Do Changes in the Western Boundary Circulation Cause Stratification Changes in the Northwest Atlantic Ocean?

The Northwest Atlantic Ocean is a climatically sensitive region influenced by two major boundary currents—the warm Gulf Stream and the cold Labrador Current—which transport water masses of contrasting temperature and salinity, and it also hosts a crucial component of the Atlantic Meridional Overturning Circulation (AMOC). Recent studies indicate substantial changes in both currents, with potential implications for regional ocean dynamics. In this study, we investigate the evolution of stratification in the Northwest Atlantic over the period 1993–2023 using an eddy-permitting reanalysis dataset. Stratification is quantified through the Brunt–Väisälä frequency, and long-term trends are assessed. To diagnose the drivers of the observed stratification changes, we further examine the variability in current pathways using Lagrangian parcel tracking. Additionally, Optimum Multiparameter (OMP) analysis reveals that changes in circulation are redistributing water masses across the study domain, which likely contributes to the modulation of water-column stratification. Stratification in this region is a key regulator of ocean primary production, oxygen ventilation, vertical mixing, and deep convection, thereby influencing both ecosystem dynamics and large-scale ocean circulation.