Dinoflagelates - recorder of Palaeogene oceanic Ca budget and climate variabilities (Dinolores)
Final Report Abstract
Changes over time in the calcium (Ca) budget of the ocean lead to shifts in the Ca isotopic composition of the ocean through time, due to the mass-dependent Ca isotope fractionation that occurs during the formation of marine biogenic carbonate sediments, the main oceanic Ca sink. Consequently Ca isotope ratios of past ocean water is used for modelling imbalances in the marine Ca input and output through Earth history. However, the establishment of reliable δ44/40Ca seawater (δ44/40Casw) records requires careful selection of appropriate archives, which is evident from discrepant records from previous studies. In this study, we tested the suitability of different archives, which have the capability to preserve Ca isotope signatures from the Paleogene and Mesozoic, for long term δ44/40Casw reconstructions. In general calcareous dinoflagellates, benthonic foraminifers and cephalopods are well suited. For the Paleogene sediments recovered during IODP Expeditions 320/321, benthonic foraminifers appeared to be the most suited in terms of availability, continuity of occurrence throughout the record and preservation. In addition, we tested the potential of calcareous dinoflagellates as recorders of δ44/40Casw and for Sr/Ca based paleo-temperatures on sediments from ODP Expedition 113 (Hole 690C). Sr/Ca ratios of two Cretaceous dinoflagellate species show a good correlation with planktic δ18O, indicating a sufficient temperature sensitivity and preservation potential to serve as temperature proxy. δ44/40Ca of the dinoflagellates show identical trends in Ca isotope seawater evolution as foraminifer based archives, but there is an offset in the absolute δ44/40Casw values. A similar observation has been made with reconstructions based on nautilus and ammonites, which resemble those of bivalves and phosphates, but deviate from brachiopod and belemnite records. The exact origin of these differences is yet not fully resolved but might be related to evolution of biomineralisation related fractionation processes through Earth history or a response to changes in ocean chemistry.
Publications
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(2010) Minor element and Ca isotope composition of calcareous dinoflagellate cysts of Thoracosphaera heimii, Earth and Planetary Science Letters 289, 180-188
Gussone N., Zonnefeld K., Kuhnert H.
