A new ocean model configuration for management of central North Pacific Marine Resources (MOM6-COBALT-HIC6kv1.0)

Abstract. Despite often being referred to as an “ocean desert”, the North Pacific Subtropical Gyre (NPSG) supports economically valuable fisheries worth hundreds of millions of dollars annually, including Pacific bigeye tuna (Thunnus obesus) and other high-value pelagic species. The waters in and around the Hawaiian Islands support valuable and culturally significant nearshore fisheries and coral reef ecosystems and fuel ocean recreation and tourism valued in the billions. To be useful in understanding and managing these interacting resources, models must adequately represent ocean dynamics across multiple scales, from basin-wide circulation patterns to finer-scale island-ocean interactions. We evaluate the capacity of an ocean and biogeochemical model with 6 km horizontal grid spacing, a resolution considered “high” for climate-scale applications, across these scales. After a number of adjustments, including but not limited to calibrating light attenuation to subtropical observations and adjusting wind forcing to better reflect wind-current feedbacks, the model demonstrates strong skill in capturing basin-scale pelagic habitat features, including seasonal sea surface temperature anomalies (r > 0.95), accurate Transition Zone Chlorophyll Front migration and anomalies, and oxycline structure critical for bigeye tuna habitat compression. It also captures key features of the high seas ecosystems as represented by observations at station ALOHA, including exceptionally deep chlorophyll maxima (DCM) and seasonal variations and trends in acidification, though modest biases are evident. At the scale of island-ocean interactions, the model captures heightened eddy kinetic energy (EKE) downstream of the Hawaiian Islands and elevated productivity associated with the island mass effect. Finally, in nearshore regions, the model captures 88 % of the temperature variance observed at coral bleaching and habitat monitoring stations despite limited resolution. Overall, the configuration provides a robust foundation for a range of marine resource applications. Potential directions for future improvement include incorporating time-varying biogeochemical boundary conditions, refining salinity dynamics and carbonate chemistry representation, along with continued enhancement of nearshore circulation processes.