Culture experiments on the gamma 13C values recorded in tests of benthic foraminifera from methane sources at high latitudes

点击翻译按钮获取中文摘要

Since methane is a powerful greenhouse gas, significant releases of methane from instable submarine CH4 clathrates into the atmosphere have been hypothesized as a cause of past and possibly future climate changes (IPCC, 2007). The carbon isotope signature of benthic foraminifers, especially that of Fontbotia wuellerstorfi, has been considered a proxy to detect such clathrate dissociation induced climate changes. However, it has never been experimentally verified to what extent the foraminiferal δ13C signature reflects the release of methane. This is the goal of this project. The necessary experimental preconditions were successfully achieved during the current grant: (1) We established a unique “high-pressure deep-sea cultivation laboratory” that allows culturing living benthic foraminifers in their original surrounding environment under in-situ (high-pressure) conditions using a newly developed autoclave system. (2) For the first time, this enabled both methane-related high-pressure cultivation experiments and successful reproduction of barophilic F. wuellerstorfi, one of the most important signal-carrier in palaeoceanography. Our future experiments are designed to (1) improve our understanding about the process of δ13C signal transfer from the methane source into the foraminiferal shell; (2) document to what extent the foraminiferal δ13C reflects the biological conversion from the CH4 source into the bottom water, which is measured by the δ13C of the dissolved inorganic carbon; and (3) examine the importance of the food source on the δ13C shell signature.