Agulhas rings pathways and the resulting MOC control

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Intellectual merit: The study will improve the understanding of nonlinear climatic processes as they relate to retroflecting currents and eddy formation. In particular, the relationship between eddy generation and coastline inclination, bottom topography, and upstream potential vorticity will be examined. A theoretical and numerical modeling approached will be used to achieve those goals.The study focus on a problem critical to the Meridional Overturning Cell (MOC): Agulhas rings injection that forces large amounts of salt into the South Atlantic and is thus critical for maintaining the Atlantic relatively high salinity. A recent analysis of paleoceanographic proxies reveals that the injection of salty Agulhas rings into the South Atlantic during the Younger Dryas (when the MOC was not operational) was dramatically reduced compared to today's injection levels. The increase to today's levels occurred toward the end of the Younger Dryas and it has been suggested that the associated increase in salt influx into the Atlantic re-started the, then-collapsed, MOC. Given that the salt anomaly that the rings inject into the Atlantic is presently roughly five times that of the Mediterranean Sea and the Bering Strait, the above MOC restart idea appears plausible. It has been hypothesized that the injection variability is due to the slanting of the South African coastline (relative to the east-west direction) at the location where the retroflection occurs. This slanting varies widely with latitude"it is almost zero near the southernmost edge of the continent and nearly 90' at lower latitudes off Madagascar. In this scenario, the rings are able to propagate freely away from the generation area in the small slant case but not in the large slant case. This is because the long-shore migration is just the open-ocean westward migration times the cosine of the slant so that there is a significant long-shore migration component in the small slant case but not in the large slant case. The approach will be to employ nonlinear analytical methods as well as process oriented studies and high-resolution numerical experiments to investigate processes associated with various configurations of the above problems. Broader Impacts: The Indian-Atlantic ocean basin exchange affects the MOC whose functioning is critical to the world climate. The proposed studies are pertinent to ocean variability on long time scales, and are thus important to the significant societal question of global climate change and predictability. One graduate Ph.D. student will be supported in this research area where new graduates are needed. The project will also enhance our outreach program of exposing underprivileged kids (boys and girls) housed and educated in the Florida Sheriffs Youths Ranches (FSYR) to science. These ranches house several hundred underprivileged girls and boys, identified by the Florida sheriffs to have a potential criminal future unless steered away from their immediate social environment and housed elsewhere. A similar outreach program will be conducted at the Federal prison in Tallahassee.