A regional biogeochemical model outperforms global Earth System Models in northwest North Atlantic shelf waters

Earth System Models (ESMs) are essential tools for building understanding of ocean biogeochemistry and to project future climate states. However, the coarse to intermediate spatial resolution of ESMs used for climate projections may not be appropriate for accurately representing processes along ocean margins. Continental shelves, in particular, are areas of complex circulation with an important role in the cycling of carbon and nutrients. Here, we compare the performance of 17 ESMs with a regional biogeochemical model for the northwest North Atlantic shelf. ESM projections from the Coupled Model Intercomparison Project Phase 5 (CMIP5) suggest that this region, which is biologically productive and influenced by the large-scale Gulf Stream and Labrador Current systems, is particularly sensitive to climate change. The regional model uses an intermediate complexity ecosystem model and was tuned to best represent local conditions. The spread within the ESM ensemble is large. The ensemble mean compares very poorly against observations suggesting that ensemble means are inappropriate here and possibly also in similar shelf regions. The regional model better resolves the shelf and compares better with surface fields than any of the ESMs. The regional model also simulates reasonably well vertically resolved observations. A ranking of the ESMs provides insight into which model could be selected for regional downscaling.