VARIATIONS OF OXYGEN ISOTOPIC COMPOSITION AND DISTRIBUTION OF CONTINENTAL ICE IN THE LAST ICE AGE (I)

Oxygen isotopic composition (δ^O) of fossil foraminifera from deep-sea sediments has been used as indicators of past climate for more than thirty years since their first determinations. The foraminiferal δ^O varies with the δ^O of sea water as well as the temperature of ambient water. Therefore, for the past decade, the fossil foraminiferal δ^O records have been derived from the benthic foraminifera living in the constant temperature abyssal ocean and have been considered to give the δ^O record of sea water. However, there has been a discrepancy between the continental ice-volume records derived from sea level change and from the δ^O change of sea water, which is based on the assumption that the δ^O of the continental ice has been constant in the last ice age. Recent studies show that about one-third of the observed δ^O variations can be due to the deep-sea water of about 1.5℃ cooler than the present temperature throughout the glacial period. I have studied the foraminiferal δ^O and sea-level relation, assuming the followings : 1) The δ^O of the continental ice should not have been constant throughout the last ice age and may have changed according to changed distributions of both the continental ice sheets and sea ice. 2) The δ^O must have changed even in the continental ice of unchanged ice-volume. And I showed that the foraminiferal δ^O record may not give the temperature record of the deep-sea but may give the records of δ^O and distribution of the continental ice