Chemical Oceanographic Monitoring of the Scotian Slope/Rise

Locations of oceanographic stations on the AZOMP XHL (HL8 to HL12) and the AZMP HL (HL1 to HL7)

Locations of oceanographic stations on the AZOMP XHL (HL8 to HL12) and the AZMP HL (HL1 to HL7)

The objectives of this component are to:

  1. Monitor interannual variability of the inorganic carbon properties and transient tracers in the Deep Western Boundary Current (DWBC) as it flows along the Scotian Rise.
  2. Obtain additional information on the variability of nutrients, oxygen and inorganic carbon properties in the Slope Water (SW) which is the primary upper-ocean water mass between the Gulf Stream and the Atlantic Canadian shelf and slope.

Sampling is carried out at as many of the eXtended Halifax Line (XHL) stations as feasible, in conjunction with sampling of the AZMP Halifax Line (HL) on the return trip from the Labrador Sea in late spring. Measurements include:

  • nutrients such as Nitrate, Phosphate and Silicate;
  • Dissolved Oxygen (DO) from bottles and CTD probes;
  • Total Alkalinity (TA) and Total Inorganic Carbon (TIC); and
  • transient tracers such as Chlorofluorocarbons (CFCs), and Sulphur Hexafluoride (SF6).
Distribution of the transient tracer CFC-12 over the Scotian Shelf, Slope and Rise from AZOMP profiles in May 2013.

Distribution of the transient tracer CFC-12 over the Scotian Shelf, Slope and Rise from AZOMP profiles in May 2013.

The distribution of Chlorofluorocarbon-12 (CFC-12) in May 2013 reflects the origin of different water masses. Lower concentrations indicate "older" water in the sense of time since ventilation by the atmosphere. Higher concentrations indicate waters that were recently ventilated. The oldest waters are found at depth at the outermost stations and the newest waters are found over the shelf and near the surface. Intermediate concentrations over the slope at 1000-2000m and over the rise at 3000-4000m are the signatures of the DWBC's Labrador Sea Water (LSW) and Denmark Strait Overflow Water (DSOW), respectively.

Distribution of Nitrate over the Scotian Shelf, Slope and Rise from AZOMP profiles in May 2008.

Distribution of Nitrate over the Scotian Shelf, Slope and Rise from AZOMP profiles in May 2008.

The distribution of Nitrate in May 2008 illustrates the importance of the SW to biological production on the Scotian and adjoining shelves. The primary source of nutrients for "new" primary production on these shelves is the subsurface offshore SW which is supplied by various shelf-slope exchange processes (e.g. subsurface intrusions into Emerald Basin).

The processed datasets are being made available through DFO's Integrated Science and Data Management (ISDM) and BIOCHEM database, and the Ocean Data and Information Section (ODIS) of OSD.

For further information on CFCs and TIC, see Carbon and Tracers in the Subpolar Gyre.

For the nutrient, DO, TA, TIC and CFC-12 distributions observed in recent years, see Recent Oceanographic Conditions over the Scotian Slope/Rise.

For further information, contact AZOMP.