Eddy compensation dampens Southern Ocean sea surface temperature response to westerly winds

Edward Doddridge, John Marshall, Hajoon Song, Maxwell Kelley & Larissa Nazarenko

Abstract

Anthropogenic influences have led to a strengthening and poleward shift of the westerly winds over the Southern Ocean (SO), especially during austral summer. We use observations, an idealized eddy-resolving ocean-ice channel model, and a global coupled climate model to explore the response of the SO to a step-change in the westerly wind. Previous work hypothesized a two timescale response for sea surface temperature. Initially, Ekman transport cools the surface before sustained upwelling causes warming on decadal timescales. We find that the fast response is robust across our models and the observations: we find Ekman-driven cooling in the mixed layer, mixing-driven warming below the mixed layer, and upwelling-driven warming at the temperature inversion. The long-term response is inaccessible from observations. Neither of our models shows a persistent upwelling anomaly, or long-term, upwelling-driven, sub-surface warming. Our results highlight the importance of accurately representing the eddy-driven contribution to the residual overturning circulation.

 

Code for computing heat budgets

The Python code used to calculate the heat budgets presented in this paper can be found here.