Evaluation of the historical and future biogeochemical boundary conditions from earth system models for the California Current System

The California Current System (CCS) is a highly productive region supporting a wide variety of marine species in the eastern North Pacific. Local and basin-scale processes stimulate high spatio-temporal variability in CCS conditions with implications for the region’s biological productivity. Projecting the future state of this region would be instructive for formulating adaptive strategies for resource management. Recent efforts have made use of coupled physical-biogeochemical models such as Earth System Models (ESMs), yet data on long-term biogeochemical changes from multiple ESMs for the CCS is still lacking. Global scale ESMs are necessarily coarse in spatial resolution but are important as forcing data for higher-resolution regional scale models. They are incorporated through Lateral Boundary Conditions (LBCs) and as such, influence the modeled trends within localized domains. This study used a multi-model ensemble of ESMs to estimate the range of future changes for LBCs in the CCS. Significant changes in LBC oceanographic parameters (temperature, salinity, nitrate, oxygen, dissolved inorganic carbon, total alkalinity and silicate) between historical (1976 to 2005) and future (RCP 8.5; 2071 to 2100) conditions were detected using 13 GCMs from the Coupled Model Intercomparison Project. The time series of flux across approximately 250 years were calculated at the boundaries by multiplying water transport with average parameter values. Flux divergence was then derived as the balance between flux across the boundaries, which allowed for the measurement of net changes in oceanographic conditions over space and time. This method isolates the impact of remote forcing through LBCs on the regional CCS domain. Overall, this work seeks to contribute to understanding how the large-scale biogeochemical and physical conditions that influence primary and ecosystem production in the CCS will evolve given a high-emission climate scenario over the next century.