ArticlePDF Available

Abstract and Figures

Many complex fjord systems cross British Columbia's coastline. A 70 year (1951–2020) time series analysis of temperature, salinity, and oxygen in four such fjords between ∼54 and 50oN (Douglas Channel, Rivers Inlet, Knight Inlet and Bute Inlet) shows that changes were greatest in deep waters between the sill and the bottom. In Rivers, Knight and Bute Inlet, the deep water temperature increased by 1.2–1.3°C over 70 years, up to two times the global average for open ocean waters at corresponding depths, while salinity increased by 0.1–0.2, and oxygen decreased by 0.4–0.7 mLL−1. The most northern inlet, Douglas Channel, showed a temperature increase of 0.8°C from 1951 to 2016, while trends in oxygen and salinity were not statistically significant. An analysis of Apparent Oxygen Utilization suggests that the deep waters in Douglas Channel are more readily exchanged with the outer coast than the three other fjords.
Content may be subject to copyright.
1. Introduction
Fjords are formed by glacial erosion and retreat, leaving behind a terminal moraine or sill at their mouth
(Farmer & Freeland,1983; Pickard,1961). Fjords are fed by rivers and streams that transport freshwater and
land-derived material properties such as dissolved (Oliver etal.,2017) and particulate organic carbon (St
Pierre etal.,2020). Fjords often serve as a gateway between fresh and marine waters for anadromous fish
species such as salmon and eulachon (see Bianchi etal.,2020).
Recent studies have documented changes to the world's fjords. In Chilean Patagonia, a southward displace-
ment of upwelling-favorable winds by 11km year−1 from 2003 to 2016 (Narvaez etal.,2019) could impact
fjord reoxygenation (Silva & Vargas,2014). In Northeast Greenland, coastal freshening from glacial melt
has constrained deep water renewal of Young Sound-Tyrolerfjord (Boone etal.,2018). In Norway, warming
of North Atlantic water has reduced the rate of deep-water renewal and increased deoxygenation of Mas-
fjorden (Aksnes etal.,2019). In British Columbia, anomalously warm water from the 2014 to 2016 marine
heatwave lingered in deep water of Rivers Inlet through at least 2018 (Jackson etal.,2018). Thus, at global
scales, climate change is impacting fjords.
Rivers Inlet, Knight Inlet, Bute Inlet, and Douglas Channel (Figure1) are fjords on British Columbia's main-
land central coast, with glacial watersheds at their heads. Importantly, each fjord has a different connection
pathway to the open ocean—Douglas Channel is a complex series of inlets with two entrances to the open
ocean via Hecate Strait, Rivers Inlet faces the open ocean via Queen Charlotte Sound, Knight Inlet connects
to the open ocean through Queen Charlotte Strait and the Broughton Archipelago, and Bute Inlet connects
to the open ocean through Juan de Fuca Strait and the Strait of Georgia. This is the first time that a time
series of temperature, salinity, and oxygen dating back to 1951 for multiple locations on the BC coast has
been jointly examined in the context of climate change.
Abstract Many complex fjord systems cross British Columbia's coastline. A 70 year (1951–2020) time
series analysis of temperature, salinity, and oxygen in four such fjords between54 and 50oN (Douglas
Channel, Rivers Inlet, Knight Inlet and Bute Inlet) shows that changes were greatest in deep waters
between the sill and the bottom. In Rivers, Knight and Bute Inlet, the deep water temperature increased
by 1.2–1.3°C over 70 years, up to two times the global average for open ocean waters at corresponding
depths, while salinity increased by 0.1–0.2, and oxygen decreased by 0.4–0.7mLL−1. The most northern
inlet, Douglas Channel, showed a temperature increase of 0.8°C from 1951 to 2016, while trends in oxygen
and salinity were not statistically significant. An analysis of Apparent Oxygen Utilization suggests that
the deep waters in Douglas Channel are more readily exchanged with the outer coast than the three other
Plain Language Summary Glacially carved fjords draw their deep waters from adjacent
offshore ocean basins through a combination of upwelling, cross-shelf transport, tidal mixing and
estuarine circulation related processes. We studied data spanning sevendecades from four such systems
covering four degrees of latitude along the Canadian Pacific and found that fjord deep waters below sill
depth were warming two times faster than their offshore source waters. Changes in temperature were
accompanied by significant trends of decreased oxygen concentrations and increased salinity. Potential
processes explaining these anomalous responses to climate change are discussed.
© 2021. American Geophysical Union.
All Rights Reserved.
Deep Waters in British Columbia Mainland Fjords Show
Rapid Warming and Deoxygenation From 1951 to 2020
Jennifer M. Jackson1 , Laura Bianucci2 , Charles G. Hannah2 , Eddy C. Carmack2 , and
Jessy Barrette1
1Hakai Institute, Victoria, BC, Canada, 2Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, BC, Canada
Key Points:
Temperature and oxygen data from
four fjords (Rivers, Knight, and Bute
Inlets and Douglas Channel) from
1951 to 2020 were examined
Over 70 years, deep water has
warmed by up to 1.3°C and lost up to
0.7mLL−1 of oxygen, with evidence
of accelerated warming since 2016
Deep warming and deoxygenation
trends are statistically alike in
at least three of the four fjords,
suggesting similar drivers
Supporting Information:
Supporting Information S1
Correspondence to:
J. M. Jackson,
Jackson, J. M., Bianucci, L., Hannah,
C. G., Carmack, E. C., & Barrette,
J. (2021). Deep waters in british
Columbia mainland fjords show rapid
warming and deoxygenation from
1951 to 2020. Geophysical Research
Letters, 48, e2020GL091094. https://doi.
Received 2 OCT 2020
Accepted 8 JAN 2021
1 of 9
Geophysical Research Letters
2. Data and Methods
2.1. Data
Temperature, salinity, and oxygen measurements have been collected in our study area since 1951 (Fig-
ureS1) through independent programs by the University of British Columbia, Fisheries and Oceans Cana-
da, and the Hakai Institute (TableS1). We examined one station in each inlet—DC (Douglas Channel), RI2
2 of 9
Figure 1. Bathymetric map of British Columbia's central coast, highlighting station DC in Douglas Channel, station RI2 in Rivers Inlet, station KN7 in Knight
Inlet, and station BU4 in Bute Inlet. Bathymetric data starting at offshore 200m isobath (from along the black lines are shown in
inset for each station.
Geophysical Research Letters
(Rivers Inlet), KN7 (Knight Inlet), and BU4 (Bute Inlet), which were selected because they were located
landward of the fjord's entrance sill (120km from the entrance sill for DC, 20km for RI2, and 50km
for KN7 and BU4), and in a deep basin (Figure1). In total, 411 CTD profiles were examined—31 from DC,
162 from RI2, 97 from KN7, and 121 from BU4. Since data were collected using different methods, we follow
Chandler etal.(2017) and interpret the temperature, salinity, and oxygen data to an accuracy of 0.1°C, 0.1
salinity units, and 0.1mLL−1, respectively. The temporal distribution of data collected at each station varied
according to observational program (FigureS1; TableS1). For all data, the seasonal cycle was removed as
reported in the supplementary information.
Trendlines for the different variables at each station were computed using ordinary least squares. The trends
were compared against each other using a z-test, where the z-score (z) was calculated as z=(A-B)/sqrt(SE_
A2+SE_B2) where A was the slope of the first trendline, B was the slope of the second trendline, and SE_ was
the standard error of the slope. The null hypothesis (i.e., the assumption that the two slopes are statistically
the same) was rejected at 95% if z>1.96 or z<−1.96.
2.2. Water Types
We define three water types for the inlets. The first is surface water, which is water lighter than a potential
density of 1,022kgm-3. The second is intermediate water, which starts at the base of surface water (typically
less than 10m) and ends at the sill depth, which is (following Pickard,1961 and Wan etal.,2017) 200m in
Douglas Channel, 137m in Rivers Inlet, 64m in Knight Inlet, and 355m in Bute Inlet. The third is deep
water, which starts at the sill depth and ends at the bottom, such that deep water is 201–370m at station
DC, 137–334m at station RI2, 65–513m at station KN7, and 356–632m at station BU4 (Pickard,1961). The
average temperature, salinity, and oxygen (DO) within each water type were calculated for each profile; we
here focus on deep water because this is where the largest changes were observed.
2.3. Calculation of Temperature Impact on Oxygen Changes
Temperature variability affects oxygen concentrations, so the dissolved oxygen saturation (DOsat) was cal-
culated using the TEOS-10 Matlab toolbox ( applied to in situ temperature and salinity
data. Afterward, the seasonal cycle was removed as described in the supplemental information. Following
the regional literature (Baker & Pond,1995; Hodal,2010; Lafond & Pickard,1975; Wan etal.,2017), it was
assumed that deep water was renewed annually in each fjord.
To remove the effect of temperature and solubility from DO changes, apparent oxygen utilization
(AOU=DOsat–DO) was calculated, which represents the change in oxygen since a water parcel was last
in contact with the atmosphere (e.g. Pytkowicz,1971; Broecker & Peng,1982), and assumes the surface
oxygen concentration was DOsat (e.g., Ito etal.,2004). AOU estimates biological processes, with positive
values indicating aerobic remineralization that consumes DO and negative values indicating photosynthe-
sis that produces DO. Mixing and advection can affect DO and DOsat, so impact the value of AOU (Koeve &
Kähler,2016). To distinguish between in situ biological processes and mixing, we follow Pytkowicz(1971)
and plot AOU against salinity for the deep waters of the fjords; a linear relationship indicates that changes
in AOU result from mixing rather than local remineralization/photosynthesis. For example, if two water
masses are mixed in the absence of local biological processes, the final values of both AOU and salinity are
simply a weighted average of the source waters’ AOU and salinities. In an AOU versus S plot, AOUfinal and
Sfinal fall on top of the line that connects water masses 1 and 2 end points. However, if there is in situ rem-
ineralization, the final AOU will change at a different proportion than S and will introduce nonlinearity in
the AOU versus S space.
3. Results
Deep waters in all four fjords revealed statistically significant trends, based on the trendline, from 1951 to
2020 of increasing temperature (Figure2a), resulting in decreased DOsat (Figure3b). In Rivers, Knight and
Bute Inlet, salinity significantly increased (Figure2b) and DO significantly decreased (Figure3a). Only in
Bute Inlet did AOU significantly increase (Figure3c). Table1 shows several metrics, including slopes, p
3 of 9
Geophysical Research Letters
values, determination coefficient, and the total change from 1951 to 2020 (based on the trendlines). Deox-
ygenation, salinity, temperature, and DOsat trends are statistically indistinguishable at 95% confidence for
the three southern inlets.
The Douglas Channel time series ended in 2016 and in 2020 at the other inlets. To determine the impact
of the shorter time series, we examined temperature in Rivers Inlet from 1951 to 2016 (Knight and Bute
Inlets had large data gaps through the 1990s) and found that trend lines were almost identical to Douglas
Channel (Figure2a), suggesting similar warming in Rivers Inlet and Douglas Channel from 1951 to 2016.
In addition, the slope of the temperature line was steeper in Rivers Inlet (1951–2020) than Douglas Channel
(1951–2016; Figure2a and Table1), suggesting that warming has accelerated since 2016. We acknowledge
that the large data gaps in Rivers Inlet are a potential source of error; however, z-tests show that the slope
of the lines are statistically similar in all inlets, suggesting that the trend in Rivers Inlet is real. Further,
boxplots of temperature and oxygen at decadal scale were constructed in all four inlets (FiguresS3 and S4)
and they showed that, based on a z-test, the trends calculated from the decadal median temperature and
oxygen were statistically similar to the trends shown in Figures2 and 3 in all inlets, except for DO in Rivers
Inlet (TableS2).
Hypoxic conditions, here taken as oxygen concentrations below 2mLL−1 (e.g., Diaz & Rosenberg,2008),
have been observed in the deep water of Rivers and Bute Inlet but not in Knight Inlet or Douglas Channel.
In Rivers Inlet, hypoxic deep water was observed in March 2009, 2014 to 2017, and 2019 and in April 2014,
2016, and 2019. In Bute Inlet, available data shows hypoxic deep waters in June 1998, July 1999, and March
and July 2018. These two inlets show the overall lowest mean DO concentrations (Figure3a), which com-
bined with the observed trends in deoxygenation, leads to the observed hypoxic conditions.
AOU is positive at all four stations (Figure3c), suggesting that consumption of DO, via biological process-
es, is occurring. The increasing AOU indicates that DO changes are larger than DOsat changes (i.e., DO
4 of 9
Figure 2. (a) Temperature and (b) practical salinity in deep water at DC (Douglas Channel), RI2 (Rivers Inlet), KN7 (Knight Inlet) and BU4 (Bute Inlet)
from 1951 to 2020. The seasonal cycle was removed as described in the supplementary material. The dashed lines represent the linear best fit for each station
(statistics are reported in Table1). The dotted orange line represents the linear best fit for station RI2 from 1951 to July 2016, the same length of time as the DC
time series.
Geophysical Research Letters
decreases faster than DOsat; see Table1); these trends are significant in the three southern inlets (at 95%
confidence with p<0.05 in Bute Inlet; Rivers and Knight Inlets would be significant at 90% with p<0.1),
suggesting that decreased oxygen solubility due to warmer waters is not the only driver of deoxygenation in
these three fjords (more detail in Section4.2).
A plot of AOU versus salinity shows different roles of water mass mixing versus in situ remineralization
in the different fjords (Figure4; see details about this kind of plot in Section2.3). The relationship is sig-
nificantly linear in Douglas Channel (r2=0.62, p<<0.01); however, in Rivers and Knight Inlet, a linear
regression explains little variability (r2=0.15 and 0.19, respectively, both with p<<0.01), while it explains
none in Bute Inlet (r20.00, p=0.64). Bute has a stronger relationship between temperature (and thus, DO-
sat) and salinity, whereas DO versus salinity dominates the AOU slope in the other three fjords (FigureS5).
4. Discussion
Multidecadal time series of deep-water properties in three different British Columbia mainland fjords have
shown, despite data gaps, statistically significant increases in temperature and salinity and decreases in
oxygen, while a fourth, Douglas Channel, showed significant trends in temperature only. The fact that the
warming and deoxygenation trends are statistically similar in the three southerly fjords infers that common
processes are driving the changes; we note, however, that differences exist between the northern Douglas
Channel and the three southern fjords.
4.1. Mechanisms for Warming
A recent assessment of 2004–2019 global ocean data by Johnson etal., (2020) found that waters at 150m
(about the depth of source water) are warming on average 0.1ºC per decade. At Ocean Station Papa in the
northeast Pacific Ocean, using data from 1956 to 2011, Freeland(2013) reported a warming trend of 0.05ºC
5 of 9
Figure 3. As in Figure4 but for (a) dissolved oxygen (DO), (b) oxygen saturation (DOsat), and (c) apparent oxygen utilization (AOU) in deep water (all in
mLL−1). Horizontal gray line in top panel highlights the hypoxic threshold (2mLL−1).
Geophysical Research Letters
per decade at 200m, which increased to 0.08ºC per decade at 150m when the timeseries was extended to
2018 (Cummins & Ross,2020). Within deep water, we observed a warming rate of 0.12°C per decade in
Douglas Channel, 0.19°C per decade in Rivers Inlet, 0.18°C per decade in Knight Inlet, 0.20°C per decade
in Bute Inlet. This rate is 1–2 times the global average found by Johnson etal.(2020), about 3 times
the warming rate reported by Freeland(2013), and twice the warming rate reported by Cummins and
Ross(2020). Why, then, are the deep waters in these fjords warming at a greater rate than the open
Upwelling causes deep-water renewal in all four inlets (Baker &
Pond, 1995; Hodal, 2010; Lafond & Pickard, 1975; Wan et al., 2017).
Upwelled water travels from the NE Pacific to Rivers Inlet along the
1,026kgm−3 isopycnal (Hare etal.,2020) and both offshore and deep Riv-
ers Inlet water were anomalously warm following the 2014–2016 marine
heatwave (Jackson etal., 2018; Scannell etal.,2020), which accelerat-
ed the warming trend after 2016 (Figure2a and Table1). Rivers Inlet
deep water is significantly denser than waters in Bute or Knight Inlet,
yet the fact that some of the warmest deep waters in Bute and Knight
Inlet were observed after 2017 suggests that, similar to Rivers Inlet, the
source waters for Bute and Knight Inletalso warmed. Once deep water
enters a fjord and is trapped behind the sill (Farmer & Freeland,1983), it
is modified only by slow processes such as vertical eddy diffusion (Paw-
lowicz, 2017) or yearly deep-water renewal events. Since the offshore
6 of 9
Temperature (ºC/decade) Slope=0.12±0.035 Slope=0.19±0.027 Slope=0.18±0.022 Slope=0.20±0.010
p=0.0025 p<0.0001 p<0.0001 p<0.0001
r2=0.30 r2=0.26 r2=0.40 r2=0.83
Δ=0.8ºC Δ=1.3ºC Δ=1.2ºC Δ=1.3ºC
Salinity (salinity units/decade) Slope=0.01±0.026 Slope=0.02±0.008 Slope=0.02±0.009 Slope=0.03±0.003
p=0.7019 p=0.0315 p=0.0364 p<0.0001
r2=0.01 r2=0.04 r2=0.05 r2=0.48
Δ=0.2 Δ=0.1 Δ=0.2
Oxygen (mLL−1/decade) Slope=−0.07±0.047 Slope=−0.11±0.043 Slope=−0.07±0.023 Slope=−0.08±0.019
p=0.1424 p=0.013 p=0.0053 p<0.0001
r2=0.09 r2=0.05 r2=0.13 r2=0.19
Δ=−0.7mLL−1 Δ=−0.4mLL−1 Δ=−0.6mLL−1
Oxygen saturation (mLL−1/decade) Slope=−0.02±0.005 Slope=−0.03±0.004 Slope=−0.03±0.004 Slope=−0.03±0.002
p=0.0005 p<0.0001 p<0.0001 p<0.0001
r2=0.38 r2=0.27 r2=0.39 r2=0.82
Δ=−0.1mLL−1 Δ=−0.2mLL−1 Δ=−0.2mLL−1 Δ=−0.2mLL−1
Apparent oxygen utilization (mLL−1/decade) Slope=0.05±0.047 Slope=0.07±0.042 Slope=0.04±0.000 Slope=0.05±0.018
p=0.2781 p=0.0671 p=0.0734 p=0.0051
r2=0.05 r2=0.03 r2=0.06 r2=0.10
Note. Changes observed were positive for temperature (warming), salinity (salinification), and AOU and negative for oxygen (deoxygenation). Slopes and their
errors are shown in units of the variable (ºC for temperature, mLL−1 for oxygen) per decade. Statistically significant relationships, here defined as when the
p-value for a linear relationship is less than 0.05, are highlighted in bold. In the latter cases, the total change Δ from 1951 to 2016 or 2020 (based on the trendline)
is given.
Table 1
Regression Slopes (With Standard Error) and Associated Metrics (p-value and r2 Value) for Time Series From 1951 to 2020 at Deep Waters of the Four Stations
Figure 4. Apparent oxygen utilization versus salinity in deep waters of
the four fjord stations (color scales as in previous figures). The dashed
lines represent the linear best fit for each station. Data at BU4 from 2017
onwards is highlighted in black symbols, and a linear fit without these data
is shown by the dotted line for BU4 only.
Geophysical Research Letters
source of upwelled water remained anomalously warm through at least 2018 (Jackson etal.,2018), fjord
deep water continued to be anomalously warm. Furthermore, winter outflow winds cool fjord waters (Mac-
Neil,1974), and winter continental temperatures are warming by more than 2°C per century (BC Ministry
of Environment, 2016), so it is possible that continental warming has meant less cooling of fjord water.
4.2. Mechanisms for Deoxygenation
The DO changes we observe in fjord deep waters are like those observed in the northeast Pacific Ocean. Cum-
mins and Ross(2020) found a deoxygenation trend from 1956 to 2020 of about 0.5mLL−1 (0.09mLL−1per
decade) at 150m in the open ocean Station Papa, which is similar to the deoxygenation we observed in fjord
deep waters (0.07–0.11mLL−1 per decade (Table1). It is important to note that oxygen over the continental
slope of the northeast Pacific has oscillated from low concentrations in the 1950s to high concentrations
in the 1980s and back to low concentrations in the 2010s (Crawford & Peña,2016), and thus these results
should be interpreted within the context of multidecadal oscillations. Waters from about 150m in the north-
east Pacific are the source for deep water in Rivers Inlet (Jackson etal.,2018); thus, it is likely that much
of the deoxygenation observed in deep fjord waters are associated with changes in source waters from the
northeast Pacific. Other processes that can impact oxygen concentrations in fjord deep waters are examined
The comparison of changes in DOsat from 1951 to 2020 (0.2mLL−1 for the three inlets) to those of DO (0.8,
0.5, and 0.6mLL−1 for Rivers, Knight, and Bute Inlet) suggests that temperature-dependent solubility effects
(either locally or at the source waters) represent 28%, 42%, and 39% of the total DO change in each of those
three inlets, respectively. Since the fjord deep water is warming faster than offshore water, it is likely that the
decreased solubility in coastal fjords, which enhances deoxygenation, plays a more important role in these
coastal waters than offshore (e.g. Crawford & Peña,2016).
Warmer waters accelerate aerobic remineralization (i.e., the decomposition of organic matter by oxy-
gen-consuming bacteria), leading to a stronger sink of DO by bacteria (e.g. Brewer & Peltzer,2017; Pomeroy
& Wiebe,2001). The remineralization rate (r(T)) can be estimated if we assume a typical Q10 formulation for
this process (e.g. Peña etal2016; Segschneider & Bendtsen,2013),
rT rQ
0 10
where Q10 is the rate change for a 10K temperature increase and r0 is the remineralization rate at a reference
temperature T0. If we apply the above equation to two temperatures, T1 and T1+ΔT, we find that Q10ΔT/10
represents the fractional change due to a temperature change ΔT. Typical values of Q10 vary between 1.5 and
3 (e.g., Lomas etal.,2002; López-Urrutia etal.,2006; Laufkötter etal.,2017), with Q10=2 a conservative es-
timate of the temperature sensitivity (Segschneider & Bendtsen,2013). Applying the change in temperature
found in the three southern inlets (1.2°C–1.3°C), we estimate that the effect of warming on remineralization
rates is around 9% (varying between 5% and 15% if we use a Q10 of 1.5 or 3, respectively). This suggests that
increased remineralization under observed warming conditions have had a quantifiable effect on deoxygen-
ation in fjord deep waters.
Increased primary production and rainout of organic matter to the deep water can also enhance the total
amount of remineralization, but unfortunately only Rivers Inlet has a useful chlorophyll timeseries, starting
in 2014. The analysis of a 2014–2018 time series of vertically integrated chlorophyll from 5 to 50m depth
shows a decline in the magnitude of the spring bloom in this station (Jackson etal, under revision). This
suggests increased rainout is not a mechanism for deoxygenation in the deep waters. However, this short
chlorophyll time series prevents us from making a sound conclusion in the context of our longer DO time
Our analysis of AOU versus salinity following Pytkowicz(1971) highlights some differences between Doug-
las Channel and the southern inlets. Specifically, changes in AOU in Douglas Channel are primarily due to
changes in the relative proportion of the source waters; in contrast, local processes are likely more impor-
tant in the three inlets. The larger range of salinity in Douglas Channel suggests that source waters experi-
ence less mixing by the time they reach the DC station compared with the stations in the southern fjords.
7 of 9
Geophysical Research Letters
Further processes that require examination include the intensity and frequency of upwelling, and changes
in deep water residence times and ventilation (e.g., Erlandson etal.,2006; Pawlowicz,2017). Understanding
these processes are important areas for future research.
5. Conclusions
An analysis of deep water from three British Columbia mainland fjords (Rivers, Knight and Bute Inlet) has
found that from 1951 to 2020, temperature and salinity increased while oxygen decreased. In these three
fjords, temperature warmed up to two times faster than the global average of waters at similar depths and
these changes can be attributed to warming of offshore waters that are the source for fjord deep water via
upwelling, and possibly continental warming that changed outflow winds. Decreased oxygen in offshore
waters can also explain the lower oxygen in fjord deep water though it is likely that enhanced remineraliza-
tion from warming further reduced oxygen in the fjords.
Douglas Channel was different. Although temperature warmed at the same rate as Rivers Inlet until at
least 2016, oxygen did not decrease at a statistically significant rate. An analysis of AOU versus S suggests
that deep waters in Douglas Channel are more readily exchanged with the outer coast than the three other
Data Availability Statement
All data used in this project are managed by CIOOS and can be found at
Aksnes, D. L., Aure, J., Johansen, P.-O., Johnsen, G. H., & Gro Vea Salvanes, A. (2019). Multi-decadal warming of Atlantic water and
associated decline of dissolved oxygen in a deep fjord. Estuarine, Coastal and Shelf Science, 228, 106392.
Baker, P., & Pond, S. (1995). The low-frequency residual circulation in Knight Inlet, British Columbia. Journal of Physical Oceanography,25,
Bianchi, T. S., Arndt, S., Austin, W. E. N., Benn, D. I., Bertrand, S., Cui, X., etal. (2020). Fjords as Aquatic Critical Zones (ACZs). Earth-Sci-
ence Reviews, 203, 103145.
Boone, W., Rysgaard, S., Carlson, D. F., Meire, L., Kirillov, S., Mortensen, J., etal. (2018). Coastal freshening prevents fjord bottom wa-
ter renewal in Northeast Greenland: A mooring study from 2003 to 2015. Geophysical Research Letters, 45, 2726–2733. https://doi.
Brewer, P. G., & Peltzer, E. T. (2017). Depth perception: The need to report ocean biogeochemical rates as functions of temperature, not
depth. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 375, 20160319. https://doi.
British Columbia. Ministry of Environment (2016). Indicators of climate change for British Columbia, 2016 update, Victoria, BC: eBook.
Broecker, W. S., & Peng, T. H. (1982). Tracers in the sea, Lamont-Doherty Earth Observatory. NY, U.S.A: Palisades.
Chandler, P. C., Foreman, M. G. G., Ouellet, M., Mimeault, C., & Wade, J. (2017). Oceanographic and environmental conditions in the Dis-
covery Islands, British Columbia. DFO Canadian Science Advisory Secretariat Research Document, 071(XIII), 51. https://waves-vagues.
Crawford, W. R., & Peña, M. A. (2016). Decadal trends in oxygen concentration in subsurface waters of the Northeast Pacific Ocean. Atmos-
phere-Ocean, 54(2), 171–192.
Cummins, P. F., & Ross, T. (2020). Secular trends in water properties at Station P in the northeast Pacific: An updated analysis. Progress in
Oceanography, 186, 102329.
Diaz, R. J., & Rosenberg, R. (2008). Spreading dead zones and consequences for marine ecosystems. Science, 321, 5891926–5891929.
Erlandsson, C. P., Stigebrandt, A., & Arneborg, L. (2006). The sensitivity of minimum oxygen concentrations in a fjord to changes in biot-
ic and abiotic external forcing. Limnology and oceanography, 51(1, part 2), 631–638.
Farmer, D. M., & Freeland, H. J. (1983). The physical oceanography of fjords. Progress in Oceanography, 12(2), 147–219. https://doi.
Freeland, H. J. (2013). Evidence of change in the winter mixed layer in the Northeast Pacific Ocean: A problem revisited. Atmosphere-Ocean,
51(1), 126–133.
Hare, A., Evans, W., Pocock, K., Weekes, C., & Giminez, I. (2020). Contrasting marine carbonate systems in two fjords in British Colum-
bia, Canada: Seawater buffering capacity and the response to anthropogenic CO2 invasion. PLoS One, 15(9), e0238432. https://doi.
Hodal, M. (2010). Net physical transports, residence times, and new production for Rivers Inlet (MSc thesis, p. 71). BC: University of British
Ito, T., Follows, M. J., & Boyle, E. A. (2004). Is AOU a good measure of respiration in the oceans? Geophysical Research Letters, 31(17),
8 of 9
Funding for this research was provided
by the Tula Foundation (J. M. Jackson,
and J. Barrette) and Fisheries and
Oceans Canada (L. Bianucci and C. G.
Hannah). We thank the scientists and
crew from the University of British Co-
lumbia, Fisheries and Oceans Canada,
and the Hakai Institute for collecting
these data. Keith Holmes created Fig-
ure1. We gratefully acknowledge that
this work took place on the traditional
territories of the Gitga'at, Wuikinuxv,
Tlowitsis, Da'naxda'xw Awaetlala, and
Homalco First Nations. This research
is not associated with any known
conflict of interest. We thank the editor
and two reviewers for their construc-
tive comments, which improved this
Geophysical Research Letters
Jackson, J. M., Johnson, G. C., Dosser, H. V., & Ross, T. (2018). Warming from recent marine heatwave lingers in deep British Columbia
fjord. Geophysical Research Letters, 45, 9757–9764.
Johnson, G. C., Lyman, J. M., Boyer, T., Cheng, L., Domingues, C. M., Gilson, J., etal. (2020). Ocean heat content [in “State of the Climate
in 2019”]. Bulletin of the American Meteorological Society, 101(8), S140–S144.
Koeve, W., & Kähler, P. (2016). Oxygen utilization rate (OUR) underestimates ocean respiration: A model study. Global Biogeochemical
Cycles, 30, 1166–1182.
Lafond, C. A., & Pickard, G. L. (1975). Deepwater exchanges in Bute Inlet, British Columbia. Journal of the Fisheries Research Board of
Canada, 32, 2075–2089.
Laufkötter, C., John, J. G., Stock, C. A., & Dunne, J. P. (2017). Temperature and oxygen dependence of the remineralization of organic
matter. Global Biogeochemical Cycles, 31(7), 1038–1050.
Lomas, M. W., Glibert, P. M., Shiah, F. K., & Smith, E. M. (2002). Microbial processes and temperature in Chesapeake Bay: Current rela-
tionships and potential impacts of regional warming. Global Change Biology, 8, 51–70.,1046/j.1365-2486.2002.00454.x
López-Urrutia, Á., Martin, E. S., Harris, R. P., & Irigoien, X. (2006). Scaling the metabolic balance of the oceans. Proceedings of the National
Academy of Sciences of the United States of America, 103, 8739–8744.
McNeil, M. R. (1974). The mid-depth temperature minimum in B.C. Inlets, Vancouver, B.C.: University of British Columbia. Retrieved from
Narvaez, D. A., Vargas, C. A., Cuevas, L. A., Garcia-Loyola, S. A., Segura, C., Tapia, F. J., & Broitman, B. R. (2019). Dominant scales
of subtidal variability in coastal hydrography of the Northern Chilean Patagonia. Journal of Marine Systems, 193, 59–73. https://doi.
Oliver, A. A., Tank, S. E., Giesbrecht, I., Korver, M. C., Floyd, W. C., Sanborn, P., etal. (2017). A global hotspot for dissolved organic car-
bon in hypermaritime watersheds of coastal British Columbia. Biogeosciences, 14, 3743–3762.
Pawlowicz, R. (2017). Seasonal cycles, hypoxia, and renewal in a coastal fjord (Barkley Sound, British Columbia). Atmosphere-Ocean,
55(4–5), 264–283.
Peña, M. A., Masson, D., & Callendar, W. (2016). Annual plankton dynamics in a coupled physical–biological model of the Strait of Geor-
gia, British Columbia. Progress in Oceanography, 146, 58–74.
Pickard, G. L. (1961). Oceanographic features of inlets in the British Columbia mainland coast. Journal of the Fisheries Research Board of
Canada, 18(6), 908–999.
Pomeroy, L. R., & Wiebe, W. J. (2001). Temperature and substrates as interactive limiting factors for marine heterotrophic bacteria. Aquatic
Microbial Ecology, 23, 187–204.
Pytkowicz, R. M. (1971). On the apparent oxygen utilization and the preformed phosphate in the oceans. Limnology and Oceanography,
16(1), 39–42.
Scannell, H. A., Johnson, G. C., Thompson, L., Lyman, J. M., & Riser, S. C. (2020). Subsurface evolution and persistence of marine heat-
waves in the northeast Pacific. Geophysical Research Letters, 47, e2020GL090548.
Segschneider, J., & Bendtsen, J. (2013). Temperature dependent remineralization in a warming ocean increases surface pCO2 through
changes in marine ecosystem composition. Global Biogeochemical Cycles, 27(4), 1214–1225.
Silva, N., & Vargas, C. A. (2014). Hypoxia in Chilean Patagonian Fjords. Progress in Oceanography, 129, 62–74.
St. Pierre, K. A., Oliver, A. A., Tank, S. E., Hunt, B. P. V., Giesbrecht, I., Kellogg, C. T. E., etal. (2020). Terrestrial exports of dissolved and
particulate organic carbon affect nearshore ecosystems of the Pacific coastal temperature rainforest. Limnology and Oceanography, 65,
Wan, D., Hannah, C. G., Foreman, M. G. G., & Dosso, S. (2017). Subtidal circulation in a deep-silled fjord: Douglas Channel, British Colum-
bia. Journal of Geophysical Research, 122, 4163–4182.
9 of 9
... Bute Inlet is undergoing warming and deoxygenation (J. M. Jackson et al., 2021) and ocean acidification (Hare et al., 2020). Thus, understanding processes that cause cooling and reoxygenation in Bute Inlet is important. ...
... CTD and oxygen sensors were calibrated yearly and data were processed using either Seabird's SeaSoft software or the RBR processing steps recommended by Halverson et al. (2017). In addition, we examine Bute Inlet temperature, salinity and oxygen data collected from 1951 to 2014 by the University of BC and Fisheries and Oceans Canada (see J. M. Jackson et al. (2021)). In Section 3.4, the historical atmospheric (1929-2022) and oceanographic (1951-2022) time series were jointly examined to gain a historical perspective of outflow winds. ...
... The oceanographic data have large gaps and are undergoing both a warming and deoxygenation trend (J. M. Jackson et al., 2021) and interdecadal variability (Crawford & Peña, 2016) so annual and decadal trends are difficult to assess. However, we found a statistically significant relationship between the atmospheric CFT below −20°C and oceanographic temperature (p-value = 0.005, R 2 = 0.22) and oxygen (p-value = 0.0001, R 2 = 0.38) the following summer. ...
Full-text available
Arctic outflow winds bring cold air from the continent to the coastline through mountain passes. Using observational data and a 2-D model, we show that a February 2019 outflow event caused the upper 100 m in Bute Inlet, British Columbia (within the traditional territory of the Homalco Nation) to cool up to 1.9°C and gain up to 4.1 mLL−1 of oxygen. The cold, oxygenated water persisted for almost 1 year within the 1,023–1,023.5 kgm−3 isopycnal range (∼50–150 m). Atmospheric (from 1929 to 2022) and oceanographic (from 1951 to 2022) data showed a statistically significant relationship between continental air temperature at Tatlayoko Lake and temperature and oxygen in Bute Inlet. This local mechanism that counters some effects of climate change could create a biological refugium as surrounding waters warm and lose oxygen at a faster rate. The number of outflow events decreased from 1951 to 2018, and increased since.
... Since 1998, temperature and salinity were measured using a Seabird or RBR CTD sensor and oxygen was measured with a Seabird or Rinko oxygen sensor. Following water type definitions in fjords (Farmer and Freeland 1983;Jackson et al. 2021), three water types were defined. These water types were surface (potential density relative to surface pressure of less than 1022 kgm -3 ), intermediate (from the base of surface layer to sill depth) and deep (below sill depth). ...
... Salinity and oxygen in 2020 were similar to the 1991 to 2020 climatology. Recent research has shown that from 1951 to 2020, deep water in Rivers Inlet became saltier by 0.2 salinity units and lost 0.7 mL L -1 of oxygen (Jackson et al. 2021). The similarity of salinity and oxygen in 2020 to the 1991 to 2020 climatology suggests that neither of these properties changed significantly in 2020. ...
... In 2020, both intermediate (Figure 33-3) and deep (Figure 33-4) water were warmer, saltier, and less oxygenated than the 1951 to 2010 climatology. Jackson et al. (2021) found that, between 1951 and 2020, deep water in Bute Inlet warmed by 1.3 °C, became saltier by 0.2 units, and lost 0.6 mL L -1 of oxygen. In 2020, deep water continued to be saltier than the 1991 to 2020 climatology, while oxygen was similar. ...
Technical Report
Report is on page 198-202.  In Saanich Inlet, biologically-relevant hypoxia exposure could not be calculated for the second year in a row as a result of a two-month data gap in the ONC-VENUS time-series.  The density of commercial shrimp (e.g. Spot Prawn Pandalus platyceros) remains at levels comparable to the benchmark period.  A sustained population of the striped nudibranch Armina californica remains after being introduced during the 2016 hypoxia event.  The Sea Whip (Halipteris willemoesi) population decreased after a brief period of recruitment. The population remains at <5% of their abundance numbers prior to the 2016 marine heatwave. 42.2. Description of the time
... In the fjords of British Columbia, deep-water also showed deoxygenation between −17.8 and −31.2 μmol L −1 over the 70-year period. The decrease in DO concentrations in British Columbia coincides with the increasing trend in temperature and salinity (Jackson et al., 2021). As possible mechanisms that drive deoxygenations, these authors propose (a) an increase in deep-water temperatures that contribute to decreased solubility, (b) multidecadal oscillations of DO concentrations, (c) DO consumption caused by the remineralization of organic matter, (d) increased primary production, and (e) rainout of organic matter to the ocean floor. ...
Full-text available
In recent decades, global dissolved oxygen (DO) measurements have registered a decrease of ∼1%–2% in oxygen content, raising concerns regarding the negative impacts of ocean deoxygenation on marine life and the greenhouse gas cycle. By combining in situ data from 2016 to 2022, satellite remote sensing, and outputs from a physical‐biogeochemical model, we revealed the deoxygenation process in the Patagonian fjords for the first time. Deoxygenation was associated with the advection of equatorial subsurface water (ESSW) mass into the northern region of Patagonia. An analysis of the circulation regime using the Mercator‐Ocean global high‐resolution model confirmed the importance of the Peru–Chile undercurrent (PCUC) in transporting the ESSW poleward, contributing to the entrance of ESSW into the northern Patagonian fjords. A mooring system installed in the water interchange area between the Pacific Ocean and Patagonian fjords detected a decreasing DO of −21.66 μmol L⁻¹ over 7 years, which was explained by the increase in PCUC transport of 1.46 Sv. Inside the Puyuhuapi fjord system, a second DO time series exhibited more marked deoxygenation with −88.6 μmol L⁻¹ over 3 years linked with the influence of ESSW and local processes, such as DO consumption by the organic matter degradation. The recent deoxygenation registered in the northern Patagonian fjords demonstrates the significance of studying DO in the context of reducing the global oxygen content, further warranting the quantification of the impacts of deoxygenation on life cycles of marine organisms that inhabit the Patagonian fjords and channels and the Humboldt current system.
... Shoaled hypoxic waters and elevated sea-surface temperatures cause vertical habitat compression (Bakun et al., 2015), which may increase interaction with predators, parasites, and pathogens, and possibly decrease feeding opportunities (Breitburg et al., 2018). Thus, projected deoxygenation and warming in fjord seawater (Jackson et al., 2021a) will likely pose an increasing threat to salmon populations. ...
Full-text available
While fjords often have low oxygen concentrations in their deep waters, this research identified seasonal, near-surface hypoxia (≤ 2 mL L-1 or 2.9 mg L-1) through a year-long monthly time series in Clayoquot Sound, British Columbia. Temperature, salinity, and oxygen data were collected monthly in the upper 50 m at three stations in Herbert Inlet from June 2020 to July 2021, marking the first time series of its kind in a Clayoquot Sound fjord. Hypoxic conditions were shallowest (minimum depth of 12 m) and most intensified in summer; near-surface hypoxia was recorded at one or more stations in all months except in winter. Considering that many local marine species, including wild Pacific salmon, experience adverse effects at oxygen concentrations much higher than the hypoxic threshold, we note that 50 to 100% of the upper 50 m of Herbert Inlet consistently presented low oxygen concentrations (defined here as a guideline as ≤ 4.9 mL L-1 or 6.9 mg L-1) during the 14-month study period. Previous observations collected sporadically since May 1959 confirmed the presence of hypoxic conditions in the past. These findings suggest that long-term, multidisciplinary studies are needed to understand and predict the impact of hypoxia and deoxygenation on wild salmon stocks as climate changes.
... These characteristics strengthen the land-ocean connection and fjords have consequently been coined "aquatic critical zones" (Smith et al., 2015;Bianchi et al., 2020). While deep waters within Rivers Inlet are strongly affected by offshore waters that are exchanged across the sill Jackson et al., 2021), surface waters are more strongly tied to the water and materials exported from land (Hare et al., 2020). These dynamics have created coastal environments that are highly sensitive to processes occurring on land that ultimately affect exports to the coastal ocean and the uptake of land-derived materials in coastal food webs (Lafon et al., 2014). ...
Full-text available
Globally, coastal waters are considered biogeochemical hotspots because they receive, transform, and integrate materials and waters from both land and the open ocean. Extending from northern California to southeast Alaska, the Northeast Pacific Coastal Temperate Rainforest (NPCTR) region is no exception to this, and hosts a diversity of watershed types (old-growth rainforest, bog forest, glaciers), and tidal (sheltered, exposed) and pelagic marine (deep fjord, shallow estuary, well-mixed channel) environments. With large freshwater fluxes to the coastal ocean, cross-ecosystem connectivity in the NPCTR is expected to be high, but seasonally variable, with pulses in runoff from rainfall, snowmelt and glacial melt, and primary production associated with changes in ocean upwelling and incident light. However, the relative contribution of each ecosystem to surface ocean organic matter pools over time and space remains poorly constrained, despite their importance for the structure and function of coastal marine ecosystems. Here, we use a four-year dataset of particulate organic matter (POM) chemical composition (δ13C, δ15N, C:N ratio) to quantify the relative contributions of watershed materials via riverine inputs, marine phytoplankton, and macrophytes (macroalgae and seagrass) to surface waters (0-10 m) at 11 stations representing fjord, shallow non-fjord estuary, sheltered channel and well-mixed coastal environments at the heart of the NPCTR in British Columbia, Canada. Watershed, marine phytoplankton, and macrophyte contributions to surficial POM ranged between 5-78%, 22-88%, and 0.1-18%, respectively, and varied by season and station. Watershed inputs were the primary source of POM across all stations in winter and were important throughout the year within the fjord. Marine phytoplankton were the principal source of POM in spring and at all stations outside of the fjord through summer and autumn, while macrophyte contributions were greatest in summer. These results demonstrated high, but seasonally and spatially variable, connectivity between ecosystems that are often considered in isolation of one another and highlight the need to consider coastal waters as integrated land-ocean meta-ecosystems. Future work should investigate how heterogeneity in POM sources determines its fate in coastal ecosystems,and the relative importance of different basal organic matter sources for the marine food web.
... DO is the measured dissolved O 2 . AOU estimates biological processes; positive values indicate aerobic remineralization processes, which consume DO, and negative values indicate photosynthetic processes, which produce DO (Pytkowicx, 1971;Ito et al., 2004;Jackson et al., 2021). ...
Full-text available
The biogeochemical dynamics of fjords in the southeastern Pacific Ocean are strongly influenced by hydrological and oceanographic processes occurring at a seasonal scale. In this study, we describe the role of hydrographic forcing on the seasonal variability of the carbonate system of the Sub-Antarctic glacial fjord, Seno Ballena, in the Strait of Magellan (53°S). Biogeochemical variables were measured in 2018 during three seasonal hydrographic cruises (fall, winter and spring) and from a high-frequency pCO2-pH mooring for 10 months at 10 ± 1 m depth in the fjord. The hydrographic data showed that freshwater input from the glacier influenced the adjacent surface layer of the fjord and forced the development of undersaturated CO2 (< 400 μatm) and low aragonite saturation state (ΩAr < 1) water. During spring, the surface water had relatively low pCO2 (mean = 365, range: 167 - 471 μatm), high pH (mean = 8.1 on the total proton concentration scale, range: 8.0 - 8.3), and high ΩAr (mean = 1.6, range: 1.3 - 4.0). Concurrent measurements of phytoplankton biomass and nutrient conditions during spring indicated that the periods of lower pCO2 values corresponded to higher phytoplankton photosynthesis rates, resulting from autochthonous nutrient input and vertical mixing. In contrast, higher values of pCO2 (range: 365 – 433 μatm) and relatively lower values of pHT (range: 8.0 – 8.1) and ΩAr (range: 0.9 – 2.0) were recorded in cold surface waters during winter and fall. The naturally low freshwater carbonate ion concentrations diluted the carbonate ion concentrations in seawater and decreased the calcium carbonate saturation of the fjord. In spring, at 10 m depth, higher primary productivity caused a relative increase in ΩAr and pHT. Assuming global climate change will bring further glacier retreat and ocean acidification, this study represents important advances in our understanding of glacier meltwater processes on CO2 dynamics in glacier–fjord systems.
Full-text available
Fjords are common geomorphological coastal features in the mid- and high-latitudes, carved by glacial erosion. These deep nearshore zones connect watersheds and oceans, typically behaving as an estuary. Many fjords in the world have shown concerning warming and deoxygenation trends in their deep waters, sometimes at faster rates than the open ocean. While that is the case in several fjords of British Columbia (BC), Canada, some of the same fjords have shown that strong Arctic outflow wind events in winter can lead to cooling and reoxygenation of subsurface waters, with effects lasting until the following autumn. The latter was observed in Bute Inlet, BC in 2019. We used a high-resolution, three-dimensional ocean model to investigate the mechanisms allowing for the persistence of these subsurface conditions through the year. The presence of the subsurface cold water mass reduced the already weak residual circulation, changing its vertical structure from three to four layers. The reduction of mixing and advection allowed for the water mass to stay in place until autumn conditions arrived (i.e., strong wind mixing and reduced freshwater forcing). The identification of mechanisms that allow for the persistence of cold and oxygenated conditions are key to understand potential areas of ecological refugia in a warming and deoxygenating ocean.
Full-text available
Fisheries science uses quantitative methods to inform management decisions that reflect cultural preferences which, in turn, indirectly influence the states of ecosystems. To date, it has largely supported Eurocentric preferences for the commodification of marine organisms under the tenets of maximum sustainable yield, whereby abundances are intentionally maintained far below their historical baselines despite broader socio‐ecological trade‐offs. In contrast, Indigenous Knowledge Systems (IKS) adhere to the principle of “take only what you need and leave lots for the ecosystem,” implementing lower fishery removals to support socio‐ecological resilience. Despite the power imbalance favouring Eurocentric preferences in decision‐making, fisheries scientists increasingly recognize that the pairing of IKS and Western science, or Two‐Eyed Seeing, would lead to more holistic management goals. For recognition to transcend tokenism, meaningful collaborations and co‐governance structures underlying knowledge co‐production must carry through to legislated policy changes. Using recent co‐governance developments for fisheries management and spatial protections involving federal, provincial and Indigenous governments in Pacific Canada, we illustrate how the precautionary approach, including reference points and harvest control rules broadly applied in international fisheries, could be revised to make collaborative fisheries management compatible with IKS and improve biodiversity and fisheries protections. Our recommendations may create socio‐economic trade‐offs at different timescales for commercial fishers. Pre‐empting that challenge, we discuss IKS‐compatible economic approaches for addressing shorter term costs arising from reduced exploitation rates. Although our case study derives from Pacific Canada, the insights provided here are broadly applicable elsewhere in the world.
Full-text available
Fjord systems are typically affected by low‐oxygen conditions, which are increasing in extent and severity, forced by ongoing global changes. Fjord sedimentary records can provide high temporal resolution archives to aid our understanding of the underlying mechanisms and impacts of current deoxygenation. However, such archives can only be interpreted with well‐calibrated proxies. Bottom‐water oxygen conditions determine redox regime and availability of redox‐sensitive trace elements such as manganese, which in turn may be recorded by manganese‐to‐calcium ratios (Mn/Ca) in biogenic calcium carbonates (e.g., benthic foraminifera tests). However, biological influences on Mn incorporation (e.g., species‐specific Mn fractionation, ontogeny, living and calcification depths) are still poorly constrained. We analyzed Mn/Ca of living benthic foraminifera (Bulimina marginata, Nonionellina labradorica), sampled at low‐ to well‐oxygenated conditions over a seasonal gradient in Gullmar Fjord, Swedish West coast (71–217 μmol/L oxygen (O2)), by laser‐ablation ICP‐MS. High pore‐water Mn availability in the fjord supported Mn incorporation by foraminifera. B. marginata recorded contrasting Mn redox regimes sensitively and demonstrated potential as proxy for low‐oxygen conditions. Synchrotron‐based scanning X‐ray fluorescence nanoimaging of Mn distributions across B. marginata tests displayed Mn/Ca shifts by chambers, reflecting bottom‐water oxygenation history and/or ontogeny‐driven life strategy preferences. In contrast, Mn/Ca signals of N. labradorica were extremely high and insensitive to environmental variability. We explore potential biologically controlled mechanisms that could potentially explain this species‐specific response. Our data suggest that with the selection of sensitive candidate species, the Mn/Ca proxy has potential to be further developed for quantitative oxygen reconstructions in the low‐oxygen range.
Full-text available
Plain Language Summary Marine heatwaves, extended periods when ocean temperatures are abnormally warm, have occurred with greater frequency and magnitude over the last few decades. As the planet continues to warm, these events will increase, with substantial effects on marine life and on the socioeconomics of communities that depend on marine resources. Here we analyze temperature and salinity data collected by northern elephant seals to better understand the development of the North Pacific Blob, a marine heatwave that began in late 2013 and continued through 2015. This was the largest, longest marine heatwave on record, with surface temperatures over six degrees above normal. Elephant seals cover much of the Northeast Pacific Ocean when they forage, and the high‐density data they collected provide a unique look into the evolution of this event. We found that abnormally warm temperatures extended down through the top 1,000 m of the ocean, and that subsurface warming continued until 2017, after surface temperatures had returned to normal. Our analyses show that the observed deep warming was likely caused in part by the northward movement of subtropical water deeper than 200 m. These findings help us understand the complexities of marine heatwaves and better predict ecosystem effects of future events.
Full-text available
Plain Language Summary Surface marine heatwaves (MHWs) are periods of prolonged and extremely warm regional sea surface temperature that can negatively impact the health and productivity of marine ecosystems. Using surface and subsurface ocean observations, we compare and contrast two recent MHWs to show that salinity variations play an important role in the vertical distribution of temperature anomalies by changing the overall stability of the water column. During the 2019–2020 MHW, the near‐surface waters in the Gulf of Alaska were fresher than normal, preventing warm sea surface temperatures from mixing as deeply into the subsurface as in the 2013–2016 MHW. The freshening in 2019 likely enhanced warming in the buoyant surface layer. As warmer temperatures gradually mix downward they can persist long after the surface MHW disappears, suggesting that the ocean can provide memory for long‐lived MHWs. The subsurface persistence of MHWs has potential ramifications for long‐lasting ecological impacts.
Full-text available
The carbonate system in two contrasting fjords, Rivers Inlet and Bute Inlet, on the coast of British Columbia, Canada, was evaluated to characterize the mechanisms driving carbonate chemistry dynamics and assess the impact of anthropogenic carbon. Differences in the character of deep water exchange between these fjords were inferred from their degree of exposure to continental shelf water and their salinity relationships with total alkalinity and total dissolved inorganic carbon, which determined seawater buffering capacity. Seawater buffering capacity differed between fjords and resulted in distinct carbonate system characteristics with implications on calcium carbonate saturation states and sensitivity to increasing anthropogenic carbon inputs. Saturation states of both aragonite and calcite mineral phases of calcium carbonate were seasonally at or below saturation throughout the entire water column in Bute Inlet, while only aragonite was seasonally under-saturated in portions of the water column in Rivers Inlet. The mean annual saturation states of aragonite in Rivers Inlet and calcite in Bute Inlet deep water layers have declined to below saturation within the last several decades due to anthropogenic carbon accumulation, and similar declines to undersaturation are projected in their surface layers as anthropogenic carbon continues to accumulate. This study demonstrates that the degree of fjord water exposure to open shelf water influences the uptake and sensitivity to anthropogenic carbon through processes affecting seawater buffering capacity, and that reduced uptake but greater sensitivity occurs where distance to ocean source waters and freshwater dilution are greater.
Full-text available
The Atlantic meridional overturning circulation (AMOC) is a key component of the ocean circulation system that is constantly moving water, heat, salt, carbon, nutrients, and other substances around the globe. The AMOC impacts the Atlantic Ocean in a unique way, making it the only ocean basin where heat is carried northward in both hemispheres. Recognizing the role of the AMOC in Earth’s climate and, hence, the importance of monitoring and understanding it, several AMOC-observing systems have been established over the last two decades (e.g., Frajka-Williams et al. 2019; McCarthy et al. 2020; Fig. 3.20). This section describes the most recent findings derived from the existing observations of the volume (MOC) and the associated meridional heat transports (MHT). Because some of the key boundary current arrays have been observed for longer than the fully trans-basin arrays, key results on those boundary currents are also reviewed.
Full-text available
Watersheds of the coastal temperate rainforests of Pacific North America export large amounts of organic carbon (OC) to the coastal ocean. While it has been suggested that terrestrially derived organic matter could subsidize marine food webs and affect ocean biogeochemistry along the coastal margin, little work has been done to quantify and characterize OC across the freshwater to marine continuum. We conducted monthly and targeted rainfall event surveys of dissolved and particulate organic carbon (DOC and POC) quantity and quality (δ13C, dissolved organic matter characterization) across a freshwater to marine salinity gradient between Calvert and Hecate Islands, British Columbia, Canada. Freshwater DOC concentrations (9.97 ± 0.25 mg L−1) far exceeded those in marine waters (1.24 ± 0.03 mg L−1), while POC concentrations were similar across all sites (0.23 ± 0.01 mg L−1). δ13C‐DOC and ‐POC in freshwaters were constant, but varied seasonally at the marine stations with freshwater and marine processes. Rainfall events facilitated the rapid export of terrestrial DOC and POC to coastal waters, altering water quality and potentially subsidizing microbial productivity across marine surface waters. On an annual basis, primary production in marine waters (21–42 Gg C) exceeded total freshwater OC contributions (1.8–2.2 Gg C); however, freshwater exports were more important during the autumn and winter months, when rainfall was highest and primary production was limited by shorter days and deep turbulent mixing. Our results highlight the importance of storms for connecting the coastal temperate rainforest with surface coastal waters, especially during the summer when connectivity between the freshwater and marine ecosystems is otherwise low.
Full-text available
In recent decades, the land-ocean aquatic continuum, commonly defined as the interface, or transition zone, between terrestrial ecosystems and the open ocean, has undergone dramatic changes. On-going work has stressed the importance of treating Aquatic Critical Zones (ACZs) as a sensitive system needing intensive investigation. Here, we discuss fjords as an ACZ in the context of sedimentological, geochemical, and climatic impacts. These diverse physical features of fjords are key in controlling the sources, transport, and burial of organic matter in the modern era and over the Holocene. High sediment accumulation rates in fjord sediments allow for high-resolution records of past climate and environmental change where multiple proxies can be applied to fjord sediments that focus on either marine or terrestrial-derived components. Humans through land-use change and climatic stressors are having an impact on the larger carbon stores in fjords. Sediment delivery whether from accelerating erosion (e.g. mining, deforestation, road building, agriculture) or from sequestration of fluvial sediment behind dams has been seriously altered in the Anthropocene. Climate change affecting rainfall and river discharge into fjords will impact the thickness and extent of the low-salinity layer in the upper reaches of the fjord, slowing the rate of the overturning circulation and deep-water renewal – thereby impacting bottom water oxygen concentrations.
Full-text available
Previous studies have shown decline in dissolved oxygen of the ocean basins. A hypothesis for this development is that ocean warming through increased stratification has caused reduced ventilation of the interior ocean. Here we provide evidence that reduced ventilation, which has been associated with a 1 °C warming of the North Atlantic Water (NAW), has contributed to recent deoxygenation of the mesopelagic zone of a Norwegian fjord, Masfjorden. Our results suggest that after the North Atlantic “Great Salinity Anomalies” around 1980, this warming has led to a decreased frequency of high-density intrusions of oxygen rich NAW and thereby reduced the renewal of the basin water of Masfjorden. From this, we infer that the basin water of other deep fjords are prone to similar development and briefly discuss some potential implications of deoxygenation in the mesopelagic zone.
Full-text available
While satellite data indicate that the surface expression of the North Pacific marine heatwave, nicknamed “The Blob”, disappeared in late 2016, Argo float and ship‐based CTD data show that warm conditions persisted below the surface mixed layer through at least March 2018. We trace this anomalously warm subsurface water from the open ocean through Queen Charlotte Sound to Rivers Inlet, on British Columbia's central coast. In Rivers Inlet, deep water below the sill depth continues to be 0.3° to 0.6°C warmer than the monthly average, suggesting that impacts of this marine heatwave have persisted in coastal waters at least 4 years after its onset, with potentially substantial effects on coastal ecosystems.
Full-text available
The freshwater content of the Arctic Ocean and its bordering seas has recently increased. Observing freshening events is an important step towards identifying the drivers and understanding the effects of freshening on ocean circulation and marine ecosystems. Here, we present a 13-year (2003-2015) record of temperature and salinity in Young Sound-Tyrolerfjord (74° N) in Northeast Greenland. Our observations show that strong freshening occurred from 2005 to 2007 (-0.92 psu; -0.46 psu y-1) and from 2009 to 2013 (-0.66 psu; -0.17 psu y-1). Furthermore, temperature-salinity analysis from 2004 to 2014 shows that freshening of the coastal water (~range at sill depth: 33.3 psu in 2005 to 31.4 psu in 2007) prevented renewal of the fjord’s bottom water. These data provide critical observations of interannual freshening rates in a remote fjord in Greenland and in the adjacent coastal waters, and show that coastal freshening impacts the fjord hydrography, which may impact the ecosystem dynamics on long term.
Oceanographic observations collected at Station P (145°W, 50°N) in the northeast Pacific extend for over six decades, representing one of the longest uninterrupted records of subsurface ocean properties. As such, this record is well suited to examine secular trends in properties of the subarctic waters of the North Pacific. In this paper, previously published trends are reviewed and updated, based on a newly compiled dataset for the station. Vertically integrated quantities such as ocean heat content and steric height are examined, as well as local water properties through the water column including temperature, salinity and, in particular, oxygen. Consideration is also extended to upper-ocean stratification, along with depths of the mixed layer and isopycnal surfaces. The results provide a comprehensive view of long-term changes to ocean conditions in the deep waters of the subarctic Pacific. Increases in 0/2000 dbar ocean heat content and steric height are evident, due primarily to ocean warming through the upper 500 dbar of the water column. However, about a third of the overall 0/2000 dbar steric height trend is due to halosteric effects. A significant freshening trend is evident through the upper layer to the top of the permanent pycnocline. Significant changes are also found below the permanent pycnocline, in particular warming on isopycnal surfaces along with downward migration of isopycnals. On the other hand, no robust trend emerges in the strength of the stratification associated with the pycnocline, a result that likely has implications for turbulent exchanges between the surface mixed layer and the deep ocean, including the supply of nutrients to the euphotic zone. Statistically significant declines in dissolved oxygen are observed on isopycnals below the pycnocline, down to great depth. Column-integrated dissolved oxygen has declined at a rate of 0.72 mol m⁻² y⁻¹, representing a net loss over six decades of 11.7±3.5% in total oxygen content per square metre. This is substantially higher than the global average of 2%, underscoring the northeast Pacific as a region of comparatively rapid deoxygenation. Changes in solubility due to local warming have made only a minor contribution to the observed decline.
Northern Patagonia, on the southeastern Pacific Ocean, is one of the largest fjord systems in the world. Its complex topography harbors an aquaculture industry that is among the top exporters of salmon and mussels worldwide. However, little is known about the scales of environmental variability of this region and how climate-related changes can alter the current conditions. This study provides a baseline understanding of the dominant scales of subtidal variability in meteorological forcing and water properties along and across the region that encompasses northern Patagonia and specifically the Inner Sea of Chiloé (ISC). We examined multiple datasets spanning multiple spatial and temporal scales. Reanalysis wind time series were combined with satellite-derived data (MODIS-Aqua) and in situ hydrographic records from the mussel farming industry as well as from instruments moored at various locations in the ISC. We assessed the influence of large-scale forcing on the variability of local conditions and used the assembled datasets to find modes of variability at interannual, seasonal and intraseasonal scales. The patterns of atmospheric and oceanographic variability along northern Patagonia are heterogeneous both in time and space. Long-term sea surface temperature (SST) averages revealed two areas with colder temperatures and attenuated seasonal variability that can be associated with stronger vertical mixing. These areas have been previously related to hotspots for whale sightings and might be important as bottom-up controls of Patagonian food webs. Northern Patagonia is strongly affected by large-scale processes at the South Pacific basin scale. Long-term wind data show a poleward displacement of the transition between upwelling and downwelling favorable conditions during spring-summer months for the last decade. The intraseasonal time scale was dominated by a band centered at 30 days that can be attributed to atmospheric variability driven by the Baroclinic Annular Mode (BAM), which induces the periodic mixing of the water column, but with substantial interannual variability. Variability in local conditions was found to closely track the large-scale variability, even in the small channels and bays. These findings highlight the strong connection between large-scale processes and the conditions faced by aquaculture in the ISC, and the need to consider such scales of variability - as well as climate trends - in planning and management decisions.