57Fe Mössbauer Study of Specific Iron Species in the Antarctic Ocean Sediments

Sea sediments can be probed as records of the environment of sedimentation. Much attention has been given to clarifying the environment of sedimentation from an elemental composition point of view. Valuable information for paleoceanography has been obtained by several projects such as the Deep Sea Drilling Project and Ocean Drilling Program. In general, the rate of sedimentation in the sea is lower than rates in rivers or estuaries, except when there is a large scale variation such as massive climate change or an eruption of an undersea volcano in the sea area. There is less pelagic sediment deposition from terrigenous materials in the deep sea than on the coast. Therefore, the long term variation in the environment of the sea can be determined with the analysis of sediment cores of short length. Sea sediments comprise many kinds of heavy metals. Almost all iron supplied to the sea is included in the terrigenous fracture. These materials are carried and finally accumulate in the sea sequentially from the area along the shore through carriers such as the atmosphere and rivers. Since iron is an essential element for many sea organisms, which take in iron from seawater, organic matter as product of the food chain accumulate in the sediments. In this paper, we focus on the chemical states of iron in Antarctic sediments. From the analysis of Fe Mössbauer spectra, ferrous and ferric iron can be represented by silicate and clay minerals respectively. Uptake of iron from seawater by phytoplankton mainly causes a redox reaction in the cycle of photosynthesis and respiration. Consequently, the difference in chemical states such as ligand and valence states depends on the origin of the iron. In addition, chemical states of heavy metals such as iron and manganese in the sediments change upon reduction by organic matter. It is important to trace the processes of these reactions in discussing the environments of sediments. 2. Experimental