The distribution of dissolved thallium in the different water masses of the western sector of the Ross Sea (Antarctica) during the austral summer.

Vertical profiles for total dissolved thallium were obtained at five sites in the western sector of the Ross Sea (Southern Ocean), Antarctica. Thallium is estimated to have a natural mean seawater concentration between 50 and 65 pmol L-1 with higher values in the North Pacific (65 +/- 5 pmol L-1) and lower in the Bay of Biscay and Irish Sea (49 +/- 3 pmol L-1). Our samples show a concentration varying from 22 to 55 pmol L-1 with a mean value of 46 pmol L-1, depending on depth, dissolved oxygen, salinity and local topographic characteristics. The analyses were performed using an ICP-SFMS that has enabled us to obtain reliable Tl concentration measurements with a relative standard deviation of better than 2.5% and a detection limit, calculated as three times the standard deviation of the "blank signal" of 0.69 pmol L-1(1.60 pmol L-1, obtained analysing four blank solutions (n=5) prepared with the same water and acid used for the dilution/acidification steps). Thallium appears to have a nearly conservative distribution in seawater as highlighted also from the comparison with the profiles of two seawater conservative elements: molybdenum and uranium; however it also highlights the presence of a reactive component of thallium, which is more influenced by the presence of particulate matter, oxygen content and fluorescence. (C) 2009 Elsevier B.V. All rights reserved.