HR: 16:30h
AN: PP52C-03 INVITED     [PDF]
TI: Paleoclimate Variability Inferred From Size Distributions of Deep-Sea Sediments: A Comparison of Different Methods
AU: * Prins, M A
EM: prim@geo.vu.nl
AF: Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, Amsterdam, 1081 HV Netherlands
AU: Weltje, G
EM: G.J.Weltje@CITG.TUDelft.NL
AF: Department of Applied Earth Sciences, Delft University of Technology, P.O. Box 5028, Delft, 2600 GA Netherlands
AB: One of the outstanding problems of paleoclimate reconstruction from physico-chemical properties of terrigenous deep-sea sediments stems from the fact that most basin fills are mixtures of sediment populations derived from different sources and transported to the site of deposition by different mechanisms. Conventional approaches to paleoclimate reconstruction from deep-sea sediments do not distinguish between provenance and dispersal-related variations, and therefore often fail to recognize the true significance of variations in sediment properties. Many attempts to extract paleo-environmental information from deep-sea sediments have focused on grain size, more specifically on the use of variations in univariate summary statistics of grain-size distributions (GSDs). This approach to characterization is unlikely to be successful because most deep-sea sediments are mixtures of different sediment types, as a consequence of time-averaging effect related to bioturbation and low accumulation rates. We present a conceptual model of spatio-temporal grain-size variation in terms of dynamic populations (DPs). Each DP results from a characteristic combination of production and transport mechanisms that corresponds to a distinct subpopulation in the data analyzed. The mathematical-statistical equivalent of the conceptual model may be solved by means of the end-member-modeling algorithm EMMA. The modeling results of a high- and low-latitude ocean basin are shown to illustrate the common degree of complexity of deep-sea grain-size records. The distinction between DPs related to selective dispersal of detritus from a single source, and DPs related to mixing of detritus from different sources is shown to be essential for successful paleoclimate interpretation. The case study of the North Atlantic is discussed in more detail to illustrate the latter. Variability in iceberg discharge and deep-ocean circulation in the North Atlantic during the last glacial period is inferred from the GSD and trace elemental composition of terrigenous sediments on Reykjanes Ridge. End-member modeling of the GSDs is used to unmix the signals of varying bottom-current speed and iceberg discharge. The GSD within the silt fraction appears to be influenced by both factors. We show that reconstructions of variations in bottom-current speed based on the raw grain-size data are opposite to inferences from the unmixed record. The discrepancy between the interpretations obtained by the conventional approach and EMMA highlights the danger of interpreting grain-size variation in terms of a single controlling factor without knowledge of the sources and dispersal mechanisms of the sediments.
DE: 3022 Marine sediments--processes and transport
DE: 3094 Instruments and techniques
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting