Sensitivity of the summer upper ocean heat content in a Western Antarctic Peninsula fjord
2020
Hahn-Woernle, Lisa | Powell, Brian | Lundesgaard, Øyvind | van Wessem, Melchior
On the Western Antarctic Peninsula (WAP), fjords make up most of the interface between the ocean and the cryosphere, and they are hotspots of biological productivity and biodiversity. Changes in the summer upper ocean (50 m) heat content, H, of a fjord could directly affect primary productivity and melting of icebergs and glacial fronts. Using the adjoint of a high-resolution Regional Ocean Model System model, we quantify the key drivers controlling changes in H to understand the summertime characteristics and potential climatic impacts. Results show that the summertime warming is mainly driven by the surface heat flux, and can be enhanced by inward along-fjord winds or northeastward winds along Gerlache strait. Opposite wind perturbations lead to a reduction of H. We learned that the sensitivity to the along-strait winds relates to the exchange of heat between the fjord and the strait, with the strait being a major heat source for the fjord in the unperturbed conditions. The sensitivity analysis of the most influential regional water masses identifies upper ocean waters from the north (<200 m) as the dominant driver. We also find that two possible consequences of climate change, warming air temperature and increasing meltwater input could have opposing effects on H. The additional meltwater leads to a cooling of the fjord that is mainly caused by a reduced import of heat from the strait. It follows that future increases of meltwater input (e.g. increased runoff) could play a crucial role for the fjord’s upper ocean physics and potentially its ecosystem.
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