Nd-Hf isotope systematics around Antarctica

The motivation to study Nd-Hf systematics around Antarctica is twofold. First of all, a wide range of bedrock ages and lithologies are found around the perimeter of the Antarctic continent, ranging from Archean basement terrains to recent volcanics. However, in Nd-Hf isotope space Antarctica remains one of the poorly known regions of the world's continents. A first order characterization of Nd and Hf isotopes in the detrital fraction of marine sediments will fill this gap and will put additional constraints on Antarctic bedrock geology and isotope systematics. Preliminary data indicate a range of Nd isotopes from -1 to -19 and a range of Hf isotopes from -2 to -20. These values reflect the variable Antarctic provenance and follow local geology. The lowest values are found in the Indian Ocean sector close to Archean outcrops and the highest values are observed in the Pacific sector close to young bedrock ages in the region between the Ross Sea and the Antarctic Peninsula. In Nd-Hf isotope space the new data scatter around the terrestrial correlation line. Two samples from the Indian sector display more radiogenic Hf isotopes for a given Nd isotopic composition, pointing towards potentially different Nd-Hf isotope systematics for the sediments with old provenance. Second, detrital inputs from Antarctica get dispersed into the Antarctic Circumpolar Current (ACC). The ACC is the connection between the Pacific, Atlantic, and Indian Oceans and distributes deep waters formed in the North Atlantic as well as exports deep water generated at sites around Antarctica. It is however not known whether there exists significant transfer of dissolved Nd and Hf from the Antarctic continent to the ACC and ultimately to the world's ocean. An improved understanding of the composition of Southern Ocean water masses and their dependence on inputs from the Antarctic continent and deep water sources on the Antarctic shelf is an important precondition to unravel past global circulation patterns and material inputs to the ocean. We will present new Hf isotope data for ferromanganese nodules from the ACC, which will be compared with existing Nd isotope data. Preliminary results indicate a small range in Hf isotopes for the Pacific sector of the ACC (3.9 to 4.5), which is almost indistinguishable within the analytical error and matches with what would have been predicted from Nd-Hf isotope systematics in seawater.