Tracing water masses and continental weathering by neodymium and hafnium isotopes in the Atlantic sector of the Southern Ocean

• Main Author: Stichel, Torben
• Other Authors: Frank, Martin, Eisenhauer, Anton
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2011
• Subjects: ddc:550; thesis; Southern Ocean; hafnium; neodymium; radiogenic isotopes; Weddell Sea; Drake Passage; Weddell; International Polar Year; IPY
• Online Access: https://nbn-resolving.org/urn:nbn:de:gbv:8-diss-60686; https://macau.uni-kiel.de/receive/diss_mods_00006068; https://macau.uni-kiel.de/servlets/MCRFileNodeServlet/dissertation_derivate_00003594/diss_torben_stichel.pdf

Radiogenic isotopes, such as the ones of hafnium (Hf) and neodymium (Nd), have been used to investigate present and past ocean circulation patterns, hydrothermal inputs and continental weathering regimes. This thesis presents a detailed study of the dissolved Hf and Nd isotope composition and concentration of seawater in the Atlantic sector of the Southern Ocean. The goal is to better understand their controlling factors, mainly weathering inputs, biogeochemical cycling, and water mass mixing. The samples were collected along the Zero Meridian, in the Weddell Sea and in the Drake Passage during expedition ANTXXIV/3 with R/V Polarstern in 2008 in the frame of the International Polar Year (IPY) and the GEOTRACES program. Volumes of seawater between 60 L (deeper than 200 m) and 130 L (surface) were collected for Hf, and a volume of 20 L for Nd isotopes following GEOTRACES protocols. For isotopic analysis, the samples were chemically and ion chromatographically purified, for which existing methods had to be significantly modified, as described in detail in Chapter 2. Hafnium and Nd concentrations were determined on aliquots of the same samples by isotope dilution. The isotope compositions and concentrations were measured by Thermal Ionisation Mass Spectrometry (TIMS) or Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS). The distribution of Hf and Nd concentrations in the surface water (Chapter 3) is generally similar with essentially constant values south of the Polar Front (~0.3 pmol/kg and ~18 pmol/kg, respectively). Minimum Hf (~0.12 pmol/kg) and Nd (~7 pmol/kg) concentrations are observed between the Subtropical Front and the Polar Front, most probably due to the limited terrigenous flux in this area, but may also result from scavenging by biogenic opal. In contrast, at the northernmost station, 200 km southwest of Cape Town, a pronounced increase of the Nd concentration is observed, while the Hf concentration is at its minimum. This indicates a lower amount of Hf than of Nd released by ...