Nd and Hf isotopic compositions in the Atlantic sector of the Southern Ocean

• Main Authors: Stichel, Torben, Frank, Martin, Haley, Brian, Rickli, Jörg, Venchiarutti, Célia
• Format: Conference Object
• Language: unknown
• Published: Washington, DC, USA 2010
• Subjects: Antarctic; Antarctic Peninsula; Drake Passage; Southern Ocean; The Antarctic; Weddell; Weddell Sea; Antarc*
• Online Access: https://oceanrep.geomar.de/id/eprint/10698/; http://www.agu.org/cgi-bin/SFgate/SFgate?language=English&verbose=0&listenv=table&application=os10&convert=&converthl=&refinequery=&formintern=&formextern=&transquery=stichel&_lines=&multiple=0&descriptor=%2fdata%2fepubs%2fwais%2findexes%2fos10%2fos10%7C699

AB: Radiogenic hafnium (Hf) and neodymium (Nd) isotopes have been used as tracers for past continental weathering regimes and ocean circulation. To date there is only very few data available on dissolved Hf and Nd isotope compositions of the modern Southern Ocean (SO). During expedition ANTXXIV/3 (February to April 2008) filtered (0.45 µm) seawater samples (20-120 liters) were collected in the Drake Passage, the Weddell Sea and the Subantarctic Atlantic Ocean (near the Zero Meridian) to determine the dissolved isotopic composition of Hf and Nd of the major water masses in the SO. The dissolved seawater isotopic compositions of both Hf and Nd in the open Drake Passage show only minor variability (εHf = 4.2 to 4.7 and εNd = -8.8 to -7.6). However, in the Weddell Sea and at stations from the southernmost part of the Drake Passage close to the Antarctic Peninsula, the Nd isotopic composition ranged from εNd = -8.9 to -6.4. At one station near the Subtropical Convergence we measuered εNd = -15.9 in surface waters and -8.9 and -9.9 in intermediate and deep waters, respectively. Compared with the previously measured particulate fraction, the dissolved Nd isotope distribution indicates that particle leaching contributes unradiogenic Nd to near surface waters, whereas the isotopic compositions of deep waters are controlled by water mass mixing. Furthermore, we infer that the Nd isotope signature of Antarctic Intermediate Water (AAIW), which is formed in the Polar Frontal Zone, has been mixed with relatively unradiogenic surface water signatures before it is subducted. Our data therefore suggest that the variability of the surface water Nd isotope composition is relevant for the final Nd isotope signature of the submerging intermediate waters in the SO.