Hydrothermal sediment geochemistry south of the Antarctic Polar Front

• Main Author: Hepburn, Laura
• Format: Thesis
• Language: English
• Published: 2015
• Subjects: Antarctic; Southern Ocean; The Antarctic; Austral; Scotia Sea; East Scotia Ridge; Bare Rock; Antarc*
• Online Access: https://eprints.soton.ac.uk/384574/; https://eprints.soton.ac.uk/384574/1/Hepburn%252C%2520Laura_PhD_Nov_15.pdf

This thesis uses a novel, combined mineralogical, geochemical (including stable S isotopes), and microbiological approach to semi-quantitatively determine Scotia Sea sediment formation processes. The factors that control the localisation of chemosynthetic, microbial consortia in metalliferous sediment beneath Southern Ocean vent fields is investigated along with the impact of hydrothermal venting on sediment composition. Circum-Antarctic ridges represent nearly 40 % of the Earth’s ~58,000 km ridge crest, but remain severely understudied. In the austral summer of 2009–2010, the Royal Research Ship James Cook expedition JC42 explored the northernmost (E2) and southernmost (E9) bare-rock segments of the East Scotia Ridge, and the sedimented Kemp Caldera (a southern feature of the South Sandwich Arc), and collected >20 co-registered vent fluid, chimney sulfide and hydrothermally-influenced sediment samples using the ISIS remotely-operated vehicle. The hydrothermal materials from E9 and the Kemp Caldera are the focus of this thesis. E9 sediment composition is controlled by the simple mixing of >90 % local basalt that is affected by subduction-related and enriched mantle components, <10 % particulate plume fallout, which is dominated by an Fe-, Cu-, Zn-, Ba-, and Pb-rich, near-plume phase, and <1 % collapsed chimney material. The major, minor, trace, and rare earth element sediment content at E9 is largely determined by proximity to active venting. The thin sediment cover throughout E9, indicates an early stage of sediment formation and the recent onset of venting at this site. Kemp Caldera sediment components include 55–60 % phreatomagmatic shards of local basalt that were most likely deposited by a recent, volcanic event, 30–45 % crystalline elemental S derived from the magmatic disproportionation of SO 2 (identified by a δ 34 S signature of +4.8 ‰ to +5.9 ‰), and 0–10 % buoyant plume particles (rich in P, K, Mn, Fe, and the rare earth elements). Biogeochemical Fe, Mn, and S cycling is investigated in ...