11 May 2016

Mechanisms of Southern Ocean Heat Uptake and Transport

Investigating the role of eddies and changing ocean circulation

Science

The Southern Ocean dominates global ocean heat uptake under climate change, because of the unique upwelling of deep waters. The upwelling in the Southern Ocean maintains a relatively constant sea surface temperature, even as the atmosphere above warms, thus allowing for sustained ocean heat uptake.

Impact

Over recent decades, the ocean has absorbed 93% of the additional energy in the climate system arising from global warming. Subsurface ocean heat gain has had a beneficial impact thus far through limiting atmospheric warming. However, ocean heat gain also leads to increasingly significant sea level rise, slower ocean carbon uptake, and potentially accelerated melting of the Antarctic ice sheets.

Summary

The Southern Ocean plays a dominant role in anthropogenic oceanic heat uptake. The air-sea heat flux anomaly is largest in the far south, collocated with the upwelling of deep waters to the surface. There is a strong northward transport of the heat content anomaly from the high-latitude uptake region into the mid-latitudes of the Southern Ocean. The combination of upwelling of old deep waters from below and northward transport of the heat content anomaly limits the warming of the sea surface temperature and allows the heat uptake to be sustained.

Using an eddy-rich global climate model with increasing CO2, we investigated the processes controlling the northward transport and convergence of the heat anomaly in the mid-latitude Southern Ocean. Heat budget analyses reveal that different processes dominate to the north and south of the main convergence region in the mid-latitudes. The heat transport in the south is driven primarily by passive advection of the heat content anomaly by the existing circulation, with a smaller 20% contribution from enhanced upwelling. In the northern part of the Southern Ocean, eddy processes drive the warming and account for nearly 80% of the northward heat transport anomaly.

Contact
Adele Morrison
Princeton University
Publications
Morrison, AK, SM Griffies, M Winton, WG Anderson, and JL Sarmiento.  2016.  "Mechanisms of Southern Ocean Heat Uptake and Transport in a Global Eddying Climate Model."  Journal of Climate 29: 2059-2075.