Masters Degrees (Earth Sciences)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/3775

Browse

Browsing Masters Degrees (Earth Sciences) by Author "Cloete, Ryan"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Measurement of bioactive trace metals (Cu and Zn) in the Southern Ocean : validation of sampling protocol and ICP-MS based analytical method
    (Stellenbosch : Stellenbosch University, 2017-03) Cloete, Ryan; Roychoudhury, Alakendra N.; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: A method comprising an improved seawater collection protocol and subsequent Inductively Coupled Plasma Mass Spectrometry (ICP-MS) based analytical technique was validated through an intercalibration exercise performed with the University of Plymouth (UK), multiple cross-over stations and analyses of certified reference materials (SAFe, GEOTRACES and NASS-5). The commercially available seaFAST-pico preconcentration module was employed for the simultaneous extraction of a suite of trace metals (Mn, Fe, Ni, Cu, Zn, Co, Cd and Pb) from their seawater matrix prior to ICP-MS analysis. Extremely low detection limits (< 0.228 nmol/kg) combined with low blank values ensured quantitive recovery on ICP-MS and minimal interferences arising from alkali and alkaline earth metals (Na, K, Mg and Ca) present in the saline matrix. The results of the certified reference materials were in excellent agreement with their corresponding consensus values and validated the methods precision and accuracy. During ICP-MS analysis, repeatability and reproducibility were monitored through analysis of an internal Stellenbosch University (SU) TM4 control and various commercially available quality controls, the results of which further confirmed a high level of precision. The distribution of Dissolved Copper (DCu) and Dissolved Zinc (DZn) was investigated in the Atlantic sector of the Southern Ocean. DCu displayed typical nutrient type behaviour reflected by sub-nanomolar surface concentrations increasing steadily until maximum observed concentrations of 2 – 3 nmol/kg in the Antarctic Bottom Waters (AABW). DZn concentrations ranged between approximately 1 and 12 nmol/kg and exhibited characteristic nutrient-type behaviour although intermediate and deepwater distributions were more conservative compared to DCu. Local subsurface minima coincided with elevated levels of chlorophyll-a (chl-a) indicating biological utilisation by phytoplankton in the euphotic zone. Remineralisation of sinking organic matter, predominantly diatom frustules, from Antarctic Surface Water (AASW) resulted in deeper sub-surface maxima for DZn. The dominant supply of trace metals to surface waters south of the Antarctic Polar Front (APF) was advective upwelling of nutrient rich Upper Circumpolar Deep Water (UCDW) and AABW. Atmospheric inputs and melting ice accounted for minor surface influxes where there was a poor DCu/salinity correlation. Both trace elements displayed significant correlations with the macronutrient silica, evidence of their role in the biological cycle. An overall Cu:Si relationship of Cu (nM) = 0.011 Si (μM) + 0.851 (R2 = 0.85, n=98) was obtained for this study while the corresponding Zn:Si relationship was Zn (nM) = 0.043 Si (μM) + 1.021 (R2 = 0.80, n=98). The APF exerted a strong control over nutrient distributions separating low nutrient low chlorophyll (LNLC) subtropical waters to the north from high nutrient low chlororphyll (HNLC) waters to the south. Keywords: Southern Ocean, Dissolved Copper, Dissolved Zinc, GEOTRACES, seaFAST, ICP-MS