Periodic changes in the Cretaceous ocean and climate caused by marine redox see-saw

• Published in: Nature Geoscience
• Main Authors: Wallmann, Klaus, Flögel, Sascha, Scholz, Florian, Dale, Andrew W., Kemena, Tronje Peer, Steinig, Sebastian, Kuhnt, Wolfgang
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Research 2019
• Subjects: North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/46769/; https://oceanrep.geomar.de/id/eprint/46769/1/s41561-019-0359-x.pdf; https://oceanrep.geomar.de/id/eprint/46769/2/41561_2019_359_MOESM1_ESM.pdf; https://doi.org/10.1038/s41561-019-0359-x

Periodic changes in sediment composition are usually ascribed to insolation forcing controlled by Earth’s orbital parameters. During the Cretaceous Thermal Maximum at 97–91 Myr ago (Ma), a 37–50-kyr-long cycle that is generally believed to reflect obliquity forcing dominates the sediment record. Here, we use a numerical ocean model to show that a cycle of this length can be generated by marine biogeochemical processes without applying orbital forcing. According to our model, the restricted proto-North Atlantic and Tethys basins were poorly ventilated and oscillated between iron-rich and sulfidic (euxinic) states. The Panthalassa Basin was fertilized by dissolved iron originating from the proto-North Atlantic. Hence, it was less oxygenated while the proto-North Atlantic was in an iron-rich state and better oxygenated during euxinic periods in the proto-North Atlantic. This redox see-saw was strong enough to create significant changes in atmospheric pCO2. We conclude that most of the variability in the mid-Cretaceous ocean–atmosphere system can be ascribed to the internal redox see-saw and its response to external orbital forcing.