Observations of the variability of the New England shelf break by shipboard echosounders

The New England Shelf Break is a dynamic region where warm salty slope water meets with colder less saline shelf water to form a distinct front. The position and shape of the front is modified by a range of processes on differing temporal and spatial scales. While seasonal changes are well documented, the influence of shorter time scale processes throughout the water column are less well understood. Of interest is the influence of meso-scale physical oceanographic processes such as meanders in the Gulf Stream and warm core rings and eddies. From March to June 2021 five cruises to the New England Shelf Break were conducted as part of the ONR Task Force Oceans New England Shelf Break Acoustics Experiments. The shipboard broadband echo sounders on the R/V Neil Armstrong were used to ensonify the front during each of these five cruises. Significant changes were observed, especially during the transit of a warm core eddy through the study area. Groups of scatterers in the study area were targeted by Deep-See (a broadband tow sled) and a broadband echo sounder equipped REMUS 600 to enable ensonification of individual targets to aide in acoustic identification of biology at the shelf break front.