Martinez Mathieu, Dera Guillaume
Laboratoire des Fluides Complexes et Leurs Réservoirs, UMR 5150, CNRS, Total, Université de Pau et des pays de l'Adour, 64013 Pau, France; Center for Marine Environmental Sciences, Universität Bremen, 28359 Bremen, Germany;
Géosciences Environnement Toulouse, UMR 5563, CNRS, Institut de Recherche pour le Développement, Université Paul Sabatier, 31400 Toulouse, France
Proc Natl Acad Sci U S A. 2015 Oct 13;112(41):12604-9. doi: 10.1073/pnas.1419946112. Epub 2015 Sep 28.
Eccentricity, obliquity, and precession are cyclic parameters of the Earth's orbit whose climatic implications have been widely demonstrated on recent and short time intervals. Amplitude modulations of these parameters on million-year time scales induce "grand orbital cycles," but the behavior and the paleoenvironmental consequences of these cycles remain debated for the Mesozoic owing to the chaotic diffusion of the solar system in the past. Here, we test for these cycles from the Jurassic to the Early Cretaceous by analyzing new stable isotope datasets reflecting fluctuations in the carbon cycle and seawater temperatures. Our results document a prominent cyclicity of ∼9 My in the carbon cycle paced by changes in the seasonal dynamics of hydrological processes and long-term sea level fluctuations. These paleoenvironmental changes are linked to a great eccentricity cycle consistent with astronomical solutions. The orbital forcing signal was mainly amplified by cumulative sequestration of organic matter in the boreal wetlands under greenhouse conditions. Finally, we show that the ∼9-My cycle faded during the Pliensbachian, which could either reflect major paleoenvironmental disturbances or a chaotic transition affecting this cycle.
偏心率、倾角和岁差是地球轨道的周期性参数，其对气候的影响在近期和短时间尺度上已得到广泛证实。这些参数在百万年时间尺度上的振幅调制会引发“大轨道周期”，但由于过去太阳系的混沌扩散，这些周期在中生代的行为和古环境后果仍存在争议。在此，我们通过分析反映碳循环和海水温度波动的新稳定同位素数据集，来检验从侏罗纪到早白垩世的这些周期。我们的结果表明，碳循环中存在一个约900万年的显著周期性，其由水文过程的季节性动态变化和长期海平面波动所驱动。这些古环境变化与一个与天文解相一致的大偏心率周期相关。在温室条件下，轨道强迫信号主要通过北方湿地中有机质的累积封存而被放大。最后，我们表明，约900万年的周期在普连斯巴奇阶期间逐渐消失，这可能反映了重大的古环境扰动，或者是影响该周期的混沌转变。
