Sources of terrigenous material in the modern Cariaco Basin and in the Cenozoic Arctic Ocean: Using geochemical provenance as a proxy for climatic and paleoceanographic change.

摘要

Because pathways of terrigenous deposition (fluvial, eolian, ice rafting) are controlled by climatic and oceanographic variations, changes of terrigenous sources in the sedimentary record are important for elucidating oceanic and atmospheric histories. In this study, the inorganic composition of marine sediment from the Cariaco Basin and the Arctic Ocean is used to give insight into the ocean-atmosphere-climate dynamics of these locations at various time scales.;Geochemical analysis of biweekly sediment trap samples collected in the Cariaco Basin from November 1996 to December 2001 by the Cariaco Ocean Time Series shows that the chemical composition of the setting particles records the annual migration of the Intertropical Convergence Zone (ITCZ). Chemical mass balances and multivariate statistical treatments performed on the trap material, sediments from the local shelf, and samples from the Orinoco Delta, identify local riverine input, and probably wind-transported material as well, as important contributors of terrigenous material. Application of these modern findings to various Cariaco paleo-records shows that the glacial-interglacial Ti/Al variation is opposite to that which would be predicted from the modern. This suggests that the glacial-interglacial terrigenous record is not solely linked to ITCZ migration but is a combination of long-term ITCZ fluctuation, shorter-term orbital precessional forcing, and sea-level changes.;The same geochemical and statistical approach was applied to a 400 m sedimentary sequence from the Arctic, recovered by Integrated Ocean Drilling Program Expedition 302. Chemical discrimination indicates that the main detrital source for the Lomonosov Ridge during the Cenozoic has been the Siberian margin. Chemical similarities between the older (>50Ma) and the younger (14Ma) sediments suggest that despite the climatic differences between these time periods, both sea-ice and ocean currents featured similar trajectories capable of transporting sediment from the Eastern-Central Laptev Sea to the Central Arctic. Subtle terrigenous compositional changes in the intermediate sequence (50Ma-14Ma) coincide with a major change in the biogenic system and suggest a higher contribution of western sources (Kara or western Laptev Sea), which exhibit a more mafic composition. Sea-level changes and coastal geomorphology appear to be the cause of this interpreted single major provenance variation.