(Table 1) Stable oxygen and carbon isotope composition of bivalve shells of sediment core CRP-1, and of Wright Valley and McMurdo Sound

Bivalve shells from the CRP-l drillhole, Cape Roberts (Victoria Land Basin), have been analysed for their stable isotope composition to obtain information on Antarctic coastal palaeoceanography during the middle Pleistocene and early Miocene. Shells from a middle Pleistocene carbonate-rich unit (lithostratigraphic Unit 3.1; 33.82-3 1.89 metres below sea floor) have d180 values between +3.64 and +4.56 per mil PDB and d13C between +0.85 and + 1.09 per mil PDB. Oxygen isotopic compositions are close to or at equilibrium conditions with scawater at a temperature in the range of c. -2 to 0°C in the absence of melt water influx. Thus, the CRP-1 carbonate-unit was deposited under 'interglacial' polar conditions, comparable to those of the present-day and isotope stage 3 in the Ross Sea. 'Chlamys' sp. 1, retrieved from a lower Miocene diamictite at 62.19 mbsf, is the only unaltered shell of this age in CRP-1 and yielded a d18O value of -4.64 per mil PDB and d13C of -3.35 per mil PDB. These values show that palaeoceanographic conditions during early Miocene time were significantly different from those of today. The depleted stable oxygen isotope composition of the Miocene shell reflects both an appreciable input of melt or fresh water and warmer-than-present seawater temperatures.