The South Atlantic AMOC Abyssal Cell from Observations and Models

• Grant number: 24/22376-7
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: August 01, 2025
• End date: July 31, 2027
• Field of knowledge: Physical Sciences and Mathematics - Oceanography - Physical Oceanography
• Principal Investigator: César Barbedo Rocha
• Grantee: Maurício Rebouças Rocha
• Host Institution: Instituto Oceanográfico (IO). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 23/10506-0 - Small scales matter: the role of submesoscale dynamics in large-scale ocean circulation and climate, AP.JP

Abstract

Winds and tides primarily drive the mass flow in the ocean. When integrated zonally across the basin and vertically, this flow results ain the so-called meridional overturning circulation (MOC, or AMOC for the Atlantic component). The AMOC transports heat northwards, contributing to a global positive interhemispheric heat content gradient. Due to observational limitations, accurately representing the AMOC in numerical simulations is crucial for a better understanding of changes in the climate system. However, a preliminary analysis indicates that the Community Earth System Model (CESM), version 2, large ensemble, released in 2021 by the National Center for Atmospheric Research, can represent the AMOC upper cell but misses significant aspects of the structure and variability of the abyssal cell. This could also be a common issue in other 1-degree, coarse-resolution climate models from the Coupled Model Intercomparison Project. In 1/10 degree high-resolution CESM simulations, the AMOC transport shows increased (but still much smaller) variability than observations in the deep/abyssal ocean. By hypothesis, larger discrepancies between models and observations regarding volume transport occur in the AMOC abyssal cell because vertical mixing is more relevant for this cell, and the resolution and topography play a crucial role in determining turbulence. This proposal aims to test this hypothesis. To that end, we will first revisit the AMOC cells' definition and compare the representation of the AMOC abyssal cell in numerical simulations from different resolutions with observations regarding means, trends, and variability, focusing on the South Atlantic. Next, we will quantify the AMOC abyssal cell differences between models and observations and investigate the processes that can explain these differences. Our proposal will advance new knowledge into the AMOC abyssal cell as well as support the climate modeling community, which spends a great deal of effort trying to simulate the AMOC. In doing so, we hope to contribute to paving the way for more accurate climate projections.