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Frequency of Marine Heatwaves
(events/year)

Figure 6.3 – Number of heatwaves experienced each year in Baynes Sound, east coast of Vancouver Island, based
on marine sea surface temperature measurements at the Chrome Island Lightstation from 1969 to 2018. Criteria
for a marine heatwave from Hobday et al. 2016, defined as at least five consecutive days that the recorded
temperature exceeded the 90 percentile for that calendar day of a baseline dataset of at least 30 years, in this
th
case, the entire available data set of 50 years was used.
The rate of increasing sea surface temperature Warmer sea surface temperatures from climate
varies significantly around British Columbia by change on top of natural climate fluctuations
region . The increases have been most pronounced increase the risk of marine heat waves . Marine
for the southern/inner coastal region (Strait of Georgia heatwaves are extreme temperature events that
stations as well as Race Rocks station in the Strait of exceed normal seasonal values . During marine
Juan de Fuca) . Based on the BC lightstation dataset, heatwaves, the thermal tolerances of marine
between 1973-2010 the southern/inner coastal species can be exceeded and result in stress or
region sea surface temperatures have been rising death . Marine heatwaves can range from a
at a rate of 0 .40°C per decade (group mean) relatively brief but intense/high temperature
whereas the temperatures in the northern/outer spike to a less intense but longer lasting event .
coastal region have been rising at 0 .12°C per decade In the future, marine heat waves are projected
(Amos et al . 2015) . For comparison, the global to increase in frequency, intensity, duration and
average rate of sea surface temperature increase spatial extent globally (Oliver et al . 2019, IPCC 2019)
has been 0 .19°C per decade (IPCC 2013) . The and El Niño events are projected to occur twice
dichotomy between the Strait of Georgia and the as often (IPCC 2019) . Figure Figure 6 .3 shows
outer shelf temperatures appears to be increasing the increasing prevalence of marine heat waves
with time and is influenced by different factors . Sea off the east coast of Vancouver Island, at
surface temperatures for the outer shelf correlate Baynes Sound .
with larger scale oceanographic phenomenon The consequences of warmer ocean temperatures
such as the Pacific Decadal Oscillation (PDO) while are far reaching . Warmer waters have been implicated
temperatures in the Strait of Georgia appear to be in the loss of important habitats such as eelgrass
influenced more locally (Amos et al . 2015) . If these meadows and kelp forests that are crucial to
trends continue, the sea surface temperatures the life cycles of many species including salmon .
in the Strait of Georgia may increase by 3°C by 2100 Pacific salmon fitness, growth and survival can
(Amos et al . 2015) . be negatively impacted by warming waters
(Vadeboncoeur 2016) while increased incidence
of harmful algal blooms, biotoxins and disease
outbreaks are also associated with warmer sea
surface temperatures . It is also anticipated that
there will be cascading impacts to the food web .

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