The Lifecycle of Tracer Variance in the North Atlantic

What is it about?

Horizontal and vertical temperature contrasts in the ocean are mixed away due to the stirring effect of kilometre‐scale swirls and centimetre‐scale turbulence. This mixing affects the ocean storage of heat, modifying how heat is transferred from the surface into the ocean interior. In this work, mixing is quantified over the North Atlantic Ocean by applying a new methodology to thousands of observations from profiling floats. In the centre of the subtropical gyre, heat is mixed vertically by centimetre‐scale turbulence. Over the flanks of the subtropical gyre and in the subpolar region, heat is instead stirred horizontally by kilometre‐scale eddies, creating warm and cold filaments. In regions of strong flows, these warm and cold filaments are carried by ocean currents for hundreds of kilometres before they blend into surrounding waters, resulting in mixing far away from the location where stirring happens.

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Photo by Jeremy Bishop on Unsplash

Photo by Jeremy Bishop on Unsplash

Why is it important?

In this paper, we expand the theory for diagnosing the contributions of microscale diapycnal (across density layers) and mesoscale isopycnal (along density layers) turbulence to the mixing of heat and salt by explicitly including the transport of property filaments by the ocean currents. The evaluated mixing and stirring processes ultimately affect how the global ocean sequesters anthropogenic heat in a warming climate. The observed patterns may carry over to the rest of the global ocean.