Reconstructing a 350 ky history of sea level using planktonic Mg/Ca and oxygen isotope records from a Cocos Ridge core

The record of oxygen isotopic variations in foraminifer shells from deep-sea cores preserves a continuous record of ice volume and sea level oscillations. To extract the ice volume record, however, it is necessary to remove the temperature and local hydrological influence on delta(18)O. We employ the strategy of estimating calcification temperatures from Mg/Ca and removing this signal from an observed delta(18)O record of planktonic foraminifera from a core on the Cocos Ridge, eastern equatorial Pacific. The residual, delta(18)O(water), reveals a pattern of changes that appears to be consistent with known ice volume and sea level variations. Over the last four glacial terminations, delta(18)O(water) decreases by 1.2 +/- 0.1 parts per thousand. The magnitude of high stands appears to be consistent with modern sea level during MIS 5.5 (5e), 7.1 and 7.5 but somewhat lower during MIS 9.1. The magnitude of low stands is similar (similar to -120m) for MIS 2.2 (LGM), 6.2, 8.2 and 10.2. The Cocos Ridge record also shows a period of intermediate sea level (similar to -30m) during MIS 6.5. At present it is not possible to validate these estimates for those periods of time in which coral reef based estimates of sea level are unavailable. (C) 2001 Elsevier Science Ltd. All rights reserved.