HR: 17:45h
AN: OS14A-08 INVITED    [Abstracts]
TI: Biotic Response of Deep-Ocean Ostracodes to the Paleocene-Eocene Thermal Maximum: An Assessment of Past, Present, and Future studies
AU: * Schellenberg, S A
EM: schellenberg@geology.sdsu.edu
AF: Department of Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, CA 92115, United States
AU: Landau, E A
EM: elandau@rohan.sdsu.edu
AF: Department of Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, CA 92115, United States
AB: Ostracodes are the only commonly preserved deep-ocean metazoans and provide an important perspective on benthic conditions through the global carbon cycle perturbation known as the Paleocene-Eocene Thermal Maximum (PETM). The classic global Cenozoic study of >250 micron size-fraction ostracode faunas from 1,000+ samples drawn from 150+ DSDP sites by Benson et al. (1984) revealed marked transient declines in abundance, richness, and Shannon diversity in the late Paleocene, but these data are discretized within relatively coarse one-Myr averaged bins and may have little direct temporal or causal relationship with the much shorter PETM. Following the "discovery" of the PETM by Kennett and Stott in the early 1990s, Steineck and Thomas (1994) examined the >150 micron size-fraction ostracode faunas through the PETM at upper bathyal Site 689B on Maud Rise, and argued for a marked relative increase in small, thin walled "opportunistic" taxa capitalizing upon transient conditions of increased food, decreased dissolved oxygen, and decreased carbonate saturation. However, our subsequent cm-scale bulk carbonate carbon-isotope chemostratigraphy for Site 689 confirms that only two of these faunal samples are located within the carbon-isotope excursion of the PETM. Recent high-resolution geochemical analyses of ODP PETM sections in the Southern Ocean are producing a new benchmark for integrative approaches to understanding the PETM. Cast within these environmental frameworks, our recent >63 micron size-fraction ostracode faunal analyses at Maud Rise (690B) and Kerguelen Plateau (738C) reveal marked declines in ostracode accumulation rates and resampled (abundance- corrected) generic richness coincident with the CIE onset and varying rates of recovery following the CIE minimum. Cluster and ordination analyses support major faunal perturbations through the CIE and subsequent recovery towards pre-CIE faunal composition and structure following the CIE. The relatively rapid recovery in ostracode accumulation rates near the CIE minimum does not support prolonged deleterious conditions for metazoans, though the faunal composition shows a significantly greater proportion of presumably dysoxia- tolerant suspension-feeding platycopid taxa. However, this platycopid signal may well reflect increased food availability as well as decreased oxygenation as has been suggested from benthic foraminiferal studies. The restriction of specific taxa, such as Munseyella and Palmoconcha, to specific CIE intervals within the highly stratigraphically resolved Site 690 suggests that faunal patterns reflect a true ecological signal versus pervasive artifacts from differential sedimentation rates and reworking. Ongoing single-valve stable-isotope analyses of various ostracode taxa should provide additional constraints on reworking as well as the arrival of CIE to these bathyal sites via thermohaline circulation. Ongoing logistical challenges to consolidating and expanding the PETM marine ostracode record include (1) obtaining sufficient specimen abundances at sufficient stratigraphic resolution given often low ostracode accumulation rates and limited sediment volumes; (2) adopting explicit and consistent inter-worker methods (e.g., size fraction picked, tallying adults vs. juveniles); (3) ensuring permanent archiving of complete faunal matrices; (4) establishing a consistent species taxonomy; and (5) stratigraphic expansion of such studies about the PETM to assess longer term faunal patterns and sensitivity to orbital forcing and other Paleogene hyperthermals.
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4944 Micropaleontology (0459, 3030)
DE: 4948 Paleocene/Eocene thermal maximum
DE: 4950 Paleoecology
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting