Tao, Ze; (2024) Late Miocene orbital forcing and palaeoceanography in the eastern equatorial Pacific. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The late Miocene is a relatively climatically stable period and is an ideal period to study climate sensitivity to orbital forcing. The central American seaway (CAS) experienced significant changes and the carbonate crash occurred globally during the middle and late Miocene, but details of these events in the late Miocene are still ambiguous. Integrated Ocean Drilling Program (IODP) Site U1338 provides a unique opportunity to explore the evolution of climate and palaeoceanographic conditions in the eastern equatorial Pacific in the late Miocene. This thesis presents high-resolution benthic and planktic foraminiferal δ18O and δ13C records at IODP Site U1338 spanning the late Miocene. Benthic and planktic foraminiferal δ18O and δ13C records exhibit distinct imprints of orbital variations according to multiple spectral analysis results. A high-resolution astronomically tuned age model at Site U1338 spanning the late Miocene is presented. Biostratigraphic and magnetostratigraphic events at Site U1338 are recalibrated to the new astrochronology built in this thesis, providing new age control. This thesis compares benthic foraminiferal δ13C values globally to investigate the evolution of palaeoceanography during the late Miocene. The higher benthic foraminiferal δ13C isotope gradient between Site U1338 and the Atlantic sites after 10.2 Ma suggests the strengthening of north Atlantic deep water after this time. The similarity of the benthic foraminifera δ13C values at Site U1338 and the Caribbean site suggests that Pacific deep water could travel freely through the CAS prior to 10.1 Ma. The similarity of the benthic foraminifera δ13C values at the Caribbean and the Atlantic sites suggests that the Atlantic flow dominates the Caribbean after 9 Ma. This thesis also explores the surface water palaeoproductivity through reconstructing the intensity of upwelling at Site U1338, and found the strength of upwelling is high prior to 10.2 Ma but decreases after 10.2 Ma.

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