Environmental Science and Engineering Seminar

The Texas-Louisiana shelf in the northern Gulf of Mexico faces numerous environmental pressures ranging from frequent hurricanes and marine heatwaves to seasonal hypoxia resulting in one of the world's largest oxygen dead zones. The vertical exchange of heat and oxygen between the ocean surface and the interior is a key control on these phenomena. Using examples from the Submesoscales Under Near-Resonant Shear Experiment (SUNRISE), I will demonstrate two mechanisms that drive vertical exchange. Both involve the interaction of near-inertial waves (NIWs), unbalanced motions forced by the winds, with lateral density gradients – fronts. In the first mechanism, NIWs periodically destabilise a front, pushing dense water over light, leading to the localised mixing of momentum that induces an overturning circulation. This secondary circulation not only restratifies the front but also exchanges warm, oxygenated surface water with the interior. The second mechanism is the refraction of NIWs by the fronts. Through refraction, horizontal motions forced by the winds become aligned with the sloping density surfaces at the fronts. Now slantwise, the waves directly facilitate vertical exchange.