Manganese cycles in Quaternary sediments of the Arctic Ocean - Climatic signals or diagenesis?

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The focus of the proposed project is a high-resolution geochemical study of manganese (Mn) cycles present in the uppermost Plio-/Pleistocene deposits recovered during IODP Expedition 302 (Arctic Coring Expedition ACEX) on Lomonosov Ridge, Central Arctic Ocean. During this project it will be explored whether cyclic peaks in sedimentary Mn content document a) primary climate-induced signals, b) are affected by diagenetic Mn redistribution, or c) are formed by a combination of both. In Arctic sediments Mn peaks, which document enhanced fluviatile input through Arctic rivers, have been suggested as a suitable chemostratigraphic tool for basin-wide correlation of climatic events on glacial- interglacial time scales. However, Mn is easilly mobilized in sediments under oxygen- depleted conditions. Therefore, multiple Mn peaks in marine sediments may also form or are altered by fluctuations of the oxic/suboxic redoxcline in the sediments. These two competitive interpretations of Arctic Mn cycles can only be unraveled by a detailed biogeochemical study. Apart from the ACEX record, we will include in our study two shorter cores recovered during R/V Polarstern Expedition ARK XXIII/3 in 2008, which show pronounced Mn cycles as well. We conducted a high-resolution pore water program onboard R/V Polarstern. This will help us to construct a conceptual model of Mn biogeochemistry in the Arctic Ocean, applicable to existing and future IODP records. Central questions are: 1) How are solid phase and dissolved Mn distributed in sediments and pore waters, and how do they relate to other sedimentary parameters?2) Which sediment layers are presently affected by Mn diagenesis, and to what degree is the primary sediment composition altered by element redistribution?3) Do relations of certain redox-sensitive/ sulfide-forming elements (e.g. Cd, Ce, Co, Cu, Fe, Mo, Ni, S, V) exist with Mn peaks and are trace metal patterns a diagnostic tool for or against a primary origin of individual cycles?4) What are the dominant Mn phases in the sediments (e.g. (oxyhydr)oxides, carbonates), and does their proportion vary with burial depth?