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Temporal variability of the South Atlantic Meridional Overturning Circulation between 20°S and 35°S


The Meridional Overturning Circulation plays a critical role in global and regional heat and freshwater budgets by carrying water properties northward and southward within individual ocean basins. This Climate Observation Division-supported research, published in Geophysical Research Letters, examines altimetry-derived synthetic temperature and salinity profiles between 20°S and 34.5°S to estimate the Meridional Overturning Circulation (MOC) and meridional heat transport (MHT).
According to Dong et al., MOC strength shows intense variation depending on time scales and latitude. “These variations in the MOC can have a pronounced impact on a variety of important climate phenomena,including Atlantic hurricane activity, precipitation and air temperature variability over North America and western Europe, and changes in African and Indian monsoon rainfall,” said the paper.
“Quantifying MOC changes over time and understanding its underlying mechanisms are, therefore, crucial for improving our knowledge of how the climate system functions and for assessing climate models and future climate change,” said the researchers. “A comprehensive MOC observing system is needed to gain a more complete understanding of its behavior.”
In this study, the researchers aimed to enhance the understanding of the MOC and MHT variability in the South Atlantic–in particular the changes on seasonal to interannual time scales. In order to meet this aim, sea surface height measurements from satellite altimetry, combined with in situ measurements, were used to estimate the MOC and MHT. Specifically, they hoped to assess how well altimetry could be used to investigate the spatial and temporal variability of the MOC and MHT and how the contributions of density and wind fields to the MOC and MHT change with time and latitude.
The study’s key points:

  • Geostrophic (Ekman) component dominates the interannual variations in the MOC before (after) 2006
  • Satellite altimeter data can be used to estimate MOC/MHT in the South Atlantic
  • The strongest MOC variations on seasonal and interannual time scales are found at 34.5°S

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