Abstract
Abstract. 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.
Highlights
Greenhouse gas emissions have imparted large physical and biogeochemical modifications on the world’s oceans (Friedlingstein et al, 2019; Gattuso et al, 2015; Le Quéré et al, 2018)
The global average changes for many of these variables are different from the 1◦ model projected values for the California Current System (CCS) region, but in only a few cases does this difference fall outside of the ensemble spread reported in column D and H of Table 1
While the downscaled projections show changes that are similar in direction to those of the global simulation, the magnitude and spatial variability of the change differ in the coastal-process-resolving downscaled projections and to a varying degree depending on the variable, depth range, and subregion of interest
Summary
Greenhouse gas emissions have imparted large physical and biogeochemical modifications on the world’s oceans (Friedlingstein et al, 2019; Gattuso et al, 2015; Le Quéré et al, 2018). The oceans have become warmer, and stratification patterns have been modified (Talley et al, 2016) These changes are occurring in tandem with biogeochemical alterations, including O2 declines, productivity changes, and increased dissolved inorganic carbon (DIC) content due to the uptake of anthropogenic carbon dioxide (Doney et al, 2009, 2020; Feely et al, 2004, 2009). Big changes are happening in the ocean, but there are reasons to believe that global trends may not accurately represent what happens in coastal regions
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