Cold Ocean Cavity and Weak Basal Melting of the Sørsdal Ice Shelf Revealed by Surveys Using Autonomous Platforms. Issue 6 (12th June 2020)

• Record Type: Journal Article
• Authors: Gwyther, David E.; Spain, Erica A.; King, Peter; Guihen, Damien; Williams, Guy D.; Evans, Eleri; Cook, Sue; Richter, Ole; Galton‐Fenzi, Benjamin K.; Coleman, Richard
• Is Part Of: Journal of geophysical research. Volume 125:Issue 6(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-06-12
• Subjects: Antarctica -- ice shelves -- AUV -- oceanography -- basal melting -- APRES; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2019JC015882
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Basal melting of ice shelves is inherently difficult to quantify through direct observations, yet it is a critical factor controlling Antarctic mass balance and global sea‐level rise. While much research attention is paid to larger ice shelves and those experiencing the most rapid change, many smaller, unstudied ice shelves offer valuable insights. Here, we investigate the oceanographic conditions and melting beneath the Sørsdal ice shelf, East Antarctica. We present results from the 2018/2019 Sørsdal deployment of the University of Tasmania's autonomous underwater vehicle nupiri muka . Oceanography adjacent to and beneath the ice shelf front shows a cold and relatively saline environment dominated by Winter Water and Dense Shelf Water, while bathymetry measurements show a deep (∼1, 200 m) trough running into the ice shelf cavity. Two multiyear deployments of Autonomous Phase‐sensitive Radar Echo Sounders on the surface of the ice shelf show weak melt rates (average of 1.6 and 2.3 m yr −1 ) with low temporal variability. These observations are supported by numerical ocean model and satellite estimates of melting. We speculate that the presence of a ∼825 m thick (350 m to at least 1, 175 m) homogeneous layer of cold, dense water blocks access from warmer waters that intrude into Prydz Bay from offshore, resulting in weak melt rates. However, the newly identified trough means that the ice shelf is vulnerable to any decrease in polynya activity that allows warm water to enter the cavity. This could lead to increased basal melting and mass loss through this sector of Antarctica. Plain Language Summary: Ice shelves, the floating extensions of Antarctic glaciers, play a key role in retarding the flow of the ice sheet toward the ocean. Enhanced ocean‐driven melting beneath these ice shelves can reduce this "buttressing" effect and increase the flow of the ice sheet into the ocean, leading to sea‐level rise. We present the results from a first‐time deployment of an autonomous underwater vehicle (AUV) to the Sørsdal ice shelf in East Antarctica. We found cold and salty water present beneath the ice shelf with a deep seafloor trough at the entrance to the ice shelf, indicative of a cold ocean environment with low melt rates. We also present results from surface‐deployed radar instruments, numerical modeling, and remote sensing techniques, which confirm weak melting is occurring beneath this ice shelf. Though many studies document the presence of warm water in the region, we posit that this cold and salty water blocks warm water incursions in front of and into the cavity, maintaining the relatively weak melt rates. However, this process may change in the future, allowing entry of warmer water and increasing melting and sea‐level contribution from this part of Antarctica. Key Points: AUV deployment to East Antarctic ice shelf finds cold ocean conditions with deep bathymetric access Melt rate estimates and observations from an integrated survey show evidence of weak basal melting We posit that dense cold waters produced in nearby polynyas block access of MCDW and reduce melting