Skip to main content

Maritimes Ecosystem Indicator Catalogue

3 Surface Salinity (AZMP)

Data Type: Tabular Data

Spatial Scope: Scotian Shelf (4X, 4V, 4W)

Duration 1948-2024

Source: DFO Atlantic Zone Monitoring Program via azmpdata

3.1 Introduction to Indicator

AZMP Surface Salinity is the spatially-averaged salinity value from Atlantic Zone Monitoring Program (AZMP) monitoring stations at 0m depth, spatially and temporally summarized to annual values for the Scotian Shelf region (NAFO divisions 4X, 4V, 4W).

Monthly mean near surface salinity values are calculated for hydrographic areas 4 to 23 defined by (Petrie et al. 1996). An annual value is calculated for each area by taking the mean of all available months, then an area-weighted mean is calculated to get a Scotian Shelf value (Layton et al. 2025).

Surface salinity in this region is driven by several factors, including inflow of rivers, melting of sea ice, precipitation, and advection by wind and ocean currents (Layton et al. 2025). Interannual changes in salinity in the Scotian Shelf region are linked to changes in these processes, and could be indicative of changes to biology in the region (Grodsky et al. 2017).

3.2 View Data 

library(plotly)
plotly_df <- data@data %>%
  mutate( 
    smooth_10yr = zoo::rollapply(mean_value, mean, width = 10, partial = TRUE),
    overall_mean = mean(mean_value))

p <- plot_ly(plotly_df, x = ~year) %>%
  add_lines(y = ~mean_value,
            name = "Annual Mean",
            line = list(color = "grey"),
            hovertemplate = "Monthly anomaly: %{y:.2f}<extra></extra>"
           ) %>%
  add_lines(y = ~smooth_10yr,
            name = "10-yr Smooth",
            line = list(color = "blue", width = 2),
            hovertemplate = "10-yr smoothed: %{y:.2f}<extra></extra>",
            ) %>%
    add_lines(y = ~overall_mean,
            name = "Overall Mean",
            line = list(color = "black", width = 2, dash = "dash"),
            hovertemplate = "Overall Mean: %{y:.2f}<extra></extra>",
           ) %>%
  layout(
    title = "AZMP Surface Salinity for Scotian Shelf (4X, 4V, 4W)<br><sup>Source: DFO Atlantic Zone Monitoring Program via azmpdata</sup>",
    xaxis = list(title = "Year"),
    yaxis = list(title = "Salinity (PSU)",
                 fixedrange = TRUE),
    hovermode = "x unified",
    margin = list( t = 80)
    
  ) %>%
  config(displayModeBar = FALSE) 

p

Figure 3.1: AZMP Salinity in Scotian Shelf Regions; 1948-2024

3.4 Relevance to Research and Stock Assessments

Most harvested species are not expected to be sensitive to salinity within the range of observed or near-future projected values in Northwest Atlantic (Chabot, Guénette, and Stortini 2013). Thus, salinity perhaps has the greatest potential relevance to stocks and fisheries through indirect effects, via changes in surface productivity and stratification.

In the Gulf of Maine-Scotian Shelf region, freshening events are associated with changes in the timing and magnitude of springtime phytoplankton blooms, ultimately reducing primary productivity in coastal waters (Ji et al. 2008). These changes in primary productivity can propagate to secondary productivity, which make up large portions of larval diets for commercially important species (Becker et al. 2020).

3.5 Variable Definitions

Table 3.2: Column names and definitions in the AZMP Surface Salinity dataset.
variable description unit
year Year of data collection
region Region of summarization (one value)
mean_value Spatially and temporally averaged salinity for Scotian Shelf region PSU

3.6 Additional Data

No additional data for AZMP Salinity.

3.7 Get the Data 

library(marea)
data('azmp_salinity')
plot(azmp_salinity)

References

Becker, James, Matthew Cieri, David Libby, Adam St. Gelais, Graham Sherwood, and Yong Chen. 2020. “Temporal Variability in Size and Growth of Atlantic Herring in the Gulf of Maine.” Journal of Fish Biology 97 (September). https://doi.org/10.1111/jfb.14430.
Chabot, D, S Guénette, and C Stortini. 2013. “A Review of the Physiological Susceptibility of Commercial Species of Fish and Crustaceans of the Northwest Atlantic to Changes in Water Temperature, Dissolved Oxygen, pH and Salinity.” Climate Change Impacts, Vulnerabilities and Opportunities Analysis of the Marine Atlantic Basin 3012: 83–167.
Grodsky, Semyon A, Nicolas Reul, Bertrand Chapron, James A Carton, and Frank O Bryan. 2017. “Interannual Surface Salinity on n Orthwest a Tlantic Shelf.” Journal of Geophysical Research: Oceans 122 (5): 3638–59.
Ji, Rubao, Cabell S Davis, Changsheng Chen, David W Townsend, David G Mountain, and Robert C Beardsley. 2008. “Modeling the Influence of Low-Salinity Water Inflow on Winter-Spring Phytoplankton Dynamics in the Nova Scotian Shelf–Gulf of Maine Region.” Journal of Plankton Research 30 (12): 1399–1416.
Layton, C, D Brickman, B Greenan, P Galbraith, and JL Shaw. 2025. “Physical Oceanographic Conditions on the Scotian Shelf and in the Gulf of Maine During 2024.” Dartmouth, Nova Scotia: Fisheries; Oceans Canada, Bedford Institute of Oceanography. https://publications.gc.ca/site/eng/9.953493/publication.html.
Petrie, B., K. Drinkwater, D. Gregory, R. Pettipas, and Sandström A. 1996. “Temperature and Salinity Atlas for the Scotian Shelf and the Gulf of Maine.” Can. Tech. Rep. Hydrogr. Ocean Sci. 171: v + 398 pp. https://publications.gc.ca/collections/collection_2015/mpo-dfo/Fs97-18-171-eng.pdf.