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Ocean Science An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 1 | Copyright
Ocean Sci., 14, 69-86, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Feb 2018

Research article | 02 Feb 2018

Response of O2 and pH to ENSO in the California Current System in a high-resolution global climate model

Giuliana Turi1, Michael Alexander2, Nicole S. Lovenduski3, Antonietta Capotondi2, James Scott4, Charles Stock5, John Dunne5, Jasmin John5, and Michael Jacox6 Giuliana Turi et al.
  • 1National Snow and Ice Data Center, Boulder, CO, USA
  • 2NOAA/ESRL, Boulder, CO, USA
  • 3Department of Atmospheric and Oceanic Sciences and Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, USA
  • 4CIRES, University of Colorado at Boulder, and NOAA/ESRL, Boulder, CO, USA
  • 5NOAA/GFDL, Princeton, NJ, USA
  • 6University of California, Santa Cruz, CA and NOAA/SWFSC, Monterey, CA, USA

Abstract. Coastal upwelling systems, such as the California Current System (CalCS), naturally experience a wide range of O2 concentrations and pH values due to the seasonality of upwelling. Nonetheless, changes in the El Niño–Southern Oscillation (ENSO) have been shown to measurably affect the biogeochemical and physical properties of coastal upwelling regions. In this study, we use a novel, high-resolution global climate model (GFDL-ESM2.6) to investigate the influence of warm and cold ENSO events on variations in the O2 concentration and the pH of the CalCS coastal waters. An assessment of the CalCS response to six El Niño and seven La Niña events in ESM2.6 reveals significant variations in the response between events. However, these variations overlay a consistent physical and biogeochemical (O2 and pH) response in the composite mean. Focusing on the mean response, our results demonstrate that O2 and pH are affected rather differently in the euphotic zone above  ∼ 100m. The strongest O2 response reaches up to several hundreds of kilometers offshore, whereas the pH signal occurs only within a  ∼ 100km wide band along the coast. By splitting the changes in O2 and pH into individual physical and biogeochemical components that are affected by ENSO variability, we found that O2 variability in the surface ocean is primarily driven by changes in surface temperature that affect the O2 solubility. In contrast, surface pH changes are predominantly driven by changes in dissolved inorganic carbon (DIC), which in turn is affected by upwelling, explaining the confined nature of the pH signal close to the coast. Below  ∼ 100m, we find conditions with anomalously low O2 and pH, and by extension also anomalously low aragonite saturation, during La Niña. This result is consistent with findings from previous studies and highlights the stress that the CalCS ecosystem could periodically undergo in addition to impacts due to climate change.

Publications Copernicus
Short summary
A high-resolution global model was used to study the influence of El Niño/La Niña events on the California Current System (CalCS). The mean surface oxygen (O2) response extends well offshore, where the pH response occurs within ~ 100 km of the coast. The surface O2 (pH) is primarily driven by temperature (upwelling) changes. Below 100 m, anomalously low O2 and low pH occurred during La Niña events near the coast, potentially stressing the ecosystem, but there are large variations between events.
A high-resolution global model was used to study the influence of El Niño/La Niña events on...