The Intermediate-depth Ventilation of the Antarctic Circumpolar Current in the Southwestern Scotia Sea project seeks answers to these climate-relevant questions: Is the export of ventilated cold waters from the Antarctic Slope Current (ASC) at the northern side of the South Scotia Ridge (SSR) sufficient to explain the observed rapid freshening and cooling of the Antarctic Circumpolar Current (ACC) downstream of Drake Passage? Where and how is Modified Circumpolar Deep Water (MCDW) injected to the deep water of the ACC? Is the proximity of the ACC to the continental slope of the SSR a critical factor in determining how much MCDW is delivered across the slope? The aim of this project in answering these question is to correctly represent the ventilation rate for the Circumpolar Deep Water (CDW) in large-scale ocean circulation models. The main goal is to identify and describe the main mechanism governing the offshore transport of ventilated upper waters from the ASC to the Scotia Sea along intermediate density layers.
The guiding hypothesis for the project is that the magnitude and location of the northward injection of cold, fresh, ventilated slope water from the ASC to the deep Scotia Sea within isopycnal layers varies with the proximity of the southern boundary of the ACC to the South Scotia Ridge, and is therefore subject to considerable mesoscale variability.
The specific objectives are to characterize the flow of the ASC in the southwestern Scotia Sea where it converges with the ACC, assess mechanisms for production of ventilated slope waters along the path of the ASC, determine the physical and chemical properties, and volume transport of ventilated slope waters carried along this path and their cross-slope outflows, identify the pathway(s) for their spreading and sinking into the Circumpolar Deep Water (CDW) layer of the ACC in the Scotia Sea, and determine the spatial distribution of diapycnal mixing across the ridge and the Antarctic Slope Front system, including its relationship to tides and intrusions.
The hydrographic data from two well coordinated international cruises in the southwestern Scotia Sea, and the one-year time series of current, salinity and temperature measurements from three moorings deployed across the northern slope of the SSR, will be analyzed and synthesized with all historical and complementary data sets relevant to the objectives of this project.
Intellectual Merit: The proposed analysis will determine the importance of direct ventilation of the deep ACC in the Scotia Sea relative to indirect ventilation through upward mixing of bottom trapped outflows of denser bottom waters. By better constraining mechanisms by which climate related changes in the cold Antarctic coastal waters can rapidly impact the rest of the World Ocean, this analysis will improve our ability to model deep ocean ventilation. The first long-term moorings from this critical interface region between the Weddell Sea and the Global Ocean will add to the regional database with current, temperature and salinity profile measurements that resolve the small cross-slope scales associated with the hypothesized ventilation mechanism. It builds on an earlier international experiment (DOVETAIL: 1997-2000) and is coordinated with a Spanish research program.
Broader Impacts: This research project provides an extraordinary opportunity to foster international collaboration with South American and European investigators involved in concurrent regional field programs. Two Ph.D. students will be supported by this grant, and will assimilate data collected in this program into their research projects. Project documentation and results publication will contribute to the US component of the IPY SASSI research program (http://sassi.tamu.edu). All data from this program will be quality controlled, submitted to NODC and added to the Southern Ocean Database disseminated to the broader community online at http://woceSOatlas.tamu.edu.
This project is a contribution to the U.S. CLIVAR (CLImate VARiability and predictability) program.
