Marine CO 2 system variability along the Inside Passage of the Pacific Northwest coast of North America determined from an Alaskan ferry

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