AOML Scientists Develop First-ever Daily Estimates of the Heat Transport in the South Atlantic Ocean

In a recent article published in the Journal of Geophysical Research – Oceans, scientists at AOML and the Cooperative Institute for Marine and Atmospheric Studies (CIMAS) evaluate the variability of the heat transport in the South Atlantic by developing a new method to measure its changes on a daily basis. This study presents, for the first time, full‐depth, daily measurements of the volume and heat transported by the Meridional Overturning Circulation (MOC) in the South Atlantic at 34.5°S based on direct observations.

Flow patterns in the South Atlantic are thought to control the stability of the entire global MOC system. The MOC is a component of global ocean circulation that plays a major role in redistributing heat, salt, dissolved oxygen, and carbon throughout the global climate system. Variations of the MOC and the associated transport of heat, known as Meridional Heat Transport (MHT), have important societal impacts on coastal sea levels, marine heat waves, extreme weather events, and shifts in regional surface temperature and precipitation patterns, all of which can directly impact human resources (agriculture, fisheries, infrastructure, etc.) and health around the globe.

A schematic of the Meridional Overturning Circulation (MOC).

The southern end of the South Atlantic Ocean serves as the gateway for water masses formed in the Pacific, Indian, and Southern oceans to exchange, mix, and flow into the Atlantic Ocean.  However, due to difficulty in observing the MOC and its heat transport, many questions remain about these key oceanic flows. 

“The South Atlantic plays a unique role in the overturning circulation, as the only basin transporting heat towards the equator and connecting the North Atlantic to the other oceans basins,” said Marion Kersale, AOML/CIMAS scientist and lead author of the study. 

To solve this problem, scientists at AOML investigated the volume of water and heat transports at the southern end of the South Atlantic by developing a new technique for estimating full-depth temperature profiles. This technique used a data set from a basin-wide array of moored oceanographic sensors at 34.5°S – the international South Atlantic MOC Basin-wide Array (SAMBA). The instruments anchored to the seafloor that are traditionally used to gather temperature profiles are too widely-spaced throughout the basin and therefore miss key details of the interior heat structure of the MOC. A new method using satellite, CTD (Conductivity, Temperature, and Depth), and Argo profiling float observations was developed and used to fill in these gaps. 

A CTD package is deployed to collect ocean observations. Image Credit: NOAA.

This new technique produced ~4 years of daily estimates of heat transport in the South Atlantic Ocean. The data gathered from the study revealed seasonal and interannual changes of these important oceanic flows with strong variations at time scales of a few days to a few weeks. During this time period the northward heat transport can increase to twice its mean value. The observations show that the volume and heat transports vary in a consistent manner with one another. 

“This allows us to use some earlier moored observations from a pilot version of the array, extending the record further back in time and producing ~6 years of daily estimates of heat transport. To do so, MOC volume transport is used as a proxy for heat transport. Going forward, we can use the MOC volume transport to estimate heat transport operationally, until a more detailed and accurate heat transport calculation can be made,” said Renellys Perez, AOML scientist.

The resulting data set from this study will be highly valuable for validating and improving ocean and climate models both at NOAA and around the globe. These improved models will enable scientists to make more accurate forecasts for our changing climate.

a) SAMBA mooring locations (green squares) and heat content in the South Atlantic. (b) Temporal variability of the total MHT at 34.5°S.

This research supports the AtlantOS program’s vision to deliver an advanced framework for the development of an integrated Atlantic Ocean Observing System that goes beyond the state-of–the-art, and benefits all of us living, working and relying on the ocean.