HR: 0800h
AN: PP11A-0200    [Abstracts]
TI: Closure of the Indonesian Seaway during the middle to late Miocene (13.2-5.8 Ma): Early history of the Western Pacific Warm Pool
AU: * Leckie, R
EM: mleckie@geo.umass.edu
AF: University of Massachusetts, Department of Geosciences 611 N. Pleasant St., Amherst, MA 01003, United States
AU: Nathan, S A
EM: snathan@geo.umass.edu
AF: University of Massachusetts, Department of Geosciences 611 N. Pleasant St., Amherst, MA 01003, United States
AB: We document the waxing and waning of a ‘proto-Western Pacific Warm Pool' and Equatorial Undercurrent (EUC) based on a study of multi-species planktic foraminiferal isotope ratios and census data spanning the 13.2-5.8 Ma interval at ODP Site 806 in the western equatorial Pacific (WEP). We hypothesize that the presence or absence of a proto-warm pool in the WEP, caused by the progressive tectonic constriction of the Indonesian Seaway and modulated by sea level fluctuations, created El Ni~{n}o/La Ni~{n}a-like alternations of hydrographic conditions across the equatorial Pacific during the late Miocene. This hypothesis is supported by the general antithetical relationship observed between carbonate productivity and preservation in the western and eastern equatorial Pacific, a phenomenon caused by these alternating ocean-climate states in the modern ocean. The two-step development and intensification of a proto-warm pool 11.6-9.6 Ma coincides with ice sheet expansion associated with Miocene isotope events Mi5 and Mi6, resulting in a cumulative sea level fall of 50 m and production of Northern Component Water. It also marks the initiation of a more modern equatorial current system as La Ni~{n}a-like conditions became established across the tropical Pacific. This situation sustained carbonate and silica productivity in the eastern equatorial Pacific (EEP) at a time when carbonate preservation sharply declined in the Caribbean. Proto-warm pool weakening after 10 Ma may have contributed to the nadir of a similar ‘carbonate crash' in the EEP. Decay of the proto-warm pool and resultant El Ni~{n}o-like conditions brought higher productivity to the WEP, particularly 9.0-8.8 Ma coincident with a major perturbation in tropical nannofossil assemblages. This interval of increased productivity records the initial phase of the widespread ‘biogenic bloom'. Resurgence of a later proto-warm pool in the WEP 6.5-6.1 Ma may have spurred renewed La Ni~{n}a-like conditions, which contributed to a strong late phase of the ‘biogenic bloom' in the EEP.
DE: 4231 Equatorial oceanography
DE: 4556 Sea level: variations and mean (1222, 1225, 1641)
DE: 4940 Isotopic stage
DE: 4944 Micropaleontology (0459, 3030)
DE: 4950 Paleoecology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting