Preprints
https://doi.org/10.5194/bg-2021-266
https://doi.org/10.5194/bg-2021-266

  20 Oct 2021

20 Oct 2021

Review status: this preprint is currently under review for the journal BG.

Marine CO2 system variability along the Inside Passage of the Pacific Northwest coast of North America determined from an Alaskan ferry

Wiley Evans1, Geoffrey T. Lebon2,3, Christen D. Harrington4, Yuichiro Takeshita5, and Allison Bidlack6 Wiley Evans et al.
  • 1Hakai Institute, Heriot Bay, BC, V0P 1H0, Canada
  • 2Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, 98115, USA
  • 3Cooperative Institute for Climate, Ocean, & Ecosystem Studies, University of Washington, 98195, USA
  • 4Alaska Marine Highway, Department of Transportation, Ketchikan, AK, 99901, USA
  • 5Monterey Bay Aquarium Research Institute, Moss Landing, 95039, USA
  • 6Alaska Coastal Rainforest Center, University of Alaska Southeast, Juneau, AK, 99801, USA

Abstract. Information on marine CO2 system variability has been limited along the Inside Passage of the Pacific Northwest coast of North America despite the region’s rich biodiversity, abundant fisheries, and developing aquaculture industry. Beginning in 2017, the Alaska Marine Highway System M/V Columbia has served as a platform for surface underway data collection while conducting twice weekly ~1600-km transits between Bellingham, Washington and Skagway, Alaska. This dataset allowed for the assessment of marine CO2 system patterns along the Inside Passage, including quantification of the relative importance of key drivers in shaping pCO2 variability. Surface water pH and aragonite saturation state (Ωarag) were determined using the pCO2 data with alkalinity from a regional salinity-based relationship, which was evaluated with discrete seawater samples and underway pH measurements. Low pH and corrosive (Ωarag < 1) Ωarag conditions were seen during winter and in persistent tidal mixing zones, and corrosive Ωarag values were also seen in areas that receive significant glacial melt in summer. The time-of-detection was computed and revealed that tidal mixing zones may be sentinel observing sites with relatively short time spans of observation needed to capture secular trends in seawater pCO2 equivalent to the contemporary atmospheric CO2 increase. Finally, anthropogenic CO2 was estimated and showed notable time and space variability. We theoretically considered the change in hydrogen ion concentration ([H+]), pH, and Ωarag over the industrial era and to an atmospheric pCO2 level consistent with a 1.5 °C warmer climate and revealed greater changes in [H+] and pH in winter as opposed to larger Ωarag change in summer. In addition, the contemporary acidification signal everywhere along the Inside Passage exceeded the global average, with Johnstone Strait and the Salish Sea standing out as potential bellwethers for biological OA impacts. In theory, roughly half the acidification signal experienced thus far over the industrial era may be expected over the coming 15 years with an atmospheric CO2 trajectory that continues to be shaped by fossil-fuel development.

Wiley Evans et al.

Status: open (until 16 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-266', Anonymous Referee #1, 16 Nov 2021 reply

Wiley Evans et al.

Wiley Evans et al.

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Short summary
Information on the marine carbon dioxide system along the Inside Passage of the Pacific Northwest coast of North America has been limited. To address this gap, we instrumented an Alaskan ferry in order to characterize the marine carbon dioxide system. Data over a 2-year period were used to assess drivers of the observed variability, identify the timing of severe conditions, and assess the extent of contemporary ocean acidification as well as future levels consistent with a 1.5 °C warmer climate.
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