Copper-Phytoplankton reciprocal interaction: Biogeochemical cycling of copper and its isotopes

• Main Author: Maharaj, Prayna
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2023
• Subjects: Southern Ocean
• Online Access: http://hdl.handle.net/1885/303387; https://doi.org/10.25911/PWJT-DW04; https://openresearch-repository.anu.edu.au/bitstream/1885/303387/3/PRAYNA%20MAHARAJ_PhD%20thesis%20-%20FINAL%20with%20Corrections.pdf.jpg

Copper (Cu) is involved in multiple metabolic processes in phytoplankton. However, dissolved Cu (dCu) concentrations that exceed a tolerance level can be toxic. Owing to its biological relevance to marine phytoplankton, there is a need to better understand the distribution of Cu in the ocean. The overarching aim of this study was to investigate the feedback interaction Cu has with marine phytoplankton and to understand better the biogeochemical cycling of Cu and its isotopes in the marine realm. Firstly, two Southern Ocean (SO) diatoms, Proboscia inermis and Chaetoceros flexuosus were cultured under various concentrations of Cu and iron (Fe) in order to investigate the effects of Cu-Fe interaction on growth rate, silicon (Si) uptake kinetics and Si isotope fractionation. Overall, divergent responses were observed in Michaelis-Menten kinetic uptake parameters and Si isotope fractionation. Our findings confirmed that Cu has a significant effect on biochemical processes in diatoms and can potentially alter community composition dynamics in the SO, particularly, by way of its interaction with Fe. To address the gaps in our knowledge of the cycling of Cu, we investigated the distribution of dCu and particulate Cu (pCu) in various biogeochemical regimes. The study region targeted a north-south transect categorised by the transition from warm waters of the East Australian Current (EAC) to cold, fresh subantarctic (SA) waters. A simple anion-exchange purification method was developed using AG-MP 1 resin which achieved near full recovery of Cu and allowed for precise measurements of Cu isotope. At the high productivity stations, the upper water column (200 m) had a relatively heavier dCu isotopic signature. This was complemented by lighter pCu isotope values and simultaneous increases in pCu concentration [pCu]. Below the euphotic zone, decreases in the [pCu] are coupled with a heavier pCu isotope value and a lighter dCu isotope signature. This distribution was largely attributed to the biological uptake of the lighter ...