Searching for the sub-Arctic Ocean response to wintertime sea ice retreat

Wu, Yue (2022) Searching for the sub-Arctic Ocean response to wintertime sea ice retreat. Doctoral thesis, University of East Anglia.

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Observations have revealed a rapid sea ice decline in polar and sub-polar regions this century, leading to corresponding changes in the ocean. This thesis explores the wintertime ocean response to rapid climate change in coupled climate models. The marginal ice zone of the sub-Arctic Ocean is the focus, including the Barents Sea, the ocean west-and-north of Svalbard, and the Nordic Seas.

Two coupled climate models HiGEM and HadGEM3 are exploited in this thesis. The two models provide good representations of historical climate at high latitudes where observational coverage is still relatively low. In the absence of anthropogenic forcing, there are complex inter-strait connectivities around the wider Arctic, which are quasi-balanced by adjustment flows through the straits connecting the Pacific and Atlantic. These flows are modified by local atmospheric forcing.

Under climate change scenarios, there is substantial warming in the ocean and atmosphere that leads to rapid wintertime sea ice retreat. This redistributes the air-sea interactions and therefore the location of convective mixing in the ocean. To the west and north of Svalbard, where the main branch of West Spitsbergen Current carries warm and saline Atlantic Water into the Arctic, increased ocean exposure to the atmosphere associated with sea ice retreat leads to enhanced mixing encroaching downstream along the Atlantic Water pathway. The submerged Atlantic origin water then rises in the water column.

The other pathway of Atlantic Water into the Arctic Ocean is through Barents Sea which acts as a cooling machine. Sea ice retreat is associated with a high volume transport into the Barents Sea, which is partly due to local wind driven processes. To the east of Greenland, the mixing becomes deeper in the region of sea ice retreat as a result of increased heat fluxes and mechanical driving by winds. Over the Greenland Sea gyre, further away from the sea ice, the upper ocean warms significantly. This results in a more stratified water column and, as a consequence, a severe reduction in the depth of convective mixing.

This thesis concludes that sea ice retreat enables a local increase in air-sea interaction and therefore an increase convective and wind-driven mixing. However, current and future climate change leads to considerable ocean warming away from the region of sea ice retreat, which conversely inhibits mixing here compared with that in the previous century.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Mathematics
Depositing User: Chris White
Date Deposited: 20 Mar 2023 09:53
Last Modified: 20 Mar 2023 09:53


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