by Mark Halverson (University of British Columbia)
The Fraser River reaches the ocean near Vancouver, and there the fresh water it carries mixes with ocean water to form a thin plume of buoyant brackish water, which according to one oceanographer is the “showpiece of the Strait of Georgia.”
Oceanographers have been studying the Fraser River plume since at least the 1960s, but more recently, VENUS has installed a radar system to measure the surface currents in this region. Furthermore, VENUS has also installed the Seakeeper seawater monitoring system on the BC Ferries MV Queen of Alberni to collect detailed information of water properties along the Duke Point – Tsawwassen ferry route which cuts through the plume eight times per day. These new observations, coupled with satellite imagery, are being used by UBC researchers Dr. Mark Halverson and Prof. Rich Pawlowicz to reveal the nature of the Fraser plume. The research is being carried out as part of the Marine Environmental Observation Prediction and Response Network (MEOPAR), which is tasked with improving Canada’s ability to respond to marine hazards.
In the early summer when the Fraser River carries high sediment loads, the plume is easy to distinguish from ocean water by its distinct light brown colour (Fig. 1). It can be highly reflective and opaque to sunlight, and because it is a mixture of river and ocean water, it can be quite “fresh.” A comparison of the measured surface currents to both surface water salinity and satellite imagery shows that a jet of swiftly flowing water can form near low tide (Fig. 2).
A sharp change in the currents occurs where the ocean colour and salinity change rapidly, signifying the edge of the plume. As the plume waters move away from the river mouth, it appears that the wind ultimately determines its fate. During northwesterly winds, the plume is driven to the south, while during southeasterly winds, it is driven to the northwest (Fig. 3). However, the relative importance of the wind might change when the river flow is much higher. Ultimately, researchers hope that a better understanding of the surface currents in this area will be useful to emergency response operations by providing a way to anticipate the trajectory of, for example, spilled oil or other contaminants.
A recent publication in Marine Ecology Progress (Marine Ecology Progress, 2013 V.480, pp 39-56) sheds more light on the complex process of diel zooplankton migration. A recent graduate of the UVic's School of Earth and Ocean Sciences, Dr. Mei Sato has completed extensive analysis of the zooplankton diel vertical migration patterns using chlorophyll and echo-sounder data collected by DFO and VENUS, respectively, in Saanich Inlet. Her research was focused on understanding the second order drivers of the diel migration timing. The first order signal is the seasonal variation due to changes in the length of day-light hours (Image: the hour-glass shape of the slice), while the second order terms look into environmental factors that impact behavior of the species that are integral part of the food web.
Dr. Mei Sato's analysis shows that there are subtle variations to the time of ascent and decent during the year, which might be attributed to both food supply and zooplankton life-cycle (body size). Other factors include variations in the presence of predators and prey competition. Some factors, such as lunar cycles and the possible influence of full moons were statistically ruled out.
Mei successfully defended her Ph.D. thesis in early May 2013.
Reference: Sato M., Dower J., Dewey, R. 2013. Second-order seasonal variability in diel vertical migration timing of euphausiids in a coastal inlet. Marine Ecology Progress Series 480: 39-56, DOI:10.3354/meps10215.
UBC oceanographer Dr. Mark Halverson has been making use of VENUS Coastal Ocean Dynamics Applications Radar (“CODAR”) data from the Strait of Georgia in his research. His analysis revealed an abrupt cutoff in data availability to the south of the coverage area, rather than the gradual fall-off with distance from the two antennae one would expect from purely physical considerations.
Subsequent investigation revealed an overly-restrictive software setting that has since been modified. All ocean-current data going back to the commissioning of the VENUS CODAR array in August 2012 has been reprocessed, extending the coverage of the array southward by about 3 km.
This animated figure shows the coverage area before and after the reprocessing. Thanks go to Dr. Halverson for pointing out this anomaly, allowing us to improve our product. Our users are not mere customers, but active collaborators in the VENUS mission to provide data to the oceanographic community.
There is currently a lack of consensus over how to average local shipping noise levels to assess the impact of such noise on marine life. Using data collected between Dec. 2011 and Apr. 2012 from an Ocean Sonics low frequency hydrophone that was deployed at the VENUS Strait of Georgia East site, this publication assesses various methods for averaging local shipping noise levels. The conclusion from this assessment is that mean sound pressure levels averaged in linear space are most relevant for determining the cumulative impact on marine life (Image-2).
Merchant N.D., Blondel P., Dakin D.T., Dorocicz J. 2012. Averaging underwater noise levels for environmental assessment of shipping. The Journal of the Acoustical Society of America, 132(4), pp. EL343-EL349.
For a year, the VENUS camera photographed the same area of seafloor in Saanich Inlet. A recent paper has examined the response of the benthic animals to changing levels of oxygen. Only a few species cope with hypoxia but the high numbers suggest that food availability and refuge from oxygen-starved predators is a good strategy for some. The research predicts marked changes on the continental shelf with growing “dead zones”.
Matabos M., Tunnicliffe V., Juniper S.K., Dean C. 2012. A year in hypoxia: epibenthic community responses to severe oxygen deficit at a subsea observatory in a coastal inlet. PLoS ONE 7(9): e45626. DOI:10.1371/journal.pone.0045626.
A group of researchers have successfully identified a new dinoflagellate species. Part of the large group of eukaryotes (approx. 1555 species), the new species has distinct morphological characteristics and was named Archaeperidinium saanichi sp.nov. after Saanich Inlet, the place where, using a VENUS sediment trap, Dr. Vera Pospelova and her MSc student – Andrea Price collected samples and conducted their research that led to a publication in Marine Micropaleontology (see reference below).
The image shows cyst (left) and motile (right) stages of the new species
Mertens K.N., Yamaguchi A., Kawami H., Ribeiro S., Leander B.S., Price A.M., Pospelova V., Ellegaard M., Matsuoka K. 2012. Archaeperidinium saanichi sp. nov.: A new species based on morphological variation of cyst and theca within the Archaeperidinium minutum JÃ¶rgensen 1912 species complex. Marine Micropaleontology, Volumes 96–97, December 2012, pp. 48-62, ISSN 0377-8398, DOI:10.1016/j.marmicro.2012.08.002.
On May 28-29 international group of researchers gather at the Institute of Ocean Sciences to share knowledge and discuss research opportunities in Saanich Inlet as a model hypoxia ecosystem. To learn more about the symposium and see the scientific program, visit the 2012 Saanich Inlet Symposium.
On February 15 & 16, the Department of Fisheries and Oceans held the annual meeting to assess the State of the Ocean for 2011. We recently submitted our fourth contribution to this important and broad-reaching document. Included in this report are the three CTD time series from our three Node locations, Saanich Inlet, and Strait of Georgia Central and East, available from our State of the Ocean page. The Saanich Inlet time series is now over 6 years long, and reveals weekly, monthly, annual and inter-annual variations. Of key note for 2011 was the relatively mild spring and slightly cooler summer, which resulted in a prolonged melting of the large coastal snow pack and a prolonged Fraser River freshet, and the capturing of May and June dense water in-flows at the SoG Central site.
Studying biorhythms in Saanich Inlet is an ongoing research project supported by the VENUS network. Following the initial deployment and analysis of results, published in Sensors (Aguzzi et al. 2011), the group of international collaborators is now using a seafloor camera (DISCo) that features a more developed control interface. The interface can automate the process of turning the lights on and taking imagery. The camera schedule is set to take 4 images every 30 min 24/7 which allows researchers to observe and assess changes in the environment as they occur.