RELATION BETWEEN LOW-LATITUDE INSOLATION AND DELTA-O-18 CHANGE OF ATMOSPHERIC OXYGEN FOR THE LAST 200-KYRS, AS REVEALED BY MEDITERRANEAN SAPROPELS

The isotopic ratio of atmospheric O-2, delta(18)O(atm), deduced from i ce cores, displays large fluctuations during climatic cycles. These ar e caused principally by changes in the oxygen isotopic ratio of sea-wa ter, delta(18)O(sw), and changes in the biosphere and in the-hydrologi cal cycle. As both delta(18)O(atm) and delta(18)O(sw) coincide closely over the last 135 kyr BP, it is generally believed that delta(18)O(at m) is driven mainly by delta(18)O(sw). Here we focus on the major disc repancy, which arises between those two signals during the prior isoto pic glacial stage 6, around 175 kyr BP, discrepancy which calls into q uestion the role of changes in delta(18)O(sw) as the driving mechanism for delta(18)O(atm). We present arguments, based on the occurrence an d pollen content of Mediterranean sapropels, for another source of the delta(18)O(atm) change: insolation at low latitudes via hydrosphere/b iosphere activity.