FY 2024

The combined effects of ocean acidification and respiration on habitat suitability for marine calcifiers along the west coast of North America

Feely, R.A., B.R. Carter, S.R. Alin, D. Greeley, and N. Bednaršek

J. Geophys. Res., 129(4), e2023JC019892, doi: 10.1029/2023JC019892, View open access article at Wiley/AGU (external link) (2024)

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 (C_anth) 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 C_anth and respired carbon (C_bio) in the CCE based on cruise data from 2007, 2011, 2012, 2013, 2016, and 2021. Over the region, the C_anth accumulation rate increased from 0.8 ± 0.1 μmol kg⁻¹ yr⁻¹ in the northern latitudes to 1.1 ± 0.1 μmol kg⁻¹ yr⁻¹ further south. The rates decreased to values of about ∼0.3 μmol 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 C_anth 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 C_anth.

Plain Language Summary. 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.