Ventilation Changes Drive Orbital‐Scale Deoxygenation Trends in the Late Cretaceous Ocean.

Mechanisms that drive cyclicity in marine sediment deposits during hothouse climate periods in response to Earth's orbit variations remain debated. Orbital cycles fingerprint in the oceanographic records results from the combined effect of terrestrial (e.g., Weathering derived nutrient supply, freshwater discharge) and oceanic (e.g., productivity, oxygenation) processes, whose respective contribution remains to be clarified. Here we investigate the effect of extreme orbital configurations on the oxygenation state of the ocean using marine biogeochemistry simulations with the IPSL‐CM5A2 Earth System Model under Cenomanian‐Turonian boundary conditions. Our simulations show that small changes in ocean ventilation triggered by orbitally induced variations in deep water formation have a strong impact on the spatial distribution of dissolved oxygen. This phenomena is amplified in enclosed and already poorly oxygenated basins, such as the proto‐Atlantic ocean, where up to 50% of the water volume become anoxic for some of the configurations. Plain Language Summary: Changes in the orbit of the Earth over time are responsible for periodic perturbations of the atmosphere and ocean dynamics that are ultimately being recorded in marine sediments through the occurrence of cyclicity. Origin of these cycles in past sedimentary records is not well understood because they are the result of the interactions between different processes that all exert a control on the nature of the deposited sediments. One of these processes is the oxygenation of the ocean that controls the potential for preservation of deposited organic matter. Here we focus on how variations in ocean dynamics modulate the oxygenation of the ocean during the late Cretaceous, using paleoclimate model simulations. We find that small changes in the oceanic circulation can lead to strong loss in oxygen in some part of the ocean, such as the Central Atlantic. Our results have implication for understanding the sedimentary record, the functioning of biogeochemical cycles and feedbacks within the climate system. Key Points: Small orbitally induced changes in ventilation produce large‐scale modification of O2 distribution in the late Cretaceous oceanDeoxygenation is strongly enhanced in already poorly oxygenated basins such as the proto‐Atlantic oceanVariations in deoxygenation strength occurs at all orbital frequency albeit with different amplitude [ABSTRACT FROM AUTHOR]