Mesoscale and submesoscale shelf-ocean exchanges initialize an advective marine heatwave

Abstract

Observations and high-resolution numerical modeling are used to investigate the dynamical processes related to the initiation of an advective Marine Heatwave in the Middle Atlantic Bight of the Northwest Atlantic continental shelf. Both the observations and the model identify two significant cross-shelf intrusions in November 2016 and January 2017, with the latter inducing large-magnitude water mass anomalies across the shelf. Model prognostic fields reveal the importance of the combination of cyclonic eddies or ringlets and upwelling-favorable winds in producing the large-distance cross-shelf penetration and temperature/salinity anomalies. The cyclonic eddies in close proximity to the shelfbreak set up local along-isobath pressure gradients and provide favorable conditions for the intensification of the shelfbreak front, both processes driving cross-isobath intrusions of warm, salty offshore water onto the outer continental shelf. Subsequently, strong and persistent upwelling-favorable winds drive a rapid, bottom intensified cross-shelf penetration in January 2017 composed of the anomalous water mass off the shelfbreak. The along-shelf settings including realistic representation of bathymetric features are essential in the characteristics of the cross-shelf penetration. The results highlight the importance of smaller scale cyclonic eddies and the intricacy of the interplay between multiple processes to drive significant cross-shelf events.