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Age–depth relationships are the key elements in paleoenvironmental studies to place proxy measurements into a temporal context. However, potential influencing factors of the available radiocarbon data and the associated modeling process can cause serious divergences of age–depth relationships from true chronologies, which is particularly challenging for paleolimnological studies in Arctic regions. This paper provides geoscientists with a tool-assisted approach to compare outputs from age–depth modeling systems and to strengthen the robustness of age–depth relationships. We primarily focused on the development of age determination data from a data collection of high-latitude lake systems (50 to 90∘ N, 55 sediment cores, and a total of 602 dating points). Our approach used five age–depth modeling systems (Bacon, Bchron, clam, hamstr, Undatable) that we linked through a multi-language Jupyter Notebook called LANDO (“Linked age and depth modeling”). Within LANDO we implemented a pipeline from data integration to model comparison to allow users to investigate the outputs of the modeling systems. In this paper, we focused on highlighting three different case studies: comparing multiple modeling systems for one sediment core with a continuously deposited succession of dating points (CS1), for one sediment core with scattered dating points (CS2), and for multiple sediment cores (CS3). For the first case study (CS1), we showed how we facilitate the output data from all modeling systems to create an ensemble age–depth model. In the special case of scattered dating points (CS2), we introduced an adapted method that uses independent proxy data to assess the performance of each modeling system in representing lithological changes. Based on this evaluation, we reproduced the characteristics of an existing age–depth model (Lake Ilirney, EN18208) without removing age determination data. For multiple sediment cores (CS3) we found that when considering the Pleistocene–Holocene transition, the main regime changes in sedimentation rates do not occur synchronously for all lakes. We linked this behavior to the uncertainty within the dating and modeling process, as well as the local variability in catchment settings affecting the accumulation rates of the sediment cores within the collection near the glacial–interglacial transition.

The PaleoLake Database contains available information on the lithostratigraphy, biostratigraphy and chronostratigraphy of bottom sediments from numerous lakes located on the East European Plain and nearby regions. The database includes results from more than 70 years of paleolimnological investigations, with information on deposits from 287 water bodies. The compiled data were published mainly in Russian and come from more than 145 monographs, journal articles, dissertations, abstracts, reports and other sources that were difficult to access by the broader science community.

The Holocene evolution of climate in easternmost Fennoscandia and adjoining regions is poorly known, compared with regions to the west. To address this, a 224-cm-long sediment core from Lake Medvedevskoe, situated on the Central Upland of the Karelian Isthmus, northwestern Russia, was examined to investigate variations in the Holocene climate. Analyses indicate that the dry and cold late Pleistocene climate was replaced by the warmer and more humid early Holocene climate after ca. 10.5 cal ka BP. During the early Holocene, the lake transitioned from an oligotrophic to a mesotrophic state, characterized by a “Corynocera ambigua/Microtendipes pedellus-type” phase, which has been found in other lakes across Fennoscandia. Taxonomic shifts in the chironomid and cladoceran communities associated with climatic amelioration were identified at ca. 10.6 and 9.17 cal ka BP using breakpoint analysis. Reconstructed July temperatures indicate climatic patterns comparable to those seen in eastern Fennoscandia. The warm period between ca. 9.5 and 5.5 cal ka BP (T July 14.5–15°C) was interrupted by a slight cooling between ca. 8.5 and 8.1 cal ka BP, possibly relating to the 8.2 event, with peak temperature reached at ca. 7.8 cal ka BP. Neoglacial cooling started after ca. 5.5 cal ka BP, the median reconstructed July temperature dropped to 2–3°C cooler than present (mean T July 13.5°C) before recovering in recent time.

Refined dating techniques and high-precision radiocarbon dating have enabled more accurate age controls for paleoenvironmental reconstruction of lake systems. However, low bioproductivity and the influence of old carbon have a profound impact on radiocarbon dating series of non-varved sediment records from Arctic lakes. Geochronological tools such as software systems for age-depth modeling provide sophisticated justifications for age-depth relationships. But because there are many different tools available with varying underlying mathematical methods and models, the model output can show diverging results, e.g., for problematic sediment cores with scatter age dating points. A detailed comparison of the results of individual modeling system is therefore often tedious and potentially error-prone. Due to time constraints and a lack of alternative options, users typically only select and apply one modeling system to provide a geochronological timeframe for paleoenvironmental interpretation. Therefore, we introduce our “Linked age and depth modeling” (LANDO) approach that links five modeling systems (Bacon, Bchron, clam, hamstr, Undatable) in a single multi-language Jupyter Notebook. LANDO reduces the effort of using established modeling systems for both single and multiple dating series and makes the results directly comparable. In addition, we introduce an ensemble age-depth model that uses the output from all models to create a data-driven, semi-informed age-depth relationship. In our talk we will highlight our adapted fuzzy change point method, in which we used independent proxy data to evaluate the performance of each modeling system in representing lithological changes. LANDO is already publicly available on GitHub: https://github.com/GPawi/LANDO.

The diatom oxygen isotope composition (δ18Odiatom) from lacustrine sediments helps tracing the hydrological and climate dynamics in individual lake catchments, and is generally linked to changes in temperature and δ18Olake. Lake Bolshoye Shchuchye (67°53′N; 66°19′ E; 186 m a.s.l) is the largest and deepest freshwater reservoir in the Polar Urals, Arctic Russia. The diatom oxygen isotope interpretation is supported by modern (isotope) hydrology, local bioindicators such as chironomids, isotope mass-balance modelling and a digital elevation model of the catchment. The Bolshoye Shchuchye δ18Odiatom record generally follows a decrease in summer insolation and the northern hemisphere (NH) temperature history. However, it displays exceptional, short-term variations exceeding 5‰, especially in Mid and Late Holocene. This centennial-scale variability occurs roughly contemporaneously with and similar in frequency to Holocene NH glacier advances. However, larger Holocene glacier advances in the Lake Bolshoye Shchuchye catchment are unknown and have not left any significant imprint on the lake sediment record. As Lake Bolshoye Shchuchye is deep and voluminous, about 30–50% of its volume needs to be exchanged with isotopically different water within decades to account for these shifts in the δ18Odiatom record. A plausible source of water with light isotope composition inflow is snow, known to be transported in surplus by snow redistribution from the windward to the leeward side of the Polar Urals. Here, we propose snow melt variability and associated influx changes being the dominant mechanism responsible for the observed short-term changes in the δ18Odiatom record. This is the first time such drastic, centennial-scale hydrological changes in a catchment have been identified in Holocene lacustrine diatom oxygen isotopes, which, for Lake Bolshoye Shchuchye, are interpreted as proxy for palaeo precipitation and, on millennial timescales, for summer temperatures.

The Kamchatka Peninsula (Russian Far East) remains among the least studied regions of eastern Asia. Recent studies revealed a high degree of palaeoenvironmental variability between different parts of the peninsula. We investigated semi-aquatic (chironomids) and terrestrial (leaf wax biomarkers) proxies from a sediment core collected from Lake Sokoch (southern Kamchatka) to provide reconstruction of the mean July air temperature and variations in limnic conditions. The lake formed after 10.0 cal. ka BP as a result of postglacial warming and was fed by glacial meltwaters from neighbouring glaciers. Our data show a later beginning of the Holocene thermal maximum (HTM) relative to more northern sites in Kamchatka, Siberia and Chukotka and support climate model experiments that suggest that the HTM was delayed in southern and central Kamchatka by about 2000 years compared with Alaska and NE Siberia. Warm conditions prevailed between 10.0 and 6.4 cal. ka BP with a short spell of cool and dry climate around 8.2 cal. ka BP that might be related to the 8.2 ka cooling event. The HTM took place between 6.5 and 3.4 cal. ka BP with the warmest phase from 6.0 to 5.0 cal. ka BP. An onset of Neoglacial cooling at 3.4 cal. ka BP is consistent with the strengthening of both the Siberian High and the Aleutian Low. Warming between 1.2 and 0.9 cal. ka BP can be attributed to the Mediaeval Climate Anomaly. The LIA cooling is related to another strengthening of the Siberian High and the Aleutian Low. The modern warming, though weakly traced in our record, is consistent with the recent meteorological observations. The presented palaeoenvironment record confirms the earlier findings of spatial differences within Kamchatka in timing and magnitude of the major Holocene climate fluctuations and contributes towards understanding the expression of Holocene climate change in Kamchatka.

A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format., Measurement(s)climateTechnology Type(s)digital curationFactor Type(s)temporal interval • geographic location • proxy typeSample Characteristic - Environmentclimate systemSample Characteristic - LocationEarth (planet) Machine-accessible metadata file describing the reported data: https://www.ncdc.noaa.gov/paleo/study/27330

Ground ice and sedimentary records of a pingo exposure reveal insights into Holocene permafrost, landscape and climate dynamics. Early to mid-Holocene thermokarst lake deposits contain rich floral and faunal paleoassemblages, which indicate lake shrinkage and decreasing summer temperatures (chironomid-based T-July) from 10.5 to 3.5 cal kyr BP with the warmest period between 10.5 and 8 cal kyr BP. Talik refreezing and pingo growth started about 3.5 cal kyr BP after disappearance of the lake. The isotopic composition of the pingo ice (delta O-18 - 17.1 +/- 0.6 parts per thousand, delta D -144.5 +/- 3.4 parts per thousand, slope 5.85, deuterium excess -7.7 +/- 1.5 parts per thousand) point to the initial stage of closed-system freezing captured in the record. A differing isotopic composition within the massive ice body was found (delta O-18 - 21.3 +/- 1.4 parts per thousand, delta D -165 +/- 11.5 parts per thousand, slope 8.13, deuterium excess 4.9 +/- 3.2 parts per thousand), probably related to the infill of dilation cracks by surface water with quasi-meteoric signature. Currently inactive syngenetic ice wedges formed in the thermokarst basin after lake drainage. The pingo preserves traces of permafrost response to climate variations in terms of ground-ice degradation (thermokarst) during the early and mid-Holocene, and aggradation (wedge-ice and pingo-ice growth) during the late Holocene.

This article presents a review of the current data on the level of paleolimnological knowledge about lakes in the Russian part of the northern Eurasia. The results of investigation of the northwestern European part of Russia as the best paleolimnologically studied sector of the Russian north is presented in detail. The conditions of lacustrine sedimentation at the boundary between the Late Pleistocene and Holocene and the role of different external factors in formation of their chemical composition, including active volcanic activity and possible large meteorite impacts, are also discussed. The results of major paleoclimatic and paleoecological reconstructions in northern Siberia are presented. Particular attention is given to the databases of abiotic and biotic parameters of lake ecosystems as an important basis for quantitative reconstructions of climatic and ecological changes in the Late Pleistocene and Holocene. Keywords: paleolimnology, lakes, bottom sediments, northern

Rapidly changing climate in the northern hemisphere and associated socio-economic impacts require reliable understanding of lake systems as important freshwater resources and sensitive sentinels of environmental changes. To better understand time-series data in lake sediment cores it is necessary to gain information on within-lake spatial variabilities of environmental indicator data. Therefore, we retrieved a set of 38 samples from the sediment surface along spatial habitat gradients in the boreal, deep, and yet pristine Lake Bolshoe Toko in southern Yakutia, Russia. Our methods comprise laboratory analyses of the sediments for multiple proxy parameters including diatom and chironomid taxonomy, oxygen isotopes from diatom silica, grain size distributions, elemental compositions (XRF), organic carbon contents, and mineralogy (XRD). We analysed the lake water for cations, anions and isotopes. Our results show that the diatom assemblages are strongly influenced by water depth and dominated by planktonic species, i.e. Pliocaenicus bolshetokoensis. Species richness and diversity is higher in the northern part of the lake basin, associated with the availability of benthic, i.e. periphytic, niches in shallower waters. δ18Odiatom values are higher in the deeper south-western part of the lake probably related to water temperature differences. The highest amount of the chironomid taxa underrepresented in the training set used for palaeoclimate inference was found close to the Utuk river and at southern littoral and profundal sites. Abiotic sediment components are not symmetrically distributed in the lake basin but vary along restricted areas of differential environmental forcings. Grain size and organic matter is mainly controlled by both, river input and water depth. Mineral (XRD) data distributions are influenced by the methamorphic lithology of the Stanovoy mountain range, while elements (XRF) are intermingled due to catchment and diagenetic differences. We conclude that the lake represents a suitable system for multiproxy environmental reconstruction based on diatoms (including oxygen isotopes), chironomids and sediment-geochemical parameters.

Results of a paleolimnological investigation of a well-dated lake sediment section from Shikotan Island (Southern Kurils) showed that from ca 8.0 to 5.8 cal ka BP a warm and humid period corresponding to middle Holocene optimum took place. Cooling thereafter corresponds to Neoglacial. A reconstructed from ca 0.9 to ca 0.58 cal ka BP warm period can correspond to a Medieval Warm Period. Cooling after 0.58 cal ka BP can be correlated with the LIA. Marine regression stages were identified at ca 6.2–5.9, 5.5– 5.1 and 1.07–0.36 cal ka BP. The general chronology of major climatic events of Holocene in the island is in accordance with the climate records from the North Pacific region. Revealed spatial differences in timing and magnitude of the Late Holocene climatic episodes (LIA, MWP) in the region needs further investigations.

The Serteyka River valley is one of the most important archaeological localities in North-Western Russia. The State Hermitage Museum has conducted research in Serteya since the 1970s. The pile-dwelling remnants located within the Great Serteya Palaeolake Basin (GSPB) are the most prominent excavation. The investigation using precise underwater techniques recovered many exceptional remains of the Neolithic settlement that were preserved below the groundwater level in biogenic deposits. The large-scale studies focused till now primarily on relicts of the human settlement and only scarce environmental data were available before the last decade. A broad environmental archaelogical project using cores of organic deposits has been conducted since 2016 in the framework of Polish-Russian cooperation. The 8 m long STIIa core from the deepest lake point has been investigated. It gives a full sequence of the lake history from the Late Valdai Glaciation to the Middle Ages. Multi-proxy analysis of the STIIa core aims at the reconstruction of regional and local habitat conditions (e.g. climate, hydrology, trophic state, water chemistry, and plant communities) at the lake side during the MIS1.

In this study, we attempted to reconstruction of level changes of the Baltic Sea in the Holocene based on investigation of more than 30 sediment cores from bottom sediments of three lakes located on the Karelian Isthmus. It is mostly that there were one phase of Ancylus transgression and two phases of Litorina transgression. The low content of individual halophilic species, indicate that the lake was only slightly affected by saline waters, therefore the level of the Baltic Sea at that time was about 12 m higher than the present one.

We investigated chironomid fauna of surface sediments and a short sediment core (Bol’shoy Kharbey Lake) from Pechora river basin, Northern Russia. Twenty three investigated lakes have thermokarst, glacial or floodplain origin and are characterised by low mineralization, mostly hydrocarbon-calcium type of water and low concentration of nutrients. Most of the lakes have circumneutral pH around ≤7 and only two lakes are slightly more acidic with pH ≤ 6. Ninety six chironomid taxa were identified in the surface sediments. Distribution of chironomids in the studied region is driven by continentality, mean TJuly and рН. Chironomid communities from the core of the B. Kharbei Lake demonstrate the highest similarity with the fauna of the deeper lakes of the glacial origin. The glacial lakes have the highest indices of continentality and the lowest winter temperatures within the investigated data set. The chironomid fauna of the glacial lakes is composed of the profundal, oligotrophic and cold-stenotherm taxa. The fauna of the floodplain and thermokarst lakes is more closely related to TJuly and is composed of littoral and phytophilic taxa of meso – or eutrophic waters and moderate temperature conditions. The fauna of the acidic thermokarst lakes considerably differs from the other lakes. Chironomid communities here are represented by tolerant to acidification taxa, and by the typically littoral and shallow water acid-tolerant taxa that apparently also can tolerate acidification. Studied sediment record covers ca last 200 years. The reconstructed TJuly during the entire period remain slightly below the modern temperatures. From 1970 reconstructed TJuly shows steady increase to the modern level. The reconstructed water depths (WDs) of the lake are higher than today till 1980. The highest WDs are reconstructed for ca 1970. After that the WDs gradually decrease to the modern level. Changes of the WDs are most probably related to changes in the precipitation rate.

Concentration and distribution of trace elements across the sequence of the Late Pleistocene sed� iments from the lake Medvedevskoye suggest the addition of materials other than those from a common source for the lake sediments of the region. The sediments of the lake Medvedevskoye carry some geochem� ical fingerprints which could be related the ET event that occurred at ca. 12.9 ka. Because such fingerprints are extremely subtle, the NW Russia can be considered to be the most remote eastern region of the extent of the Late Pleistocene airborne ET material. The sediments of the lake Medvedevskoye can also contain vol� canic material from the eruption of the Laacher See (Germany) volcano and probably from other Late Pleis� tocene volcanoes of Western Europe and/or Iceland.

The main objective of this study was to reconstruct and analyze changes in the natural and climatic conditions in the Karelian Isthmus over the Holocene. Bottom sediment samples from Lake Medvedevskoye were taken in the spring 2012. The sediments were AMS dated, and the datings were found to embrace the Late Glacial period and the entire Holocene. The integrated treatment of the bottom sediments included lithological, LOI and chironomid analyses. Based on the results of chironomid analysis, four stratigraphic zones were distinguished, and the natural environments corresponding to these zones were reconstructed.