Description: Oxygen isotopes in biogenic silica (δ18OBSi) from lake sediments allow for quantitative reconstruction of past hydroclimate and proxy-model comparison in terrestrial environments. The signals of individual records have been attributed to different factors, such as air temperature (Tair), atmospheric circulation patterns, hydrological changes, and lake evaporation. While every lake has its own local set of drivers of δ18O variability, here we explore the extent to which regional or even global signals emerge from a series of paleoenvironmental records. This study provides a comprehensive compilation and combined statistical evaluation of the existing lake sediment δ18OBSi records, largely missing in other summary publications (i.e. PAGES network). For this purpose, we have identified and compiled 71 down-core records published to date and complemented these datasets with additional lake basin parameters (e.g. lake water residence time and catchment size) to best characterize the signal properties. Records feature widely different temporal coverage and resolution, ranging from decadal-scale records covering the past 150 years to records with multi-millennial-scale resolution spanning glacial–interglacial cycles. The best coverage in number of records (N = 37) and data points (N = 2112) is available for Northern Hemispheric (NH) extratropical regions throughout the Holocene (roughly corresponding to Marine Isotope Stage 1; MIS 1). To address the different variabilities and temporal offsets, records were brought to a common temporal resolution by binning and subsequently filtered for hydrologically open lakes with lake water residence times 〈 100 years. For mid- to high-latitude (〉 45° N) lakes, we find common δ18OBSi patterns among the lake records during both the Holocene and Common Era (CE). These include maxima and minima corresponding to known climate episodes, such as the Holocene Thermal Maximum (HTM), Neoglacial Cooling, Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). These patterns are in line with long-term air temperature changes supported by previously published climate reconstructions from other archives, as well as Holocene summer insolation changes. In conclusion, oxygen isotope records from NH extratropical lake sediments feature a common climate signal at centennial (for CE) and millennial (for Holocene) timescales despite stemming from different lakes in different geographic locations and hence constitute a valuable proxy for past climate reconstructions.

Description: Isotope records are crucial for proxy-model comparison in paleoclimatology because of their advantage of being directly comparable with isotope-enabled paleoclimate model outputs. Oxygen isotopes (δ18O) are commonly measured on carbonates (i.e. ostracods, authigenic carbonates) and biogenic silica (mainly diatoms). Oxygen isotopes in lacustrine carbonates (δ18OCaCO3) have been studied extensively for several decades, yet they are subject to complex species-dependent fractionation processes and not available globally. Lacustrine oxygen isotope records from biogenic silica (δ18OBSi), on the other hand, likely do not display species-dependent fractionation effects (or only very minor) and offer insight even in data-sparse regions devoid of carbonates, such as the Arctic. To date, more than 70 lacustrine δ18OBSi records have been published. These case studies have been complemented with additional efforts addressing climatic and hydrological backgrounds, laboratory techniques and possible species-dependent fractionation as well as deposition and dissolution effects. Here, we present the first comprehensive review and global compilation of lacustrine δ18OBSi records, with explicit regard to their individual lake basin parameters. With this work, we aim at contributing to bridging the gap between modelling and isotope geochemistry approaches regarding terrestrial archives in paleoclimatology. Departing from hitherto prevalent case studies, we assess what we can learn from lacustrine δ18OBSi records globally, considering lake basin characteristics, spatial and temporal coverage as well as hydrological background information. This improves both the usability of δ18OBSi for proxy-model comparison and our understanding of the general constraints for interpreting lacustrine δ18OBSi records.

Description: Lake sediments constitute important terrestrial archives of past climate and environments. While different kinds of proxy data can be obtained from these sediments, oxygen isotopes (δ18O) are of particular interest in paleoclimatology. They record changes of climate and hydrology in a quantitative way. Commonly, δ18O is measured on carbonates (i.e. ostracods) and biogenic silica (mainly diatoms). While oxygen isotopes in lacustrine carbonates (δ18OCaCO3) have been studied extensively for several decades, they are subject to complex species-dependent fractionation processes and not available globally. Lacustrine oxygen isotope records from biogenic silica (δ18OBSi), on the other hand, likely do not display species-dependent fractionation effects (or only very minor) and offer insight even in data-sparse regions devoid of carbonates, such as the Arctic. More than 40 lacustrine δ18OBSi records from mid- and high-latitude regions of the northern hemisphere have been published to date. Interpreting case studies of δ18OBSi, however, is challenging due to a complex interplay of climatic and hydrological factors. Therefore, these individual case studies have been complemented with additional efforts addressing climatic and hydrological backgrounds, laboratory techniques, possible species-dependent fractionation as well as deposition and dissolution effects. Here, we combine records from sites across northern Eurasia and North America to a circum-arctic stack in order to infer common underlying trends throughout the Holocene. With this work, we aim at providing new insight on the variability of Holocene hydroclimate as well as on the interplay between lacustrine archives and the δ18O-proxy. This improves both the usability of δ18OBSi for proxy-model comparison and our understanding of the general constraints for interpreting lacustrine δ18OBSi records

Description: Diatom oxygen isotopes (δ18Odiatom) from lacustrine sediments have proven to be reliable proxies to trace the hydrological and climate dynamics in the catchment of a respective lake, and are generally linked to the temperature and the water isotope composition (δ18Olake). These background conditions may vary over time constrained by the individual hydrological changes in a given climate field. Diatom oxygen isotopes are excellent recorders of these changes, especially in high-latitudes where carbonates are widely absent, and have been linked to changes in the individual hydrological characteristics in the catchment, such as: (1) air temperature, (2) air-mass contributions, (3) inflow changes, (4) evaporation rates and (5) glacial meltwater influx. In general, the corresponding diatom isotope-based hydroclimate records show a ~5‰ variability over the Holocene and are rather smooth depending on the residence time and turn-over rate of each lake. Lake Bolshoye Shchuchye (67°53’N; 66°19’ E; 187 m a.s.l) is the largest and deepest freshwater lake located in the Polar Urals, Arctic Russia. Its δ18Odiatom record generally follows a decrease in summer insolation, in line with the northern hemisphere (NH) temperature history. However, Lake Bolshoye Shchuchye is exceptional, as short-term, centennial-scale changes of 5-7‰ are notable in the δ18Odiatom values. As most of these minima and maxima are confirmed by more than one data point, and were measured twice, these are no methodological artefacts. The question arises why these extremes occur and what could be the responsible mechanism(s) behind this short-term variability. The recent isotope geochemical background helps setting Lake Bolshoye Shchuchye in its recent hydrological context as a well-mixed monomictic lake, covered more than half of the year by ice, implying negligible evaporative effects. As a deep and voluminous lake, ca. 30-50% of the water of Lake Bolshoye Shchuchye need to be exchanged with isotopically light water within short time to account for these 5‰-isotopic shifts in δ18Odiatom. These changes occur in the Holocene, contemporaneous with and similar to NH glacier advances (Nesje, 2009). However, potential Holocene glacier advances in the Lake Bolshoye Shchuchye catchment are not known and have left no significant imprint on the lakes’ sediment biogeochemistry. Accordingly, the only other source of light isotope composition is snow, known to be transported in significant quantities and with large variability to the leeward side of the Polar Urals (Mangerud et al., 2008). Hence, we hypothesize snow being the dominant agent responsible for the observed short-term changes in the δ18Odiatom record. To our understanding, this is the first time such drastic hydrological changes have been documented for a lacustrine diatom oxygen isotope record.

Description: 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.

Description: Transient simulations of the global fully coupled climate model COSMOS under realistic varying orbital and greenhouse gas forcings are systematically compared to diatom oxygen isotope (δ18O_diatom ) records from Russian lakes with focus on Eurasian Holocene climate trends. The measured δ18O_diatom decrease and other temperature proxies are interpreted as large‐scale cooling throughout the Holocene while the model simulations are biased too warm, likely through missing radiative forcings. This large‐scale warm bias also dictates the modeled δ18O_precipitation. Hence, at locations where the signs of model and proxy temperature/precipitation trends agree, measured δ18O_diatom and modeled δ18O_precipitation trends show notable accordance. An increased temporal variability of modeled δ18O_precipitation is linked to persistent atmospheric circulation patterns. Applying the transient forcings in an accelerated way (every 10th year only) yields a similar, yet weaker or delayed model response, especially in the ocean.

Description: Oxygen isotopes in biogenic silica (δ18OBSi) from lake sediments allow for quantitative reconstruction of past hydroclimate and proxy-model comparison in terrestrial environments. The signals of individual records have been attributed to different factors, such as air temperature (Tair), atmospheric circulation patterns, hydrological changes, and lake evaporation. While every lake has its own local set of drivers of δ18O variability, here we explore the extent to which regional or even global signals emerge from a series of paleoenvironmental records. This study provides a comprehensive compilation and combined statistical evaluation of the existing lake sediment δ18OBSi records, largely missing in other summary publications (i.e. PAGES network). For this purpose, we have identified and compiled 71 down-core records published to date and complemented these datasets with additional lake basin parameters (e.g. lake water residence time and catchment size) to best characterize the signal properties. Records feature widely different temporal coverage and resolution, ranging from decadal-scale records covering the past 150 years to records with multi-millennial-scale resolution spanning glacial-interglacial cycles. The best coverage in number of records (NCombining double low line37) and data points (NCombining double low line2112) is available for Northern Hemispheric (NH) extratropical regions throughout the Holocene (roughly corresponding to Marine Isotope Stage 1; MIS 1). To address the different variabilities and temporal offsets, records were brought to a common temporal resolution by binning and subsequently filtered for hydrologically open lakes with lake water residence times 〈100 years. For mid- to high-latitude (〉45°N) lakes, we find common δ18OBSi patterns among the lake records during both the Holocene and Common Era (CE). These include maxima and minima corresponding to known climate episodes, such as the Holocene Thermal Maximum (HTM), Neoglacial Cooling, Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). These patterns are in line with long-term air temperature changes supported by previously published climate reconstructions from other archives, as well as Holocene summer insolation changes. In conclusion, oxygen isotope records from NH extratropical lake sediments feature a common climate signal at centennial (for CE) and millennial (for Holocene) timescales despite stemming from different lakes in different geographic locations and hence constitute a valuable proxy for past climate reconstructions.

Description: Between 6th August and 2nd September, 2021, a total of 66 lakes in Central and Eastern Yakutia were assessed as part of the joint Russian-German expedition (NEFU-AWI; RU-Land_2021_Yakutia). Samples and data were obtained with a large variety of different methods and for a wide range of sampling purposes. This dataset presents the results of hydrochemical laboratory analyses of ion concentration. Of those 66 hydrochemical analyses, 15 are from mountain lakes located within the Verkhoyansk mountain range, at the eastern end of the expedition route, including mostly intermontane basin or glacial lakes (average elevation: c. 1080 m a.s.l.). 13 lakes were sampled in Oymyakonsky District and two lakes in Tomponsky District. The hydrochemical dataset from the other 52 lakes that lie within the eastern extent of the Central Yakutian Lowland (average elevation: c. 190 m a.s.l.) represents thermokarst lakes. Thermokarst lakes originate from thawing of ice-rich permafrost and were found in different stages of their development, with a wide range of anthropogenic impact. These 52 thermokarst lakes include seven lakes within the Churapchinsky District, two are located in the Tattinsky District further east within a freshly burned forest. 42 lakes are located in Megino-Kangalassky District, of which 17 lakes are around Tungulu, and 24 lakes around Maya settlements.