The Antarctic CRossroad Of Slope Streams (ACROSS) project was a U.S. contribution to the IPY SASSI program (IPY Activity # 9) during 2008-2010. It was an oceanographic experiment in the Weddell-Scotia Seas, Antarctica, in collaboration with Laurence Padman of the Earth and Space Research (ESR).

ACROSS sought to (1) better understand the physical processes governing northward outflow of ventilated slope waters from the Weddell Sea across the western South Scotia Ridge (SSR), and (2) 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.

US-Spain-Argentina Collaborative 3-year Field Program

The ACROSS/E-SASSI experiment was part of the IPY program and included three summer hydrographic cruises to the SSR.

The initial cruise was carried out in January 2008 as part of E-SASSI aboard the Spanish R.V. Hesperides. An IMEDEA cruise REPORT (in Spanish) is available here.

The middle cruise during February-March 2009 was the ACROSS deployment cruise aboard the Argentine R. V. Puerto Deseado.

The final cruise in January-February 2010 was the recovery cruise aboard the Spanish R.V. Hesperides. An IMEDEA cruise REPORT (in Spanish) is available here.

ACROSS CTD/LADCP/XBT survey of 2009

It consisted of full water column profiling for temperature, salinity and dissolved oxygen (T/S/DO) using a SeaBird CTD system; upper layer temperature profiling using XBTs; and for ocean currents using a Lowered Acoustic Doppler Current Profiler (LADCP); and rosette water sampling with Nisking bottles for S and Dissolved Oxygen (DO) measurements. All of the CTD, LADCP and rosette equipped were provided by TAMU.

A TAMU cruise REPORT is available here.

Station CTD and XBT data sets are available here.

ACROSS 1-Year Mooring Array of 2009-2010

A moored array of current meters and C/T/P recorders were deployed on two moorings during the ACROSS cruise in early 2009, and recovered during the E-SASSI cruise in early 2010. All moored equipment belonged to US (TAMU and OSU) and Spanish (University of Ballearic Islands) collaborators.

A TAMU buoy REPORT is available here.

Moored Time Series from SeaBird C/T/D recorders SBE-37 and SBE-39, Norterk AQUADOPP and Aanderaa RCM current meters are available here.

Outreach

To watch the documentary video of the ACROSS 2009 cruise produced by Polar Palooza for the IPY click on the image below.

Acknowledgements

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

RPSC 2008-2009 Event O-401-E