Coastal processes modify projections of some climate-driven stressors in the California Current System

Samantha A. Siedlecki1, Darren Pilcher2,5, Evan M. Howard3, Curtis Deutsch3, Parker MacCready3, Emily L. Norton2, Hartmut Frenzel3, Jan Newton4, Richard A. Feely5, Simone R. Alin5, and Terrie Klinger6

  • 1Department of Marine Sciences, University of Connecticut, Groton, CT 06340, USA
  • 2Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, WA, 98105, USA
  • 3School of Oceanography, University of Washington, Seattle, WA 98195, USA
  • 4Applied Physics Laboratory, Washington Ocean Acidification Center, University of Washington, Seattle, WA 98105, USA
  • 5NOAA Pacific Marine Environmental Laboratory (PMEL), Seattle, WA 98115, USA
  • 6School of Marine Environment and Affairs, Washington Ocean Acidification Center, University of Washington, Seattle, WA 98105, USA

Correspondence: Samantha A. Siedlecki (

Received: 17 Jul 2020 – Discussion started: 05 Aug 2020 – Revised: 04 Mar 2021 – Accepted: 13 Mar 2021 – Published: 11 May 2021



Global projections for ocean conditions in 2100 predict that the North Pacific will experience some of the largest changes. Coastal processes that drive variability in the region can alter these projected changes but are poorly resolved by global coarse-resolution models. We quantify the degree to which local processes modify biogeochemical changes in the eastern boundary California Current System (CCS) using multi-model regionally downscaled climate projections of multiple climate-associated stressors (temperature, O2, pH, saturation state (Ω), and CO2). The downscaled projections predict changes consistent with the directional change from the global projections for the same emissions scenario. However, the magnitude and spatial variability of projected changes are modified in the downscaled projections for carbon variables. Future changes in pCO2 and surface Ω are amplified, while changes in pH and upper 200 m Ω are dampened relative to the projected change in global models. Surface carbon variable changes are highly correlated to changes in dissolved inorganic carbon (DIC), pCO2 changes over the upper 200 m are correlated to total alkalinity (TA), and changes at the bottom are correlated to DIC and nutrient changes. The correlations in these latter two regions suggest that future changes in carbon variables are influenced by nutrient cycling, changes in benthic–pelagic coupling, and TA resolved by the downscaled projections. Within the CCS, differences in global and downscaled climate stressors are spatially variable, and the northern CCS experiences the most intense modification. These projected changes are consistent with the continued reduction in source water oxygen; increase in source water nutrients; and, combined with solubility-driven changes, altered future upwelled source waters in the CCS. The results presented here suggest that projections that resolve coastal processes are necessary for adequate representation of the magnitude of projected change in carbon stressors in the CCS.



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