Ocean mesoscale mixing linked to climate variability

Abstract

Mesoscale turbulence in the ocean strongly affects the circulation, water mass formation, and transport of tracers. Little is known, however, about how mixing varies on climate timescales. We present the first time-resolved global dataset of lateral mesoscale eddy diffusivities at the ocean surface, obtained by applying the suppressed mixing length theory to satellite-observed velocities. We find interannual variability throughout the global ocean, regionally correlated with climate indices such as ENSO, NAO, DMI, and PDO. Changes in mixing length, driven by variations in the large-scale flow, often exceed the effect of variations in local eddy kinetic energy, previously thought of as the primary driver of variability in eddy mixing. This mechanism, not currently represented in global climate models, could have far-reaching consequences for the distribution of heat, salt, and carbon in the global ocean, as well as ecosystem dynamics and regional dynamics such as ENSO variance.