Lake paleoenvironment indicated by sedimentary photosynthetic pigments

1. 最近~ 25000年贝加尔湖和Hovsgol沉积物岩心浮游植物（藻类）光合色素剖面揭示了末次冰期/后冰期湖泊初级生产力的增加。贝加尔湖中部BDP98岩心0 ~ 200 m段沉积物中，来源于叶绿素（Chls）的Steryl chlorin酯（SCEs）实际上是唯一的沉积色素群，代表了最近5 Ma。因此，藻类中常见的Chl - a衍生的sce a可以作为湖泊初级生产的长期趋势指标，而Chl - b衍生的sce b表示绿藻和C_<30>-甾醇- sce a鞭毛虫。sce极小期与偶数海洋氧同位素期（MIS），即北半球冰盖发育期相对应。因此，全球气候变化已成为控制该湖泊藻类生产力的主要因素。绿藻和鞭毛藻相对丰度较大的时期对应于该地区第一次（260 Ma）和第二次（150 Ma）降温时期。在实验室中，从以藻类为食的甲壳类动物排出的粪便颗粒中发现了SCE的组成，这为沉积SCE的组成提供了关键信息。在哈马纳湖中部近250年的沉积物岩心中，除了藻类光合色素外，还发现了生活在缺氧水中的硫细菌，表明缺氧在这一时期发生过。紫硫菌在20世纪30年代末的增殖期与文献报道一致。由颜料和钼所显示的缺氧水层的发展趋势，受到今口水道修建训练墙导致海水入湖增加的强烈影响。

1. Profiles of photosynthetic pigments of phytoplankton (algae) in sediment cores of Lake Baikal and Hovsgol representing the last 〜25,000 years revealed increase in the lake primary productivity through the last glacial/post glacial transition.2. Steryl chlorin esters (SCEs) derived from chlorophylls (Chls) were shown to be actually a sole group of the sedimentary pigments in the 0-200 m portion of a long sediment core from central Lake Baikal, the BDP98 core, representing the last 5 Ma. Thus SCEs a derived from Chl a common in algae serves as an indicator of long-term trend of primary production in the lake, while SCEs b derived from Chl b indicates green algae and C_<30>-sterol-SCE a dinoflagellates. The periods of SCEs a minima well correspond to those of even-numbered marine oxygen isotope stage (MIS), that is, those of ice-sheet development in the northern hemisphere. Accordingly, global climate changes have been a primary factor controlling the algal productivity in the lake. The periods when relative abundance of green algae and dinoflagellates were large correspond to the first (260 Ma) and second (150 Ma) cooling periods of this region.3. SCE composition found in fecal pellets egested from crustaceans fed on algae in laboratory gave key information on the composition of sedimentary SCEs.4. In a sediment cores obtained from central Lake Hamana, which represents the last 〜250 years, in addition to the algal photosynthetic pigments, those of sulfur bacteria live in anoxic water were found, indicating the occurrence of anoxia through the period. The period of indicated proliferation of purple sulfur bacteria in the late 1930s is consistent with that reported in literatures. The trend in the development of anoxic water layers indicated by the pigments and Mo is strongly influenced by the training wall constructed at the Imagireguchi channel causing increase of the seawater intrusion into the lake.