Climate.html

Signal Analyses of Paleoclimate Time Series

Recent research on the origin of the 100-kyr cycle

One basic difficulty in understanding the influence of the earth's orbital eccentricity on the climate evolution of the Pleistocene is that the amplitude of the 100-kyr (1kyr=1,000 years) radiation cycle associated to the earth's orbital eccentricity (one of the so-called Milankovitch cycles) is one order of magnitude smaller than the radiation in the 23-kyr or 41-kyr bands, whereas the resulting 100-kyr glaciation cycle is normally twice the amplitude of the other two combined. Another fundamental difficulty is the notable absence in the data of any significant response to the 413-kyr eccentricity band, whose power is of the same order of magnitude as the 100-kyr radiation cycle.

These difficulties are compounded by the fact that the apparent strong sensitivity to the 100-kyr radiation cycle appears to have abruptly begun about 1.2 million years ago, when the ice sheets expanded to unprecedented size. The transition occurred suddenly, as observed more clearly in the Wavelet Transform (WT) of one of the records (Site607) shown below. The Wavelet Transform produces a three-dimensional plot of time, period and power (the color coded height) that shows the relative arrival times of each frequency component. From the image below it is clear that at about 1.2 million years ago, the 41-kyr dominated glaciations suddenly changed to predominantly 100-kyr cycles, an unpredictable switch from one climate regime to another, the causes of which are still unknown.

DSDP Site 607 ( mid-latitude Atlantic ) and its Wavelet Transform

Wavelet Transform of Greenland Ice Core Data (GRIP)

Below, the WT and the time series of oxygen isotope reatios observed in a set of ice cores drilled in Greenland are displayed. The abcissa is the normalized oxygen isotope level. In this much shorter interval the time resolution is high, and it is possible to recognize very high frequency variations (centuries or less) in the global climate. For the long periods, a 100 -120 kyr strong component is clearly observed, as well as two strong ~41 kyr peaks, which appear at the time of the interglacials.

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References

Rial, J.A. (1995) Geophysical Research Letters 1995, Vol. 22, No5, 1997-2000.

Lou, M. and J.A. Rial (1995): Application of the wavelet transform in detecting multievents in microearthquake data; Geophysical Research Letters (22) No. 16, pp. 2199-2202.

Research Activities and Projects

Computer Simulations of Wave Phenomena
Shear-wave Splitting in Fractured Reservoirs
Earthquake Response of Sedimentary Basins
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J.A. Rial, jar@wave.gphys.unc.edu

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