Surface cooling caused by rare but intense near-inertial wave induced mixing in the tropical Atlantic

Abstract:

The direct response of the tropical mixed layer to near-inertial waves (NIWs) has only rarely

been observed. Here, we present upper-ocean turbulence data that provide evidence for a

strongly elevated vertical diffusive heat flux across the base of the mixed layer in the presence

of a NIW, thereby cooling the mixed layer at a rate of 244Wm−2 over the 20 h of

continuous measurements. We investigate the seasonal cycle of strong NIW events and find

that despite their local intermittent nature, they occur preferentially during boreal summer,

presumably associated with the passage of atmospheric African Easterly Waves. We illustrate

the impact of these rare but intense NIW induced mixing events on the mixed layer heat

balance, highlight their contribution to the seasonal evolution of sea surface temperature, and

discuss their potential impact on biological productivity in the tropical North Atlantic.