The role of entrained sediments in sea ice in the distribution of aluminium and iron in the surface waters of the Arctic Ocean

The distribution of reactive Al and Fe was determined in surface water samples collected by hand from ice floes and by shipboard rosette at 28 stations occupied during the 1994 US–Canadian Arctic Ocean Section. The data show significant variations in the concentration of both species over short spatial scales superimposed on a general trend of higher values in the Canada Basin and lower values in the Eurasian Basin. Detailed examination of the distributions indicates that the highest concentrations correspond to regions in which shipboard observations indicate the presence of significant amounts of sea-ice containing entrained sediments “dirty ice”. In many of these regions, strong vertical gradients in trace element concentrations are also observed. The observed correlation of high trace element concentrations and dirty ice suggests that ice-rafted sediment may be an important transport mechanism for supplying reactive trace elements such as Al and Fe to the surface waters of the central Arctic Ocean. Input of this sedimentary material through seasonal ice melt into strongly stratified surface waters leads to enrichment of properties in near surface layers which may have biogeochemical consequences for organisms living on the undersides of ice floes. Extreme concentration gradients in the upper 1–2 m though are likely to be missed or destroyed by conventional shipboard rosette sampling.