Modelling the freshwater balance and influence of icebergs in the Amundsen Sea, Antarctica

Abstract

The Amundsen Sea has some of 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 behaviour of fresh water in the region is lacking. This thesis addresses that question. Firstly, an idealised model, with a passive ice shelf freshwater tracer, is used to show that the vertical distribution of ice shelf meltwater changes with CDW layer thickness variation. This model is used to determine the local freshwater feedback effect of ice shelf meltwater on ice shelf melt rates. Secondly, a model of the Amundsen Sea is used, with passive freshwater tracers, to investigate the relative magnitudes and spatial distributions of freshwater components from different sources. In the surface and on a depth-average all freshwater tracer concentrations are of comparable magnitude, though on a depth-average sea ice and ice shelf meltwater are largest. The total freshwater tracer distribution is similar to that of the ice-shelf meltwater tracer field. This implies a potential for ice-shelf meltwater feedbacks, whereby abundant ice-shelf meltwater alters the ocean circulation and stratication, affecting melting. Thirdly, the effect of including grounded icebergs and their 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.
Author's note: Some of the results in Chapter 4 and 5 in this thesis are summarised in Bett et al. (2020), which has been accepted by the Journal of Geophysical Research:Oceans.

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