Autumnal deep scattering layer from moored acoustic sensing in the subtropical Canary Basin

Abstract

An enhanced acoustic scatterer reflectance layer was observed in the bathypelagic zone around 1650 m in the subtropical NE-Atlantic Ocean for about 2 months during autumn. It resembles a classic pattern of diapause resting, possibly of large zooplankton, shrimp, and/or Cyclothone, at great depths well below any sunlight penetration, which is more commonly found at higher latitudes. The observed slow sink and rise of about 2–5 m per day into and out of this deep layer is considerably slower than the more than 1000 m per day of diel vertical migration (DVM). During the 2-month period of deep scattering, DVM is observed to be greatly reduced.