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 ( δ 18 O 0.1em diatom0.1em) records from Russian lakes with focus on Eurasian Holocene climate trends. The measured δ 18 O 0.1em diatom0.1em 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 δ 18 O 0.1em precipitation. Hence, at locations where the signs of model and proxy temperature/precipitation trends agree, measured δ 18 O 0.1em diatom0.1em and modeled δ 18 O 0.1em precipitation0.1em trends show notable accordance. An increased temporal variability of modeled δ 18 O 0.1em precipitation0.1em 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.

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Abstract. 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 will have its own set of drivers of d18O, here we explore the extent to which regional or even global signals emerge from a series of palaeoenvironmental records. 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 last 150 years to records with multi–millennial scale resolution spanning glacial–interglacial cycles. Best coverage in number of records (N = 37) and datapoints (N = 2112) is available for northern hemispheric (NH) extra–tropic regions throughout the Holocene (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 yrs. For mid– to high–latitude (> 45° N) lakes, we find common δ18OBSi patterns during both the Holocene and the Common Era and 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 Tair changes supported by previously published climate reconstructions from other archives as well as Holocene summer insolation changes. In conclusion, oxygen isotope records from NH extratopic lake sediments feature a common climate signal at centennial (for CE) and millennial (for Holocene) time scales despite stemming from different lakes in different geographic locations and constitute a valuable proxy for past climate reconstructions.

&lt;p&gt;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 (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O) are commonly measured on carbonates (i.e. ostracods, authigenic&amp;#160;carbonates) and biogenic silica (mainly diatoms). Oxygen isotopes in lacustrine carbonates (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;CaCO3&lt;/sub&gt;) 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 (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;BSi&lt;/sub&gt;), 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 &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;BSi&lt;/sub&gt; 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.&lt;/p&gt;&lt;p&gt;Here, we present the first comprehensive review and global compilation of lacustrine &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;BSi&lt;/sub&gt; 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 &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;BSi&lt;/sub&gt; records globally, considering lake basin characteristics, spatial and temporal coverage as well as hydrological background information. This improves both the usability of &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;BSi&lt;/sub&gt; for proxy-model comparison and our understanding of the general constraints for interpreting lacustrine &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;BSi&lt;/sub&gt; records.&lt;/p&gt;

The diatom oxygen isotope composition (d 18 O diatom ) from lacustrine sediments helps tracing the hydrological and climate dynamics in individual lake catchments, and is generally linked to changes in temperature and d 18 O lake . Lake Bolshoye Shchuchye (67 53 0 N; 66 19 0 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 d 18 O diatom 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 30e50% of its volume needs to be exchanged with isotopically different water within decades to account for these shifts in the d 18 O diatom 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 d 18 O diatom 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.

&lt;p&gt;The diatom oxygen isotope composition (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;diatom&lt;/sub&gt;) from lacustrine sediments is a reliable proxy to trace hydrological and climate dynamics in individual lake catchments, and is generally linked to lake temperature and water isotope variations. Diatom oxygen isotopes are excellent recorders of these changes, especially in high-latitudes where carbonates are widely absent.&lt;/p&gt;&lt;p&gt;In this study, Lake Bolshoye Shchuchye (67&amp;#176;53'N; 66&amp;#176;19' E; 186 m a.s.l) is explored being the largest and deepest freshwater reservoir in the Polar Urals, Arctic Russia. The recent isotope geochemistry helps identifying Lake Bolshoye Shchuchye as a well-mixed monomictic lake, covered more than half of the year by ice, and with negligible evaporative effects. Its Holocene &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;diatom&lt;/sub&gt; record generally follows a decrease in summer insolation and the northern hemisphere (NH) temperature history interpreted as Holocene cooling. However, it is overprinted by short-term variations in &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;diatom&lt;/sub&gt; exceeding 5&amp;#8240;, especially in Mid and Late Holocene. This centennial-scale variability is similar to Holocene NH glacier advances. However, presently glaciers in the Lake Bolshoye Shchuchye catchment are not known, nor have left any significant imprint on the lake sedimentary record. As the lake is deep (max water depth 160 m) and voluminous, about 30&amp;#8722;50% of its volume need to be exchanged with isotopically different water within decades to account for the short-term shifts in the &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;diatom&lt;/sub&gt; 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. We propose snow melt and influx changes being the dominant mechanism responsible for the observed short-term changes in the &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;diatom&lt;/sub&gt; 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 summer temperatures and palaeo precipitation.&lt;/p&gt;