Abstract. Detailed studies of processes of sediment record formation are necessary for accurate sediment-derived paleo-environmental reconstructions. We conducted the multi-year seasonal sediment evolution of sediment fluxes of chemical elements, organic and inorganic carbon, total nitrogen, and photosynthetic pigments for a period from 2012 to 2017. In 2013, 2016, 2017, and 2018, we estimated the contents of photosynthetic pigments in the uppermost sediment layers frozen in situ with a freeze-corer. In 2015 and 2016, a rare event of transition from meromixis (i.e. long-term hypolimnetic anoxia) to holomixis was observed, which was accompanied by the temporary disappearance of hydrogen sulfide from the water column in spring and a decrease in hydrogen sulfide in other seasons compared to the meromictic state. We have demonstrated that okenone and Mo in the Lake Shira sediments reflect the presence of hydrogen sulfide in the water column. However, the okenone showed smoothened multi-year dynamics without a pronounced seasonal one. Therefore, the okenone can be a proxy of sulphidic conditions in photic zone and weakly depend on seasons whereas Mo can be used as an indicator of winter periods when analyzed in cores with annual resolution. Sedimentation fluxes of other substances showed typical seasonal dynamics with a minimum in winter and a maximum in late summer and autumn. All chemical elements in the sedimentation flow can be roughly divided into those associated with organic matter and terrigenous-chemogenous. The components of the second group showed a pronounced peak of sedimentation in autumn 2012 and summer 2017 presumably due to the increased amount of precipitation at that time. This demonstrates the relationship between the terrigenous components and the climate humidity for this lake. Besides, it reflects the irregularity of annual varves composition.

Abstract. Microscopic analysis of the core from the bottom sediments of Lake Shira (southern Siberia, Khakassia, Russia), have shown that for the last 100 years the sedimentation flux of charcoal particles sharply increased. This increase is consistent with the results for many lakes in the world and is presumably due to the current increase in anthropogenic impact, both in the form of accidental and deliberate arson, and in the form of burning wood and coal for heating residential buildings and recreation in the area adjacent to the lake. A flux of charcoal particles >100 m into Lake Shira was estimated base on sedimentation traps in 2012-2019. It was shown that the particle flux increasing from October to May, which can be explained by two factors: the burning of fuel from surrounding villages at cold time and fires of steppe in April-May. During the warm season, this flow are significantly decreased, therefore, a impact of campfires is likely minor compare to village sources. Our data show a significant contribution of anthropogenic factors to the flow of coal particles from burning fuel and spring fires.