Benthic foraminifera as proxies in Contourite Drift Systems

The reconstruction of oceanic circulation during different climatic states in Earth history plays a pivotal role in our understanding of Earths climate system. Reliable reconstruction methods, so called proxy methods, are the basis for these endeavors. Amongst those, benthic foraminifera single-celled, shell-bearing organisms living at the seafloor play an important role. The abundances of distinct foraminiferal species are controlled by bottom current intensity and the carried nutrient load. These species are particularly abundant in contourite drift systems, sediments under the influence of persistent bottom currents. As foraminiferal shells are embedded and preserved in the sediment after death, their abundances have been used to reconstruct oceanic currents along the continental margin of the Iberian Peninsula. New data from the Iberian continental margin by the applicant Dr. Patrick Grunert (University of Graz) from samples of Expedition 339 of the International Ocean Drilling Program (IODP) suggest, however, that the uncritical application of this method is problematic. The comparison of living and fossil foraminifera shows that certain shells are lost in the fossilization process through dissolution. Furthermore, abundances may be additionally biased by input of shells from the shelf in unstable areas of the continental margin. Finally, the applicability of the method beyond the Iberian continental margin is largely unknown. The proposed project intends to address these problems and associated processes for the first time on a broad scale, and to develop solutions that will ultimately lead to a fundamental improvement of this essential proxy method. Two objectives are identified in the scope of the project. First, the study area will be expanded beyond the Iberian continental margin. An extensive set of new samples will be collected from contourite drift systems of the Atlantic Ocean. Large-scale distribution patterns will be statistically extracted from surface samples which allows the examination of the control of bottom currents at different latitudes on foraminifera for the first time. The documentation of regional and large-scale patterns will ensure the universal applicability of the proxy method. Second, the comparison of surface and fossil samples from sediment cores will allow studying those processes in detail which inhibit the applicability of the proxy method, i.e. the loss of foraminiferal shells in the fossilization process and the input of shells from shelf areas. Through the understanding of these factors in detail for the first time, new and innovative methods will be developed and tested to overcome biases and to ensure the reliability of the proxy method. The successful implementation of the project will result in a significantly improved proxy method for the reconstruction of ocean circulation. It is easily applicable, time and cost efficient, and will ultimately contribute for a better understanding of ocean-climate dynamics.