AUTHOR=Matsuoka Kazumi , Kojima Natsuhiko , Kuwae Michinobu 

TITLE=Marine Environmental Change Induced by Anthropogenic Activities – From a Viewpoint of Aquatic Palynomorph Assemblages Preserved in Sediment Cores of Beppu Bay, West Japan

JOURNAL=Frontiers in Marine Science

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.843824

DOI=10.3389/fmars.2022.843824

ISSN=2296-7745

ABSTRACT=<p>Stratigraphic cluster analysis using aquatic palynomorphs preserved in the core sediments revealed a rapid eutrophication due to anthropogenic activities from the mid 1960s in Beppu Bay, East Kyushu, Japan. These assemblages were divided into three major units: BP-I, BP-II and BP-III, and also only dinoflagellate cyst assemblages were divided into the following four units in Beppu Bay: BP-A, BP-B, BP-C, and BP-D. Unit boundaries based on aquatic palynomorphs and dinoflagellate cysts were different except in the upper part, BP-III and BP-D, both of which clearly indicated anthropogenic eutrophication in both sea water and bottom sediments. On the other hand, in dinoflagellate cyst assemblages, Unit BP-A was characterized by stable occurrence of <italic>Spiniferites bulloideus</italic> and <italic>Spiniferites hyperacanthus, Lingulodinium machaerophorum</italic> of Gonyaulacales, and reduction of heterotrophic Peridinioid <italic>Brigantedinium</italic> spp. In Unit BP-C there was a clear decrease of <italic>L. machaerophorum.</italic> Unit BP-B was characterized by decreases of <italic>S. bulloideus</italic>, <italic>S. hyperacanthus</italic>, and <italic>L. machaerophorum</italic>, and little increase of <italic>Spniferites bentori.</italic> Unit BP-C was characterized by an increase in <italic>S. bulloideus</italic> and heterotrophic Peridinioid <italic>Echinidinium</italic> spp. Unit BP-D was subdivided into Subunit BP-D1 where dinoflagellate cysts showed a marked increase in <italic>S. bulloideus</italic> accompanied by the appearance of <italic>L. machaerophorum</italic> and <italic>Tuberculodinium vancampoae</italic>, and Subunit PB-D2 where there was a decrease of total dinoflagellate cysts. From the dinoflagellate cyst assemblages, the marine environment of the period of BP-A Unit was suggested to be warm and stable. However, <italic>L. machaerophorum</italic> started to decrease in BP-B. The clear decrease of <italic>L. machaerophorum</italic> suggest that the marine environment became cooler than that of Unit BP-A. Significant increases of <italic>S. bulloideus, S. hypearcanthus, L. machaerophorum, T. vancampoae, Brigantedinium</italic> spp., and <italic>Polykrikos kofoidii</italic> were characteristic of Unit BP-D. The increase in total dinoflagellate cyst density and the increase of the ratio of heterotrophic dinoflagellate cysts in Subunit BP-D1 are manifestations of the Oslo fjord Signal and Heterotroph Signal, respectively. In addition, the decrease in microforaminiferal lining that continued from Unit BP-C to Unit BP-D might indicate deterioration of the bottom sediment environment.</p>