NPI seminar: Arctic Ocean bottom pressure from GRACE - Lessons about ocean circulation and the flow variability through Bering Strait
Satellite observations of ocean bottom pressure (OBP) from the Gravity Recovery and Climate Experiment (GRACE), available since 2002, have become an invaluable tool for investigating Arctic environmental changes. This presentation provides an overview of what we have learned about the Arctic Ocean using GRACE, including the patterns of variability in ocean circulation that we didn't know existed before, and their associated atmospheric forcing; the combination of GRACE OBP with altimetry-derived sea surface height, resulting in changes and distribution of the freshwater content of the Arctic Ocean; and more recently, the combination of GRACE OBP with mooring data from Bering Strait from 2002 to 2016, to investigate the driving mechanisms of the oceanic flow into the Arctic through the strait. The Bering Strait flow is known to be driven by local winds and a (poorly defined) far-field “pressure-head” forcing, typically related to sea surface height differences between the Pacific and the Arctic. We identify the spatial structure of this pressure-head forcing, finding that the variability of the Bering Strait throughflow is predominantly driven from the Arctic (not the Pacific), specifically by sea level changes in the East Siberian Sea, and related to westward winds along the Siberian shelves. This pressure-head forcing explains ~70% of the Bering Strait flow variability during the summer, when the local winds are weak. During the winter, however, both the local winds and the pressure-head forcing are important.