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.

Detailed studies of processes of sediment record formation are necessary for accurate sediment-derived paleo-environmental reconstructions. In order to understand the formation of sediments in meromictic Lake Shira (southern Siberia, Russia), we conducted the multi-year seasonal sediment trap study of sediment uxes of chemical elements, organic and inorganic carbon, total nitrogen, and photosynthetic pigments for a period from 2012 to . In parallel, in 2013, we estimated the contents of photosynthetic pigments in 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 sul de from the water column in spring and a decrease in hydrogen sul de in other seasons compared to the meromictic state. Using the freeze-corer, we observed that sediment structure changed from laminated to homogeneous after holomixis. The content of algal photosynthetic pigments slightly increased in uppermost sediments in 2017 and 2018, which was probably caused by an increase in lake primary production resulting from the release of nutrients during the mixing events in 2015 and 2016. The content of okenone, a speci c carotenoid of purple sulfur bacteria, decreased during the holomictic state both in traps and in uppermost sediments and did not considerably increase two years after the meromixis restoration. The sedimentation ux of molybdenum re ected the seasonality of hydrogen sul de content in the water column, and it was maximal in winter, in contrast to all other sediment components. Other components re ected the seasonality of organic production and terrigenous inputs, with the maximum in late summer and autumn. An increase in the sedimentation rate of terrigenous elements in the autumn of 2012 was supposedly caused by the anomalous amount of atmospheric precipitation in August 2012. Since detailed inter-annual observations of sedimentation processes are not often found in limnology, we hope that our results will be useful for reconstructing regional climate and, further, for understanding the dynamics of strati ed temperate water bodies.