Filtered particles from a Southern Ocean meridional transect (from 42°S to 54°S along 142°E) off Tasmania were studied between surface and 600-m water depth (SAZ 1998 expedition, February-April 1998). Particulate Ba, Sr, Ca, P, U, Th, Ti, Al, Mn, light rare earth elements, and Zr contents were analyzed by inductively coupled plasma-mass spectrometry and inductively coupled plasma-atomic emission spectroscopy. Mesopelagic Baxs (total Ba minus a lithogenic fraction estimated from Al) contents were higher within the Polar Front Zone (PFZ) in comparison with the northern areas, indicating that C export to the intermediate and deep ocean is more important in the PFZ. Average surface Uxs versus latitude covaries with mesopelagic Baxs, contrasting with organic matter proxies such as Pp and chlorophyll a. This similar behavior suggests that U might be preferentially adsorbed on organic material, which subsequently becomes involved with barite precipitation. Srp and Cap contents decrease sharply with depth, following total particle content. For the northern area (42°-47°S), surface Ce anomaly reflects essentially a lithogenic signature (0.6 < Ce/Ce* < 1) ascribed to the supply from the Tasmanian continental shelf. Suspended matter from surface waters at stations south of 47°S shows an enhanced seawater signature (0.3 < Ce/Ce* < 0.6). In all stations, Ce anomalies increase with depth, toward values close to 1. This is likely due to the increase of lithogenic/authigenic ratio of particles with depth, rather than redox processes. Finally, an advective event is identified at 45°S below 200 m by a strong increase of lithogenic element contents, which affects Baxs. |
