‌melt‌‌quantity‌‌and‌‌spatial‌

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