Modeling the circulation and timescales of the Mid-Atlantic Bight and Gulf of Maine
Creators: name: López, Alexander Gordon
Publisher: name: No Publisher Supplied
Year: 2020

description: The Mid-Atlantic Bight and Gulf of Maine regions of the northeast U.S. seaboard are dynamic regions, with complex inflows, intricate bathymetry, and the world’s largest tidal range. Accurately modeling the Gulf of Maine has proven difficult in the past. We create, assess, and implement a new ROMS (Regional Ocean Modeling System) model called “Doppio” for these regions to determine the circulation timescales and transport pathways.Doppio is a free-running regional ROMS model for the Mid-Atlantic Bight and Gulf of Maine, used for circulation simulations covering 2007-2017. The ROMS model configuration is detailed, and the forcing and open boundary data choices are described and explained. Model skill is assessed in comparison to a comprehensive suite of observations from a variety of satellites and in situ platforms, including but not limited to moorings, gliders, surface current measuring coastal radar, and fishing fleet sensors. Lastly, Doppio’s performance is evaluated against these observations as sub-regional temperature and salinity error statistics, and also as velocity and sea level coherence spectra. Doppio’s mean dynamic topography and mean circulation also demonstrate the model’s capabilities.To determine the transport pathways and circulation timescales of the Gulf of Maine, for general inflows and in the case of observed salinity anomalies, passive tracer simulations were conducted predominantly with a 7 km grid resolution version of the Doppio model. Our simulations indicate that inflows to the Gulf quickly circulate around a path principally following the coast before subsequently entering the center of the Gulf in a matter of months, in agreement with observed time lags. Scotian Shelf source water is the dominant water mass in the coastal waters of the Gulf, while the center of the Gulf is predominantly waters that enter via the Northeast Channel. Eleven-year (2007-2017) ensemble simulations were used to determine mean and anomalous dynamics. Using simulations initialized from a separate data assimilative version of Doppio, we found that a pronounced salinity anomaly observed in late 2017 in the Gulf of Maine was due to a combination of anomalous waters on the Scotian Shelf and conditions outside the Gulf that fostered advection into the Gulf of Maine.Development of an improved physical circulation model for the Gulf of Maine was motivated by the objective of better simulating biogeochemistry and ecosystems in the Gulf. Simulations were conducted with a native ROMS biogeochemical using initial and open boundary inferred from historical observations and World Ocean Atlas data via interpolation and property-to-property relations with respect to the physical parameters of temperature, salinity, and depth. Reasonable fidelity to available biogeochemistry observations was achieved, and more biogeochemical data are needed to better inform the initialization, open boundary data, and coupled physical-biogeochemical model skill assessment. A foundation is laid for future ecosystem studies using Doppio.