The Impact of the Amundsen Sea Freshwater Balance on Ocean Melting of the West Antarctic Ice Sheet. Issue 9 (18th September 2020)

• Record Type: Journal Article
• Authors: Bett, David T.; Holland, Paul R.; Naveira Garabato, Alberto C.; Jenkins, Adrian; Dutrieux, Pierre; Kimura, Satoshi; Fleming, Andrew
• Is Part Of: Journal of geophysical research. Volume 125:Issue 9(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-09-18
• Subjects: Amundsen Sea -- West Antarctica -- freshwater -- grounded icebergs; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2020JC016305
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: The Amundsen Sea has the highest thinning rates of ice shelves in Antarctica. This imbalance is caused by changes in ocean melting induced by warm Circumpolar Deep Water (CDW) intrusions. The resulting changing freshwater balance could affect the on‐shelf currents and mixing. However, a clear understanding of the sources and sinks of freshwater in the region is lacking. Here we use a model of the Amundsen Sea, with passive freshwater tracers, to investigate the relative magnitudes and spatial distributions of the different freshwater components. In the surface layer and as a depth average, all freshwater tracer concentrations are of comparable magnitude, though on a depth average, sea ice and ice shelf are largest. The total freshwater tracer distribution is similar to that of the ice‐shelf tracer field. This implies a potential for ice‐shelf meltwater feedbacks, whereby abundant ice‐shelf meltwater alters the ocean circulation and stratification, affecting melting. Ice‐shelf and sea‐ice freshwater fluxes have the largest interannual variability. The effect of including grounded icebergs and iceberg freshwater flux are studied in detail. The presence of icebergs increases CDW intrusions that reach the base of ice shelves. This suggests another possible feedback mechanism, whereby more icebergs induce greater ice‐shelf melting and hence more icebergs. However, the strength of this potential feedback is dependent on poorly constrained sea‐ice model parameters. These results imply that poorly constrained parameters relating to the ocean freshwater balance, such as those relating to icebergs and sea ice, impact predictions for melting of the West Antarctic Ice Sheet. Plain Language Summary: The Amundsen Sea in Antarctica is an important region for understanding future sea‐level rise from the West Antarctic Ice Sheet, as the region's ice shelves (the floating extension of ocean terminating glaciers) are thinning due to changes in ocean melting. This could affect the amount of freshwater in the Amundsen Sea, possibly affecting ocean currents. In order to understand the distribution of freshwater from different sources (snowfall, ice‐shelf melting, iceberg melting, and sea‐ice melting) we use a specialized ocean model. This model shows that freshwater from all different sources have comparable magnitudes, though ice‐shelf and sea‐ice sources are largest. The fact that ice‐shelf meltwater is an important component implies a potential feedback in the system, whereby more ice‐shelf melting could alter ocean currents, and thereby cause more melting. We also investigated the effect of icebergs that ground on a seabed ridge. Icebergs increase the amount of warm water that reaches ice shelves. This provides a potential for another feedback, where more icebergs increase ice‐shelf melting, thereby producing more icebergs. These results imply that poorly known aspects of freshwater sources can impact predictions for future sea‐level rise contributions from the West Antarctic. Key Points: Sea ice and ice shelves provide the strongest freshwater fluxes in the Amundsen Sea, with the largest interannual variability Parameterized icebergs affect oceanic heat content at ice shelves, with a strong potential for ice‐shelf meltwater and iceberg feedbacks Poorly constrained parameters relating to the freshwater balance may impact predictions for melting of the West Antarctic Ice Sheet