Dinocyst microlaminations and freshwater "red tides" recorded in Lake Xiaolongwan,northeastern China |
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| Authors: | Guoqiang Chu Qing Sun Patrick Rioual Andrés Boltovskoy Qiang Liu Peiqi Sun Jintai Han Jiaqi Liu |
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| Institution: | (1) Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China;(2) National Research Center of Geoanalysis, Beijing, China;(3) Departamento Científico Ficología, Museo de La Plata, Paseo del Bosque, La Plata, 1900, Argentina;(4) Longwan National Natural Protection Bureau, Huinan, Jilin, 135102, China |
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| Abstract: | We reported a special type of lamination formed in the sediments of Lake Xiaolongwan, northeastern China. The lamination consists
of light- and brown-colored laminate couplets in the thin sections. The brown-colored layer is composed mainly of dinoflagellate
cysts. The grey-colored layer consists of other organic and siliceous matter (plant detritus, diatoms, chrysophyte cysts)
and clastics. Preliminary sediment trap results show that a distinct peak of dinocyst flux occurred in November. The dinocyst
flux maximum also corresponds to the peaks of diatom flux and chrysophyte stomatocyst flux. These suggest that "red tide blooms"
occur in this freshwater lake. We speculate that the dinocyst flux maximum could be related to autumn overturn due to increased
nutrients, and the availability of cysts for germination from the lake bottom. Additionally, it may also reflect increasing
dissolved organic matter after leaf fall. An independent chronology derived from 137Cs and 210Pb shows a good agreement with counted laminations. From the sediment trap data and the independent chronology data, the dinocyst
microlaminae appear to be annually laminated, and probably could be called dinocyst varves. Although vegetative (thecate stage)
cells of Peridinium volzii and Ceratium furcoides are found in the water samples, it is not possible to relate the dinocysts to these two dinoflagellate species. Based on
morphological and ecological analyses, we suggested that they have affinities with species of Peridinium (sensu lato), most probably to P. inconspicuum. Detailed investigations should be carried out to understand the red tide history in this freshwater lake. Annually laminated
dinocyst microlayers in freshwater and marine sediments not only provide an uncommon archive for understanding the history
of red tides and harmful algal blooms, and why and how certain species periodically bloom over several thousands years, but
also provide important records of paleoenvironmental and paleoclimatic changes at seasonal to annual resolution. |
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| Keywords: | Dinocyst microlamination Sediment trap Dinocyst flux Radiometric dating Red tide history |
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