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Title: Late Miocene and early Pliocene palaeoceanography at the eastern Equatorial Pacific IODP Site U1338 : implications for climate evolution and stability
Author: Drury, Anna Joy
ISNI:       0000 0005 0734 3708
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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The short-term background climate variability during the climatically stable latest Miocene to early Pliocene (LM-EP) is not well understood, owing to the lack of continuous, high-resolution climate records. Assessing variability during an interval of long-term climatic stability will constrain how sensitivity of major Earth's system components (Earth system response - ESR) to external radiative forcing has changed through time. This study investigated LM-EP climate, focussing on changes in ESR, El-Nino-Southern-Oscillation state, glacio-eustacy and the Messinian Salinity Crisis (MSC), and the origin of the Late Miocene Carbon Isotope Shift (LMCIS). This project produced the first high-resolution benthic foraminiferal δ18O and δ13C record in the eastern equatorial Pacific (IODP Site U1338) from 8.0-3.5 Ma that resolves all Milankovitch cyclicities. A high-resolution, orbitally-based age model, planktic foraminiferal δ18O, δ13C and Mg/Ca, coccolith-rich 'clumped isotopes' Δ47, spectral analyses and multi-site benthic foraminiferal isotope compilations were also produced. Planktic foraminiferal Mg/Ca sea surface temperatures (SSTs) were ~25 °C. Coccolith-rich Δ47 temperatures were unrealistically cold at ~10-15 °C, reflecting moderate coccolith preservation and vital effects that cause higher Δ47. Site U1338 and 982 combined benthic foraminiferal (δ18O; δ13C) wavelet analyses show moderate ESR from 6.3-4.7 Ma and after 3.7 Ma, but lower ERS from 7.0-6.3 Ma. The δ18O-minimum stage ~5.33 Ma, during long-term minimum δ18O, suggests that glacio-eustacy played a role in the MSC termination. The benthic foraminiferal δ13C compilation confirms that the LMCIS was globally synchronous and caused by a negative shift in oceanic reservoir δ13C, driven by changes in the continental carbon flux (increased sea-floor-spreading / C4-grass expansion). Data syntheses show that global warmth, dominant El-Nino state, high cryosphere sensitivity, lower ice volume and short-term ice sheet variations characterised the LM-EP pre-7.0 and post-5.7 Ma. Stable conditions occurred ~7.0-5.7 Ma, with dominant La-Nina, higher ice volume, low cryosphere sensitivity and lower SSTs.
Supervisor: John, Cedric Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral