Multi-Decadal Global Surveys of Benthic Nepheloid Layers

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An accurate knowledge of the abundance and distribution of suspended particles in the ocean is essential to the study of marine biogeochemical cycles, especially trace elements and isotopes that interact with these particles. Particles in the benthic nepheloid layer (BNL), a layer of ocean water just above the seafloor, can accumulate radionuclides that are used in studying past global changes, as paleo-proxies, and in investigating modern and glacial ocean circulation. This project aims to assess the relationship between global maps of benthic nepheloid layers and surface and deep sea kinetic energy to document how these processes influence deep-sea processes of sediment resuspension and redistribution. Results from the research will be shared broadly with the oceanographic community. A graduate student who qualifies for the National Science Foundation Scholarships in Science, Technology, Engineering, and Mathematics Program would be supported and trained as part of this project.Over the past 35 years, the investigators have collected more than 8000 transmissometer - an optical instrument calibrated to estimate particle mass - profiles from conductivity-temperature-density casts on approximately 70 cruises. These archived and ongoing collections of transmissometer data along with nephelometer data from the Lamont Doherty Earth Observatory, are the only collections of particle distributions in the ocean encompassing significant temporal and global scales. The main goals of the project are to 1) convert beam attenuation data to mass concentrations, 2) integrate the Net Standing Stock (NetSS) for each of the thousands of profiles, 3) map the NetSS globally from the 1980s-to-2016 transmissometer data, 4) compare these maps against global distributions of nephelometer data from the 1960s-1980s for which a preliminary global map has been constructed, and 5) compare nepheloid layers along 9 Repeat Hydrography lines where multiple cruises have occurred. The global maps (and supporting data) of the benthic nepheloid layers will be widely disseminated to the oceanographic community, enhancing the scientific understanding of BNL formation, decadal persistence, and their relationship to kinetic energy regimes for studying, deciphering and modeling biogeochemical cycles through the water column and near the seafloor.