Ventilation and mixing of surface and intermediate waters in the tropical Atlantic: perspectives from Lagrangian particles and tracers

Texas A&M University, College Station TX

Investigators

Abstract

The net movement of surface and intermediate waters in the Atlantic basin is northward: waters enter the basin south of Africa and South America, and sink in the North Atlantic. The project will examine how northward flowing water masses are modified in the Tropical Atlantic before they reach the North Atlantic. Understanding the effects of ocean ventilation and mixing on this water's properties is essential to explain modern Atlantic Meridional Overturning Circulation (AMOC) variability, heat transport, and to prediction of how changes in Southern Ocean carbon uptake might impact the North Atlantic carbon sink. This work is also pertinent to understanding local societally-relevant processes in the Tropical Atlantic region, such as how oxygen reaches central waters in the western equatorial Atlantic, and how heat transport by the AMOC affects the location of the Intertropical Convergence Zone. Broader impacts include support of an early career investigator, public education, scientific workforce training, and model development. Both particles and tracers will be advected for 60yrs in two different global versions of MOM6: a 1/4deg resolution version and a 1/8deg resolution version. Existing code (from the PI) that advects Lagrangian particles online in MOM6’s native coordinate system creates accurate particle trajectories by performing particle advection online. This code will be further developed to include a stochastic advection term to parameterize subgrid-scale processes. Using a variety of methods, including probability density functions and the water mass transformation framework, locations where water properties are exchanged between the North Brazil Current and the surrounding water will be identified. The transfer matrix will be used to objectively identify the most likely pathway of a particle from 10S to 10N in the Atlantic basin. How model resolution affects ocean particle pathways and the timescales on which particles travel northward will be investigated. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.