Impacts on water-mass transformation from ice shelf melting over the Southern Ocean

Tuesday, December 11, 2018 - 08:00
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The Southern Ocean is an important driver for the meridional overturning circulation and it plays a key role in the transport of heat, the uptake of carbon and the global climate system. The strength of the global abyssal overturning circulation is proportional to the rate at which AABW is produced and this production rate is determined by net surface buoyancy loss. Due to the low thermal expansion of seawater at low temperatures, buoyancy loss in polar waters is strongly dominated by the surface freshwater flux rather than heat flux. Data-assimilating models show that sea-ice freezing and melting are the most important processes for water formation over the Southern Ocean, followed by precipitation. Even though glacial melt is relatively small in magnitude, it is located spatially very close to convection areas, where it may also have an influence on dense water formation. Furthermore, ice shelves can contribute to the freshwater flux both directly by meltwater input, and indirectly by impacting stratification and circulation in ways that feedback on sea-ice formation and melt. Recently, the Department of Energy (DOE) has developed a new global coupled climate model, the Energy Exascale Earth System Model (E3SM). Using ocean and sea-ice simulation results with and without ice shelf melting, forced with the CORE-II surface flux fields for the period of 1948-2009, we analyze the water-mass transformation/formation rates from E3SM to investigate the impacts on water-mass transformation from glacial melt over the Southern Ocean. E3SM simulation results show that the freshwater flux from land ice to the ocean can further induce the upwelling water by as much as 1.3 Sv per year and the upwelled water can be directly converted into Antarctic Intermediate Water. We have also found that the freshwater flux from land ice can affect the water-mass transformation caused by sea-ice freezing.

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