Seasonality and response of ocean acidification and hypoxia to major environmental anomalies in the southern Salish Sea, North America (2014–2018)
<p><span id="page1640"/>Coastal and estuarine ecosystems fringing the North Pacific Ocean are particularly vulnerable to ocean acidification, hypoxia, and intense marine heatwaves as a result of interactions among natural and anthropogenic processes. Here, we characterize varia...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2024-04-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/21/1639/2024/bg-21-1639-2024.pdf |
| Summary: | <p><span id="page1640"/>Coastal and estuarine ecosystems fringing the North Pacific Ocean are particularly vulnerable to ocean acidification, hypoxia, and intense marine heatwaves as a result of interactions among natural and anthropogenic processes. Here, we characterize variability during a seasonally resolved cruise time series (2014–2018) in the southern Salish Sea (Puget Sound, Strait of Juan de Fuca) and nearby coastal waters for select physical (temperature, <span class="inline-formula"><i>T</i></span>; salinity, <span class="inline-formula"><i>S</i></span>) and biogeochemical (oxygen, O<span class="inline-formula"><sub>2</sub></span>; carbon dioxide fugacity, <span class="inline-formula"><i>f</i></span>CO<span class="inline-formula"><sub>2</sub></span>; aragonite saturation state, <span class="inline-formula">Ω<sub>arag</sub></span>) parameters. Medians for some parameters peaked (<span class="inline-formula"><i>T</i></span>, <span class="inline-formula">Ω<sub>arag</sub></span>) in surface waters in summer, whereas others (<span class="inline-formula"><i>S</i></span>, O<span class="inline-formula"><sub>2</sub></span>, <span class="inline-formula"><i>f</i></span>CO<span class="inline-formula"><sub>2</sub></span>) changed progressively across spring–fall, and all parameters changed monotonically or were relatively stable at depth. Ranges varied considerably for all parameters across basins within the study region, with stratified basins consistently the most variable. Strong environmental anomalies occurred during the time series, allowing us to also qualitatively assess how these anomalies affected seasonal patterns and interannual variability. The peak temperature anomaly associated with the 2013–2016 northeast Pacific marine heatwave–El Niño event was observed in boundary waters during the October 2014 cruise, but Puget Sound cruises revealed the largest temperature increases during the 2015–2016 timeframe. The most extreme hypoxia and acidification measurements to date were recorded in Hood Canal (which consistently had the most extreme conditions) during the same period; however, they were shifted earlier in the year relative to previous events. During autumn 2017, after the heat anomaly, a distinct carbonate system anomaly with unprecedentedly low <span class="inline-formula">Ω<sub>arag</sub></span> values and high <span class="inline-formula"><i>f</i></span>CO<span class="inline-formula"><sub>2</sub></span> values occurred in parts of the southern Salish Sea that are not normally so acidified. This novel “CO<span class="inline-formula"><sub>2</sub></span> storm” appears to have been driven by anomalously high river discharge earlier in 2017, which resulted in enhanced stratification and inferred primary productivity anomalies, indicated by persistently and anomalously high O<span class="inline-formula"><sub>2</sub></span>, low <span class="inline-formula"><i>f</i></span>CO<span class="inline-formula"><sub>2</sub></span>, and high chlorophyll. Unusually, this CO<span class="inline-formula"><sub>2</sub></span> anomaly was decoupled from O<span class="inline-formula"><sub>2</sub></span> dynamics compared with past Salish Sea hypoxia and acidification events. The complex interplay of weather, hydrological, and circulation anomalies revealed distinct multi-stressor scenarios that will potentially affect regional ecosystems under a changing climate. Further, the frequencies at which Salish cruise observations crossed known or preliminary species' sensitivity thresholds illustrates the relative risk landscape of temperature, hypoxia, and acidification anomalies in the southern Salish Sea in the present day, with implications for how multiple stressors may combine to present potential migration, survival, or physiological challenges to key regional species. The Salish cruise data product used in this publication is available at <span class="uri">https://doi.org/10.25921/zgk5-ep63</span> (Alin et al., 2022), with an additional data product including all calculated CO<span class="inline-formula"><sub>2</sub></span> system parameters available at <span class="uri">https://doi.org/10.25921/5g29-q841</span> (Alin et al., 2023).</p> |
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| ISSN: | 1726-4170 1726-4189 |