A biogeochemical model intercomparison for the eastern Bering Sea shelf

Uncertainty related to biogeochemical model structure, i.e. the equations, parameters, and variables used to simulate nutrient cycling and lower trophic level dynamics, can contribute significantly to overall uncertainty of regional model predictions of living marine resources metrics like primary production and trophic transfer efficiency. This may be particularly true in shallow coastal regions, where there is growing interest in using these types of regional models to inform ecosystem management. Here, we use a biogeochemical model intercomparison to quantify the uncertainty of key ecosystem metrics in the eastern Bering Sea shelf region and isolate poorly constrained biogeochemical processes that may lead to this uncertainty. We run three biogeochemical models with varying complexity coupled to the same regional ocean model and run a series of 30-year hindcast simulations spanning 1990-2020. We find that the models differ widely in their spatial and temporal patterns of simulated primary production, and that these differences propagate to most of the higher trophic level metrics examined. We highlight key structural elements that lead to these differences, including a) the representation of benthic processes and their role in retaining nitrogen on the shelf, b) the role of grazing control on spring bloom timing, and c) the role of micro- and mesozooplankton groups in supporting regenerated production through the summer months. Overall, we conclude that even well-validated biogeochemical models may have high uncertainty, particularly when pushed beyond the original contexts under which they were developed.