Abstract
Double diffusion can result in the formation of thermohaline staircases, typically observed in the ocean interior. The observations presented here were acquired in the ocean surface boundary layer with the autonomous microstructure Air‐Sea Interaction Profiler. An intense rain event (rainfall rates of up to 35 mm/h) resulted in cooler, fresher water (up to 0.15 practical salinity unit (psu) over the upper 7–10 m) overlaying warmer, saltier water, a situation potentially conducive to double‐diffusive mixing. Although not as crisp as interfaces in the interior ocean because of elevated background mixing, a total of 303 thermohaline interfaces were detected within and at the base of the fresh layer, with mean changes in temperature (T) and salinity (S) across interfaces of 20 × 10−3∘C and 22 × 10−3 psu, respectively. These results call for new studies to disambiguate whether such interfaces are formed through double‐diffusive mixing or shear instabilities and understand any long‐term impacts on near‐surface stratification.
Key Points
We made microstructure observations in the upper ocean during a rain event
We observed thermohaline interfaces associated with double diffusion
Double‐diffusive mixing may occur in the tropics as a result of rain
