HR: 13:55h
AN: PP43C-02 INVITED     [Abstracts]
TI: Geological "Ground Truth" of Sea-level Highstand Events During Warm Interglaciations (MIS 11 and 5e): Taking the Punch out of Proxy Precision
AU: * Hearty, P J
EM: paulh@uow.edu.au
AF: School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW 2522 Australia
AB: High-resolution sea-level records for marine isotope stages (MIS) 11 and 5e from coastal outcrops in Bahamas, Bermuda, Hawaii, and Western Australia provide physical confirmation of extreme ice-melting events during Pleistocene interglacials. Field evidence indicates MIS 11 sea level rose in a series of oscillations to c. +20 m, while that of MIS 5e reached its maximum of +6-10 m. Because these were brief events (100s yrs), their true magnitude is generally muted or obscured in deep-sea oxygen isotope records; generally averaged over thousands of years by the combined effects of sampling, bioturbation, and sedimentation rates. Further unresolvable variables such as temperature and salinity further cloud the isotope proxy record. Thus, the tangible rock record is of greatest importance in understanding the nature of these extreme events. Geomorphology, sedimentary structures, taphonomy of and dating of organisms, and petrology provide ground truth at field sites. Sea-level highstands preserve terraces and benches by erosion and subsequent deposition of sub- and intertidal sediments. Fenestral porosity is a measure of intertidal wetting and drying of sand, while decimetre-scale, high-angle cross beds of poorly-sorted sand and gravel indicate shallow subtidal conditions. In situ coral heads describe similar subtidal conditions. Delicate, sometimes partially articulated skeletons of birds and reptiles in sea caves reveal a protected shoreline. An early generation of isopachous, fibrous cement verifies the presence of marine phreatic water over a sustained period of time. These features, often misinterpreted (McMurtry, 2004, AGU Fall Meeting, OS21E-06), categorically exclude emplacement by tsunami waves. Oceanic isotope records cannot produce an equivalent level of resolution of short, extreme events via (in terms of age, duration, rates of sea-level and ice-volume changes), thus shifting the `burden of proof' to proxy methods to identify such events. In our quest to understand past catastrophic global changes caused by the melting of major polar ice sheets, it is incumbent that we refer to the most direct and tangible data source at the paleoshoreline. Evidence from past interglacial rock records hints that rapid shifts in sea level and climatic instability may be an integral part of a "wild card" scenario in a future greenhouse world.
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1635 Oceans (1616, 3305, 4215, 4513)
DE: 3020 Littoral processes
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4936 Interglacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005