Upwelling and Lateral Exchange Over the Patagonian Shelf and Impacts on Southern Ocean Primary Productivity

Oregon State University, Corvallis OR

Investigators

Abstract

The South Atlantic sector hosts the largest chlorophyll-a blooms of the Southern Ocean, which are likely associated with off-shelf flows from the Patagonian region. To have such a significant impact on the productivity of the deep ocean the off-shelf flows from Patagonia must be large and exhibit a high nutrient content. The overall goal of this project is to characterize the physical processes underlying the high fertility and high volume transport of Patagonia's outflows. It is hypothesized that the high nutrient content of the Patagonia shelf outflows are partially sustained by a unique shelfbreak upwelling system extending from the Drake Passage to the Brazil/Malvinas Confluence. The hypotheses will be addressed with the analysis of a series of nested high resolution model simulations. This research is relevant to the climate and marine ecosystem community research. Any change in the circulation in the western South Atlantic, 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 carbon dioxide and uptake of anthropogenic carbon dioxide. A close study of the input of iron and its control on the ecosystem will further enlighten us on future changes of carbon dioxide fluxes in these regions. Furthermore, it will provide some insight on which processes and on which scale the climate community model will have to resolve them. The research may also help in the design of future field campaigns to address the unresolved questions of differences in primary production between the Pacific and Atlantic sectors of the Southern Ocean and target sites where observations will provide answers to these questions. Graduate training will also be an important component of this research. It is hypothesized that this highly productive system is composed of three localized upwelling centers: the first extending along the northern portion of the Patagonian shelfbreak, from 48 S to the Brazil/Malvinas Confluence; the second centered on the Burdwood Bank, a relatively shallow bank located in the northern portion of the Drake Passage; and the third centered on the Malvinas (Falkland) Islands. A second hypothesis is that the large off-shelf flows from Patagonia are driven by interactions between the Antarctic Circumpolar Current (ACC) and the bottom topography in the northern portion of the Drake Passage. To address these hypotheses, several process-oriented numerical experiments will be analyzed. These experiments, which are based on a high-resolution nested model configuration, will also allow an investigation of the impact of sub-mesoscale processes on the regional circulation. There are very few studies on the physical mechanisms sustaining Patagonia's extraordinary shelfbreak blooms and its mass exchanges with the Southern Ocean. In fact, there are no previous studies on the Burdwood Bank and the Malvinas Islands upwelling centers and very few on the exchanges between the Patagonian shelf and the Southern Ocean. There are also no previous studies on the impact of sub-mesoscale processes on the southwestern Atlantic circulation. A pilot study, however, shows that these processes influence important and novel changes within the regional circulation. The numerical experiments to be analyzed by this project are the state-of-the-art for this region. Some of them are the legacy of previous research efforts by this team, while others will be executed during the course of this program.