The distribution of aluminium in the Greenland Sea and its relationship to ventilation processes

Abstract

During two cruises to the Greenland Sea in 1988 and 1989 a total of 690 on‐board aluminium (Al) determinations were performed on samples collected from profiles located along four transects in the Greenland Sea, as part of the Greenland Sea Project. Al concentrations range from extremely low values (0.4 nM) in the Polar waters of the East Greenland Current draining the Arctic Ocean, to 17.9 nM in the newly formed Norwegian Sea Deep Water (NSDW) at the periphery of the Greenland gyre. The Al content in the component water masses serves to constrain the make‐up of these water masses from the various mixing products of the region. The enrichment of Al in the NSDW both at its site of formation within the Greenland Sea (up to 17.9 nM) and in the Lofoten Basin of the Norwegian Sea (up to 40.3 nM) leads to the conclusion that there must be an additional, external, source of Al to these water masses. The apparent inability of water column or sedimentary diagenetic processes to provide this enrichment and the observation of enriched Al values associated with a high‐salinity shelf brine leads us to the conclusion that these brines may be responsible for the observed enrichments. The high concentration of Al in the Greenland Sea Deep Water compared with the water masses that produce it, suggests that Al may be acting as an inverse tracer of the processes that ventilate this basin by convective overturn, i.e. the Al concentration which increases with time, as a result of continuous brine or other external inputs, is reduced during convective events. It is also argued that this flushing of elevated Al water during convective events may have a similar counterpart in the Iceland Sea and that this mechanism could go some way toward solving the Al deficit that exists between the enriched North Atlantic Deep Water and its depleted precursor water masses observed in the intermediate waters of the Greenland and Iceland seas.