Speaker

Xuan Shan, Ph.D., Postdoctoral Fellow, Woods Hole Oceanographic Institution

High-Resolution Climate Model Projections of Beaufort Gyre Freshwater and AMOC Decline

Abstract

Increased liquid freshwater supply to the Arctic Ocean in a warming climate makes high-latitude regions susceptible to dramatic changes. To investigate future freshwater changes in the Arctic and Subarctic regions and its influence on the AMOC, we use an eddy-resolving (0.1-degree ocean) CESM simulation following the CMIP5 protocol. The Beaufort Gyre liquid freshwater content (LFWC) and its decadal variability increases under GHG warming in the simulation. Its long-term increase from 1960-2030 is mainly due to meltwater from sea ice, that from 2030-2100 is owing to stronger anticyclonic surface stress curl. The latter is caused by more efficient air-sea momentum transfer with weaker sea ice rather than a stronger wind forcing. The enhanced LFWC variability is attributed to both stronger variability in wind and strengthened air-sea momentum transfer. Although the strong decadal variability of the Beaufort Gyre LFWC sheds light on the Arctic freshwater export, it does not have significant impact on the subpolar overturning. In the Labrador Sea, the freshwater from the Davis Strait is carried by the Labrador Current which is trapped by topography. In that case, the freshwater goes directly to further downstream along the shelf instead of spreading into the interior Labrador Sea and reducing the deep convection in our simulation. Contrast with high-resolution simulation, its 1-degree counterpart allows freshwater into convection region and shuts down Labrador overturning by the end of the 21st century. Our study implies that traditional climate models may overestimate the role of freshwater and the AMOC weakening in the future.