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首页> 外文期刊>Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine >Evidences of precession and obliquity orbital forcing in oxygen-18 isotope composition of Montalbano Jonico Section (Basilicata, southern Italy)
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Evidences of precession and obliquity orbital forcing in oxygen-18 isotope composition of Montalbano Jonico Section (Basilicata, southern Italy)

机译：Montalbano Jonico剖面（意大利南部巴斯利卡塔）的氧18同位素组成中的进动和倾斜轨道强迫的证据

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摘要

Quantitative signal processing methods have been applied to a δ~(18)0 profile for a land-based stratigraphic section, extending from the upper part of lower Pleistocene to the lower part of middle Pleistocene. The section is well exposed with a continuous succession of muds and muddy silts, about 400 m thick, located in the southernmost part of Bradano Trough, near Montalbano Jonico in Basilicata (south Italy). The sampled part of the section is about 240 m thick, in which a foram benthic species (Cassidulina carinata) is continuously available for oxygen isotope ratio measurements. The aim of the data treatment is to discover how much of the Earth's orbital periodic movements, precession and obliquity, which represent the dominant periodicities in paleoclimatic variations from the base of the Pleistocene until 0.735 Myr BP, are responsible for the oscillations observed in the oxygen-18 record of the Montalbano Jonico section. A time framework of the section was constructed on the basis of calcareous nannofossil biostratigraphic analyses, preliminary magnetostratigraphic results and oxygen isotope correlation with the record from DSDP s607 (isotope data collected in the NOAA World Data Center). The resulting time-scale extends from 1.15 to 0.74 Myr. Power spectrum analysis was performed on the isotope data to illuminate the most important periodicity components of the Montalbano Jonico record. The periodic components of 41,000 and 21,000 yr are present in this record; the former associated with periodic changes in the tilt of Earth's axis and the latter with periodic changes with the precession of the equinoxes, as predicted by the astronomical theory of ice ages. They are, however, not the most important components of the power spectrum, in which a lower frequency component contains most of the variance. This low-frequency component is centered at a period around 208,000 yr. This periodicity seems not to be attributable to any known astronomical or paleoclimatic phenomenon. An attempt was made to verify if this periodicity was due to the composite effect of precession and obliquity signals together at different frequencies from their forcing frequencies. In order to investigate this effect, isotope data have been parameterized in terms of a sum of simple functions of precession and obliquity signals with unknown coefficients. The coefficients are estimated from the time series with the assumption that the best coefficients are those which minimize the 'noise' i.e. the difference between the data function and the precession and obliquity functions. Cross-spectra analyses were also performed on the data and the precession signal and on the data and the obliquity signal. The power spectrum of the residual 'noise' functions and the cross-spectra demonstrate that precession and obliquity signals are not in phase with the data at their forcing frequencies and so damp. The precession and obliquity signals were then shifted towards lower frequencies at equally spaced lags, the resultant 'noise' power spectra were plotted for every combination of lags of precession and obliquity. The results of this data processing demonstrate that it is possible to have a combination of precession and obliquity cyclicities that could be responsible for the signal with 208 kyr periodicity.
机译：定量信号处理方法已应用于陆基地层剖面的δ〜（18）0剖面，从下更新世的上部延伸到中更新世的下部。该断面暴露在位于巴西利卡塔（意大利南部）蒙塔尔巴诺乔尼科附近的布拉达诺海槽最南端，连续不断的约400 m厚的泥浆和淤泥。该部分的取样部分约为240 m厚，其中有一个连续的底栖物种（卡西迪纳藻）可以用于氧同位素比测量。数据处理的目的是发现地球上有多少轨道周期运动，进动和倾斜，这代表了从更新世以来直到0.735 Myr BP的古气候变化的主要周期，是造成氧气中观测到的振荡的原因-18蒙塔尔巴诺乔尼科的记录。根据钙质纳米化石生物地层学分析，初步地磁地层结果和氧同位素与DSDP s607的记录（NOAA世界数据中心收集的同位素数据）建立了该部分的时间框架。所得的时间范围从1.15扩展到0.74 Myr。对同位素数据进行了功率谱分析，以阐明Montalbano Jonico记录的最重要的周期性成分。该记录中包含41,000和21,000年的周期性分量;正如冰河时代的天文学理论所预言的，前者与地球轴倾斜的周期性变化有关，而后者随着春分线的进动而周期性变化。但是，它们不是功率谱中最重要的组成部分，其中较低的频率部分包含了大部分方差。低频分量的中心时间约为208,000年。这种周期性似乎不归因于任何已知的天文或古气候现象。试图验证这种周期性是否是由于进动信号和倾斜信号在其强迫频率不同的频率下的综合作用所致。为了研究这种影响，已经根据旋进和倾角信号的简单函数之和对未知系数进行了参数化，对同位素数据进行了参数化。从时间序列中估计系数，并假设最佳系数是使“噪声”最小的系数，即数据函数与进动和倾斜函数之间的差。还对数据和进动信号以及数据和倾斜信号进行了互谱分析。残留“噪声”函数和互谱的功率谱表明，进动和倾斜信号在其强制频率处与数据同相，因此非常潮湿。然后，进动和倾斜信号以等间隔的滞后移向较低的频率，并对进动和倾斜的滞后的每种组合绘制所得的“噪声”功率谱。该数据处理的结果表明，旋进和倾斜周期可能组合在一起，这可能导致周期为208 kyr的信号。

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