The oxygen isotope of was measured for the clean tests of Globigerinoides sacculifer planktonic foraminifera reacted with 100% orthophosphoric acid at 70 °C for 12 hours. Oxygen Isotope and Mg/Ca ratios were analysed using a Delta-V mass spectrometer in combinatin with a GasBench II continuous flow and a Varian Vista Pro inductively coupled plasma atomic emission spectrometer (ICP-AES Varian 720-ES), respectively. Sea surface temperature (SST) was calculated using the equations SST= (log (Mg/Ca) - log 0.491)/0.033 (Nürnberg et al.,2000).