33
Investigate the response of phytoplankton to
different climate drivers
What causes the differences in bloom timing/abundance?
Data for the following environmental drivers were collated:
satellite-derived sea-surface temperature (SST ) and photo-
synthetically active radiation (PAR), river input (with a focus
on Fraser River discharge), wind speed and wind direction
(with a focus on Halibut Bank in the central region and
Sentry Shoal in the northern region), and Conductivity-
Temperature-Depth (CTD) data (for calculation of a strat-
ification parameter). Regression analysis was carried out
in order to determine which environmental drivers best
explained variations in Chl_a in the northern vs. central
regions of the Strait of Georgia.
Results showed that a combination of increased Fraser
River discharge and weak winds likely results in favourable
bloom conditions in the Salish Sea. Positive anomalies in
stratification in spring 2005 and 2015 corresponded with
negative wind anomalies and thus allowed for the devel-
opment of the anomalously high Chl_a concentrations
very early in these years (i.e., during the week of February 18).
Median monthly Chl_a in the northern region was positively,
and significantly, correlated with monthly Fraser River
discharge, SST and PAR; and negatively correlated with
wind speed. In the central region, chlorophyll was
significantly, positively correlated with Fraser River discharge
and PAR; and negatively correlated with wind speed.
Analysis of the relationships between annual median
Chl_a anomalies and larger-scale climate indices revealed
significant positive relationships between annual Chl_a
anomalies in the northern region and the Pacific Decadal
Oscillation or PDO, a significant negative relationship
between northern Chl_a anomalies and the southern
Oscillation Index or SOI, and a nearly significant negative
relationship between northern Chl_a anomalies and the
North Pacific Gyre Oscillation (NPGO) (Figure 5).
No significant relationships were observed between
annual Chl_a anomalies in the central region and any of
the climate indices, suggesting that Chl_a in the central
region is most strongly influenced by local and annual
weather patterns.
Figure 3. Spatial extent of the northern and central regions of the
Strait of Georgia. Figure provided by Dr. Karyn Suchy, UVic.
Figure 4. Satellite-derived spring bloom start dates from 2003-2016
in the central Strait of Georgia. Grey line indicates average start date.
Figure 5. Relationships between annual median chlorophyll a
anomalies and climate indices (PDO, NPGO, SOI). Figures 4 and 5
provided by Dr. Karyn Suchy, UVic.
