UC San Diego

Strong, year-round eastward wind forcing drives the Antarctic Circumpolar Current (ACC), the Southern Ocean's dominant current, on an unbroken path around the Antarctic continent. This near-constant source of eastward wind stress momentum must find a sink, lest the current accelerate indefinitely. The path that this wind stress momentum travels from source to sink plays an essential role in setting the strength and structure of the upwelling branch of the meridional overturning circulation, a key nexus of heat and carbon exchange between the deep ocean and the atmosphere.

This thesis maps Southern Ocean momentum sinks and the pathways that momentum travels through the fluid from source to sink. Using the Southern Ocean State Estimate, a 1/6 degree, data-assimilating model of the Southern Ocean south of 24.7 S, we find that 95% of wind stress momentum exits the fluid via topographic form stress: 58% across submerged ridges, and 42% across the land masses that block the ACC (Chapter Two). We isolate the interfacial form stress field for the first time in a general circulation model, finding that interfacial form stress carries zonal momentum from source to sink, balancing wind stress, topographic form stress, and thermodynamic forcing to help set the structure of the meridional overturning circulation in the Southern Ocean (Chapter Three). We find that transient eddy interfacial form stress dominates the total interfacial form stress field and tends to concentrate along the six largest topographically steered currents in the ACC. Finally, we explore interfacial form stress via observational data from the cDrake experiment, a four-year deployment of current and pressure recording inverted echo sounders across a standing meander in the Subantarctic and Polar Fronts in the Drake Passage (Chapter Four). The cDrake observational estimate aligns closely with previous observational estimates in the region, and provides a strong ground-truth for the model interfacial form stress field.