A high-resolution coupled physical-biogeochemical model of the northeastern US continental shelf: MOM6-COBALT-NEUS25v1.0

Abstract. Coastal communities along the northeastern U.S. depend on marine resources that have been increasingly affected by ocean warming, marine heatwaves and associated ecosystem shifts over recent decades. High-resolution regional ocean-biogeochemical modeling using the Modular Ocean Model 6 (MOM6) enables studies of fisheries production, marine carbon dioxide removal and sediment biogeochemistry. The northeastern US (NEUS) continental shelf is one of the most widely sampled and measured ocean areas, providing a favorable testbed for regional model development. In this context, we present an assessment of MOM6 coupled with the Carbon, Ocean Biogeochemistry and Lower Trophics (COBALT) model in the NEUS at 1/25° resolution (MOM6-COBALT-NEUS25 version 1.0). The model is validated against a suite of observation databases, satellite products, ocean reanalysis and climatologies for the period between 1993 and 2019 considering different skill metrics. A reasonable representation of the Gulf Stream separation led to realistic simulation of parameters on the continental shelf based on the evaluation of seasonal structure, long-term time series, and spatial variability patterns. For temperature, and salinity, the main biases in the model are located in the Mid-Atlantic Bight, where the vertical and bottom structure show mixed-quality results that are dependent on season and depth, while surface fields and the vertical structure results in the Gulf of Maine are comparable with global ocean reanalysis and other regional model results. The inclusion of tides allowed the regional patches of cold sea surface temperature to develop, a feature generally absent in global ocean reanalysis. Simulated biogeochemical parameters for surface chlorophyll, nutrients and integrated mesozooplankton showed the expected seasonal structure with peaks occurring in spring and fall. Discrepancies between the performance of the model in representing physical and biogeochemical parameters indicate that improved boundary conditions of biogeochemistry parameters may be necessary to a further enhance representation of seasonal and interannual variability of biogeochemistry in this domain. Despite these challenges, this version of the model reproduces the major physical and biogeochemical patterns of the NEUS, providing a robust foundation for various future applications.