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

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, 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 meter Ω are dampened relative to the projected change in global models. 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 source waters lower in oxygen, higher in nutrients, and in combination with solubility-driven changes, altered future upwelled waters in the CCS. The results presented here suggest coastal process resolving projections are necessary for adequate representation of the magnitude of projected change in pH and carbon stressors in the CCS.

Future Temperature and Salinity in Puget Sound, Washington State, Under CMIP6 Climate Change Scenarios

“…Over the 21st century, both models predict warming and freshening of Puget Sound. This general result is in-line with the Puget-Sound-speci c ndings in Khangaonkar et al (2019) and the broader ndings in the California Current (Xiu et al 2018;Siedlecki et al 2020). Warming and freshening is greater in the long-term than in the short-term.…”

Seasonality and Life History Complexity Determine Vulnerability of Dungeness Crab to Multiple Climate Stressors

“…The incorporation of seasonality should, therefore, improve vulnerability assessments for species in seasonal seas (Jones et al., 2018; Spencer et al., 2019). The regional model used to project the ocean conditions continues to experience seasonality in the projected ocean conditions in the future (2100), but despite an increase in the projected winds in the CMIP5 projections, the future upwelling intensity does not change much due to compensation from increased stratification (Howard et al., 2020; Siedlecki et al., 2021). The timing and duration of the upwelling season in the N‐CCS also remain the same in the future model projections (Siedlecki et al., 2021).…”

“…The model has a high horizontal resolution ranging from 1.5 km at the coast to 4.5 km far offshore, allowing it to resolve coastal processes, such as upwelling, that are not well‐resolved in global‐scale models. Hindcast model fields have been validated against observations for the variables of interest and exhibit skill on all regions of the shelf (Davis et al., 2014; Giddings et al., 2014; Siedlecki et al., 2015, 2016, 2021). Model versus observation comparisons for 2007 revealed a significant cold temperature bias in the upper ocean introduced by atmospheric forcing (Siedlecki et al., 2021).…”

“…We corrected this bias by adding the Root Mean Square Error (RMSE) for the upper 200 m (2.79°C; Figure ) to present and future modeled temperatures in that depth range. Future downscaled projections are forced by anomalies from modern conditions using an ensemble mean of five global CMIP5 simulations under the RCP 8.5 carbon emissions scenario (Howard et al., 2020; Siedlecki et al., 2021), which predicts 936 ppm of atmospheric CO 2 in 2100 (Bopp et al., 2013). The downscaled, high resolution CMIP5 projections are consistent with the direction of the future change projected by the global simulations, but the magnitude and spatial patterns of the future changes are modified by the inclusion of coastal processes—particularly for the carbon variables (Siedlecki et al., 2021).…”

Utility of Occupancy Models with Environmental DNA (eDNA) from Olympic Coast National Marine Sanctuary

“…Impacts from climate change are already being observed in the Pacific Northwest, from significant losses to oyster aquaculture caused by acidification, to major die off and displacement of fish and Dungeness crab from hypoxia [5,6]. As ocean acidification and hypoxic events are expected to increase in frequency and severity [7], it is vital to be able to understand how these changes will impact the biological community as a whole. Until recently it has been difficult to collect biological community data, particularly in remote and difficult to access habitats like OCNMS.…”