Brunhes time scales and the interpretation of climatic change |
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| Authors: | MA Kominz GR Heath T-L Ku NG Pisias |
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| Institution: | 1. Graduate School of Oceanography, University of Rhode Island, Kingston, RI 02881, USA;2. School of Oceanography, Oregon State University, Corvallis, OR 97331, USA;3. Department of Geological Sciences, University of Southern California, University Park, Los Angeles, CA 90007, USA |
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| Abstract: | Two new δ18O time scales have been developed for the Brunhes Epoch using equatorial Pacific core V28-238. The first is based on a constant accumulation rate of aluminum, an assumption which has been shown to be acceptable for the last 360,000 years of the record by comparison with 230Th ages determined via the continuous strip-sample technique. The aluminum scale yields an age of 138,000 years for termination II and 693,000 years for the Brunhes-Matuyama reversal. Spectral and cross spectral analysis of the δ18O records of V28-238 and a detailed composite Indian Ocean record, using the aluminum time scale as well as two earlier time scales, indicates that the Pleistocene climate has been forced by periodic fluctuations of the earth's obliquity and precession. Based on this result, the second new time scale (TWEAQ) has been derived by tuning the δ18O record of V28-238 to the record of the earth's obliquity. TWEAQ yields an age of 127,000 years for termination II and 728,000 years for the Brunhes-Matuyama reversal. Spectral analysis of the δ18O record dated by TWEAQ indicates that 30% of the variance of the ice volume record can be ascribed to linear forcing by the earth's orbital parameters, but the trend of the data is consistent with a stochastic model. |
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