The extension of the Antarctic Peninsula into the Antarctic Circumpolar Current (ACC) in southern Drake Passage leads to the injection of Weddell Sea waters, with unique physical and biogeochemical properties, into the global circulation. This is a region of strong mesoscale eddy generation that enables exchange between coastal and ACC waters. This region will be the site of the observational field program, ChinStrAP (Changes in Stratification at the Antarctic Peninsula), during which both in situ buoyancy glider, Seagliders, and a surface Waveglider will be deployed for a period of five months. This will provide an unprecedented opportunity to explore eddy formation mechanisms at meso- and submesoscale resolution along with key surface forcing characteristics.
Exchange between the Weddell Sea and the ACC depends intricately on a collection of interacting frontal currents that occupy the continental shelf and slope along the southern boundary of Drake Passage. Satellite and insitu observations suggest that mesoscale eddies and variability emanating from the Weddell Sea are prevalent, yet the physical processes that lead to their formation and evolution (e.g., baroclinic and barotropic instabilities, thermohaline intrusions, tides, interactions with bathymetry) remain uncertain. The objective of this proposal is to observe and quantify the dominant spatial and temporal scales of variability in this region as well as the physical mechanisms that give rise to it. We will continuously monitor the fronts in southern Drake Passage by deploying and piloting a pair of ocean gliders that will collect approximately 1000 profiles of temperature, salinity, dissolved oxygen, fluorescence and optical backscatter. Multiple re-occupations of two transects across the continental slope will allow tracking of the southern ACC fronts and will permit direct calculation of cross-shelf eddy fluxes of heat and salinity. Analysis of the glider data will provide key insight into the physical processes that control upwelling and ventilation along the southern boundary of the ACC in Drake Passage.
In addition to the ocean gliders, the field program will be augmented with a surface Waveglider, which will permit an analysis of how small-scale submesoscale dynamics influence mixed layer variability across the southern boundary of the ACC. A major driver of submesoscale variability is the interaction between atmospheric winds and oceanic surface velocities, especially at ocean fronts. At present direct measurements of wind velocities at the relevant temporal and spatial scales—typically 1 to 10 kilometers and one day—are extremely rare. The use of a surface Waveglider that includes a weather station will enable these direct measurements. An understanding of mixed layer dynamics in the southern region of Drake Passage is critical as this is a key site of isopycnal outcropping and thus carbon exchange with the atmosphere. Global estimates of carbon fluxes are typically based on infrequent ship-based transects and the range of variability in these fluxes are poorly constrained. This component of the project will be critical to improving models of mixed-layer variability that influence ventilation and air-sea exchange processes.
For more detailed information on this project, including details of data access, see the ChinStrAP Endorsement webpage.
This project involves collaboration between the California Institute of Technology, Scripps Institution of Oceanography and South Africa's Council for Scientific and Industrial Research. The work is supported by the National Science Foundation, the Caltech's Stanback Discovery Fund and the David and Lucile Packard Foundation.