Seasonal deposition processes and chronology of a varved Holocene lake sediment record from Lake Chatyr Kol (Kyrgyz Republic)

A finely laminated lake sediment record with a basal age of 11,619 ± 603 years BP was retrieved from Lake Chatyr Kol (Kyrgyz Republic). Microfacies analysis reveals the presence of seasonal laminae (varves) from the sediment basis to ~ 360 ± 40 years BP. The Chatvd19 floating varve chronology covers the time span from 360 ± 40 years BP to the base and relies on replicate varve counts on overlapping petrographic thin sections with an uncertainty of ± 5 %. The uppermost non-varved interval was chronologically constrained by 210Pb and 137Cs γ-spectrometry and interpolation based on varve thickness measurements of adjacent varved intervals with an assumed uncertainty of 10 %. Six varve types were distinguished, are described in detail and show a changing predominance of clastic-organic, clastic-calcitic or -aragonitic, calcitic-clastic, organic-clastic and clastic-diatom varves throughout the Holocene. Variations in varve thickness and the number and composition of seasonal sublayers are attributed to 1) changes in the amount of summer or winter/spring precipitation affecting local runoff and erosion and/or to 2) evaporative conditions during summer. Radiocarbon dating of bulk organic matter, daphnia remains, aquatic plant remains and Ruppia maritima seeds reveal reservoir ages with a clear decreasing trend up core from ~ 6,150 years in the early Holocene, to ~ 3,000 years in the mid-Holocene, to ~ 1,000 years and less in the late Holocene and modern times. In contrast, two radiocarbon dates from terrestrial plant remains are in good agreement with the varve-based chronology

Mass balance observations and reconstruction for Batysh Sook Glacier, Tien Shan, from 2004 to 2016

In this study we present an analysis of measured annual mass balances for the period 2011 to 2016 and a reconstruction of seasonal mass balances from 2004 to 2010 for Batysh Sook Glacier located in the Kyrgyz Tien Shan. Conventional methods and a model-based extrapolation of the point measurements were used to obtain glacier- wide mass balances and to analyze glaciological measurements. Especially at the beginning of the re-established glacier mass balance monitoring program, deviations between the different methods were significant, having a range of 0.40 m w.e. a− 1. With the improvement of the measurement network in later years, the results of the different extrapolation methods showed better agreement (range of 0.10 to 0.22 m w.e. a− 1). For 2011 to 2016, the profile method revealed a mass loss of − 0.41 ± 28 m w.e. a− 1. The contour line method yielded a negative mean mass balance of − 0.34 ± 20 m w.e a− 1, whereas the model-based extrapolation clearly resulted in the most negative value of − 0.43 ± 16 m w.e. a− 1 for the same period.The same distributed accumulation and temperature index melt model used to extrapolate point measurements from 2011 to 2016 was applied in order to reconstruct the mass balance from 2004 to 2010. The model was driven by daily air temperature and precipitation data from a nearby meteorological station and the model parameters were calibrated with in-situ measurements of annual mass balances collected from 2011 to 2016. Winter accumulation measurements taken in May 2014 were used for calibration purposes and to deduce snow distribution patterns. Subseasonal model performance was validated based on the snow cover depletion pattern observed on satellite images during the summer months from 2004 to 2016. For Batysh Sook Glacier an average annual mass balance of − 0.39 ± 0.26 m w.e. a− 1 was found for the period 2003/04 to 2015/16

Re-analysis of seasonal mass balance at Abramov glacier 1968–2014

Abramov glacier, located in the Pamir Alay, Kyrgyzstan, is a reference glacier within the Global Terrestrial Network for Glaciers. Long-term glaciological measurements exist from 1968 to 1998 and a mass-balance monitoring programme was re-established in 2011. In this study we re-analyse existing mass-balance data and use a spatially distributed mass-balance model to provide continuous seasonal time series of glacier mass balance covering the period 1968–2014. The model is calibrated to seasonal mass-balance surveys and then applied to the period with no measurements. Validation and recalibration is carried out using snowline observations derived from satellite imagery and, after 2011, also from automatic terrestrial camera images. We combine direct measurements, remote observations and modelling. The results are compared to geodetic glacier volume change over the past decade and to a ground-penetrating radar survey in the accumulation zone resolving several layers of accumulation. Previously published geodetic mass budget estimates for Abramov glacier suggest a close-to-zero mass balance for the past decade, which contradicts our results. We find a low plausibility for equilibrium conditions over the past 15 years. Instead, we suggest that the glacier's sensitivity to increased summer air temperature is decisive for the substantial mass loss during the past decade

Mass-balance reconstruction for Glacier No. 354, Tien Shan, from 2003 to 2014

This study presents a reconstruction of the seasonal mass balance of Glacier No. 354, located in the Akshiirak range, Kyrgyzstan, from 2003 to 2014. We use a distributed accumulation and temperature-index melt model driven by daily air temperature and precipitation from a nearby meteorological station. The model is calibrated with in situ measurements of the annual mass balance collected from 2011 to 2014. The snow-cover depletion pattern observed using satellite imagery provides additional information on the dynamics of mass change throughout the melting season. Two digital elevation models derived from high-resolution satellite stereo images acquired in 2003 and 2012 are used to calculate glacier volume change for the corresponding period. The geodetic mass change thus derived is used to validate the modelled cumulative glacier-wide balance. For the period 2003–12 we find a cumulative mass balance of –0.40±10mw.e.a-1. This result agrees well with the geodetic balance of –0.48±0.07mw.e.a-1over the same period

Precipitation in the mountains of Central Asia: isotopic composition and source regions

Over 900 event-based precipitation samples were collected in 2019–2021 in the Tien Shan and its foothills and analysed using cavity ring-down spectroscopy. δD and δ18O values were highest in summer and lowest in winter, and annual cycles of deuterium excess (d-excess) varied between sites, reflecting local conditions. The δ18O and δD values increased from north to south in all seasons except autumn, and latitude was a statistically significant predictor of δ 18O and δD in the overall data set, along with elevation in winter and elevation and longitude in autumn. Elevation was a significant predictor of d-excess in all seasons, and local air temperature was a more important control over δ 18O and δD than precipitation depth. Local meteoric water lines were derived using seven regression methods applied to non-weighted and weighted precipitation. Non-weighted ordinary least squares regression and reduced major axis regression methods are recommended overall, except for summer when the precipitation-weighted least squares regression should be used, particularly in the south. Atmospheric back-trajectory and mixing-model analyses were applied in combination to identify air mass source regions and their relative contribution to precipitation. Recycled moisture from irrigated land in the Amu Darya and Syr Darya basins and from the study catchments accounted for 29 %–71 % of precipitation, depending on the site and season. In the Chon Kyzyl-Suu catchment, local re-evaporation from Issyk-Kul accounted for up to 85 % of precipitation. These findings highlight the importance of moisture from terrestrial sources, especially irrigated land, for the formation of precipitation in the Tien Shan

Age model and microfacies analysis results obtained from microscopic analysis of overlapping petrographic thin sections of composite sequence CHAT12 from Chatyr Kol Lake, Kyrgyzstan

This dataset comprises the Chatvd19 age model and the microfacies analysis results of the Chatyr Kol Lake sedimentary composite profile. The composite profile relies on parallel piston cores, which were retrieved in 2012 with an UWITEC piston corer from the deepest part of the lake (~20m) (Kalanke et al., 2019). Analysis have been performed at the GFZ German Research Centre for Geosciences in Potsdam, Germany. The dataset "Age model and replicate varve counts of composite profile CHAT12 from Chatyr Kol Lake, Kyrgyzstan" contains the Age model with the composite depth, interpolated based varve thicknesses (column B), the age model and varve counting uncertainty estimates. The age model is based on the results of replicate varve counts, which were performed on overlapping large-scale petrographic thin sections along the whole composite profile from 63.0 to 623.5 cm depth. Thin section preparation followed the method described by Brauer and Casanova (2001) and included freeze-drying and vacuum impregnation of the sediment slabs with Araldite epoxy resin. Microfacies analysis was carried out on a Zeiss Axioplan microscope using different magnifications (25-400 x). The dataset "Microfacies analysis of thin sections including distribution of microfacies (varve) types and thicknesses, varve characteristics and semi-quantitative species abundances of composite profile CHAT12 from Chatyr Kol Lake, Kyrgyzstan" displays the results of the microfacies analysis, including the varve thicknesses, the distribution of observed microfacies (varve) types and thicknesses, the varve quality index and its distribution and the semi-quantitative analysis of species abundances. Species abundances were classified according to their low (=1), middle (=2) and high (=3) abundances. The dataset "Varve thickness measurements of discontinuous varves between 63.0 and 41.9 cm composite depth of composite profile CHAT12 from Chatyr Kol Lake, Kyrgyzstan" displays varve thickness measurements of discontinuous varves between 63.0 and 41.0 cm composite depth, which were i.a. used for interpolation of the upper homogenous sediments (0-63.0 cm depth)