Meeting Documents

Water Mass Transformation in the Arctic Ocean from Observationally Constrained Ocean State Estimates

Abstract

Located at the northern terminus of the Atlantic Meridional Overturning Circulation (AMOC), water mass transformations in the Arctic Ocean are important for both regional dynamics and the global ocean circulation. Understanding how inflowing Atlantic Water – and to a lesser extent Pacific Water – is modified within the Arctic Ocean is crucial, especially in a rapidly changing Arctic climate. Water mass transformation occurs through both interior mixing and surface buoyancy fluxes, with ongoing sea ice loss introducing complex and sometimes opposing effects. For example, while declining sea ice formation reduces brine rejection, which may weaken dense water formation, the retreat of sea ice cover also enhances atmosphere-ocean coupling, potentially intensifying cooling of exposed Atlantic Water, which promotes dense water formation. The net impact of these sometimes competing processes on future Arctic water mass transformation remains uncertain.

The water mass transformation (WMT) framework in density space provides an integrated approach to quantify how waters across different density classes are modified by various processes. We apply this framework to the Arctic Ocean using two observationally constrained ocean state estimates: the global ECCO-V4r4 and the regional Arctic Subpolar gyre sTate Estimate (ASTE R1). We compare these products and analyze temporal changes in Arctic WMT throughout their respective periods of coverage, with particular emphasis on the lightening and densification of the Atlantic Water layer. Additionally, we investigate spatiotemporal patterns in surface WMT to better understand the evolving role of air-sea interactions in shaping Arctic Ocean properties.