Distribution, Sources, and Dynamics of Particulate Matter Along Trans‐Arctic Sections

Abstract

AbstractIn order to better understand the sources, sinks, and hydrodynamic influences on particulate matter distribution and variability in Arctic basins, we combined transmissometer data from two 2015 fall expeditions: one from Bering Strait (USCGC Healy) and the other from Barents Sea (R/V Polarstern) meeting at the North Pole. These first trans‐Arctic sections of beam attenuation were overlain by salinity, temperature, and chlorophyll‐a fluorescence (Chl‐a) contours. Chl‐a sections were overlain by nitrate contours. Particle composition analyzed from filtered samples throughout the full water column aided significantly in discerning sources, distribution, and dynamics of particles. Dense Pacific water moving swiftly through Bering Strait erodes and carries sediment‐laden waters onto the Chukchi Shelf and into the Canada Basin. This nutrient‐rich Pacific water sinks below a low‐salinity, nutrient‐poor polar mixed layer, forming a thick lens of high salinity water known as Pacific halocline water (salinity 31–33). Ice and the nutrient‐poor mixed layer inhibit photosynthesis in surface waters of Canada and Makarov Basins, but subsurface chlorophyll‐a maxima are observed if nutrients and light are available. Surface‐water biomass is greater in the Barents Sea than in the Beaufort Gyre because nutrient‐rich Atlantic water entering Barents Sea is not isolated from surface waters by ice or strong stratification. Surface water cools, creating high‐density water that cascades into ∼400 m basins in Barents Sea and into deep Nansen Basin, eroding sediment that creates patches of nepheloid layers in the shallow basins. Intense nepheloid layers in the deep basins are rare, suggesting weak bottom currents.