The ventilation of South Georgia's Deep Waters

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This project aims to characterize the physical processes contributing to the entrainment of deep and benthic waters into the surface layers of the South Georgia Island (Southern Ocean) and to assess their sensitivity to climate variability. South Georgia (SG) hosts some of the largest chlorophyll blooms of the Southern Ocean. Observations suggest that the ocean circulation drives these blooms, but the nature of the physical processes underlying the fertilization process are unknown. A process-oriented modeling program will seek, on the one hand, to identify the sources and dynamical mechanisms underlying the fertilization of the SG region and, on the other hand, to evaluate their sensitivity to climate variability and climate change. The research is relevant to the climate and marine ecosystem community research.Understanding of SG's fertilization processes will not only contribute to the forecast of the impact of climate change on the regional ecosystems but also to anticipate the potential feedbacks that those ecosystems will have on the changing climate. Any change in the circulation in the SG, nutrient and iron input to the euphotic zone, continental margin discharge and biological activity will have a substantial effect on the balance of outgassing of natural CO2 and uptake of anthropogenic CO2. Furthermore, this study will provide some insight on which processes and on which scale the climate community model will have to resolve them. This research will also help in the design of field campaigns to address the unresolved questions of primary production in the Atlantic sector of the Southern Ocean and target sites where observations will provide answers to these questions. Graduate training will be an important component of the research.There are very few studies on the physical mechanisms sustaining SG's extraordinary blooms and, in particular, on its regional circulation. This is a matter of concern because observations suggest that South Georgia's blooms, which are an important component of the climate system, are primarily driven by physical processes. There are, for example, few studies on SG's shelf circulation and virtually none on its mass exchanges with the Southern Ocean. A pilot study, however, shows that shelf processes and its interaction with the deep ocean are critical to bio-geochemical balance of this region. The numerical experiments to be analyzed by this project are the state-of-the-art for this region. It is hypothesized that SG high productivity is based on vigorous water exchange between the shelf and the deep ocean and a persistent, albeit still under-appreciated, coastal upwelling system. Further, it is posited that SG fertilization is strongly dependent on wind forcing and the expected strengthening of the SO winds will also amplify the fertilization processes leading, therefore, to a negative feedback for climate change.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.