Ocean sediments tell the story of Palaeogene environmental change

given by Prof Bridget Wade (Department of Earth Sciences, University College London)

Abstract:
Numerous oceanic, climatic, and biotic conditions relating to biogeochemical cycles and environmental change impact the composition and distribution of deep- sea sediments. Utilising the extensive sediment archives of the International Ocean Discovery Program (IODP) and its predecessors, maps of deep-sea sediment type have been assembled across two critical boundaries in the Paleogene, one characterised by an interval of extreme warmth (Paleocene/Eocene) and the other by global cooling (Eocene/Oligocene). Ocean sediment distribution shows significant divergence both between the latest Paleocene and Paleocene Eocene Thermal Maximum (PETM), across the Eocene- Oligocene Transition (EOT), and in comparison to modern sediment distributions. In the latest Paleocene, carbonate sedimentation extends to high southern latitudes. Disappearance of carbonate sediments at the PETM is well documented and can be attributed to dissolution caused by significant ocean acidification as a result of carbon-cycle perturbation. Biosiliceous sediments are rare and it is postulated that the lowered biogenic silica deposition at the equator is due to an absence of equatorial upwelling in the early Paleogene ocean. In the Southern Ocean, we attribute the low in biosiliceous burial, to the warm deep water temperatures which would have impacted biogenic silica preservation. Our sediment depositional maps record a tongue of radiolarian ooze in the late Eocene eastern equatorial Pacific. Enhanced biosiliceous deposits in the late Eocene equatorial Pacific and Southern Ocean are due to increased productivity and the spin-up of the oceans. The compilation documents the enhanced global carbonate sedimentation in the early Oligocene, confirming that the drop in the carbonate compensation depth was global.

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