Marine CO 2 system variability along the northeast Pacific Inside Passage determined from an Alaskan ferry

[摘要] Information on marine CO 2 system variability has beenlimited along the northeast Pacific Inside Passage despite the region's richbiodiversity, abundant fisheries, and developing aquaculture industry.Beginning in 2017, the Alaska Marine Highway System M/V Columbia has served as aplatform for surface underway data collection while conducting twice weekly ∼1600  km transits between Bellingham, Washington, and Skagway,Alaska. Marine CO 2 system patterns were evaluated using measurementsmade over a 2-year period, which revealed the seasonal cycle as the dominantmode of temporal variability. The amplitude of this signal varied spatiallyand was modulated by the relative influences of tidal mixing, net communityproduction, and the magnitude and character of freshwater input. Surfacewater pH T (total hydrogen ion scale) and aragonite saturation state( Ω arag ) were determined using carbon dioxide partial pressure ( p CO 2 ) data withalkalinity derived from a regional salinity-based relationship, which wasevaluated using intervals of discrete seawater samples and underway pHmeasurements. High- p CO 2 , low-pH T , and corrosive Ω arag conditions ( Ω arag <1 ) were seen during winter andwithin persistent tidal mixing zones, and corrosive Ω arag values were also seen in areas that receive significant glacial melt insummer. Biophysical drivers are shown to dominate p CO 2 variability overmost of the Inside Passage except in areas highly impacted by glacial melt.pH T and Ω arag extremes were also characterized based ondegrees of variability and severity, and regional differences were evident.Computations of the time of detection identified tidal mixing zones asstrategic observing sites with relatively short time spans required tocapture secular trends in seawater p CO 2 equivalent to the contemporaryrise in atmospheric CO 2 . Finally, estimates of anthropogenic CO 2 showed notable spatiotemporal variability. Changes in total hydrogen ioncontent ([H + ] T ), pH T , and Ω arag over theindustrial era and to an atmospheric p CO 2 level consistent with a1.5  ∘ C warmer climate were theoretically evaluated. Thesecalculations revealed greater absolute changes in [H + ] T andpH T in winter as opposed to larger Ω arag change in summer.The contemporary acidification signal everywhere along the Inside Passageexceeded the global average, with specific areas, namely Johnstone Straitand the Salish Sea, standing out as potential bellwethers for the emergenceof biological ocean acidification (OA) impacts. Nearly half of the contemporary acidificationsignal is expected over the coming 15 years, with an atmospheric CO 2 trajectory that continues to be shaped by fossil–fuel development.

[学科分类] 大气科学