Changes in physical and chemical properties of archived sediment

摘要

Marine sediment cores are usually stored in archives after collection until they are utilized. Few studies, however, have investigated changes in the physical and chemical properties of sediment cores during storage. Therefore, it has not been known how long archived sediment cores are useful for determining certain physical, geochemical or chemical components. To clarify changes in physical and chemical properties of archived sediments, we monitored moisture ratio, magnetic susceptibility, lightness, color reflectance, total carbon, total nitrogen, and organic carbon contents in archived sediments stored at 20 - 25°C, 4°C, or -20°C, using sediment cores collected from the North. Pacific seafloor near Japan. We also monitored magnetic susceptibility in foraminiferal ooze and diatomaceous pelagic clay sediments from the North Pacific. The moisture ratio changed toward a constant value at all depths with increasing time because pore water in the sediment could easily move throughout the sediment core. There was no significant difference in magnetic susceptibility in hemipelagic and diatom-bearing clay sediments archived at 4°C and at 20 - 25°C. In foraminiferal ooze, diatom-bearing foraminiferal ooze, and diatom-bearing pelagic silty clay, magnetic susceptibility showed a reducing trend throughout the monitoring period, and the magnitude of reduction was larger at 20 - 25°C than at 4°C. Changes in lightness and color reflectance were significant and rapid, occurring within weeks of the collection date. Slight differences in the preservation of carbon and nitrogen were observed at different storage temperatures, with a smaller degradation rate at -20°C than at 4°C or 20 - 25°C. The presence of an inert gas, argon, was not effective at preserving organic materials. The possible effectiveness of other inert gases for this purpose should be investigated. Our results will be useful for estimating the alteration rate of physical and chemical properties of archived sediment samples under various storage conditions.