Aluminium in the northwest Atlantic

Abstract

A series of profiles between Woods Hole and Bermuda has been measured on board ship for Al. The extrema in the upper waters can be explained by the accumulation of aeolian inputs in the thin summer mixed layer, the depletion of the underlying “Winter Water” by scavenging during the Spring bloom and the enrichment of the Subtropical Mode (18°C) Water by aeolian accumulation during winter and local convection before the Spring bloom. The pronounced minimum at mid-depth is associated with the Antarctic Intermediate Water and the underlying Labrador Sea-Med Water complex. Presumably, the AAIW and the Med Water are depleted by the ageing effect on this short residence time element during their transit to the area. The LSW is formed from surface waters containing a large component of Arctic waters, extremely depleted in Al, advected south in the East Greenland Current. The linear increase to the bottom is caused by mixing of enriched lower North Atlantic Deep Water with the depleted Bottom Water and LSW cores. The enrichment in the Deep Water appears to be produced by the entrainment of high-Al waters from the North European Shelf by the gyre in the Norwegian-Greenland Sea and its injection into the Denmark Straits overflow waters in a manner recently described for the radiocaesium releases from the Windscale reprocessing plant on the Irish Sea. An additional contribution probably comes from the shelf north of Iceland.