CORC-ARCHES Southern Ocean Modern Observations –

Moorings Recovered after More than 3 Years

The export of Antarctic dense shelf water from the Weddell Gyre is being investigated with the Consortium on Oceans Role in Climate: AbRupt climate CHangE Studies (CORC-ARCHES) Southern Ocean Modern Observations program. Three deep and bottom water focused moorings south of the South Orkney Islands in the Northwest Weddell Sea provide a time series of the combined outflow (currents and temperature/salinity) of Antarctic Bottom Water drawn from various sites within the Weddell Sea.

First installed in April 1999, the moorings are serviced using ship time made available by other programs. The moorings were last visited in late 2001. Severe sea ice conditions prevented servicing the moorings in 2003 and 2004. In March of this year, we succeeded in reaching the mooring sites, recovering two, and redeploying a mooring at the southernmost site. The new data set extends the CORC-ARCHES Weddell Sea time series to nearly 6 years overall. Several CTD stations were occupied near the mooring sites and at several stations between the mooring locations.

The newly recovered records continuously span more than 3 years in some cases, including the time period corresponding to the breakup of the Larsen B ice shelf of the eastern Antarctic Peninsula in early 2002. It has been hypothesized that the Larsen ice shelves play a significant role in the production of deep and bottom waters in the western Weddell Sea, so the CORC-ARCHES time series may be uniquely positioned to investigate the oceanographic conditions leading up to and following the breakup of the Larsen B.

Preliminary analysis of the near-bottom potential temperature and salinity records of the CORC-ARCHES moorings from April 1999 to November 2001 suggested a seasonal cycle, albeit with some year-to-year variability. These are likely a consequence of changes in the production of dense Weddell Sea bottom water associated with varying amounts or source changes of the shelf water component. In addition, cold bottom water events lasting 1 to 2 days are embedded in the 0.1 m/s mean isobath-following eastward flow. Adding the newly recovered data to the time series clearly reveals the seasonality of the deep temperatures, with longer period signals superimposed.

With the continuation of ARCHES, we plan to revisit the mooring sites in early 2006, to service the moorings still in place, replace some aging instrumentation, and potentially add moorings to the array in collaboration with investigators from the British Antarctic Survey.

Further details and preliminary data are available at the project web site: http://www.ldeo.columbia.edu/res/div/ocp/projects/corc.shtml

This Lamont-Doherty Earth Observatory research is supported by NOAA funding under CICAR / CORC-ARCHES