Southampton Oceanography Centre, United Kingdom

Paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial Pacific Ocean Drilling Program Site 1218. The records include the two largest abrupt increases in the Cenozoic benthic oxygen isotope record: Oi-1 in the earliest Oligocene (34 Ma) and Mi-1 in the earliest Miocene (23 Ma). The paired Mg/Ca and oxygen isotope records are used to calculate seawater delta (super 18) O (delta w). Calculated delta w suggests that a large Antarctic ice sheet formed during Oi-1 and subsequently fluctuated throughout the Oligocene on both short and long timescales, between about 50 and 100% of its maximum earliest Oligocene size. The magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy. Bottom water temperatures decreased by 2 degrees C over the 150 kyr immediately prior to both rapid delta (super 18) O excursions. (mod. journ. abstr.)