Dynamical and thermodynamical drivers of regional warming in the Northeastern United States

Abstract

The Gulf of Maine (GoM) is among the fastest-warming regions in the global ocean, with an observed basin-wide warming rate of approximately 0.05°C per year, substantially exceeding the global upper-ocean average. Although this accelerated warming has been well documented, the relative contributions of local atmospheric forcing and remote ocean heat transport have not been quantitatively determined. This thesis addresses this knowledge gap using the Northeast Coastal Ocean Forecast System (NECOFS) hindcast dataset. Atmospheric and oceanic fields from the NECOFS hindcast were used to construct a volume-integrated heat budget model for the GoM, enabling the relative contributions of surface air-sea heat fluxes and lateral heat transport to be quantified. The hindcast was first evaluated against observations of near-surface atmospheric variables, ocean currents, seawater temperature, and sea surface elevation, demonstrating good agreement across all evaluated variables. The heat budget was decomposed into local thermodynamic forcing (air-sea heat flux) and remote advective transport (lateral heat transport through the GoM boundaries). Comparisons between two representative periods (19952001 and 2017-2023) show that changes in local heating account for approximately 3.97°C of the fast warming observed in recent years, while lateral heat transport exerted a cooling effect of approximately -3.80°C over the GoM. Further decomposition of the advective term reveals a substantial reorganization of the primary heat transport pathways: the dominant warming inflow shifted from the Northeast Channel during 1995-2001 to the southwestern side of the Northeast Channel during 2017-2023, while the cooling contribution shifted only in relative proportion between the Scotian Shelf and the Middle Atlantic Bight. At the same time, reduced outflow through the Middle Atlantic Bight likely increased the residence time of warm water within the basin, further enhancing regional warming. River heat input remained negligible throughout both periods.These results demonstrate that the recent acceleration of warming in the GoM is controlled primarily by changes in local atmospheric heating. This study provides a quantitative framework for distinguishing the relative roles of atmospheric forcing and oceanic heat transport in regional climate change and offers new insight into the physical mechanisms responsible for long-term warming in the northeastern U.S. shelf ecosystem.