Subsurface acoustic ducts near the Gulf Stream

Oceanic fronts are regions of rapid change in seawater properties. We examine a collection of approaching 10,000 oceanic sound speed profiles from the surface to 1000 m measured by autonomous underwater gliders within 200 km of the Gulf Stream front between 35 and 41 °N in the North Atlantic Ocean. The underwater gliders sample with approximately 5 km resolution in the cross-front direction and allow us to study subsurface acoustic ducts across the front. We algorithmically detect ducts in the sound speed profiles and examine statistics of subsurface duct axial sound speed, width, and cutoff frequency depending on depth and distance from the Gulf Stream. We associate the formation of subsurface sound speed ducts with ocean water mass properties and dynamics. In particular, we examine the case of ducts formed by cool, fresh water from the continental shelf that is exported, entrained, and subducted beneath the Gulf Stream.