University of California at Santa Cruz, United States

At Ocean Drilling Program (ODP) Site 1090 on the Agulhas Ridge (subantarctic South Atlantic) benthic foraminiferal stable isotope records span the late Oligocene through the early Miocene (25-16 Ma) at a temporal resolution of 10 kyr. In the same time interval a magnetic polarity stratigraphy can be unequivocally correlated to the geomagnetic polarity timescale (GPTS), thereby providing secure correlation of the isotope record to the GPTS. On the basis of the isotope-magnetostratigraphic correlation we provide refined age calibration of established oxygen isotope events Mi1 through Mi2 as well as several other distinctive isotope events. Our data suggest that the 18O maximum commonly associated with the Oligocene/Miocene (O/M) boundary falls within C6Cn.2r (23.86 Ma). Site 1090 stable isotope records also provide the first deep Southern Ocean end-member for reconstructions of circulation patterns and late Oligocene to early Miocene climate change. Oxygen isotope gradients between sites suggest that the deep Southern Ocean was cold in comparison to the North Atlantic, Indian, and the Pacific Oceans.(modified journ. abst.)