The Combined Effects of Acidification and Hypoxia on PH and Aragonite Saturation in the Coastal Waters of the California Current Ecosystem and the Northern Gulf of Mexico

• Published in: Continental Shelf Research
• Main Authors: Feely, Richard A., Okazaki, Remy R., Cai, Wei-Jun, Bednaršek, Nina, Alin, Simone R., Byrne, Robert H., Fassbender, Andrea
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Digital Commons @ University of South Florida 2018
• Subjects: Ocean acidification; CaCO3 undersaturation; Hypercapnia; Hypoxia; Life Sciences
• Online Access: https://digitalcommons.usf.edu/msc_facpub/1792; https://doi.org/10.1016/j.csr.2017.11.002

Inorganic carbon chemistry data from the surface and subsurface waters of the West Coast of North America have been compared with similar data from the northern Gulf of Mexico to demonstrate how future changes in CO2 emissions will affect chemical changes in coastal waters affected by respiration-induced hypoxia ([O2] ≤ ~ 60 µmol kg−1). In surface waters, the percentage change in the carbon parameters due to increasing CO2 emissions are very similar for both regions even though the absolute decrease in aragonite saturation is much higher in the warmer waters of the Gulf of Mexico. However, in subsurface waters the changes are enhanced due to differences in the initial oxygen concentration and the changes in the buffer capacity (i.e., increasing Revelle Factor) with increasing respiration from the oxidation of organic matter, with the largest impacts on pH and CO2 partial pressure (pCO2) occurring in the colder West Coast waters. As anthropogenic CO2 concentrations begin to build up in subsurface waters, increased atmospheric CO2 will expose organisms to hypercapnic conditions (pCO2 >1000 µatm) within subsurface depths. Since the maintenance of the extracellular pH appears as the first line of defense against external stresses, many biological response studies have been focused on pCO2-induced hypercapnia. The extent of subsurface exposure will occur sooner and be more widespread in colder waters due to their capacity to hold more dissolved oxygen and the accompanying weaker acid-base buffer capacity. Under present conditions, organisms in the West Coast are exposed to hypercapnic conditions when oxygen concentrations are near 100 µmol kg−1 but will experience hypercapnia at oxygen concentrations of 260 µmol kg−1 by year 2100 under the highest elevated-CO2 conditions. Hypercapnia does not occur at present in the Gulf of Mexico but will occur at oxygen concentrations of 170 µmol kg−1 by the end of the century under similar conditions. The aragonite saturation horizon is currently above the hypoxic zone in the ...