The last deglacial sea-level and climatic changes. Coral Reef records in the south Pacific : Tahiti (French Polynesia) - IODP Expedition #310 -, Australian Great Barrier Reef - IODP Proposal #519: Potential of diagenetically altered corals for sub-seasonal climate reconstructions
Final Report Abstract
Fossil corals are unique archives of past seasonal climate variability, providing vital information about seasonal climate phenomena such as the El Niño-Southern-Oscillation (ENSO) and the monsoons. However, submarine diagenetic processes can potentially obscure the original climate signals and lead to false interpretations. Here we demonstrate the potential of laser ablation ICP-MS to rapidly detect secondary aragonite precipitates in fossil Porites coral colonies recovered by Integrated Ocean Drilling Program (IODP) Expedition 310 from submerged deglacial reefs off Tahiti. High resolution (100 μm) measurements of coralline B/Ca, Mg/Ca, S/Ca, and U/Ca ratios are used to distinguish areas of pristine skeleton from those afflicted with secondary aragonite. The laser ablation ICP-MS technique that we describe here is an extremely powerful tool for assessing the preservation of fossil corals by virtue of its (1) high resolution length scale sampling, (2) multi-element capability, (3) relatively fast data acquisition (>6 cm/day), (4) microdestructive nature, and (5) the minimal sample preparation required. We demonstrate that areas affected by secondary aragonite cements exhibit lower B, Mg and S/Ca ratios and have elevated Sr and U/Ca ratios relative to the primary aragonite skeleton. Moreover, the results that we have obtained for fossil Tahiti corals suggest that laser ablation ICP-MS analyses of B/Ca and Mg/Ca provide an effective geochemical fingerprint for the presence of secondary aragonite in the coral skeleton. In order to assess the preservation state of fossil corals, we recommend first using laser ablation ICP-MS to scan for aragonite and calcite cements before conducting petrographic investigations on any areas deemed suspicious. Using parts of fossil corals confirmed to be pristine in this way, we demonstrate that the seasonal variation in sea surface temperature at Tahiti during the last deglaciation (14.7 and 11 ka) was similar to that of today.
Publications
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Laser ablation ICP-MS screening of corals for diagenetically affected areas applied to Tahiti corals from the last deglaciation. Geochimica et Cosmochimica Acta
Hathorne, E.C., Felis, T., James, R.H., Thomas, A.
