Summer distribution of trace metals in the western sector of the Ross Sea, Antarctica

Abstract

The more important water masses generated by the interaction of Circumpolar Deep Water and the shelf waters in the western sector of the Ross Sea are characterized for trace element contents. The distribution of cadmium, lead, copper, zinc, iron, manganese and chromium during the austral summer is analysed and discussed according to the physical, chemical and biological processes which affect the composition of the water masses. The Cd concentration is found to have a relative high variability that can be related to biological activity and the water mass age, MCDW presents a mean dissolved concentration (SD) of 0.77 (0.07) nmol kg(-1), while the HSSW and AASW have a mean concentration of 0.63 (0.06) and 0.61 (0.16) nmol kg(-1), respectively. Lead features the typical distribution of a scavenged element with a surface maximum ranging between 22 and 130 pmol kg(-1) decreasing to 11 pmol kg(-1) in deep waters. However, the vertical distribution in the shelf area features a maximum concentration in intermediate/deep waters and we can hypothesize that the distribution may be influenced by more than one source. The surface dissolved concentration of zinc and copper were un-homogeneously distributed, the mean (SD) values were 5.25 (2.92) and 1.99 (1.49) nmol kg(-1) for zinc and copper, respectively and increased with depth for both the elements. We may therefore hypothesize enrichment in the dissolved phase deriving from recycling in deep waters. 95% of the chromium was in dissolved form and showed a superficial depletion; the mean concentrations were 1.6 +/- 0.2 and 2.6 +/- 0.8 nmol kg(-1) for surface and deep waters respectively. The vertical distribution of dissolved manganese was quite homogeneous with a mean concentration 0.96 +/- 0.7 nmol kg(-1). The particulate iron and manganese concentration trends are similar and feature a significant bottom increase implying a significant input from resuspension; the mean concentration of particulate ranged between 1.4 and 7.4 nmol kg(-1) for iron and ranged between 0.072 and 0.29 nmol kg(-1) for manganese.