Effects of Drake Passage on a strongly eddying global ocean

TL;DR

This study uses an eddy-resolving global ocean model to investigate how the opening of Drake Passage affected heat transport and circulation during the Eocene-Oligocene transition, highlighting the importance of model resolution.

Contribution

It provides a detailed comparison between eddy-resolving and non-eddying models, revealing resolution-dependent differences in climate response mechanisms.

Findings

Closing Drake Passage warms Antarctica by 2.5°C in eddy-resolving model

Non-eddying model shows larger Antarctic warming of 5.5°C

Eddy heat transport near Antarctica is significant and resolution-dependent

Abstract

The climate impact of ocean gateway openings during the Eocene-Oligocene transition is still under debate. Previous model studies employed grid resolutions at which the impact of mesoscale eddies has to be parameterized. We present results of a state-of-the-art eddy-resolving global ocean model with a closed Drake Passage, and compare with results of the same model at non-eddying resolution. An analysis of the pathways of heat by decomposing the meridional heat transport into eddy, horizontal, and overturning circulation components indicates that the model behavior on the large scale is qualitatively similar at both resolutions. Closing Drake Passage induces (i) sea surface warming around Antarctica due to changes in the horizontal circulation of the Southern Ocean, (ii) the collapse of the overturning circulation related to North Atlantic Deep Water formation leading to surface cooling in the North Atlantic, (iii) significant equatorward eddy heat transport near Antarctica. However, quantitative details significantly depend on the chosen resolution. The warming around Antarctica is substantially larger for the non-eddying configuration (5.5{degree sign}C) than for the eddying configuration (2.5{degree sign}C). This is a consequence of the subpolar mean flow which partitions differently into gyres and circumpolar current at different resolutions. We conclude that for a deciphering of the different mechanisms active in Eocene-Oligocene climate change detailed analyses of the pathways of heat in the different climate subsystems are crucial in order to clearly identify the physical processes actually at work.