Scotian Slope/Rise Monitoring Program

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)

Since 2006, physical, chemical and biological observations have been obtained at least once annually at deep-water stations added to the offshore end of the AZMP Halifax Line (HL). The stations, referred to as the "eXtended Halifax Line (XHL)", are located over the continental rise and complement the AZMP stations over the continental slope and shelf.

Sampling at the XHL stations is usually carried out during the CCGS Hudson's return trip from the Labrador Sea in late spring. For most variables, the measurement protocol is the same as that in the Labrador Sea Monitoring Program.

The objectives are to:

  1. Monitor interannual variability of the water mass properties of the Deep Western Boundary Current (DWBC) as it flows along the Scotian Rise.
  2. obtain additional information on oceanographic and lower-trophic-level variability of the Slope Water (SW) affecting the Scotian and adjacent shelves.

The equatorward-flowing DWBC carries water masses that were created in the subpolar North Atlantic, such as Labrador Sea Water and Denmark Strait Overflow Water. It is a key component of the Atlantic portion of the ocean's Meridional Overturning Circulation (MOC). The MOC is sometimes referred to as the "global ocean conveyor belt" of the coupled atmosphere-ice-ocean climate system.

The Physical Oceanographic component focuses on the temperature, salinity and other physical properties of the DWBC and the upper-ocean SW.

The Chemical Oceanographic component focuses on nutrients, oxygen, carbon and chemical tracers which are important to SW influences on the Scotian Shelf, and from which variability in the DWBC can be inferred.

The Biological Oceanographic component focuses on off-shelf biomass and growth dynamics of phytoplankton and zooplankton and how those populations influenced the growth and distribution of plankton on the shelf and downstream.

During 2008-2013 DFO monitoring on the Scotian Slope/Rise is being complemented by a collaborative moored measurement project with the National Oceanography Centre, as part of the UK Rapid Climate Change (RAPID) program.

For displays of observed distributions in recent years, see Recent Oceanographic Conditions over the Scotian Slope/Rise.

Datasets from the program are available from relevant DFO data archives (see component subpages).

Information on related Ocean Climate Research can be found under:

Physical

Physical

The objectives of this component are to:

  1. Monitor interannual variability of the physical properties of the Deep Western Boundary Current (DWBC) as it flows along the Scotian Rise.
  2. Obtain additional information on variability in the Slope Water 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 on the return trip from the Labrador Sea in late spring. Measurements include:

  1. temperature, salinity and density profiles at XHL and AZMP stations from a CTD system;
  2. additional upper-ocean temperature profiles from XBTs (when available); and
  3. current profiles from Acoustic Doppler Current Profiler (ADCP) observations.

The distribution of water masses is illustrated by the cross-slope vertical distribution of temperature and salinity in 2007. In the upper ocean, there is relatively fresh SW over the Scotian Slope, and much more saline water as the Gulf Stream is approached offshore. Labrador Sea Water (LSW) lies beneath the SW at intermediate depths, and Denmark Strait Overflow Water (DSOW) lies along the bottom below 3000m. Temperature is highest in the surface waters, particularly those offshore, and coldest in the deep abyss. LSW and DSOW are key components of the DWBC.

The processed CTD data are being made available through DFO's Integrated Science and Data Management (ISDM), and OSD's Climate Database.

For the Temperature, Salinity and Density distributions observed in recent years, see Recent Oceanographic Conditions over the Scotian Slope/Rise

Information on related Ocean Climate Research, including the moored measurements in the RAPID Climate Change program, can be found under

Locations of oceanographic stations on the AZOMP XHL (HL8 to HL12) and the AZMP HL (HL1 to HL7). Moored measurement sites in the UK RAPID Climate Change program during 2008-2013 are also shown
Locations of oceanographic stations on the AZOMP XHL (HL8 to HL12) and the AZMP HL (HL1 to HL7). Moored measurement sites in the UK RAPID Climate Change program during 2008-2013 are also shown
Distribution of Potential Temperature (left) and Salinity (right) over the Scotian Slope and Rise from AZOMP profiles in May 2007. Key water masses are labeled. Distribution of Potential Temperature (left) and Salinity (right) over the Scotian Slope and Rise from AZOMP profiles in May 2007. Key water masses are labeled.

Distribution of Potential Temperature (left) and Salinity (right) over the Scotian Slope and Rise from AZOMP profiles in May 2007. Key water masses are labeled.

Chemical

Chemical

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).

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.

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.

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)
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.
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.
Biological

Biological

The objectives of this component are to:

  1. Monitor interannual variability of plankton abundance in the Deep Western Boundary Current (DWBC) as it flows along the Scotian Rise.
  2. Obtain additional information on the variability of phytoplankton, bacterioplankton, and zooplankton 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:

  • Chlorophyll a fluorescence and PAR (photosynthetically active radiation) attenuation from a CTD system;
  • Chlorophyll a concentration from Niskin bottles;
  • Microbial (bacteria, picoplankton, nanoplankton) abundance from Niskin bottles; and
  • Zooplankton biomass and composition from net hauls.

The distribution of bacteria shows a logarithmic decline with depth. This reflects the heterotrophic dependence by bacteria on the products of photosynthesis from phytoplankton in the illuminated euphotic zone. Bacteria in the dark mesopelagic and bathypelagic depths remineralise organic matter delivered by sinking particles, by diffusion and mixing of surface waters rich in dissolved substrates, by vertically migrating zooplankton, and by advection from coastal ecosystems. Dark waters of the DWBC over the continental slope and rise have a low abundance of bacteria.

The distribution of chlorophyll a in post spring bloom surface waters suggests lower offshelf phytoplankton biomass related to stratification-controlled nutrient limitation. Phytoplankton community composition cannot be directly discerned from measurements of chlorophyll a but other evidence indicates abundant populations of picophytoplankton and nanophytoplankton in low chlorophyll offshelf waters.

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 the chlorophyll, bacteria, picoplankton, nanoplankton, and zooplankton distributions observed in recent years, see Recent Oceanographic Conditions over 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)
Averaged concentrations of bacteria over the Scotian Shelf, Slope and Rise from the annual May surveys in the period 2006-2010.
Averaged concentrations of bacteria over the Scotian Shelf, Slope and Rise from the annual May surveys in the period 2006-2010.
Averaged concentrations of chlorophyll <em>a</em> in the euphotic zone over the Scotian Shelf, Slope and Rise from the annual May surveys in the period 2006-2010.
Averaged concentrations of chlorophyll a in the euphotic zone over the Scotian Shelf, Slope and Rise from the annual May surveys in the period 2006-2010.
Recent Conditions

Recent Conditions

Displays of the late spring distributions of oceanographic variables over the Scotian Slope and Rise for individual years during 2006-2010 can be viewed or downloaded using the drop-down menus below. These displays are derived from observations taken during the annual May survey of the eXtended Halifax Line (XHL) as part of AZOMP and the Halifax Line (HL) as part of AZMP.

The variables are divided into four groups to facilitate the viewing:

Separate panels for each variable and year are available. The year of interest can be selected from the drop-down menu, and the variable(s) by checking the appropriate box(es). Thumbnails of the cross-shelf vertical section plots of the requested variables will be displayed, and a higher-quality plot can be obtained by clicking on the thumbnail of interest. The individual plots can be combined (by the user) to provide comparative displays across variables and years.