Factors influencing pH and pCO2 variability in seagrass and adjacent nearshore habitats across climate zones

Alexander T. Lowe1, Amanda Reynolds2, Rachel Collin3 and Whitman Miller1, (1)Smithsonian Institution, MarineGEO, Edgewater, MD, United States, (2)Smithsonian Institution, Smithsonian Environmental Research Center, MD, United States, (3)Smithsonian Tropical Research Institute, Calzada de Amador, Panama
Ocean acidification threatens marine ecosystem function at a global scale, yet the drivers of acidification and associated water chemistry changes over space and time are poorly understood, especially in coastal systems. Air-sea exchange of carbon dioxide (CO2) causes predictable changes to the carbonate system in systems with limited biological productivity, but coastal waters are in addition influenced by numerous physical, chemical, biological, and biogeochemical processes. Land-sea carbon exchange, photosynthesis, and respiration are far more pronounced in coastal ecosystems, resulting in a greater magnitude of variability of carbonate chemistry than in open ocean habitats. We adopt an ecological perspective to address questions regarding 1) the relative magnitude of biological and physical factors driving pH variability as a function of CO2, 2) the relationship of pH variability to biological community dynamics within a system, and 3) the generalizability of biological influences across systems. Using spatially replicated, habitat-scale observations of pH, oxygen, physical (temperature and salinity) and biological (macrophyte composition and biomass, total suspended solids and seston composition) parameters we assessed the factors associated with short-term pH variability in seagrass and adjacent habitats across 6 temperate, subtropical and tropical sites within the Smithsonian MarineGEO network. We found dramatic, habitat-specific pH variability associated with changes in benthic and water column biological productivity. These biological patterns determined exposure to extremes of pH, patterns of pH change, and the magnitude of air-sea diffusion gradients – and thus have important implications for biogeochemical cycling and biological responses to ocean acidification.