| 18 Feb 2026
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.
This manuscript presents and evaluates MOM6-COBALT-NEUS25 version 1.0, a high-resolution (1/25 deg.) coupled physical-biogeochemical model for the northeastern US designed to support marine carbon dioxide removal assessments and benthic modeling applications. The configuration consists of the MOM6 ocean model coupled with COBALT using a z* coordinate with 75 vertical layers, incorporating tidal forcing, river discharge, and multiple data sources (Glorys, ERA5, TPXO9, WOA23) for initialization and boundary conditions. A thorough validation against observational databases, satellite products, and climatologies is presented for the simulation period in order to assess model performance. Key findings demonstrate that the model realistically simulates Gulf Stream dynamics, seasonal temperature and salinity structures with small SST biases, and realistic surface chlorophyll and nutrient seasonal cycles with expected spring and fall peaks. The configuration successfully captures regional circulation patterns and the development of cold SST patches through the inclusion of tidal mixing, an improvement over current reanalysis products. The work represents a significant advancement in regional ocean modeling by providing improved spatial resolution and process representation compared to global reanalyses, offering a robust foundation for climate impact studies and fisheries applications in this ecologically and economically important region. Some limitations include persistent biases in the Mid-Atlantic Bight's vertical temperature-salinity structure, a northward bias in Gulf Stream position with reduced meandering that affects tracer field representation, weak coastal freshwater signals leading to positive salinity biases, underestimation of mesozooplankton biomass, and limited skill in capturing subinertial sea surface height variability— however, many of these shortcomings arise from known modeling limitations and not necessarily from poor configurations choices. On the contrary, the authors have done a good job in with their parameter choices to ensure the best representation for their desired applications. The authors also present evidence on how these biases do not precluded the intended purpose of the configuration in its totality. This manuscript would be an excellent addition to the growing body of work on high-resolution regional modeling using MOM6. I would recommend this manuscript for publication after the authors consider the following comments:
The authors attribute the warm shallow water temperature biases during summer and fall partly to "overmixing associated with the upper ocean boundary layer scheme". Whereas Ross et al. (2023) (using ePBL alone) found that adjusting the submesoscale restratification front length parameter in the Fox-Kemper et al. (2011) scheme represented a key trade-off between mixed-layer depth and bottom-temperature bias in their configuration. Why was the hybrid approach selected over ePBL and the Fok-Kemper restratification scheme?. (1) what motivated the choice of the hybrid max(ePBL, KPP) scheme over ePBL with the Fox-Kemper restratification (as in Ross et al. 2023)? , and (2) was the sensitivity of bottom temperatures to the restratification front length parameter identified in Ross et al. (2023) explored in NEUS25? (it is unclear from lines 6210-623 which paremeterizations were tested).