How does coastline shape influence meridional overturning and ocean heat transport?
Sarah Ragen, University of Washington, School of Oceanography, Seattle, United States, Kyle Armour, University of Washington, Dept. of Atmospheric Sciences and School of Oceanography, Seattle, United States, Andrew Shao, University of Victoria, School of Earth and Ocean Sciences, Victoria, BC, Canada, Elizabeth Maroon, University of Wisconsin Madison, Madison, WI, United States and LuAnne Thompson, University of Washington, Oceanography, Seattle, WA, United States
Abstract:
Hierarchies of idealized ocean models are critical tools for building understanding of large-scale climate-relevant phenomena like northward ocean heat transport (OHT) and the meridional overturning circulation (MOC). Previous studies used aquaplanet simulations with simple meridional continental barriers to examine their influence on OHT, the localization of deep convective sites and meridional overturning, and global climate. Here, we use a state-of-the art ocean—sea-ice model (MOM6 and SIS2) with idealized, zonally-symmetric surface forcing and a range of idealized continental configurations to answer the following questions: How much does the shape of the Atlantic basin coastlines affect northward OHT and the MOC? Does the shape of the eastern boundary or the western boundary play a larger role? How do basin width and coastline shape modulate the subtropical overturning cells and associated OHT?
We consider the ocean circulation in a large Pacific-like basin and a small Atlantic-like basin and explore four different coastline geometries along the small basin: 1) straight meridional boundaries used as a control case, 2) a western boundary shaped like a simplified version of the east coast of the Americas to target the impact on the western boundary currents, 3) an eastern boundary like the African west coast to investigate cross-equatorial OHT, and 4) realistic boundaries on both sides of the basin to estimate any nonlinear effects on overturning and heat transport caused by the shape of both coasts. With realistically shaped coastlines in the small basin, the MOC and the northward OHT strengthen by about 10 Sv and 4 PW respectively, both an increase of about 30%. Because of the zonally-symmetric atmospheric forcing, asymmetries that arise between the basins must be due to ocean circulation driven by coastline geometry of the small basin.
