Orbital pacing of carbon fluxes by a ~9-Myr eccentricity cycle during the Mesozoic

Abstract:

A 73.6-Myr long signal of d¹⁸O and d¹³C from the Sinemurian (Early Jurassic) to the Aptian (Early Cretaceous) measured on belemnite rostra from NW Tethys has been compiled and analyzed for measuring the trends and Myr-cycles in the Jurassic and the Early Cretaceous. The resulting series have more than 3500 points and an average sample step of 0.04 Myr, which currently constitutes the highest-resolution series for this time interval. The long-term trend in the d¹⁸O series shows three warming events in the Jurassic linked to the activity of three major volcanic provinces, but no significant cycle has been observed in the series. Unlikely, the d¹³C series shows a prominent cycle of 9.1 Myr, having an amplitude of 1-2‰ on the d¹³C throughout the whole time interval. This cycle is attributed to a Myr-eccentricity forcing, already identified in the Cenozoic, the late Cretaceous and the Triassic. In addition, the d¹³C series also displays a minor-amplitude cycle at 1.9 Myr, which can be related to the 2.4-Myr eccentricity. The fluctuations of the d¹³C at the 9.1-Myr time scale follows the 2^nd-order eustatic changes and we suggest that Myr-eccentricity cycles, by controlling humid-arid cycles in the tropical realms and sea-level changes, modulated the continental and oceanic primary productivity, storage of organic matter, carbonate platform production which triggered the observed fluctuations in the d¹³C.