EESS Winter Seminar Series, Assistant Professor Leif Thomas, EESS, Stanford
EESS Winter Seminar Series, Assistant Professor Leif Thomas, Environmental Earth System Science, Stanford, "Mixing at the gyre boundary: Discovery of wave breaking and a new form of ocean turbulence in the Gulf Stream front", Abstract: The Gulf Stream front marks the sharp boundary between the subtropical and subpolar gyres in the North Atlantic. Crossing the front, the seawater rapidly transitions from the salty, warm, nutrient-poor waters of the subtropics to the fresh, cold, nutrient-replete waters of the subpolar gyre over a distance of about 10 km.
The mixture of these distinct waters and its subsequent transport by the ocean circulation supplies nutrients to the subtropics and salt to the high-latitudes, and has direct implications for climate: it facilitates a biologically-induced drawdown of atmospheric CO2 in the subtropics and the formation of North Atlantic Deep Water that feeds the thermohaline circulation. This mixing at the gyre boundary involves motions that span 100 m to 10 km in the horizontal. These so-called submesoscale flows have been relatively unexplored both observationally and theoretically, and their physics is currently missing in climate models.
In this seminar I will describe observations collected on a research cruise to the Gulf Stream in the winter of 2012 that reveal a new form of submesoscale turbulence and how the front acts as a surf zone, where internal waves that ride on the ocean’s density surfaces break. These findings are consistent with theoretical predictions and high-resolution numerical simulations of submesoscale flows performed by my group. We find that the lateral mixing on the submesoscale at the Gulf Stream front is significant, and, in particular, is large enough to sustain the nutrient supply to the subtropical gyre needed to explain the primary production and carbon sequestration estimated for this region.