5:15 PM - 6:30 PM
[MIS17-P24] Comparison between fossil diatom assemblages and algal biomarkers in modern sediments from Seto Inland Sea.
Keywords:diatom assemblage, algal biomarker, modern sediment, coastal area, Seto Inland Sea, human-induced eutrophication
Diatomaceous species such as small Thalassiosira spp. and Neodelphyneis pelagica, which were reported by previous study (Hirose et al., 2008), are observed as the dominant taxa in all samples. The valve contents (valves / 1 g dry sediment) are higher in sediments from the Osaka Bay than Harima-nada Bay, indicating variations of their productivity. The vertical distribution of valve content show a increasing trend reflecting eutrophication in Harima-nada, on the other hand, it doesn’t show clear trend in Osak Bay. To the contrary, the concentrations of steroids (except dinoflagellate-derived dinosterols), which are synthesized in eukaryotic microalgae, are higher in Harima-nada Bay than Osaka Bay, and decrease toward the upper layers. Futhermore, highly branched isoprenoids (HBIs), which are biomarkers of specific diatom taxa, shows very similar distributions to those of fossil diatoms. These results suggest the effect of productivity of other algal taxa that are hardly preserved in the sediment as fossils, and the different process of diagenesis of diatom valves and organic molecules. We also discuss the detailed characteristics of each diatom taxa and biomarker molecules which are contained in specific taxa.
Yasuhara et al., 2007., Limnol. Oceano. 69, 225-239.
Hirose et al., 2008 The Quat. Res. (Daiyonki-Kenkyu; in Japanese). 47, 273-285.