Long-term variability of ocean fronts in the Northwest Atlantic

The ocean fronts, such as the Gulf Stream North Wall (GSNW) and the Shelf-Slope Front (SSF), along the eastern coast of North American continent in the Northwest Atlantic, at both surface and subsurface levels, significantly influence regional climate, oceanic energy and mass exchanges, marine ecosystems and fisheries. Many previous studies have examined the variability in the positions of the GSNW or SSF separately, usually based on oceanographic variables at a single depth. In this study, we investigate the leading mode (Northwest Atlantic Temperature Gradient Mode, NATG) of the sea temperature gradient at multiple depths from observations and models, which reflects the combined long-term variability of the SSF and GSNW. The NATG index shows a significant spectral peak at ~100 years in the power spectrum and underwent a significant multi-decadal trend turning around early 1960s. We find that the velocity difference between the Gulf Stream and Labrador Current has a strong positive correlation with the NATG. Additionally, the NATG may be associated with an anomalous surface atmospheric cyclone-anticyclone configuration along the east coast of the North American continent.