[B-PT02_1PO1] Biocalcification and the Geochemistry of Proxies

[BPT02-P03] 15N/14N mapping of the isotope labeling cultured foraminifera using ultra thin section

*Hidetaka NOMAKI¹, Akizumi ISHIDA², Kotaro SHIRAI², Yoshito CHIKARAISHI¹, Katsuyuki UEMATSU³, Akihiro TAME³, Masashi TSUCHIYA¹, Takashi TOYOFUKU¹, Naoto TAKAHATA², Yuji SANO², Naohiko OHKOUCHI¹ (1.JAMSTEC, 2.AORI, University of Tokyo, 3.Marine Works Japan)

Keywords:Benthic foraminifera, nitrate respiration, symbiotic microbe, NanoSIMS

Shallow water benthic foraminifera, Ammonia beccarii, survive under anoxic conditions in conjunction with possible endobionts. Based on the amino acid analysis, those endobionts are expected to utilize nitrate pool in the foraminifera. However, nitrogen cycles in the foraminiferal cell and endobionts are still unclear. Here, we obtained two dimensional-nitrogen isotopic compositions of A. beccarii which had been incubated under oxic and anoxic conditions with ¹⁵N-labeled nitrate. After observing with transmission electron microscope to confirm cellular ultrastructure and endobiont distribution, same ultra thin section was examined for nitrogen isotopic composition analysis using secondary ion mass spectrometer. Nitrogen isotopic compositions were measured with spatial resolution better than 400 nm. ¹⁵N-enriched parts were found in certain structures in the cell, but not in the endobionts in this experiment.