Isotopic and elemental composition of calcareous dinoflagellate cysts

The isotopic composition and elemental chemistry of carbonatic microfossils form oft the backbone of palaeoceanographic and palaeoclimatic studies. However, biological factors such as the migration of several planktonic species through different water masses, the influence of calcite shell isotopic composition by photosynthetic activity of symbionts and consumption of other organisms and the ontogeny of individual species can hamper the interpretation of these signals

Consequently, species specific equations of photosynthetic species that form their calcite walls at a stable position within the water column could and do not contain symbionts, might overcome some of these problems.

The photosynthetic dinoflagellate cyst Thoracosphaera heimii (in former days thought to be a coccolithophorid) can relatively easily be isolated from sediments. Calculated temperatures based on the palaeotemperature equation for inorganic calcite precipitation generally reflect mean annual temperatures at thermocline (Deep Chlorophyll Maximum) depths, which represent its preferred depth habitat.

The aim of the study is to establish the relationship between the stable oxygen and carbon isotopic composition of individual calcareous dinoflagellate cyst species with physical parameters such as temperature and to determine the occurrence and origin of potential disequilibrium or “vital effects”. Furthermore the elemental composition, notably the Mg/Ca and Sr/Ca ratio’s in relationship with temperature gradients and dinoflagellate production is investigated.

For this several Thoracosphaera heimii is cultured in gradient boxes under different light and temperature regimes. The extensive culture collection and long experience of calcareous dinoflagellate culturing available at the division of micropalaeontology of the Bremen University forms the basis for these culture studies.
Isotopic and elemental compositions of the cyst walls is being determined using MS, ICP-MS and "flow-through2 techniques. Pilot studies revealed that for dinoflagelle cyst theuse of Laser-Ablation is not required.
Cleaning methods for elemental analysis have been developed using the experience that has been gathered in coccolithophorid and foraminiferal studies at the University of Bremen and Barcelona (Spain).
Monospecific associations have been extracted from surface sediments of the South Atlantic and Indian Oceans and the isotopic and elemental composition of T.heimii has been related to environmental conditions at the sampling sites.

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Kohn, M., Steinke, S., Baumann, K-H., Donner, B., Meggers, H. and Zonneveld K.A.F. (2011). Stable oxygen isotopes of the calcareous dinoflagellate Thoracosphaera heimii as a proxy for mixed layer temperatures. Palaeoclimatology, Palaeoecology, Palaeoceanography. 302, 3-4: 311-322.

Kohn, M and Zonneveld, K.A.F. (2010). Calcification and depth and spatial distribution of Thoracosphaera heimii; implications for palaeoceanographic reconstructions. Deep Sea Research I, 57, 12:1543-1560.

Gussone, N., Zonneveld, K.A.F. and Kuhnert, H. (2010). Minor element and Ca isotope composition of calcareous dinoflagellate cysts of Thoracosphaera heimii in relationship to temperature and pH, a culture experiment. Earth and Planetary Science Letters 289: 180-188.

Zonneveld, K.A.F., Mackensen, A. and Baumann, K-H. (2007). Stable oxygen isotopes of Thoracosphaera heimii (Dinophyceae) in relationship to temperature; a culture experiment. Marine Micropaleontology 64, 80 – 90.

Zonneveld, K.A.F., Meier, K.J., Esper, O., Siggelkow, D., Wendler, I. and Willems, H. (2005). The (palaeo-) environmental significance of modern calcareous dinoflagellates: a review. Paläontologische Zeitschrift 79, 61-77.

Zonneveld, K.A.F. (2004). Potential use of stable oxygen isotope composition of Thoracasphaera heimii for upper water column (thermocline) temperature reconstruction. Marine Micropaleontology 50, 307–317.