Climatic ups and downs in a disturbed Jurassic world

The tropical, warm, and equable climate of the Jurassic world is regularly challenged by geoscientists, especially since oxygen isotopes (δ 18 O) of fossil hardparts have been used to reconstruct the paleotemperature history of seawater. By applying the innovative "SiZer" (sig- nifi cant zero crossings of the derivatives) statistical approach to a newly compiled δ 18 O data- base for the Jurassic, we demonstrate the occurrence of major and multiscale δ 18 O changes mainly related to climate disturbances. For the fi rst time, two long-term anomalies in δ 18 O are identifi ed during the Toarcian and the Late Jurassic, in conjunction with intensive volcanism in large igneous provinces. These results support a strong infl uence of repeated volcanic pulses on the modulation of pCO 2 , temperatures, and polar ice cap volumes over protracted periods. At shorter time scales, 13 relatively rapid (0.5-1 m.y.) and signifi cant warming and cooling events are identifi ed, the causes of which include transient fl uctuations in greenhouse gas con- centrations related to still-debated mechanisms.

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