Zinc isotopes as a tool to investigate zinc biogeochemical cycling in the SW Pacific Ocean

• Main Author: Samanta, Moneesha
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Canberra, ACT : The Australian National University
• Subjects: Zinc; isotope; double spike; seawater; phytoplankton; Emiliania huxleyi; Phaeocystis antarctica; iron bioavailibility; Tasman Sea; Southern Ocean; GEOTRACES; Pacific; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/1885/142139; https://doi.org/10.25911/5d51448c1557f; https://openresearch-repository.anu.edu.au/bitstream/1885/142139/4/MS%20Thesis%202018.pdf.jpg

Marine phytoplankton account for more than 40% of global primary production and hence play an important role in moderating global climate through ocean-atmosphere CO2 exchange. Zinc (Zn) is an essential micronutrient and plays an important role in the carbon acquisition system within marine phytoplankton, thus, it has the potential to influence marine primary production. In seawater, Zn bioavailability is dependent on its concentration and its chemical speciation. The free Zn2+ ion concentration of the surface ocean is usually in the low picomolar range with the potential to be growth limiting for some phytoplankton species. The aim of this research is to better understand Zn cycling in the ocean and the relationship between primary production and Zn bioavailability by exploiting variations in the Zn isotope composition of phytoplankton and seawater samples. To realise this aim, a procedure was developed to measure the Zn isotope composition of marine samples. This procedure utilises the double spike (DS) technique in conjunction with the pre-concentration of Zn from seawater to determine processes that influence the Zn biogeochemical cycling in the ocean. Seawater samples, collected as part of a 2010 GEOTRACES process study, contrasting oligotrophic waters of north Tasman Sea and the mesotrophic waters of south Tasman Sea, were analysed using this technique. In this study, variability in δ66Zn of dissolved Zn is observed in the upper ocean (0-200 m) for the mesotrophic waters and is attributed to biological activity of eukaryotic phytoplankton. At stations where eukaryotic phytoplankton dominated, heavier δ66Zn values coincided with the chlorophyll maxima suggesting preferential uptake of lighter Zn isotopes by phytoplankton. To complement the field work, a Tasman Sea isolate of the coccolithophore Emiliania huxleyi was cultured across a range of free Zn2+ ion concentrations to determine the extent of Zn isotope fractionation during Zn uptake. The laboratory results support the field observation that the ...