Seasonality and response of ocean acidification and hypoxia to major environmental anomalies in the southern Salish Sea, North America (2014–2018)

• Main Authors: Alin, Simone R., Newton, Jan A., Feely, Richard A., Siedlecki, Samantha A., Greeley, Dana J.
• Format: Text
• Language: English
• Published: 2023
• Subjects: Ocean acidification
• Online Access: https://doi.org/10.5194/bg-2023-181; https://bg.copernicus.org/preprints/bg-2023-181/

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 in the southern Salish Sea (Puget Sound, Strait of Juan de Fuca) and nearby coastal waters for select physical (temperature, T; salinity, S) and biogeochemical (oxygen, O 2 carbon dioxide fugacity, f CO 2 aragonite saturation state, Ω arag ) parameters. Medians for some parameters peaked (T, Ω arag ) in surface waters in summer, while others (S, O 2 , f CO 2 ) 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 2015–2016 timeframe. The most extreme hypoxia and acidification measurements to date were recorded in Hood Canal (which consistently has 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 Ω arag and high f CO 2 occurred in parts of the southern Salish Sea that are not normally so acidified. This novel “CO 2 storm” appears to have been driven by anomalous river discharge earlier in 2017, which resulted in enhanced stratification and inferred primary productivity anomalies, indicated by persistently ...