DFG-Schwerpunktprogramm 1158 "Antarktisforschung"

Culture experiments on the δ¹³C values recorded in tests of benthic foraminifera from methane sources at high latitudes

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 foraminifera δ¹³C signature reflects the release of methane. This is the goal of this project. The necessary experimentalpreconditions 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 (Fig. 1). (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 (Fig. 2). 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.

Fig. 1: High-pressure deep-sea cultivation laboratory

Fig. 2: F. wuellerstorfi: successful cultured foraminiferal offspring (fluorescent) under in situ pressure (135 bar)

Scientists

Ralf Tiedemann
Jutta Wollenburg
Jeroen Groeneveld
Alfred-Wegener-Institute Bremerhaven

Research areas

Circum Antarctica

Publications

Groeneveld J, Chiessi CM, 2011. Mg/Ca of Globorotalia inflata as a recorder of permanent thermocline temperatures in the South Atlantic. Paleoceanography 26, PA2203. doi:10.1029/2010PA001940

Raitzsch M, Hathorne E, Kuhnert H, Groeneveld J, Bickert T, 2011. Modern and Late Pleistocene B/Ca ratios of the benthic foraminifer Planulina wuellerstorfi determined with laser ablation ICP-MS. Accepted in Geology.

Raitzsch M, Hathorne E, Kuhnert H, Groeneveld J, Bickert T, 2011. B/Ca in benthic foraminifers: Seawater carbonate system proxy and correction of the Mg/Ca paleo-thermometer. Accepted in G-cubed

Greaves M, Caillon N, Mg/Ca-Intercalibration Team, 2008. Interlaboratory comparison study of calibration standards for foraminiferal Mg/Ca thermometry. Geochemistry, Geophysics, Geosystems 9-8. doi:10.1029/2008GC001974

Groeneveld J, Nürnberg D, Steph S, Tiedemann R, Reichart GJ, Crudeli D, Reuning L, 2008. Increasing Mg/Ca ratios in the Pliocene Caribbean: Diagenetic overprint, salinity influence or initiation of the Western Atlantic Warm Pool? Geochemistry, Geophysics, Geosystems 9, Q01P23. doi:10.1029/2006GC001564

Raitzsch M, Kuhnert H, Groeneveld J, Bickert T, 2008. Benthic foraminifer Mg/Ca anomalies in South Atlantic core top sediments and their implications for paleothermometry. Geochemistry, Geophysics, Geosystems 9-5. doi:10.1029/2007GC001788

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