Indian Ocean warming as a driver of the North Atlantic warming hole

Shineng Hu,Alexey V Fedorov

doi:10.1038/s41467-020-18522-5

Abstract

Over the past century, the subpolar North Atlantic experienced slight cooling or suppressed warming, relative to the background positive temperature trends, often dubbed the North Atlantic warming hole (NAWH). The causes of the NAWH remain under debate. Here we conduct coupled ocean-atmosphere simulations to demonstrate that enhanced Indian Ocean warming, another salient feature of global warming, could increase local rainfall and through teleconnections strengthen surface westerly winds south of Greenland, cooling the subpolar North Atlantic. In decades to follow however, this cooling effect would gradually vanish as the Indian Ocean warming acts to strengthen the Atlantic meridional overturning circulation (AMOC). We argue that the historical NAWH can potentially be explained by such atmospheric mechanisms reliant on surface wind changes, while oceanic mechanisms related to AMOC changes become more important on longer timescales. Thus, explaining the North Atlantic temperature trends and particularly the NAWH requires considering both atmospheric and oceanic mechanisms.

Highlights

Over the past century, the subpolar North Atlantic experienced slight cooling or suppressed warming, relative to the background positive temperature trends, often dubbed the North Atlantic warming hole (NAWH)
Following our observational analysis and coupled model simulations, we argue that the historical NAWH can potentially result from the strengthening of overlying surface westerly winds and the latter can be remotely driven by the concurrent Indian Ocean warming
While the NAWH was developing, surface westerly winds over the subpolar North Atlantic significantly strengthened since the a Extended Reconstructed Sea Surface Temperature (ERSST) v4

Summary

Introduction

The subpolar North Atlantic experienced slight cooling or suppressed warming, relative to the background positive temperature trends, often dubbed the North Atlantic warming hole (NAWH). A recent modeling study identified a similar NAWH pattern in atmospheric simulations coupled to a mixedlayer ocean wherein the effects of large-scale ocean circulation were suppressed, suggesting that the NAWH could be driven solely by atmospheric processes[10]. In another example, in-situ measurements reveal that wind-induced cooling was probably responsible for the substantial heat loss in the Irminger Sea during the winter of 2014–201511. Following our observational analysis and coupled model simulations, we argue that the historical NAWH can potentially result from the strengthening of overlying surface westerly winds and the latter can be remotely driven by the concurrent Indian Ocean warming. We find that on longer timescales the Indian Ocean warming will warm the subpolar North Atlantic by strengthening the AMOC, and we treat this analysis as a case study of the relative importance of wind versus AMOC changes for the NAWH

Methods

Results

Conclusion