The Deep Western Boundary Current on the Scotian Rise

Map with schematic representations
Map with schematic representations of the pathways of DSOW (mauve), NEADW (red) and LSW (yellow) which are the primary water masses carried by the DWBC.

The Deep Western Boundary Current (DWBC) flows equatorward along the western margin of the North Atlantic, forming the lower limb of the AMOC. It carries water masses such as Labrador Sea Water (LSW), Denmark Strait Overflow Water (DSOW) and NE Atlantic Deep Water (NEADW) that are formed in the northern North Atlantic by severe winter surface cooling and then spread at depth to other parts of the Atlantic.

In collaboration with the UK Rapid Climate Change (RAPID) program, OSD has made moored current and hydrographic measurements in the DWBC over the Scotian Rise since 2004.

From 2004 to 2008 with support from the Federal Program on Energy Research and Development (PERD), measurements were made at two sites on a cross-slope line to the east of the AZMP Halifax line where the UK's National Oceanography Centre (NOC) had moorings at six sites.

Since 2008, in collaboration with NOC, moored measurements have made at six sites on the AZMP Halifax Line and the eXtended Halifax Line (XHL) of AZOMP, as part of the UK's RAPID WATCH ("Will the Atlantic Thermohaline Circulation Halt?") project. The moored measurements are complemented by the annual AZOMP survey of physical and biogeochemical variables on the Scotian Slope/Rise, and by an additional survey of temperature, salinity, oxygen, nutrients and biological variables on the XHL during the annual mooring expedition. This project is planned to continue until at least 2013.

Map showing the locations of moored measurements
Map showing the locations of moored measurements on the Scotian Rise during 2004-2008 (red triangles) and 2008-2013 (red x's). Oceanographic stations on the AZMP's Halifax line (mauve)and the AZOMP's XHL (green) are also shown.

The observations from these programs are being used by NOC scientists to describe and understand variability in the transports of the DWBC and AMOC, and by BIO scientists to describe and understand the variability in water mass properties such as temperature, salinity and oxygen.

Examples of the near-bottom temperature variability observed at the Scotian Rise mooring sites and of interannual temperature variations in the DSOW at various locations between Greenland and the Scotian Rise are shown in the figures below.

Variability in near-bottom temperature
Variability in near-bottom temperature at mooring sites between the 2200- and 3800-m isobaths on the Scotian Rise during 2004-2009.
Variability in the temperature of DSOW
Variability in the temperature of DSOW during 2000-2009 from OSD observations at various sites between the Labrador Sea and Scotian Rise, in relation to variability off Greenland (Yashayaev and Dickson 2008).

For details on the moored measurement sites, see Moored Current Measurements on the Scotian Rise.

For further information on this project, contact Dr. John Loder or Dr. Igor Yashayaev