Evolving Southern Ocean overturning in warming climates

Area of Science:

• Climate Science
• Oceanography
• Paleoclimatology

Background:

• The Southern Ocean Meridional Overturning Circulation (MOC) has intensified recently.
• Future changes in its Eulerian and eddy components under warming are uncertain.

Purpose of the Study:

• To investigate the interplay between Eulerian and eddy components of the Southern Ocean MOC under future warming scenarios.
• To compare future MOC responses with past warming events like the Mid-Pliocene Warm Period.

Main Methods:

• Utilizing ensemble climate simulations for future projections.
• Analyzing paleoclimate data for the Mid-Pliocene Warm Period.

Main Results:

• Eulerian-mean MOC shifts poleward under high emissions, with eddy compensation maintaining uniform residual overturning.
• Low-emission scenarios show a less pronounced MOC shift.
• The Mid-Pliocene Warm Period showed a poleward Eulerian-mean MOC shift with weaker eddy compensation, resulting in non-uniform residual overturning.
• Eddy-induced MOC is modulated by surface heat and freshwater fluxes, driving Antarctic upwelling and bottom water formation.

Conclusions:

• Southern Ocean MOC dynamics exhibit distinct responses to past and future warming.
• Buoyancy forcing changes are key drivers of Antarctic upwelling and ventilation in warming climates.
• Ocean ventilation intensifies in the Southern Ocean's lower latitudes, particularly during past warm periods.