Dissolved Al in the zonal N Atlantic section of the US GEOTRACES 2010/2011 cruises and the importance of hydrothermal inputs

Abstract

The distribution of dissolved aluminium determined during GA03, the US GEOTRACES North Atlantic Transects (US GT NAZT) shows large inputs to the basin from three main sources, atmospheric deposition, outflow from the Mediterranean, and inputs from hydrothermal sources along the Mid Atlantic Ridge (MAR). The partial dissolution of atmospheric aerosols emanating from the Sahara yield high concentrations of dissolved Al in the surface waters of the basin and are used to estimate the geographical pattern of dust deposition. The Mediterranean outflow delivers a large source of dissolved Al to the intermediate waters of the eastern basin and its subsequent distribution within the basin can be explained by simple isopycnal mixing with surrounding water masses. Hydrothermal venting at the Trans-Atlantic Geotraverse (TAG) hydrothermal field in the MAR produces a neutrally buoyant plume that introduces copious quantities of dissolved Al (with concentrations of up to 40nM) to the deeper waters of the North Atlantic that can be seen advecting to the west of the MAR. The concentration of dissolved Al in the deep waters of the eastern basin of the Atlantic can be accounted for by admixing the MAR Al enriched plume water and Antarctic Bottom Water (AABW) as they pass through the Vema Fracture Zone. The data sets show no evidence for biological remineralisation of dissolved Al from Si carrier phases in deep waters.