Evolving carbon sinks in the young South Atlantic: Drivers of global climate in the early Cretaceous greenhouse?
Final Report Abstract
The break-up of supercontinents in the Earth’s past has generated new oceanic basins. In the initial phase of the development these basins (i.e. when they are comparatively small) a high supply of nutrients from the surrounding continents spurs the production of marine organic matter in these basins. At the same time, restricted water mass circulation hinders the degradation of the organic matter and fosters its sequestration in sediments. The sequestration of organic matter in large quantities, in turn, has an impact on Earth’s carbon cycle and can be traced in ancient sediments by their carbon isotope signature. In this project we studied carbon sequestration processes associated with the initial phase of opening of the Southern Ocean and South Atlantic in the Early Cretaceous (Aptian and Albian time period). During this time interval, two major carbon sequestration events occurred associated with the Oceanic Anoxic Event 1a and the Late Aptian Cold Snap. We reconstructed the history of organic carbon burial in the Southern Ocean and South Atlantic by using multiple geochemical and sedimentological proxies within a refined stratigraphic framework and simulated the opening of both basins with a general circulation model in order to decipher the controls on carbon sequestration such as the opening of oceanic gateways, water mass circulation and climate. Our results show that carbon sequestration is asynchronous in the three sub-basins investigated. The timing of organic carbon burial is linked to the tectonic development and the opening of gateways such as the precursor of the Drake Passage between the Pacific and Southern Ocean, the Falkland Plateau and Georgia Basin Gateway between the Southern Ocean and the southern sub-basin of the South Atlantic and the Walvis Ridge and the Equatorial Gateway for the northern sub-basin of the South Atlantic. The development of these gateways regulated the flow of water masses to and from the respected sub-basins, thus exerting influence on organic carbon production and preservation. PCO2 and climate forcing further modulated organic carbon burial, in particular during the restricted basin phases of each basin with little water exchange to other sub-basins. The partial offset in the timing of organic carbon burial in the Southern Ocean and southern and northern sub-basin of the South Atlantic make a significant influence on the global carbon cycle not very likely. This assessment, however, needs to be tested in the future by further biogeochemical modeling.
Publications
- 2020: Evidence for a regional warm bias in the Early Cretaceous TEX86 record, Earth Planet Sc. Lett, 539, 116184
Steinig, S., Dummann, W., Park, W., Latif, M., Kusch, S., Hofmann, P., and Flögel, S.
(See online at https://doi.org/10.1016/j.epsl.2020.116184) - 2020: The impact of Early Cretaceous gateway evolution on ocean circulation and organic carbon burial in the emerging South Atlantic and Southern Ocean basins, Earth Planet Sc Lett, 530, 115890
Dummann, W., Steinig, S., Hofmann, P., Flögel, S., Osborne, A. H., Frank, M., Herrle, J. O., Bretschneider, L., Sheward, R. M., and Wagner, T.
(See online at https://doi.org/10.1016/j.epsl.2019.115890)
