The Response of the Northwest Atlantic Ocean to Climate Change

ROMS, a high-resolution regional ocean model, was used to study how climate change may affect the northwest Atlantic Ocean. A control (CTRL) simulation was conducted for the recent past (1976-2005), and simulations with additional forcing at the surface and lateral boundaries, obtained from three different global climate models (GCMs) using the RCP8.5 scenario, were conducted to represent the future (2070-2099). The climate change response was obtained from the difference between the CTRL and each of the three future simulations.

All three ROMS simulations indicated large increases in sea surface temperatures (SSTs) over most of the domain except off the eastern US seaboard due to weakening of the Gulf Stream. There are also substantial inter-model differences in the response, including a southward shift of the Gulf Stream in one simulation and a slight northward shift in the other two, with corresponding changes in eddy activity. The depth of maximum warming varied among the three simulations, resulting in differences in the bottom temperature response in coastal regions, including the Gulf of Maine and the west Florida Shelf. The surface salinity decreased (increased) in the northern (southern) part of the domain in all three experiments, but in one, the freshening extended much further south in ROMS than in the GCM that provided the large-scale forcing, associated with changes in the well resolved coastal currents. Thus, while high resolution allows for a better representation of currents and bathymetry, the response to climate change can vary considerably depending on the large-scale forcing.