Global Distribution and Intensity of Deep-Water Benthic Nepheloid Layers

We are mapping the intensity of benthic nepheloid layers in the deep ocean based on profiles of beam attenuation coefficient obtained with transmissometers interfaced with CTDs during WOCE, SAVE, JGOFS, CLIVAR-Repeat Hydrography, GO-SHIP and other programs during the last four decades using data from over 8000 profiles from >70 cruises. The Repeat Hydrography cruises have provided re-occupations of some transects in the Atlantic and Pacific about 10 years apart. Intense benthic nepheloid layers are found in areas where eddy kinetic energy is high in overlying waters. Areas of intense benthic nepheloid layers include the western North Atlantic, Argentine Basin, parts of the Southern Ocean and areas around South Africa. Benthic nepheloid layers are weak or absent in most of the Pacific, Indian, and Atlantic basins away from margins. Despite high surface eddy kinetic energy associated with the Kuroshio current east of Japan, limited data show weak nepheloid layers in that vicinity. Understanding the distribution and underlying causes of intense and weak benthic nepheloid layers will help in assessing geochemical processes such as scavenging of adsorption-prone elements in the deep ocean as measured in the GEOTRACES program. It will also help in quantifying the impact of renewed deep-sea mining and understanding deep ocean sediment dynamics