Haline Сontrol of Unusually Deep Winter Mixing in the Gulf of Maine Investigated Using a Regional Data‐Assimilative Model

An unusually large positive salinity anomaly was observed across the eastern Gulf of Maine in winter 2017–2018. Buoy measurements Jordan Basin found this extended down to at least 100 m, deepest mixing past 19 years. Similarly, is strongest regional salt ever sea surface (SSS) satellite observations. To determine source waters driving event and diagnose relative importance forcing processes, passive tracer adjoint sensitivity experiments are performed using a data assimilating version Regional Ocean Modeling System. The model suggests that northeastward Scotian Shelf wind anomalies one factor dramatic decrease freshwater transport Basin, which leads an early upper water column surplus. This change weakens normally haline-controlled vertical stratification Gulf. Modeled ocean density diffusivity from 2007 2021 both show maximum January 2018. Winter 2017–2018 only period where enhanced extends below m. Thus, anomalous entrainment saltier subsurface major extreme satellite-observed SSS including Basin. Other factors, modest increase wind-forced slope transport, fall 2017 on Slope Sea, appear play lesser roles salinification. analysis demonstrates its utility for back tracing pathways periods several months.