HR: 0830h
AN: PP51B-0928    [PDF]
TI: Identification of Dissolution Patterns in Nannofossil Assemblages: A High-Resolution Comparison of Synchronous Pliocene Records From Ceara Rise, ODP Leg 154
AU: * Gibbs, S
EM: sjg51@cam.ac.uk
AF: Godwin Institute for Quaternary Research, University of Cambridge, Pembroke Street, Cambridge, CB2 3SA United Kingdom
AU: Shackleton, N
EM: njs5@cam.ac.uk
AF: Godwin Institute for Quaternary Research, University of Cambridge, Pembroke Street, Cambridge, CB2 3SA United Kingdom
AU: Young, J
EM: j.young@nhm.ac.uk
AF: The Natural History Museum, Cromwell Road, London, SW7 5BD United Kingdom
AB: Nannofossil assemblages in sediment samples are being increasingly used as paleoceanographic proxies of surface water conditions. However, these records can be scrambled by a number of taphonomic factors since fossil nannoplankton assemblages are controlled not only the initial production of the plankton in the surface waters but also dissolution throughout the water column and on the seafloor. An assessment of the relative contributions of these controls is therefore necessary for reliable use of nannofossil population abundance data, in particular in the critical early stages when assemblages are still sufficiently diverse to make assemblage analysis for paleoceanography attractive, but when nonetheless relative abundances of species may have been significantly skewed. This study demonstrates that even where nannofossil preservation is qualitatively good to very good, there can be significant distortion by dissolution in the composition of nannofossil assemblages and temporal assemblage patterns. However, a comparison of synchronous well-preserved Pliocene nannofossil and non-nannofossil records from Ceara Rise Site 929 (4397 m depth) with Site 926 (3598 m depth), shows that nannofossil abundance patterns that have been controlled primarily by the original production of the individual taxa can be clearly differentiated from those patterns that have experienced significant subsequent dissolution overprinting. This overprinting can be detected by the number of co-varying relationships within the nannofossil taxa, the taxa that form those co-varying relationships, the coupling of dissolution indices with each other and with nannofossil abundances, and the loss or reduction of dissolution-susceptible taxa. Furthermore, by the unique comparison of absolute nannofossil abundance variations at the two sites (achieved by normalising nannofossil to terrigenous abundances), the dissolution signal present at Site 929 can be isolated from the original productivity signal.
DE: 3030 Micropaleontology
DE: 4267 Paleoceanography
DE: 4805 Biogeochemical cycles (1615)
DE: 4855 Plankton
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting