The Impact of the Amundsen Sea Freshwater Balance on Ocean Melting of the West Antarctic Ice Sheet

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.

阿蒙森海中冰架的变薄速度在南极洲是最快的。这种不平衡是由温暖的环极深层水（CDW）侵入所导致的海洋融化变化引起的。由此产生的淡水平衡变化可能会影响陆架上的水流和混合。然而，目前对该地区淡水的源和汇缺乏清晰的了解。在此，我们使用一个带有被动淡水示踪剂的阿蒙森海模型，来研究不同淡水成分的相对大小和空间分布。在表层以及平均深度上，所有淡水示踪剂浓度具有相当的量级，不过在平均深度上，海冰和冰架的浓度是最大的。总的淡水示踪剂分布与冰架示踪剂场相似。这意味着存在冰架融水反馈的可能性，即大量的冰架融水改变海洋环流和分层，从而影响融化。冰架和海冰的淡水通量具有最大的年际变化。文中详细研究了包含搁浅冰山以及冰山淡水通量的影响。冰山的存在增加了到达冰架底部的环极深层水侵入。这表明了另一种可能的反馈机制，即更多的冰山导致更大的冰架融化，从而产生更多的冰山。然而，这种潜在反馈的强度取决于受约束较差的海冰模型参数。这些结果意味着，与海洋淡水平衡相关的受约束较差的参数，比如那些与冰山和海冰相关的参数，会影响对西南极冰盖融化的预测。