South Atlantic Meridional Overturning Circulation: Pathways and Modes of Variability

Previous observational and modeling efforts on the meridional overturning circulation (MOC) have been focused on the North Atlantic and the Southern Oceans, which are the preferential sites for deep-water formation. Our pending challenge is to understand how the dynamical and thermodynamical processes controlling the MOC in these two basins relate to each other, in particular how they will react to changing climate conditions. To understand the feedbacks between the North Atlantic and the Southern Oceans we need to improve our understanding of the pathways of the upper and lower limbs of the MOC in the South Atlantic (SA) Ocean, which are the most important links between them. The SA is not just a passive conduit for the transit of remotely formed water masses, but actively influences them through air–sea interactions, mixing, subduction, and advection. Therefore, we intend to characterize the pathways of the upper and lower limb of the MOC in the SA and identify the dynamical mechanisms that control these pathways. The study will focus on identifying the natural modes of variability in the SA and their impact on the MOC. We will also determine the response of the SA pathways to predicted climate change scenarios and assess the impact of this response on the MOC.

Our research will focus on the analysis of state-of-the-art eddy-permitting and eddy-resolving NOAA/GFDL climate model simulations. Specifically, we will use a suite of experiments done with the CM2.5 and CM2.6 coupled models, which were forced with present day conditions and different climate change scenarios. We intend to compare those simulations against the noneddying Coordinated Model Intercomparison Project and Intergovernmental Panel on Climate Change Fifth Assessment Report models including the NOAA/GFDL coarse resolution models (CM2.1, CM3), a suite of process-oriented numerical experiments using regional ocean models, and global in-situ and satellite observations. This project will be conducted by PIs at the Cooperative Institute for Marine and Atmospheric Studies (CIMAS), Oregon State University (OSU) and NOAA/Atlantic Oceanographic and Meteorological Laboratory (NOAA/AOML), in collaboration with Rym Msadek at University Corporation for Atmospheric Research (UCAR) and NOAA/Geophysical Fluid Dynamics Laboratory (NOAA/GFDL).

This proposal is relevant to the Atlantic MOC (AMOC) Mechanisms and Decadal Predictability priority for the Earth System Science program and the NOAA Strategic Goal: Climate Adaptation and Mitigation – Improved scientific understanding of the changing climate system and its impacts. The proposed research is consistent with CIMAS Research Theme 1: Climate Research and Impact and Theme 4: Ocean Modeling. Our proposed collaboration with NOAA/GFDL will help in the development and refinement of next generation of climate models. This project will also contribute to the international SAMOC field program to measure the strength and variability of the MOC as well as the meridional heat and fresh-water transport across 34.5°S in the SA, which has been endorsed by the International CLIVAR Scientific Steering Group.