Terrigenous climate signals in deep-sea sediments: Assessment and quantification of alteration processes on primary signals

PhD student: Wiebke Kallweit
Project partners:
Bremen: Matthias Zabel
Newcastle: Thomas Wagner

Follow up project of Project II-9

This process-oriented research concept provides a rare opportunity to combine systematic investigations of alteration processes on inorganic and organic terrigenous components in the modern marine realm (s. b.). We expect that this approach will enable improved specification of the most useful sets of proxy parameters preserving well defined continental climate conditions. Although the main focus will be on the assessment and quantification of these alteration processes affecting the primary input signals, we also plan to examine the potential importance of specific components for element cycling and budgeting (s. b.). Two complementary areas in the eastern low latitude Atlantic with strong contribution from African sources are proposed for this “source-to-sink” approach: 1) the continental margin off NW-Africa, well known to be governed by the eolian input of a huge amounts of lithogenic dust from the African Sahara and Sahel (e.g. Sarnthein et al. 1982; deMenocal 1995; Ratmeyer et al. 1999), and 2) the Congo Deep Sea Fan, which is supplied by one of the largest tropical river systems on Earth (e.g. Van der Gaast & Jansen 1984, Schneider et al. 1997, Schefuß et al. 2003). A set of sediment surface samples from both regions is already available. Additional sample material necessary for this project is planned to be obtained during forthcoming ship cruises as part of other research programs (e.g. DFG-RCOM) and/or EUROPROX initiatives. Detailed information on the properties of eolian input exists from several previous cruises and it is assured that these investigations will be continued in related projects. A promising approach to address the outlined general questions requires extensive analysis on the suspension load of the water column and on sediment surface samples. The planned analytical approach contains investiagation of mineral phases, concentrations of Al, K, Ti, Ba, Fe, TOC, IC, molecular and compound specific stable isotopes signals on plant waxes, lignin, and inert carbon. As a novel organic geochemical approach to trace soil OM in marine sediments analysis of specific hopanoids (e.g. Farrimond et al. 2000; Talbot et al. 2001, 2003) are planed. Despite numerous studies demonstrate that variations in the mineral and element composition in marine sediments can be used as indicators for climate conditions and change (e.g. Boyle 83, Sirocko et al. 2000, Haug et al. 2001, Zabel et al 2004 and references therein) hardly any results exist showing a direct correspondence between input signals and their preservation below the sea floor. Specification and quantification of transfer and transformation rates from the primary continental signal to its marine sink achieves a major progress in marine and climate research. While the potential of preservation and the specific structure of some lipids is reasonably well constrained for various marine settings, specific biomarkers can be applied to determine the source, transformation stage, and fate of terrestrial organic material (e.g. Summons 1993 and references therein), and specific paleoenvironmental conditions (e.g. Brassell 1993). As a special focus of the organic geochemical work we hope to find supplementary evidence for soil organic matter in deep marine sediments.