3:15 PM - 3:30 PM
[AOS23-05] Stable isotope study using Fe: implication to understand the Fe-biocycles in marine environment
Keywords:stable isotope of iron, iron biocycle, marine organisms, multiple collector-ICP-mass spectrometry, trophic level
In this presentation, Peponocephala electra (n=23; TL=4.3), Thunnus alalunga (n=7; TL=4.0), Thunnus obesus (n=1; TL=4.0), Kajikia audax (n=1; TL=4.0), Berryteuthis magister (n=5; TL=3.4), and Octopus longispadiceus (n=2; TL=3.3) were subsidized to the Fe isotope ratio analysis. After the chemical decomposition and chemical separation procedures, the 56Fe/54Fe and 57Fe/54Fe ratios were measured by the multiple collector-ICP-mass spectrometer (MC-ICP-MS). The measured 56Fe/54Fe and 57Fe/54Fe ratios varied significantly from those for lower trophic level organisms. Several important features of the Fe isotopes for marine organisms could be derived from the present results. The changes in the 56Fe/54Fe isotopes could be explained either by the poor intake efficiency of Fe from the dietary foods, or by the changing chemical form of Fe in the dietary foods for the marine organisms of higher trophic levels. If in the case that the Fe was adsorbed as a heme-Fe (Fe(II)) from the dietary foods, the magnitude of the isotope fractionation would be smaller than that found in adsorption of non-heme Fe (e.g., Fe (III)). This suggests that the major source of Fe for higher trophic animals would be non-heme Fe. Another possible cause of changes in the 56Fe/54Fe ratio would be originating from the definition of the trophic level of the marine organisms. This suggests that the food-chain for the inorganic nutrients should be defined by the separate definitions. The details of the mechanism in the variation of the 56Fe/54Fe ratios for the marine organisms will be discussed in this presentation.