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Elemental concentration and Isotopic composition of biogenic carbonate (Foraminifera and Corals): proxies calibrations and applications


12.00pm - 1.00pm, Tuesday 8 March 2011

ARC Centre of Excellence Conference Room 114, Sir George Fisher Building, JCU (DB32)
Dr Delphine Dissard, ARC Centre of Excellence for Coral Reef Studies, University of Western Australia

Delphine has recently started a new postdoctoral research position in BioGeochemistry at the University of Western Australia. Her research topic focussed on Paleo pH and ocean acidification (anthropogenic) reconstructions based on Boron isotopes and B/Ca ratios in biogenic carbonates (corals and foraminifera). Having previously completed a Post Doc Position at the Scientific Laboratory for Climate Science and Environment (LSCE-CNRS, Gif-sur-Yvette (Paris)/France) and a PhD at the Alfred Wegener Institute in Germany (AWI Bremerhaven), she has gained a wide range of transferable skills and experience in field work, lab experiments (foraminifera culture, carbonate chemistry sampling DIC, ALK, Boron isotope and B/Ca ratios sample handling, cleaning, and chemical extractions) and analysis (LA-ICPMS, ICP-QMS, MC-ICP-MS, ICP-EOS). Throughout her studies, she developed research skills with particular interest in paleoclimatology, geochemistry, biomineralisation, and calibration of geochemical (and ecological) proxies, an important tool to evaluate the validity of climate change scenarios.


The trace element composition of biogenic carbonate tests has become an important tool by which paleoceanographers reconstruct past oceanic conditions. On timescales much shorter than their residence time, the elements strontium and magnesium occur in seawater with nearly constant ratios to calcium. Variation in Sr/Ca and Mg/Ca in benthic foraminiferal tests can then be explained as a function of environmental parameters that control their incorporation into the tests. For benthic foraminifera, temperature appears to be the dominant parameter, however, a better understanding of the possible impact of other parameters such as pH or [CO32-], and salinity is needed to increase the accuracy of element ratio proxies. Towards this goal the benthic foraminifer Ammonia tepida was cultured under three different salinities (20, 33 and 40) and two different pCO2 conditions (120 and 2000ppm), both sets of experiment were run at two different temperatures (10 and 15°C). Weights and elemental composition were determined. Similarly, the boron isotopic composition (δ11B) and B/Ca ratios of marine carbonates have been suggested as proxies for pH and [CO32-]/T˚C, respectively. However, here again, the recognition of potential complications have enlightened the need of species specific calibrations. Preliminary results of light and temperature effect on Boron isotopic and B/Ca ratios measured in Acropora specimens maintained under culture experiments will be presented. Envisaged future applications of these proxies will be described.


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