Oceanographic influences on Deep Scattering Layers across the North Atlantic

Abstract

The distribution and density of Deep Scattering Layers (DSLs) were quantified along North Atlantic transits from Ireland to the Grand Banks of Newfoundland in the springs of 2012, 2013 and 2014 employing a calibrated Simrad EK60 echo sounder at 38kHz. Concurrently, Sippican T5 XBTs (eXpendable Bathy Thermographs) were used to profile temperatures to 1800m. In each year the scattering layers spanned the deep basin at depths ranging from near surface to approximately 900m, but annual mean densities differed significantly. Higher DSL densities were recorded during years that exhibited higher sea temperatures at the depths of major DSL concentration (400–600m), higher sea level anomalies and stronger eastward geostrophic currents. The highest concentration of the DSLs in each year was found in the area east of the Grand Banks that corresponded with areas of anticyclonic eddies. In this region DSL densities in 2014 were among the highest recorded worldwide (>7000m2nauticalmile–2). Midwater fishing indicated DSLs were dominated by Myctophids and Sternoptychids. Anticyclonic eddy formation is discussed as a possible means of transport and aggregation of the DSLs in that region, where oceanographic influences may play a dominant role in the distribution and density of the DSLs and upper trophic level fishes.