Importance of simulating coastal biogeochemical processes for projections of ocean acidification on the Bering Sea shelf

The Bering Sea is highly vulnerable to ocean acidification (OA) due to naturally cold, low carbonate concentration waters. Expected negative impacts of OA to marine organisms pose a significant threat to this highly productive marine ecosystem, which supports critical commercial and subsistence fisheries. Carbonate chemistry and oxygen cycling were recently added to a regional ecosystem model of the Bering Sea at 10km horizontal resolution. A decadal hindcast illustrated that local processes generate considerable spatial variability in the biogeochemistry of Bering Sea shelf water. These prior results highlight how vulnerability to future environmental changes can vary substantially within a coastal shelf system. However, coastal ecosystem projections are typically produced from global-scale Earth System Models (ESM), which generally do not contain the spatial resolution and coastal biogeochemical processes required to capture these shelf features. Thus, we use our regional model to produce dynamically downscaled projections of OA for the Bering Sea shelf, using multiple ESMs and emissions scenarios. The regional downscaled results provide a substantially different spatial pattern of projected OA compared to the ESM output, including a reversed shelf spatial gradient in the greatest rates of OA, resulting primarily from the inclusion of freshwater biogeochemistry in the regional model. Interannual variability is also significantly greater in the regional projections, illustrating how variability from the ESM is amplified when downscaled to the regional biogeochemical model. These features simulated by the regional projections are similar in spatial scale to key ecosystem habitats and services, therefore, resolving these features is critical to addressing emerging stakeholder needs.