Abstract
Oceanic mesoscale eddies play a profound role in mixing tracers such as heat, carbon and nutrients, thereby regulating regional and global climate. Yet, it remains unclear how the eddy field has varied over the past few decades. Furthermore, climate model predictions generally do not resolve mesoscale eddies, which could limit their accuracy in simulating future climate change. Here we show a global statistically significant increase of ocean eddy activity using two independent observational datasets of surface mesoscale eddy variability (one estimates surface currents, and the other is derived from sea surface temperature). Maps of mesoscale variability trends show heterogeneous patterns, with eddy-rich regions showing a significant increase in mesoscale variability of 2–5% per decade, while the tropical oceans show a decrease in mesoscale variability. This readjustment of the surface mesoscale ocean circulation has important implications for the exchange of heat and carbon between the ocean and atmosphere.
Highlights
Version of Record: A version of this preprint was published at Nature Climate Change on April 22nd, 2021
It remains unclear how global oceanic eddy kinetic energy has evolved over the past few decades
Coupled climate model predictions generally fail to resolve oceanic mesoscale dynamics, which could limit their accuracy in simulating future climate change
Summary
Version of Record: A version of this preprint was published at Nature Climate Change on April 22nd, 2021. Oceanic eddies play a profound role in mixing tracers such as heat, carbon, and nutrients, thereby regulating regional and global climate. Mesoscale eddies are ubiquitous in the global ocean and feed back onto all scales, from regional processes[10] up to the meridional overturning circulation[3 ] These eddies act to transport and mix tracers such as heat, salt, and nutrients . We use two independent datasets, namely AVISO+ SSH and NOAA optimal interpolated sea surface temperature (OISST)[23 ], to estimate EKE and SST gradients respectively These fields are temporally smoothed using a running average of 12 months; the trends and the significance of each field are computed using a linear regression and a modified Mann–Kendall test[24] (see Methods for further details). We explore the mesoscale time-series for the global ocean, for individual ocean basins, and over regions characterized by their dynamical properties
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