PLEISTOCENE-AGE CLIMATE VARIATION DERIVED FROM OXYGEN-ISOTOPE MEASUREMENTS FROM MARINE ORGANISMS

In this study, δ¹⁸O values (i.e., ratios of oxygen isotopes) from the depth-derived Pleistocene age model of Huybers and Wunsch (2004) and Huybers (2007) were used to analyze climate variability. This model was developed from oxygen-isotope data derived from 21 sediment cores and provides a convenient synthesis of these data on a global scale. Each model uses depth as a proxy for time and accounts for sediment compaction. The estimated time error in this model is on the order of ± 9,000 years over a total time interval ~2.1 Ma. On this time scale, climate variability is believed to be associated with astronomical causes, i.e., changes in the nature of Earth’s orbit about the Sun, the so-called Milankovitch cycles. Using the mathematical tools of spectral analysis, we were able to analyze the data and document the nature of astronomical climate forcings. In analyzing the results, we find that the data supports the hypothesis that Pleistocene paleoclimate has a direct correlation to changes in the Earth’s orbital parameters with the strongest signals appearing at approximately 100,000 and 41,000 years before present. In addition, we were able to isolate the 23,000 year cycle, the 41,000 year cycle, and the 100,000 year cycle in order to show how the amplitude of each cycle varies throughout time. In analyzing the cycles individually, we find that, in the past, the 41,000 year cycle had the strongest signal, however, in the most recent history, the 100,000 year cycle has been predominant.