Salinity and Temperature at BC Lighthouses

From  ”State of physical, biological, and selected fishery resources of Pacific Canadian marine ecosystems in 2012

Peter Chandler, Physical Oceanographer at the Institute of Ocean Sciences supervises DFO’s British Columbia Shore Station Oceanographic Program with responsibility for the operation and development of the long-term monitoring of sea surface temperature and salinity at 13 stations extending from the mouth of Juan de Fuca Strait up to the northern end of the Strait of Georgia. This program includes the analysis, interpretation and presentation of oceanographic information, the maintenance of the monitoring instruments and the coordination of lighthouse keepers who collect the data.

Figure 1. Location of the 13 lighthouse stations currently monitored for water temperature and salinity on the west coast of B.C.

Figure 1. Location of the 13 lighthouse stations currently monitored for water temperature and salinity on the west coast of B.C.

 

Figure 2. The average daily sea surface temperature in 2010 (blue dots) and 2011 (red dots) in the stations monitored in the Strait of Georgia. The crosses show the mean annual temperature based on 30 years of data (1981-2010).

Figure 2. The average daily sea surface temperature in 2010 (blue dots) and 2011 (red dots) in the stations monitored in the Strait of Georgia. The crosses show the mean annual temperature based on 30 years of data (1981-2010).

 

 

 

 

 

 

 

 

 

 

 

 

This program was begun in 1914. Since 1999, the 13 stations are monitored four times each year; (1) low winter discharge (December), (2) early freshet (April), (3) peak freshet (June), and (4) end of freshet period (September). The methodology used to collect information on water temperature and salinity remains unchanged, and thus the database maintained at IOS allows one to examine long-term trends in conditions in our coastal waters.

The following link allows one to search these data: http://www.pac.dfo-mpo.gc.ca/science/oceans/data-donnees/lighthouses-phares/index-eng.html

Figure 3. Daily temperatures observed in 2100, and the annual cycle (calculated from 1981-2010 data) at Race Rocks and Departure Bay stations. Positive (negative) anomalies from the average 30 year temperature for each day are shown in red (blue). The black dots represent the monthly temperature anomalies observed in 2010.

Figure 3. Daily temperatures observed in 2100, and the annual cycle (calculated from 1981-2010 data) at Race Rocks and Departure Bay stations. Positive (negative) anomalies from the average 30 year temperature for each day are shown in red (blue). The black dots represent the monthly temperature anomalies observed in 2010.



Figure 4. Daily salinity observed in 2011, and the annual cycle (calculated from 1981-2010 data) at the Departure Bay station in the Strait of Georgia. Positive- saltier (negative-fresher) anomalies from the average 30 year salinity for each day are shown in red (blue).

Figure 4. Daily salinity observed in 2011, and the annual cycle (calculated from 1981-2010 data) at the Departure Bay station in the Strait of Georgia. Positive- saltier (negative-fresher) anomalies from the average 30 year salinity for each day are shown in red (blue).

 

 

 

 

 

 

 

 

 

 

 

 In general sea surface temperatures were cooler on the west coast of North America in 2011 than 2010. The annual salinity signal is affected by the Fraser River freshet, and in 2011 conditions were fresher than normal due to a large and late snowmelt. 

Figure 5 shows that there has been a general warming trend at Departure Bay, and this is also the case for all the other BC shore stations. In general, the Strait of Georgia waters have been warming at a faster rate than the west and north coast stations monitored. A similar trend analysis for the salinity data (Figure 6) shows a trend towards fresher water, which is also apparent for all the stations along the BC coast.

Figure 5. Long-term time series of daily temperature anomalies, averaged over 12 months, at the Departure Bay station. Positive (negative) anomalies from the average temperature  are shown in red (blue). Black lines shows the trend. The panel to the right shows the slope of the trend line calculated using only data upto the year shown in the x axis.

Figure 5. Long-term time series of daily temperature anomalies, averaged over 12 months, at the Departure Bay station. Positive (negative) anomalies from the average temperature are shown in red (blue). Black lines shows the trend. The panel to the right shows the slope of the trend line calculated using only data upto the year shown in the x axis.


Figure 6. Long-term time series of daily salinity anomalies, averaged over 12 months for the Departure Bay. Positive-saltier (negative-fresher) anomalies from the average salinity  are shown in red (blue). Black lines are the trends. The panel to the right shows the slope of the trend line calculated using only data up the year shown on the x axis.

Figure 6. Long-term time series of daily salinity anomalies, averaged over 12 months for the Departure Bay. Positive-saltier (negative-fresher) anomalies from the average salinity are shown in red (blue). Black lines are the trends. The panel to the right shows the slope of the trend line calculated using only data up the year shown on the x axis.