1Section Marine Biogeology, Institute of Earth Sciences, Faculty of Earth- and Life Sciences, VU University Amsterdam, de Boelelaan 1085, 1081 HV Amsterdam, The Netherlands
2Faculty of Science, Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
3School of Geosciences, University of Edinburgh, Edinburgh, UK
4Royal NIOZ, Landsdiep 4, 1797 SZ't Horntje, Texel, The Netherlands
Abstract. The oxygen isotopic composition of planktonic foraminifera tests is one of the widest used geochemical tools to reconstruct past changes of physical parameters of the upper ocean. It is common practice to analyze multiple individuals from a mono-specific population and assume that the outcome reflects a mean value of the environmental conditions during calcification of the analyzed individuals. Here we present the oxygen isotope composition of individual specimens of the surface dwelling species Globigerinoides ruber and Globigerina bulloides from sediment cores in the Western Arabian Sea off Somalia inferred as indicators of past seasonal ranges in temperature. Combining the δ18O measurements of individual specimens to obtain temperature ranges with Mg/Ca based mean calcification temperatures allows us to reconstruct temperature extrema. Our results indicate that over the past 20 kyrs the seasonal temperature range has fluctuated from its present value of 16 °C (14 to 30 °C), to 11 °C (15 to 26 °C) during the LGM. The range during the LGM suggests that the maximum temperature was lower, whilst minimum temperature remained approximately constant.