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Inorganic carbon dynamics during northern California coastal upwelling |
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| Authors: | Andrea J Fassbender Christopher L Sabine |
| Institution: | a School of Oceanography, University of Washington, 1503 NE Boat Street, mailbox #355351, Seattle, WA 98195-4340, USA b Pacific Marine Environmental Laboratory/National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, WA 98115-6349, USA c Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149-2507, USA d Joint Institute for the Study of the Atmosphere and Ocean, Box 355672, University of Washington, Seattle, WA 98105-5672, USA |
| Abstract: | Coastal upwelling events in the California Current System can transport subsurface waters with high levels of carbon dioxide (CO2) to the sea surface near shore. As these waters age and are advected offshore, CO2 levels decrease dramatically, falling well below the atmospheric concentration beyond the continental shelf break. In May 2007 we observed an upwelling event off the coast of northern California. During the upwelling event subsurface respiration along the upwelling path added ∼35 μmol kg−1 of dissolved inorganic carbon (DIC) to the water as it transited toward shore causing the waters to become undersaturated with respect to Aragonite. Within the mixed layer, pCO2 levels were reduced by the biological uptake of DIC (up to 70%), gas exchange (up to 44%), and the addition of total alkalinity through CaCO3 dissolution in the undersaturated waters (up to 23%). The percentage contribution of each of these processes was dependent on distance from shore. At the time of measurement, a phytoplankton bloom was just beginning to develop over the continental shelf. A box model was used to project the evolution of the water chemistry as the bloom developed. The biological utilization of available nitrate resulted in a DIC decrease of ∼200 μmol kg−1, sea surface pCO2 near ∼200 ppm, and an aragonite saturation state of ∼3. These results suggest that respiration processes along the upwelling path generally increase the acidification of the waters that are being upwelled, but once the waters reach the surface biological productivity and gas exchange reduce that acidification over time. |
| Keywords: | Carbon Upwelling Acidification California Continental shelf Phytoplankton |
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