Impacts of freshwater changes on Antarctic sea ice in an eddy-permitting sea-ice–ocean model

Verena Haid,Simona Masina,Doroteaciro Iovino

doi:10.5194/tc-11-1387-2017

Abstract

Abstract. In a warming climate, satellite data indicate that the sea ice extent around Antarctica has increased over the last decades. One of the suggested explanations is the stabilizing effect of increased mass loss of the Antarctic ice sheet. Here, we investigate the sea ice response to changes in both the amount and the spatial distribution of freshwater input to the ocean by comparing a set of numerical sensitivity simulations with additional supply of water at the Antarctic ocean surface. We analyze the short-term response of the sea ice cover and the on-shelf water column to variations in the amount and distribution of the prescribed surface freshwater flux.Our results confirm that enhancing the freshwater input can increase the sea ice extent. Our experiments show a negative development of the sea ice extent only for extreme freshwater additions. We find that the spatial distribution of freshwater is of great influence on sea ice concentration and thickness as it affects sea ice dynamics and thermodynamics. For strong regional contrasts in the freshwater addition the dynamic response dominates the local change in sea ice, which generally opposes the thermodynamic response. Furthermore, we find that additional coastal runoff generally leads to fresher and warmer dense shelf waters.

Highlights

Sea ice is one of the key components of the polar climate system controlling air–ocean exchange and driving deep ocean convection
We have investigated the hypothesis that increasing freshening of the Southern Ocean could explain, at least partially, the Antarctic sea ice expansion
A set of coupled ocean–sea-ice simulations with varying freshwater forcing were performed and compared to the control run in order to assess the impact of enhanced surface freshening on sea ice properties and dense water formation in the Southern Ocean

Summary

Introduction

Sea ice is one of the key components of the polar climate system controlling air–ocean exchange and driving deep ocean convection. The positive net (circumpolaraveraged) trend is the sum of partly opposing regional trends of the same order of magnitude (Parkinson and Cavalieri, 2012). The causes of this positive trend in a generally warming world are still debated. The strengthening of the circumpolar westerly winds alters the sea ice drift patterns and could result in the regionally different trends observed in the sea ice cover (e.g., Thompson and Solomon, 2002; Liu et al, 2004; Lefebvre and Goosse, 2005; Turner et al, 2009). An increase of precipitation over the Southern Ocean has influence on surface salinity, albedo of ice covered areas, and ice thickness by submersion and could be a possible contributor to the observed increase in Antarctic sea ice extent (Liu and Curry, 2010)

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