The biogeochemistry of bioactive trace elements cadmium and cobalt in the Southern Ocean, Atlantic Sector

• Main Author: Loock, Jean Christian
• Other Authors: Roychoudhury, Alakendra N., Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
• Format: Thesis
• Language: English
• Published: Stellenbosch : Stellenbosch University 2017
• Subjects: Biogeochemical cycles > Southern Atlantic; Cobalt; Cadmium; Biogeochemistry; UCTD; Antarctic; Southern Ocean; The Antarctic; Austral; Weddell; Antarc*
• Online Access: http://hdl.handle.net/10019.1/100925

Thesis (MSc)--Stellenbosch University, 2017. ENGLISH ABSTRACT: The biogeochemical cycling of the bio-active dissolved trace metals cadmium (DCd) and cobalt (DCo), are reported on a meridional transect of the Southern Atlantic, spanning 36°S to 68°S. Seawater samples were collected using an adaptation of the GEOTRACES clean sampling method concurrent to the austral mid-summer (2015). A multi-element inductively coupled plasma mass spectrometry (ICP-MS) technique, coupled with the commercially available seaFAST pre-concentration module was set up and validated for 8 trace elements (Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb). The method proved highly precise (≤10%RSD) in the repeated analysis of an in-house control (TM4A), and accurate in the analysis of the SAFe (D2) international natural seawater reference material. Iron (Fe) quantification proved precise (≤5%RSD) and accurate under repeat analysis. Furthermore, two GEOTRACES standards, GSP and GSC, were analysed for contributing to the determination of their consensus values. DCo concentrations within the oligotrophic sub-surface waters (500m) of the Sub-Tropical Zone (STZ) are heavily depleted (12.57 pmol/kg) owing to strong bio-utilization. Conversely, sub-surface Antarctic Intermediate Waters (AAIW) near the Sub-Antarctic Front (SAF) were elevated (36.1 pmol/kg). Concentrations subsequently decline meridionally through the Antarctic Circumpolar Current (ACC) steadying within the Weddell Gyre (20.3 pmol/kg). STZ DCd sub-surface concentrations are notably depleted (74.1 pmol/kg). However, sub-surface concentrations increase within the ACC at the SAF (450 pmol/kg), continuing into the Weddell Gyre (700.8 pmol/kg). DCd exhibits a typical nutrient-like profile, with bio-utilization in the surface (MLD), followed by regeneration and conservation. The nutrient like behaviour of bio-utilized DCd was exemplified by an excellent Cd/P sub-surface correlation in the ACC, waning somewhat in the sub-optimal productivity of the Weddell Gyre. However, abiotic factors may have ...