Diatom assemblage as an indicator of bathymetry

概要

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Two diatom bathymetric indices are proposed as proxies of water depth in sea bottom. They are defined as follows: Bd1=Xp/(Xs+Xp) and Bd2=(0.5Xt+Xp)/(Xs+Xt+Xp), where Xs, Xt and Xp are frequencies of diatom species characteristic to shelf, transitional and pelagic regions, respectively. The diatoms characterizing shelf regions include benthic diatoms such as Paralia sulcata and Actinoptychus senarius with low-salinity meloplanktonic diatoms, whereas the diatoms typical of pelagic regions are oceanic planktonic species such as Neodenticula seminae and Denticulopsis spp. The transitional assemblage is composed of Thalassionema nitzschioides that has a maximum abundance in the transitional area between neritic and oceanic regions. Of the two indices, Bd1 is more sensitive to a change in bathymetry, but has more limitted applicablity in bathymetric range. These two indices are useful indicators of bathymetry not only in the Recent Bering Sea, but also in a Middle Miocene sequence of the Taga Group in Joban area of Japan, and thus they seem to be potentially of wide application.
日本堆積学会の論文