6:15 PM - 7:30 PM
[BPT03-P03] Reliable stable isotopic compositions of individual Uvigerina spp. as sea environmental proxy
Keywords:stable isotope, benthic foraminifera, microscale analysis, Uvigerina
The stable carbon and oxygen isotopic composition (δ13C, δ18O) of benthic foraminiferal carbonate shells have been used to reconstruct the past sea environment. Especially, Uvigerina spp. is often used to estimate the sea level changes and deep-sea circulations. However, it is difficult to analyze the isotopic compositions of individual foraminifera in the traditional analytical method, and thus the reliability of δ13C and δ18O of individual Uvigerina spp. as sea environmental proxy is still unclear. In this study, the isotopic compositions of individual U. akitaensis and U. ochotica were analyzed by using the micro-scale isotopic analytical system.
Surface sediment samples were collected from the four sites in the Sea of Okhotsk during cruise MR06-04 of R/V Mirai (JAMSTEC) in October 2006. Those samples were cut for each 1 cm (0-8cm below the seafloor) and used in this study. Then the living (Rose Bengal stained) individuals of U. akitaensis and U. ochotica from samples were analyzed by the micro-scale isotopic analytical system (Ishimura et al. 2008).
As a result, the isotopic dispersions of Uvigerina spp. indicated about < +/- 0.2 ‰ for both δ13C and δ18O in all sampling sites. In addition, isotopic values of Uvigerina spp. showed almost constant values in same species regardless of sediment depth, individual weight, and variation of shell structure. The observed homogeneous isotopic compositions of Uvigerina spp. were comparable with isotopic homogeneity and dispersions of NBS-19 (international isotopic standard). Therefore, we concluded that the individual Uvigerina spp. have highly reliable isotopic composition as sea environmental proxy. However, δ13C values represented about 0.7 ‰ differences between U. akitaensis and U. ochotica, thus we have to consider this δ13C difference in Uvigerina spp. when we reconstruct the past sea environment based on δ13C of Uvigerina spp.
Our main conclusion in this study is that the individual Uvigerina spp. have highly reliable stable isotopic compositions as sea environmental proxy.
Surface sediment samples were collected from the four sites in the Sea of Okhotsk during cruise MR06-04 of R/V Mirai (JAMSTEC) in October 2006. Those samples were cut for each 1 cm (0-8cm below the seafloor) and used in this study. Then the living (Rose Bengal stained) individuals of U. akitaensis and U. ochotica from samples were analyzed by the micro-scale isotopic analytical system (Ishimura et al. 2008).
As a result, the isotopic dispersions of Uvigerina spp. indicated about < +/- 0.2 ‰ for both δ13C and δ18O in all sampling sites. In addition, isotopic values of Uvigerina spp. showed almost constant values in same species regardless of sediment depth, individual weight, and variation of shell structure. The observed homogeneous isotopic compositions of Uvigerina spp. were comparable with isotopic homogeneity and dispersions of NBS-19 (international isotopic standard). Therefore, we concluded that the individual Uvigerina spp. have highly reliable isotopic composition as sea environmental proxy. However, δ13C values represented about 0.7 ‰ differences between U. akitaensis and U. ochotica, thus we have to consider this δ13C difference in Uvigerina spp. when we reconstruct the past sea environment based on δ13C of Uvigerina spp.
Our main conclusion in this study is that the individual Uvigerina spp. have highly reliable stable isotopic compositions as sea environmental proxy.