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 samp les collected by hand from ice flees and by shipboard rosette at 28 station s occupied during the 1994 US-Canadian Arctic Ocean Section. The data show significant variations in the concentration of both species over short spat ial scales superimposed on a general trend of higher values in the Canada B asin and lower values in the Eurasian Basin. Detailed examination of the di stributions indicates that the highest concentrations correspond to regions in which shipboard observations indicate the presence of significant amoun ts of sea-ice containing entrained sediments ''dirty ice''. In many of thes e regions, strong vertical gradients in trace element concentrations are al so observed. The observed correlation of high trace element concentrations and dirty ice suggests that ice-rafted sediment may be an important transpo rt mechanism for supplying reactive trace elements such as Al and Fe to the surface waters of the central Arctic Ocean. Input of this sedimentary mate rial through seasonal ice melt into strongly stratified surface waters lead s to enrichment of properties in near surface layers which may have biogeoc hemical consequences for organisms living on the undersides of ice flees. E xtreme concentration gradients in the upper 1-2 m though are likely to be m issed or destroyed by conventional shipboard rosette sampling. (C) 1999 Els evier Science B.V. All rights reserved.