Sophie N Chu1,2, Adrienne J Sutton2, Burke R Hales3, Derek Manzello4, John Buchanan Mickett5, Julio M Morell6, Jan A Newton7, Scott Noakes8, Mark D Ohman9, Virginia C Parker10, Christopher Sabine11, Joseph Salisbury II12, Uwe Send13, Douglas C Vandemark14 and Treasure A Warren15, (1)University of Washington, Cooperative Institute for Climate, Ocean and Ecosystem Studies, Seattle, WA, United States, (2)NOAA Pacific Marine Environmental Laboratory, Seattle, WA, United States, (3)Oregon State Univ, Corvallis, OR, United States, (4)CIMAS, Miami, FL, United States, (5)Applied Physics Laboratory University of Washington, Seattle, WA, United States, (6)University of Puerto Rico Mayaguez, Caribbean Coastal Ocean Observing System, Mayaguez, PR, United States, (7)University of Washington, Applied Physics Laboratory, Seattle, WA, United States, (8)The University of Georgia, Center for Applied Isotope Studies, Athens, GA, United States, (9)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, (10)Washington College, United States, (11)University of Hawaii at Manoa, Honolulu, United States, (12)University of New Hampshire, Durham, NH, United States, (13)University of California, San Diego, CA, United States, (14)University of New Hampshire Main Campus, Durham, NH, United States, (15)University of California Davis, United States
Many of the most sensitive organisms to ocean acidification (OA) are benthic organisms and pelagic vertical migrators that respond to subsurface water chemistry (e.g. pteropods, corals, shellfish). While OA is driven by uptake of anthropogenic carbon dioxide (CO2) from the atmosphere into the surface ocean, natural coastal processes can have strong influences on subsurface water chemistry. Organic matter remineralization consumes oxygen (O2), releases CO2, and decreases pH. In highly productive coastal waters, more organic matter produced in the surface can naturally lead to more enhanced subsurface acidification. Here, we describe a synthesis of existing subsurface data at multiple locations within U.S. coastal ecosystems and conduct an analysis of sub-seasonal to inter-annual dynamics in the subsurface carbonate chemistry. Subsurface observations are compared to available surface data to examine how surface and subsurface patterns vary over time and space. For example, in coastal waters of the Northern California Current, high-frequency autonomous pCO2and O2 profile data in the summer of 2017 show how surface chemistry is controlled by high biological productivity. There is strong stratification between the surface and subsurface where subsurface variability is driven by periods of upwelling. The upwelled seawater contains naturally low pH and low aragonite saturation state due to build-up of respiration-induced acidification at depth. In a shallow, well-mixed coral reef off the southwest coast of Puerto Rico, however, carbonate chemistry conditions are uniform throughout the water column. Analysis at a variety of locations will inform recommendations for designing sampling protocols for future subsurface studies. More high-frequency, long-term observations will expand our understanding of the range of subsurface OA conditions in coastal environments and allow us to quantify natural sources of ocean chemistry variation and separate them from anthropogenic sources.