05 Oct 2023
 | 05 Oct 2023
Status: this preprint is currently under review for the journal BG.

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

Simone R. Alin, Jan A. Newton, Richard A. Feely, Samantha A. Siedlecki, and Dana J. Greeley

Abstract. 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, O2; carbon dioxide fugacity, fCO2; aragonite saturation state, Ωarag) parameters. Medians for some parameters peaked (T, Ωarag) in surface waters in summer, while others (S, O2, fCO2) 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 Ωarag and high fCO2 occurred in parts of the southern Salish Sea that are not normally so acidified. This novel “CO2 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 and anomalously high O2, low fCO2, and high chlorophyll. Unusually, this CO2 anomaly was decoupled from O2 dynamics compared to past Salish Sea hypoxia and acidification events. The complex interplay of weather, hydrological, and circulation anomalies revealed distinct multiple 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 in the future. The Salish cruise data product used in this publication is available at (Alin et al., 2022), with an additional data product including all calculated CO2 system parameters available at (Alin et al., 2023b).

Simone R. Alin et al.

Status: open (until 13 Dec 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2023-181', Anonymous Referee #1, 25 Nov 2023 reply
  • RC2: 'Comment on bg-2023-181', Anonymous Referee #2, 04 Dec 2023 reply

Simone R. Alin et al.

Data sets

A compiled data product of profile, discrete biogeochemical measurements from 35 individual cruise data sets collected from a variety of ships in the southern Salish Sea and northern California Current System (Washington state marine waters) from 2008-02-04 to 2018-10-19 (NCEI Accession 0238424) Simone R. Alin, Jan Newton, Dana Greeley, Beth Curry, Julian Herndon, Alex Kozyr, and Richard A. Feely

A multi-stressor data product for marine heatwave, hypoxia, and ocean acidification research, including calculated inorganic carbon parameters from the southern Salish Sea and northern California Current System from 2008-02-04 to 2018-10-19 (NCEI Accession 0283266) Simone R. Alin, Jan Newton, Richard A. Feely, Dana Greeley, Julian Herndon, and Alex Kozyr

Simone R. Alin et al.


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Short summary
We provide a new multi-stressor data product allowed us to characterize the seasonality of temperature, oxygen, and carbon dioxide in the southern Salish Sea and provided insight into impacts of major marine heatwave and precipitation anomalies on regional ocean acidification and hypoxia. We also described the present-day frequencies of temperature, oxygen, and ocean acidification conditions that cross thresholds of sensitive regional species that are economically or ecologically important.