Benthic foraminifera as proxies in Contourite Drift Systems

地球历史上不同气候状态下海洋环流的重建对我们理解地球气候系统起着关键作用。可靠的重建方法，所谓的代理方法，是这些努力的基础。其中，底栖有孔虫-生活在海底的单细胞带壳生物-发挥着重要作用。不同有孔虫种类的丰度受底流强度和携带的营养盐负荷的控制。这些物种在等深流漂流系统中特别丰富，这些漂流系统是受持续底流影响的沉积物。由于有孔虫壳在死亡后被嵌入并保存在沉积物中，它们的丰度被用来重建沿着伊比利亚半岛大陆边缘的洋流。然而，申请人帕特里克·格鲁内特博士（格拉兹大学）从国际大洋钻探计划第339次考察的样品中获得的伊比利亚大陆边新数据表明，不加评判地应用这种方法是有问题的。活有孔虫和化石有孔虫的比较表明，某些贝壳在石化过程中通过溶解而丢失。此外，来自大陆边不稳定地区大陆架的贝壳的输入也可能使丰度产生偏差。最后，该方法在伊比利亚大陆边以外的适用性在很大程度上是未知的。拟议的项目旨在首次大规模地解决这些问题和相关过程，并制定最终将导致这一基本替代方法得到根本改进的解决方案。首先，研究区域将扩大到伊比利亚大陆边以外。将从大西洋的等深流漂流系统中收集大量的新样品。将从表层样品中统计出大规模的分布模式，这将首次检查不同纬度的底流对有孔虫的控制。区域和大规模模式的记录将确保代理方法的普遍适用性。第二，通过比较沉积物岩心的表层样品和化石样品，可以详细研究那些妨碍代用方法适用性的过程，即在泥化过程中有孔虫壳的损失和来自大陆架地区的壳的输入。通过首次详细了解这些因素，将开发和测试新的创新方法，以克服偏差并确保替代方法的可靠性，该项目的成功实施将大大改进用于重建海洋环流的替代方法。它很容易应用，时间和成本效益。

The reconstruction of oceanic circulation during different climatic states in Earth history plays a pivotal role in our understanding of Earth’s 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.