The stable oxygen isotope signal of the calcareous-walled dinoflagellate Thoracosphaera heimii as a new proxy for sea-surface temperature

Abstract

Palaeoceanographic and palaeoclimatic studies are often based on information derived from stable oxygen and carbon isotope measurements on planktonic microfossils. The present study shows that the stable oxygen isotope signal of the calcareous-walled dinoflagellate Thoracosphaera heimii constitutes a promising new proxy for the reconstruction of past sea surface temperature. In a downcore study covering the last 45 ka within the upwelling region off Cape Blanc (NW Africa) we compare it to other well-established proxies like the planktonic foraminifera Globigerinoides ruber (pink) and Globigerina bulloides and the Mg/Ca ratio of G. ruber (pink).Detailed studies on both, the ecology and physiology of T. heimii improve the accuracy of future palaeotemperature reconstructions. Therefore, we investigated its recent seasonal and spatial distribution pattern and its calcification depth habitat in relation to environmental parameters. Past and future scenarios show changes in seawater pH in relation to surface water CO2 concentrations. In a culture experiment, we revealed the relationship between pH and stable oxygen isotopes.