As part of the Atlantic Zone Monitoring Program (AZMP), scientists from the Maurice Lamontagne Institute (IML) have developed a monitoring program for the St. Lawrence ecosystem. “The St. Lawrence Monitored” presents a detailed description of the program, the oceanographic variables measured, the station locations, and the methods used to sample the waters of the St. Lawrence.

Different oceanographic variables are measured in the Estuary and Gulf of St. Lawrence in an effort to describe the annual and interannual variability in the environmental conditions of this ecosystem. The data, interpolated to create time series for each of the fixed stations and presented as cross-sections for each of the transects, are available.

The St. Lawrence
The St. Lawrence River begins as the outflow of the Great Lakes and widens into a large estuary near Ile d’Orléans, where the river’s fresh water first encounters oceanic salt water and where the typical two-layer estuarine circulation begins. Continuing downstream, the surface water of the St. Lawrence becomes more and more salty, finally having a true oceanic character at the head of the Laurentian Channel (off-shore of Tadoussac), where strong upwellings bring deep waters to the surface. Among the deepest and largest estuaries in the world, the St. Lawrence maritime estuary extends nearly 250 km before it widens at Point-des-Monts into the Gulf of St. Lawrence. This enclosed sea is connected to the Atlantic Ocean by Cabot Strait and the Strait of Belle-Isle.

As it makes its way toward the ocean, the fresh water of the St. Lawrence estuary remains on the surface, above the saltier oceanic waters, much like a layer of oil floats above water. It takes a parcel of water about three months to travel down the estuary and reach Cabot Strait and the Atlantic Ocean beyond. The surface outflow of water from the St. Lawrence entrains the deep entry of much saltier water from the Atlantic via Cabot Strait and the Strait of Belle-Isle. This deep water gradually moves into the St. Lawrence Gulf and up the estuary toward the head of the Laurentian Channel, near Tadoussac, a voyage that can take several years. These large-scale, counter-current water movements generate the estuarine circulation that gives the St. Lawrence its distinctive character.

As part of the Atlantic Zone Monitoring Program (AZMP), which includes the Newfoundland, Maritimes, Québec, and Gulf regions of the Canadian Department of Fisheries and Oceans (DFO), scientists from Institut Maurice-Lamontagne (IML) began oceanographic monitoring of the St. Lawrence ecosystem in 1996. This program provides DFO with the information necessary to detect, track, and predict changes in the productivity and state of the marine environment. This information is essential to the understanding of large issues, such as the impacts of climate change. The data gathered from the monitoring program also support the ecosystem approach for sound management of the St. Lawrence ecosystem, the aim of which is to conserve and protect the marine environment and resources for future generations. Another important aspect of the program is that the data collected as part of the AZMP are used to build time series and add to historical data sets that will be required to respond to future problems.

Data can also be accessed by consulting the Oceanographic Data Management System (ODMS).

Stations
The data are presented as time series for each of the variables measured at the fixed stations. At each station, measurements are made from the surface to the bottom. The time series are obtained by interpolation, showing data variability as a function of time.

For the temperature, salinity, and sigma-t (density anomaly), the dots above the graphs indicate when sampling occurred. For the other variables, each small circle represents a measured value resulting from the analysis of a water sample taken at a given depth.

Transects
The data are presented as graphs showing the vertical variability (bottom–surface) of each variable measured on a given date along the horizontal axis formed by the transect stations.

For the temperature, salinity, and sigma-t (density anomaly), the dots above the graphs indicate when sampling occurred. For the other variables, each small circle represents a measured value resulting from the analysis of a water sample taken at a given depth at a given station.

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