Isotopes of oxygen (O-18, O-16, O-13) are found in calcium carbonate in sea water. The production of O18 is highly dependent on temperature. The oxygen isotope record in marine sediments varies locally with temperature and globally with variations in continental ice volume. Oxygen isotope analyses have been carried out on deep sea cores from areas of calcareous sedimentation throughout the world and similar variations in O18 are recorded everywhere. The O18 signal is that of ice volume changes on the continents and concomitant changes in the isotopic content of the oceans.
Relative percentage diatom profile for BAIK38 (BAIK94-38A), using uncorrected taxa. The core has been dated using 210Pb analysis (to c. 1840 AD), and subsequent dates have been extrapolatedsee text for details. Zones are defined using cluster analysis.