HR: 14:00h
AN: PP52B-02 INVITED     [PDF]
TI: Paleoproductivity Reconstructions Using Radiolarians
AU: * Lazarus, D B
EM: david.lazarus@rz.hu-berlin.de
AF: Museum f. Naturkunde, HU, Invalidenstrasse 43, Berlin, 10115 Germany
AB: This talk reviews the use of radiolarian assemblages in paleoproductivity reconstruction. Molina-Cruz and CLIMAP co-workers first identified a distinct radiolarian assemblage whose modern geographic distribution closely matched that of an upwelling region (eastern Pacific Peru-Chile). Nigrini and Caulet subsequently identified additional species largely endemic to various upwelling environments. They applied this in the form of an Upwelling Radiolarian Index (URI) in down-core studies of upwelling history. Recently, Jacot des Combes and Weinheimer have used published distributions of living radiolarians in the water-column to assign fossil taxa to surface vs subsurface groups. They used ratios of thermocline to surface taxa (e.g., the Thermocline to Surface Radiolarian Index, or TSRI), which measures relative enhancement of thermocline to surface radiolarian production in regions of upwelling, to reconstruct past ocean productivity. Both methods appear to perform well, although neither is always reliable. Both the URI and TSRI methods are based on a small number of taxa (ca. 10 each), although biogeographic and water depth information are now available for ca. 100 living species. The use of additional taxa should make reconstructions more robust by reducing the effects of single species ecology, and making index values less sensitive to evolutionary changes in taxa over Neogene time intervals. Taxonomic assemblage reconstructions of productivity have some inherent advantages over bulk flux proxies, being less sensitive to preservation problems or the age model employed. Radiolarian assemblages are particularly useful in upwelling regions where carbonate fossils are poorly preserved. All are however limited by our sparse knowledge of the ecology of the various species used. Among the major microfossil groups, radiolarian ecology and biology are in particular relatively poorly known; even the descriptive taxonomy of living species is not yet complete. Despite these limitations, radiolarian assemblages provide a useful tool for paleoproductivity research. Their power will continue to improve in the future as radiolarian biology becomes better known.
DE: 3030 Micropaleontology
DE: 4267 Paleoceanography
DE: 4279 Upwelling and convergences
DE: 4855 Plankton
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting