Collaborative Research: Autonomous sampling of upper ocean mixing in the Southern Ocean due to wind forcing and double-diffusion
The Southern Ocean is responsible for about half the uptake of anthropogenic carbon and an even larger fraction of the atmosphere's flux of heat into the sea. The Southern Ocean is the only sector of the global ocean that connects all three major ocean basins through the Meridional Overturning Circulation (MOC). Despite its importance, the region is under sampled largely due to its remote location and severe conditions. The dearth of observations in the Southern Ocean is not limited to ocean measurements. Meteorological measurements such as wind speed and heat fluxes are scarce and often from sensors mounted on sparse ship traffic. With the maturing of autonomous platforms, there is now an opportunity to collect high-resolution spatial and temporal measurements in the full range of conditions characteristic of the Southern Ocean. While climate models have advanced substantially, the inadequate representation of unresolved mixing processes is still a significant source of error. This is perhaps the most severe in the near-surface boundary layer of the ocean where Langmuir physics, frontal processes, and double-diffusion are active in the Southern Ocean, yet the lack of observations have slowed progress in developing parameterizations. This novel observational study will allow sampling of the upper-ocean physics of this region on spatial and timescales much shorter than those sampled during previous experiments, allowing the resolution of inertial and diurnal processes forced by winds and radiation, and on spatial scales that give insight into the turbulent cascade influencing the upper ocean. The results from this project will lead to more realistic parameterizations of subgrid-scale processes in numerical models of ocean circulation, of the coupled ocean-atmosphere system and of climate models. The proposed project will recruit two undergraduate summer fellow through the Women in Science At Yale (WISAY) to provide them hands-on experience in using autonomous platforms to sample the ocean. This project is motivated by the need to understand the overturning circulation of the global ocean in a region that is both rich in small-scale physical processes and severely under-sampled. This circulation governs the transport and storage of heat and carbon dioxide within the huge oceanic reservoir, and thus plays a major role in regulating the Earth's climate. The specific goals of this project are to 1) obtain measurements of turbulent dissipation rates, temperature, salinity and fluorescence in the upper 1000 m collocated with surface wave spectral data and meteorological measurements. The use of autonomous platforms will provide a dataset with unprecedented spatial and temporal resolution of mixing in the Southern Ocean and 2) investigate the turbulent response of the upper ocean to the extreme surface forcing (wind stress, radiative fluxes) in the Southern Ocean. The dataset will eliminate the fair-weather bias of shipboard measurements and will provide motivation for theoretical and model studies of submesoscale and boundary layer dynamics in the region. The study will be conducted in the region of the ACC fronts between Drake Passage and the Argentine Basin. A Wave Glider and drifter constellation will measure wind, waves, air temperature and radiation quantities, and sea surface temperature and salinity. Gliders with microstructure sensors will measure temperature and salinity fine structure and turbulence in the upper 1000 m of the water column where the eddy field is active and water masses interact, and in the near-surface boundary layer where the ocean interacts with the atmosphere. At the end of the deployment the glider array will sample around the Ocean Observatory Initiative site in the Argentine basin to validate the meteorological measurements from the wave glider. This dataset will provide an opportunity to study the physics underpinning mixing rates in this region, while simultaneously contributing valuable insights to the modeling community.