Effects of Iron limitation on Silicon Metabolism and Silicon Isotopic Discrimination in Southern Ocean Diatoms

• Main Author: Meyerink, Scott William
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Subjects: Southern Ocean; Diatom; Silicon isotopes; Silicon; Silicon uptake kinetics; E. antarctica; P. inermis; Antarctic; The Antarctic; Antarc*; Antarctica; E. Antarctica
• Online Access: http://hdl.handle.net/1885/110544; https://doi.org/10.25911/5d7637318cd2f; https://openresearch-repository.anu.edu.au/bitstream/1885/110544/4/Meyerink%20Thesis%202016.pdf.jpg

The marine biogeochemical cycle of Silicon (Si) in the Southern Ocean is effectively ‘decoupled’ from that of Carbon (C) and Nitrogen (N). This is because the lack of bio- available iron (Fe) in the region prevents the complete utilisation of Nitrate (NO3-) relative to silicic acid (Si(OH)4) by diatoms in Antarctic surface waters. Consequently, higher Si:N and Si:C ratios in Antarctic diatoms results in the preferential export of Si(OH)4 from surface waters relative to NO3-, leading to surface waters north of the Antarctic Polar Frontal Zone becoming depleted with respect to Si(OH)4. Regional variations in the export flux of Si and C in the Southern Ocean has the potential to alter global atmospheric CO2 concentrations and marine Si(OH)4 inventories. However, the ability to make predictions on how these fluxes will vary in response to future climate change is confounded by the general lack of knowledge on the mechanisms behind how Si and C metabolisms in Southern Ocean diatoms change in response to variations in the physico-chemical environment. This study attempts to determine how Southern Ocean diatom physiology changes in response to chronic Fe-limitation. Specifically, attempts are made to elucidate mechanisms driving variations in cell morphology, elemental stoichiometry, Si(OH)4 uptake kinetics and Si-isotope fractionation in two Southern Ocean diatoms (Probocia inermis and Eucampia antarctica) and the coastal isolate, Thalassiosira pseudonana. All diatoms cultured under Fe-limiting conditions exhibited respective decreases in cellular growth rate, C and N content and maximal Si(OH)4 uptake (VSi-max), whilst responses varied in cell morphology and biogenic silica (BSi) content. T. pseudonana exhibited little variation in cell volume and BSi content under varying Fe- concentrations, while both Southern Ocean diatoms increased their respective cell surface area and cell volume in response to Fe-limiting conditions. BSi content on a cell-surface area basis in both Southern Ocean diatoms either did not change ...