DISSOLVED ZIRCONIUM AND HAFNIUM DISTRIBUTIONS ACROSS A SHELF BREAK INTHE NORTHEASTERN ATLANTIC-OCEAN

Dissolved Zr and Hf distributions have been determined for five statio ns located across the shelf break. in the northeastern Atlantic Ocean on the Celtic Approaches. For stations in deep water, the range in Zr concentrations has been found to be 70-180 pmol/kg, and the range in h afnium concentrations 0.4-1.1 pmol/kg. The distributions with depth ar e indicative of a nutrient-like scavenging-regeneration behavior in se awater, although the dissimilarity with silicate and nitrate for sampl es below the nutricline suggest that other mechanisms are also importa nt in defining the oceanic distribution of these elements. In contrast , the concentrations of Zr and Hf at the station located closest to la nd are highest in surface waters and decrease with depth, although sal inity does not indicate dilution of seawater with freshwater with high Zr and Hf concentrations. The ratio of dissolved Zr to Hf in seawater is higher and more variable than is found for the majority of terrest rial rocks, or predicted from thermodynamic considerations. Fractionat ion due to small differences in their interactions with particulate ma terial is implicated.