HR: 0800h
AN: B41A-0099    [Abstracts]
TI: Phytoplankton Community Change in the Eocene Greenhouse
AU: * Harrington, G J
EM: g.j.harrington@bham.ac.uk
AF: The University of Birmingham, Earth Sciences Dept.,, Birmingham, B15 2TT United Kingdom
AU: Higgs, K T
EM: k.higgs@ucc.ie
AF: National University of Ireland Cork, Geology Dept., Cork, N/A Ireland
AU: Jacovides, J
EM: jake.jacovides@millennia.com
AF: Millennia Ltd., Unit 3 Weyside Park, , Alton, GU34 2PJ United Kingdom
AB: Dinoflagellate cyst data are presented from core 16/28-sb01 from the northern flank of the Porcupine High, 220 km west of county Mayo, Ireland (54N, 13W). The Porcupine High is currently on the eastern fringe of the North Atlantic Drift (NAD). The core represents a window onto part of the Early Eocene Climatic Optimum (EECO, 52-50 Ma) because a thick (60 m) unit of homogenous calcareous muds is present containing calcareous nannoplankton from entirely within NP12 (c. 53-51 Ma). Dinoflagellate cysts are diverse (118 taxa; 41 samples) and record environmental changes over time. Detrended correspondence analyses indicate that there are no pronounced changes in composition between contiguous samples but long-term changes in composition occur instead. Separate ordinations on presence-absence and relative abundance data demonstrate that changes in the co-occurrence patterns of taxa (presence-absence matrix) are separate from changes in relative abundance. To further show composition changes, we applied the squared chord distance metric to the relative abundance matrix and plotted the distances between every sample. On average, samples become more dissimilar to one another with increasing distance apart. The Bray-Curtis metric was applied to the presence-absence matrix and also demonstrates that on average samples are less similar to one another with increasing distance apart. These results are statistically significant. They are probably not related to sampling intensity either; bootstrap, jackknife 2, rarefaction and Chao 1 all show that after c. 15 samples have been randomly pooled, new taxa are encountered with very low frequency. Changes in the P:G ratio and the decreasing abundance of sporomorphs indicates that basin deepening drove community change. Provisionally, our results indicate that; (1) if the NAD was active at this time, it was stable in the EECO, (2) community change is directional and responds to regional processes, (3) changes in relative abundance are not necessarily coupled with changes in co-occurrence patterns.
DE: 9335 Europe
DE: 9604 Cenozoic
DE: 4815 Ecosystems, structure and dynamics
DE: 4855 Plankton
DE: 4267 Paleoceanography
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting