A Numerical Study of the Patagonia Upwelling Region

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The Patagonia shelf is a broad submarine terrace that extends from the mouth of the La Plata River (~36S) to the tip of Tierra del Fuego (~55S). Satellite and in-situ observations indicate that this region is an active upwelling center harboring some of the largest chlorophyll blooms of the world ocean, the most distinctive of which is located at the shelfbreak. Patagonia's shelfbreak upwelling brings iron and other nutrient from the deep layers of the Southern Ocean to the photic zone, fertilizing not only the shelf waters, but also the entire subpolar portion of the South Atlantic. Satellite observations, for example, show chlorophyll plumes extending from South America to Australia. Yet, in spite of its regional and hemispheric impact, we know little about Patagonia's upwelling regime or its interaction with the deep-ocean circulation, which this project intends to address. This is a modeling study to investigate the dynamical mechanisms driving Patagonia's shelfbreak upwelling and the interactions between the shelf and the deep ocean. The basic premise is that the shelfbreak upwelling is primarily modulated by the along-shelf variations of the bottom topography and time variations of the Malvinas Current transport. The study seeks to quantify the spatial and temporal variability of the upwelling and link it to the atmospheric forcing. It is hypothesized that, although local wind might have little impact over the upwelling, large-scale wind variations, particularly those over the Pacific and Indian basins might significantly influence its variability. The study will also identify the regions of Patagonia with the largest cross-shelf exchanges and identify the dynamical mechanisms controlling these exchanges. It is anticipated that Patagonia entrains Subantarctic waters through the Le Maire Straits and the shelfbreak region between ~50S and 46S, and primarily detrains at the Subtropical Shelf Front.Broader ImpactsThis study will contribute to the development to ongoing and future biological and geochemical projects of the southwestern Atlantic region. For example, the upwelling index that will be developed by this project will help to relate observed changes in the Patagonia's ecosystems to variations in the magnitude of the shelfbreak upwelling and to large-scale modes of climate variability. The identification of cross-shelf exchanges mechanisms (and regions) will contribute to our understanding of carbon cycles and the development of future observational programs. The multi-disciplinary workshop proposed as part of this project will foster international cooperation. The project includes support for a PhD student who, throughout her/his studies, will work in close collaboration with oceanographers in Latin America. This strategy should help to foster the north-south integration of the next generation of scientists interested in shelf dynamics.Intellectual MeritAt its most basic level this project proposes to test new ideas about the dynamical mechanisms generating shelfbreak upwelling and controlling cross-shelf exchanges in regions bounded by cyclonic western boundary currents. The arguments are general enough to be applicable to other similar regions (e.g., New Zealand, Japan, the Weddell Sea, etc), thus broadening the potential impact of the intellectual work developed in this project.