The ? 18O spectrum of oceanic deep water over a five-decade band

Autor: J. Imbrie, N. J. Shackleton
Rok vydání: 1990
Předmět:
Zdroj: Climatic Change. 16:217-230
ISSN: 1573-1480
0165-0009
DOI: 10.1007/bf00134658
Popis: We have examined the climatic variance in a series of deep-water oxygen-isotope records which range in length from 0.3 to 130 million years and have temporal resolutions between one thousand and 10 million years. These variations in δ 18O are interpreted as a generalized index of temperature change in high latitudes. Over five frequency decades the relation between log (variance density) and log (frequency) is approximately linear with a slope between −1 and −1.5. This relationship is interpreted as a background continuum of the sort postulated by Mitchell (1976) in which the spectrum is built up by layers of variance representing contributions from various processes acting within the climate system on different time scales. Our observed continuum slope is much steeper than that visualized by Mitchell. Additional variance is distributed at periods longer than about 3 million years, where it probably originates from forcing by tectonic processes; and at periods between 20,000 and 100,000 years where the Milankovitch forcing operates. Between these two regions there is a clear variance minimum which we predict will appear in the spectrum of other geological variables that are controlled by climate. A broad-band concentration of variance at periods near 30 My rises well above the background. Another concentration occurs at frequencies too low to be estimated accurately from our data. We assume this is a climatic response to the ∼400 My cycle of continental fragmentation and assembly.
Databáze: OpenAIRE
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