Ice shelf-ocean interaction and meltwater transport - Updates on modelling the present state and future scenarios with FESOM


Contact
Ralph.Timmermann [ at ] awi.de

Abstract

In the Amundsen Sea, warm Circumpolar Deep Water (CDW) intrudes onto the continental shelf and flows into the ice shelf cavities of the West Antarctic Ice Sheet (WAIS), resulting in high basal melt rates. This affects the world ocean in two ways: First, melting of the ice sheets contributes to changes in the global sea level. Given that most of the Antarctic ice sheet drains into ice shelves, which serve as buttresses to the ice flow, variations of ice shelf basal melting are an important component in the southern hemisphere’s contribution to sea level rise. Second, ice-shelf meltwater is a freshwater source which may cause freshening of the shelf water locally in the Amundsen Sea as well as remotely in the Ross Sea. This may lead to a change in the characteristics of the Antarctic Bottom Water (AABW) formed in the Ross Sea and thus may influence the global thermohaline circulation as suggested by previous studies. Thus, investigations on possible connections between the melting of small ice shelves in West Antarctica and the large-scale ocean circulation are crucial for understanding climate change in the Southern Ocean. We study these regions using the Finite-Element Sea ice-ice shelf-Ocean Model (FESOM). Like other global models resolving all the ice shelves around Antarctica, FESOM has been unable to reproduce a realistic CDW flow onto the Amundsen Sea continental shelf. This caused large uncertainties for FESOM's present-day simulations and future projections of ice shelf basal melting. Based on an extensive suite of sensitivity studies, we have now identified the most important ingredients to a faithful representation of Amundsen Sea hydrography in ocean general circulation models. To simulate the CDW intrusion through submarine glacial troughs in a way that closely matches the observations and to obtain realistic basal melt rates for the ice shelves in West Antarctica, a horizontal resolution of about 5 km or smaller is required. The choice of atmospheric forcing data is shown to be important; a cold bias in the NCEP/NCAR reanalysis prevents warm CDW from intruding onto the continental shelf. The effect of grounded icebergs located off Bear Peninsula is minor but they may act as buffers in anomalously cold years. It has been suggested that an increased melting of continental ice in the Amundsen and Bellinghausen Seas is a likely source of the observed freshening of Ross Sea water. To test this hypothesis, we simulate the spreading of glacial melt water. Based on the spatial distribution of simulated passive meltwater tracers, most of the basal melt water from Amundsen Sea ice shelves flows towards the Ross Sea, with more than half of the meltwater originating from the Getz Ice Shelf. Sensitivity studies show that already a slight increase of the ice shelf basal mass loss can substantially intensify the transport of melt water into the Ross Sea due to a strengthening of the melt-driven shelf circulation and the westward flowing coastal current. This supports the idea that the basal melting of Amundsen/Bellingshausen Sea ice shelves contributes substantially to the observed Ross Sea freshening.



Item Type
Conference (Invited talk)
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Primary Division
Programs
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Research Networks
Peer revision
Not peer-reviewed
Publication Status
Published
Event Details
Rising Coastal Seas on a Warming Earth, 26 Oct 2014 - 29 Oct 2014, NYUAD, Abu Dhabi, United Arab Emirates.
Eprint ID
36548
Cite as
Timmermann, R. and Nakayama, Y. (2014): Ice shelf-ocean interaction and meltwater transport - Updates on modelling the present state and future scenarios with FESOM , Rising Coastal Seas on a Warming Earth, NYUAD, Abu Dhabi, United Arab Emirates, 26 October 2014 - 29 October 2014 .


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