The Combined Effects of Ocean Acidification and Respiration on Habitat Suitability for Marine Calcifiers Along the West Coast of North America

The California Current Ecosystem (CCE) is a natural laboratory for studying the chemical and ecological impacts of ocean acidification. Biogeochemical variability in the region is due primarily to wind-driven near-shore upwelling of cold waters that are rich in re-mineralized carbon and poor in oxygen. The coastal regions are exposed to surface waters with increasing concentrations of anthropogenic CO2 (Canth) from exchanges with the atmosphere and the shoreward transport and mixing of upwelled water. The upwelling drives intense cycling of organic matter that is created through photosynthesis in the surface ocean and degraded through biological respiration in subsurface habitats. We used an extended multiple linear-regression approach to determine the spatial and temporal concentrations of Canth and respired carbon (Cbio) in the CCE based on cruise data from 2007, 2011, 2012, 2013, 2016, and 2021. Over the region, the Canth accumulation rate increased from 0.8 +/- 0.1 mu mol kg-1 yr-1 in the northern latitudes to 1.1 +/- 0.1 mu mol kg-1 yr-1 further south. The rates decreased to values of about similar to 0.3 mu mol kg-1 yr-1 at depths near 300 m. These accumulation rates at the surface correspond to total pH decreases that averaged about 0.002 yr-1; whereas, decreases in aragonite saturation state ranged from 0.006 to 0.011 yr-1. The impact of the Canth uptake was to decrease the amount of oxygen consumption required to cross critical biological thresholds (i.e., calcification, dissolution) for marine calcifiers and are significantly lower in the recent cruises than in the pre-industrial period because of the addition of Canth. The combined effect of ocean acidification and respiration in the California Current Ecosystem is to reduce water column pH and aragonite saturation state, resulting in a compression of the overall size of suitable habitat for marine calcifiers. The addition of excess anthropogenic CO2 also makes it more likely that critical biological thresholds are crossed and shell dissolution begins to occur. Consequently, the addition of the excess CO2 also has the added effect of reducing the amount of biological consumption of oxygen that is required to drop the ecosystem below these thresholds. In the California Current Ecosystem the anthropogenic carbon (Canth) uptake rate at the surface ranges from 0.8 to 1.1 mu mol kg-1 yr-1 This corresponds to a total pH decrease of about 0.002 yr-1, whereas the decrease in aragonite saturation ranges from 0.006 to 0.011 yr-1 Dissolved oxygen consumptions required to cross critical biological thresholds are significantly lower in 2021 than in the pre-industrial