Preglacial environments in Lake Ladoga, the largest European lake, located within the limits of the Scandinavian glaciations, are very poorly investigated compared to postglacial ones. They were primarily reconstructed based on the studies of terrestrial boreholes and outcrops, often incomplete and poorly dated. Previous diatom studies established that during the Eemian marine transgression, the Ladoga basin became a part of the marine Baltic-White Sea connection. However, the environments established in Lake Ladoga after the regression of the Eemian Sea are not known. This article discusses the first Early Weichselian (MIS5, ~ 118–80 ka) diatom record in Lake Ladoga obtained within the frame of the Russian-German research project PLOT. Low concentrations and selective preservation of diatoms in the preglacial sediments point to unstable high-energy environments. The presence of marine diatoms is thought to result from reworking of marine Eemian sediments, rather than direct marine influence. We argue that post-Eemian environments in Lake Ladoga were neither marine nor glaciolacustrine, as previously suggested. The Early Weichselian diatom record formed in a shallow-water part of a lake affected by inflowing streams transporting large amounts of eroded material. No analogues of the preglacial environments can be found in the postglacial Lake Ladoga. Our record demonstrates close similarity to other Early Weichselian diatom records in the Ladoga region suggesting their formation under the same conditions. Similar trends in concentrations of diatoms, diatom fragments and other siliceous microfossils reflect changing sediment supply, hydrodynamics or reworking intensity. Their lower values ~ 118–113 and ~ 90–80 ka could reflect the Early Weichselian cooling stages, while their increase between ~ 113 and 90 ka might indicate enhanced erosion intensity and increased sediment supply corresponding to the climate amelioration.

中文翻译：

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拉多加湖的第一个冰前硅藻记录：长期海洋影响还是再沉积故事？

与冰后环境相比，位于斯堪的纳维亚冰川范围内的欧洲最大湖泊拉多加湖的冰前环境研究很少。它们主要是基于对陆地钻孔和露头的研究而重建的，这些研究通常不完整且年代久远。先前的硅藻研究表明，在伊米亚海侵期间，拉多加盆地成为波罗的海-白海海洋连接的一部分。然而，埃米安海回归后在拉多加湖建立的环境尚不清楚。本文讨论了在俄罗斯-德国研究项目 PLOT 框架内在拉多加湖中获得的第一个早期 Weichselian (MIS5, ~ 118–80 ka) 硅藻记录。冰前沉积物中硅藻的低浓度和选择性保存表明不稳定的高能​​环境。海洋硅藻的存在被认为是海洋伊米亚沉积物再加工的结果，而不是直接的海洋影响。我们认为拉多加湖的后伊米亚环境既不是海洋也不是冰川，如前所述。早期Weichselian 硅藻记录形成于受流入河流影响的湖泊浅水部分，该部分受到输送大量侵蚀物质的影响。在冰后拉多加湖中找不到与冰前环境类似的环境。我们的记录与拉多加地区的其他早期魏克塞尔硅藻记录非常相似，表明它们是在相同条件下形成的。硅藻浓度的类似趋势，硅藻碎片和其他硅质微化石反映了沉积物供应、流体动力学或再加工强度的变化。它们的较低值~118-113 和~90-80 ka 可以反映早期Weichselian 冷却阶段，而它们在~113 和90 ka 之间的增加可能表明与气候改善相对应的侵蚀强度增强和沉积物供应增加。