| || || Naidu, Roselyn|
| || || Impact of ocean acidification on carbonate production by large benthic foraminifera Marginopora Vertebralis in coastal waters of Fiji|
Institution: University of the South Pacific.
Subject: Ocean acidification -- Environmental aspects -- Fiji, Seawater -- Carbon dioxide content -- Environmental aspects -- Fiji
Call No.: pac GC 117 .C37 N35 2015
Copyright:20-40% of this thesis may be copied without the authors written permission
Abstract: Increased CO2 emissions into the atmosphere lead to increased concentrations of dissolved CO2 in the ocean. A chemical reaction between the dissolved CO2 and seawater produces HCO3 - , CO3 2- and H+ ions. These H+ ions increase the acidity of seawater and decrease the pH. Increased acidity and decreased availability of CO3 2- ion affect calcite and aragonite production by marine calcifiers in the ocean. Large benthic foraminifera, such as Marginopora vertebralis Quoy and Gaimard, 1830, produce calcite with high magnesium (Mg) content and have an important role in sand building in the Pacific Islands. Foraminifera also have the ability to integrate trace elements and isotopes from the seawater into their calcareous shells and serve as paleoceanographic archives. It is thus important to better understand the biomineralization processes in foraminifera to predict their calcification responses to ocean acidification. To assess the response of a porcelaneous benthic foraminifer with algal endo-symbionts to changing CO2 levels, M. vertebralis were cultured at pH 7.5, pH 7.8 and pH 8.1 (ambient seawater). The fluorescent compound Calcein (̴ 40 M) was added to the culture tanks to mark the calcite produced prior to the experiment. The specimens grown in the laboratory were analysed using Laser Ablation-Inductively Coupled Plasma Mass Spectroscopy (LA-ICPMS) and Electron Probe Micro Analyser (EPMA) to measure elemental compositions, providing data to calculate boron and strontium isotope ratios and Mg/Ca, Sr/Ca and S/Ca ratios. Shell growth, in terms of both radius and weight, decreased with decreasing pH, as did the boron isotope ratios. The Mg/Ca ratios decreased, while Sr/Ca ratios increased, with decreasing pH. The S/Ca ratio also increased with a decreasing pH. Isotopic ratios for B (δ 10/11B) and Sr (δ 88/86 Sr) both increased with decreasing pH. Since it is possible to calibrate the shell composition against the controlling factors, foraminiferal trace elements and isotopic ratios can provide researchers with vital and relevant proxies to investigate the physical, biological and chemical changes in the ocean.