Isotopic and biostratigraphical records of calcareous nannofossils in a Pleistocene core

The carbon and oxygen isotopic composition as well as the relative abundance of coccolith species on the 3-25 μm fractions of the Caribbean core P6304-4 have been determined. Oxygen isotope variations clearly define glacial-interglacial oscillations and, except in the upper part of the core, carbon isotopic compositions are not related to the oxygen isotope stratigraphy. The occurrence of three coccolith datum levels in the core correlates almost exactly with globally-synchronous horizons. The amplitude of the coccolith delta 18O record 2.4 0/00 is significantly greater than that for the planktonic foraminifera Globigerinoides sacculifer in P6304-4 and adjacent cores. It is suggested that selective dissolution or deep calcification during interglacials reduced the amplitudes of G. sacculifer in these cores and that the coccolith record is a more reliable indicator of temperature and delta 18O changes in surface seawater. (U.K.)