Arctic Ocean Circulation Patterns Revealed by Ocean Bottom Pressure Anomalies

Abstract

Over the last few decades, the Arctic Ocean has experienced drastic changes that include increased temperature, changes in freshwater distribution, and decrease in sea ice extent and thickness. These changes, which potentially affect global climate, are intimately linked to changes in the Arctic Ocean circulation. Thus, understanding Arctic Ocean circulation patterns is fundamental to monitoring and predicting the fate of the Arctic System. Since 2002, NASA's Gravity Recovery and Climate Experiment (GRACE) has provided continuous measurements of the time-varying gravity field of the Arctic Ocean. The gravitational variations represent mass variations, or the time-varying ocean bottom pressure (OBP) field. OBP variations are the sum of the mass change due to the sea surface height change and the integrated density variations through the water column. In this dissertation, <italic>in situ</italic> and GRACE measurements of OBP anomalies, complemented by information from ocean models, are used to investigate the relative contribution of sea surface height and density-variations on the Arctic OBP field. The dynamics associated with the observed OBP changes are investigated. Major findings include the identification of three primary temporal-spatial modes of OBP variability at monthly to inter-annual timescales with the following characteristics: - Mode 1 is a wintertime basin-coherent Arctic mass change forced by southerly winds through Bering and Fram Straits. - Mode 2 reveals mass change along the Siberian shelves, driven by surface Ekman dynamics and associated with the Arctic Oscillation. - Mode 3 reveals a mass drop in Western Arctic shelves forced by the strengthening of the anticyclonic Beaufort Gyre, and wintertime along-shore westerly winds that increase OBP in the Eastern Arctic shelves. The OBP changes in the Kara Sea reveal a more baroclinic ocean character than modeling results have previously suggested, due to the complex bathymetry of this region and runoff-derived large density changes through the water column. This work integrates the character of the Arctic mass changes at different timescales, and provides information about the ocean mass re-distribution during years of rapidly thinning and disappearing seasonal sea ice.