Rutherford S, D'Hondt S
University of Rhode Island, Graduate School of Oceanography, Narragansett 02882, USA.
Nature. 2000 Nov 2;408(6808):72-5. doi: 10.1038/35040533.
Between 1.5 and 0.6 Myr ago, the period of the Earth's glacial cycles changed from 41 kyr, the period of the Earth's obliquity cycles, to 100 kyr, the period of the Earth's orbital eccentricity, which has a much smaller effect on global insolation. The timing of this transition and its causes pose one of the most perplexing problems in palaeoclimate research. Here we use complex demodulation to examine the phase evolution of precession and semiprecession cycles--the latter of which are phase-coupled to both precession and eccentricity--in the tropical and extratropical Atlantic Ocean. We find that about 1.5 Myr ago, tropical semiprecession cycles (with periods of about 11.5 kyr) started to propagate to higher latitudes, coincident with a growing amplitude envelope of the 100-kyr cycles. Evidence from numerical models suggests that cycles of about 10 kyr in length may be required to explain the high amplitude of the 100-kyr cycles. Combining our results with consideration of a modern analogue, we conclude that increased heat flow across the equator or from the tropics to higher latitudes around 1.5 Myr ago strengthened the semiprecession cycle in the Northern Hemisphere, and triggered the transition to sustained 100-kyr glacial cycles.
在距今150万年至60万年前，地球冰川周期的时长从与地球倾斜周期时长一致的4.1万年，转变为对全球日照影响小得多的、与地球轨道偏心率周期时长一致的10万年。这一转变的时间及其成因是古气候研究中最令人困惑的问题之一。在此，我们运用复解调技术来研究热带和温带大西洋中岁差周期与半岁差周期的相位演化，其中半岁差周期与岁差和偏心率均存在相位耦合关系。我们发现，约150万年前，热带半岁差周期（周期约为1.15万年）开始向更高纬度传播，与此同时，10万年周期的振幅包络线不断增大。数值模型的证据表明，可能需要长度约为1万年的周期才能解释10万年周期的高振幅。将我们的研究结果与一个现代类似情况相结合，我们得出结论，约150万年前，赤道或从热带到更高纬度地区的热流增加，增强了北半球的半岁差周期，并引发了向持续10万年冰川周期的转变。
