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ACROSS: The Antarctic Crossroad Of Slope Streams

The Antarctic Crossroad of Slope Streams (ACROSS) Project is a U.S. contribution to the IPY SASSI program (IPY Activity # 9). ACROSS is an oceanographic experiment in the Weddell-Scotia Seas, Antarctica, in collaboration with Laurence Padman of the Earth and Space Research (ESR).

ACROSS seeks to better understand the physical processes governing northward outflow of ventilated slope waters from the Weddell Sea across the western South Scotia Ridge (SSR), and to quantify their contribution to the conspicuous cooling and freshening of the Antarctic Circumpolar Current (ACC) as it transits the deep Scotia Sea.

Guiding Hypotheses

  1. Rapid ventilation of the ACC in the Scotia Sea results from mechanisms involving the slope frontal distribution and associated intermediate outflows in the northwestern Weddell Sea.

  2. These mechanisms are more efficient than the commonly cited rapid upward diffusion of older bottom waters entering the Scotia Sea through much deeper and narrower gaps in the SSR.

Distinguishing between these two ventilation pathways is critical, as the sensitivity and time scales of the two mechanisms to climate variability may differ significantly from each other.

Objectives

  1. Determine physical and chemical properties of the northward flow associated with the Antarctic Slope Front (ASF);

  2. Better constrain the pathway(s) for spreading and sinking of ventilated slope waters into the Scotia Sea;

  3. Estimate the northward transport of new deep waters between Elephant and Orkney islands;

  4. Assess processes causing local production of slope waters that can ventilate the ACC through isopycnal spreading across the SSR; and

  5. Determine the spatial distribution of diapycnal mixing across the ridge and ASF, including its relationship to tides and intrusions.

Field Program

Field work included a cruise on the Argentine research vessel Puerto Deseado sailing from Ushuaia, Argentina in the austral summer of 2009 to carry out all planned CTD/LADCP work and all mooring deployments.

Broad summary of the various AnSlope components and principal investigators:

  • CTD and Lowered ADCP survey: In early 2009 the full water column was profiled for temperature, salinity and dissolved oxygen (T/S/DO) using a SeaBird CTD system provided by TAMU and water samples were collected for S and DO measurements using a rosette. The rosette will be equipped with a Lowered Acoustic Doppler Current Profiler (LADCP) provided by TAMU.

  • Moored Current Meter Array: An array of three moorings were deployed during the summer cruise of 2009 and recovered during the summer of 2010. All three ACROSS moorings were deployed after the Philip Ridge section has been occupied. Stations spanning the moorings were repeated immediately after deployments. Spanish collaborators furnished two of these moorings (M1 and M2) as part of the funded E-SASSI program. The ACROSS array is aligned with the northern edge of the Philip Ridge between 52W and 50W. These measurements will be the first long-term (~1 years) current measurements of the Antarctic Slope Current across the Philip Ridge. Three moorings were recovered in the austral summer of 2010, tentatively by Spanish collaborators on the R/V Hesperides as an opportunity during a scheduled biological program in the area.

Acknowledgements 

ACROSS is funded by the National Science Foundation, Office of Polar Programs. It is part of a series of integrated field and modeling programs coordinated by the International Antarctic Zone (iAnZone) group, a SCOR/SCAR-affiliated program.

NSF logo

RPSC 2008-2009 Event O-401-E
Spanish E-SASSI cruise aboard RV Hesperides: January 2008
IMEDEA Cruise report (in Spanish)


ACROSS Deployment Cruise aboard RV Puerto Deseado: February-March 2009

Cruise report

Recovery Cruise aboard RV Hesperides: January-February 2010Recovery Cruise aboard RV Hesperides: January-February 2010

IMEDEA Cruise report (in Spanish)

TAMU recoveries

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