Insight into the Last Glacial Maximum climate and environments of the Baikal region

This study presents a multi-proxy record from Lake Kotokel in the Baikal region at decadal-to-multidecadal resolution and provides a reconstruction of terrestrial and aquatic environments in the area during a 2000-year interval of globally harsh climate often referred to as the Last Glacial Maximum (LGM). The studied lake is situated near the eastern shoreline of Lake Baikal, in a climatically sensitive zone that hosts boreal taiga and cold deciduous forests, coldsteppe associationstypical for northern Mongolia, and mountain tundravegetation.The results provide a detailed picture of the period in focus, indicating (i) a driest phase (c. 24.0–23.4 cal. ka BP) with low precipitation, high summer evaporation, and low lake levels, (ii) a transitional interval of unstable conditions (c. 23.4–22.6 cal. ka BP), and (iii) a phase ( c. 22.6–22.0 cal. ka BP) of relatively high precipitation (and moisture availability) and relatively high lake levels. One hotly debated issue in late Quaternary research is regional summer thermal conditions during the LGM. Our chironomid-based reconstruction suggests at least 3.5 °C higher than present summer temperatures between c. 22.6 and 22.0 cal. ka BP, which are well in line with warmer and wetter conditions in the North Atlantic region inferred from Greenland ice-cores. Overall, it appears that environments in central Eurasia during the LGM were affected by much colder than present winter temperatures and higher than present summer temperatures, although the effects of temperature oscillations were strongly influenced by changes in humidity

Chironomid-based palaeotemperature estimates for northeast Finland during Oxygen Isotope Stage 3.

Quantitative palaeotemperature estimates for the earlier part of Oxygen Isotope Stage (OIS-) 3 are inferred from subfossil chironomid remains. The high-latitudinal study site of Sokli, northeast Finland, provides for a unique lacustrine deposit covering the earlier part of OIS-3, and the chironomid remains found in the sediments show that a shallow lake with a diverse fauna was present at the study site throughout the record. Using a Norwegian calibration data set as a modern analogue, mean July air temperatures are reconstructed. The chironomid-inferred July air temperatures are surprisingly high, reaching values similar to the current temperature at the study site. Other proxies that were applied to the sediments included the analysis of botanical and zoological macro-remains, and our results concur with temperature estimates derived from climate indicator taxa. Summer temperatures for interstadial conditions, reconstructed with climate models, are as high as our proxy-based palaeotemperatures

Rock glaciers and mountain hydrology: A review

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.In mountainous regions, climate change threatens cryospheric water resources, and understanding all components of the hydrological cycle is necessary for effective water resource management. Rockglaciers are climatically more resilient than glaciers and contain potentially hydrologically valuable ice volumes, and yet havereceived lessattention, even though rock glacier hydrologicalimportance may increase under future climate warming. In synthesising data from a range of global studies, we provide the first compre-hensive evaluation of the hydrological role played by rock glaciers. Weevaluate hydrological significanceover a range of temporal and spatial scales, alongsidethe complex multiple hydrological processes with which rock glaciers can interact diurnally, seasonally, annually, decadally and both at local and regional extents.We report that although no global-extent, complete inventory for rock glaciers exists currently, recent research efforts have greatly elaborated spatialcoverage.Using these research papers,we synthe-sise information on rock glacier spatial distribution, morphometric characteristics, surface and subsurface features, ice-storage and hydrological flow dynamics, water chemistry, and future resilience, from which we provide the first comprehensive evaluation of their hydrological contribution. We identify and discuss long-, intermediate-and short-term timescales for rock glacier storage, allowing a more balanced assess-ment of the contrasting perspectives regarding the relative significance of rock glacier-derived hydrological contributions compared to other water sources.We show that further empirical observations are required to gain a deeper hydrological understanding of rock glaciers, in terms of(i) their genesis and geomorpho-logical dynamics (ii) total ice/water volume; (iii) water discharge; and (iv) water quality. Lastly, we hypothesisethat at decadal and longer timescales, under future climate warming, degradation of ice within rock glaciers may represent an increasing hydrological contribution to downstream regions, and thus in-creased hydrological significance while rock glacier water stores persist.Royal Geographical SocietyNatural Environment Research Council (NERC

Variations in the isotopic composition of molybdenum in freshwater lake systems

Variations in molybdenum isotopic composition, spanning the range of similar to 2.3 parts per thousand in the terms of Mo-97/Mo-95 ratio, have been measured in sediment cores from three lakes in northern Sweden and north-western Russia. These variations have been produced by both isotopically variable input of Mo into the lakes due to Mo isotopic heterogeneity of bedrock in the drainage basins and fractionation in the lake systems due to temporal variations in limnological conditions. Mo isotope abundances of bedrock in the lake drainage basins have been documented by analysis of Mo isotope ratios of a suite of molybdenite occurrences collected in the studied area and of detrital fractions of the lake sediment cores. The median delta Mo-97 value of the investigated molybdenites is 0.26 parts per thousand with standard deviation of 0.43 parts per thousand (n=19), whereas the median delta Mo-97 value of detrital sediment fractions from two lakes is -0.40 parts per thousand with standard deviation of 0.36 parts per thousand (n=15). The isotopic compositiori of Mo in the sediment cores has been found to be dependent on redox conditions of the water columns and the dominant type of scavenging phases. Hydrous Fe oxides have been shown to be an efficient scavenger of Mo from porewater under oxic conditions. Oxidative precipitation of Fe(II) in the sediments resulted in co-precipitation of Mo and significant authigenic enrichment at the redox boundary. In spite of a pronounced increase in Mo concentration associated with Fe oxides at the redox boundary the isotopic composition of Mo in this zone varies insignificantly, suggesting little or no isotope fractionation during scavenging of Mo by hydrous Fe oxides. In a lake with anoxic bottom water a chironomid-inferred reconstruction of O-2 conditions in the bottom water through the Holocene indicates that increased O-2 concentrations are generally associated with low delta Mo-97/Mo-95 values of the sediments, whereas lowered O-2 contents of the bottom water are accompanied by relatively high delta Mo-97/Mo-95 values, thus confirming the potential of Mo isotope data to be a proxy for redox conditions of overlying waters. However, it is pointed out that other processes including input of isotopically heterogeneous Mo and Mn cycling in the redox-stratified water column can be a primary cause of variations in Mo isotopic compositions of lake sediments

Stacking of discontinuous regional palaeoclimate records: Chironomid-based summer temperatures from the Alpine region

International audienc

Quaternary Environment of NE-Siberian Arctic inferred from permafrost sequences of Bol'shoy Lyakhovsky Island

Permafrost sequences exposed at the coast of the southernmost New Siberian Island multidisciplinary studied by a Russian-German team present several stages of the Saalian to Holocene environmental and landscape history of Siberian Arctic. The deposits were studied using cryolithology, sedimentology, geochronology, stable isotope geochemistry of ground ice as well as investigations of biological remains (pollen, insects, rhizopods, chironomids). The oldest frozen deposits contains remains of a reworked tertiary weathering crust as proved by the yellowish colour and the occurrence of weathering products like kaolinite and montmorillonite. In addition it is characterized by separate epigenetic ice wedges and the absence of pollen. The Late Saalian climate variations are documented by two units dated between > 200 to c. 170 ky. The older unit is cryolithological similar to Late Pleistocene Ice Complex because of large ice wedges and ice rich deposits. The lower part of this unit contains pollen associations of sparse grass-sedge vegetation and reflects stadial climate conditions. The upper part of these ice-rich unit is characterized by pollen spectra of a dense grass dominated tundra probably of the Tasovsky Interstadial. The Saalian Ice Complex deposits were eroded and covered with a sharp boundary by a younger Saalian unit 170 to 130 ky old). This well-sorted fine-grained sand contains less ground ice and again pollen spectra of a sparse grass-sedge dominated vegetation assigned to the Kuchchugui Stadial. The most interesting unit was assigned to the Eemian (Kazantsevo/Krest Yuryakh) Interglacial because of the occurrence of large ice wedge casts as well as many paleo-ecological evidences of a warm stage. The Early Weichselian (Zyryan) Stadial is reflecting again of fine-grained, well-sorted sands with rare grass-sedge pollen. These deposits turn gradually into the about 20 m thick ice-rich Late Weichselian Ice Complex horizon, dated to about 50 to 30 ky and containing the pollen spectra of a typical mammoth tundra-steppe. Whereas peaty deposits of the Kargin Interstadial often occur within the studied Ice Complex sequences the Sartan Stadial sequences were not found. The Ice Complex deposits seem to be cut about 30 ky before and than covered by Late Glacial/Holocene deposits. The Late Pleistocene/Holocene transition including the Alleroed warming and Younger Dryas cooling events is preserved within lacustrine thermokarst deposits flanking the Late Weichselian Ice Complex sequences

Interglacial History of a Palaeo-lake and Regional Environment: A Multi-proxy Study of a Permafrost Deposit from Bolshoy Lyakhovsky Island, Arctic Siberia

Chironomid, pollen, and rhizopod records from a permafrost sequence at the Bolshoy Lyakhovsky Island (New Siberian Archipelago) document the evolution of a thermokarst palaeo-lake and environmental conditions in the region during the Last Interglacial (MIS 5e, ca. 130120 ka). Open Poaceae and Artemisia associations dominated vegetation at the beginning of the interglacial period, ca. 130 ka. Rare shrub thickets (Salix, Betula nana, Alnus fruticosa) grew in more protected and wetter places as well. Saalian ice wedges started to melt during this time, resulting in the formation of an initial thermokarst water body. The high percentage of semi-aquatic chironomids suggests that a peatland-pool palaeo-biotope existed at the site, when initial water body started to form. A distinct decrease in semi-aquatic chironomid taxa and an increase in lacustrine ones point to a gradual pooling of water in basin, which could in turn create thaw a permanent pond during the subsequent period. The highest relative abundance of Chironomus and Procladius reflects an existence of unfrozen water remaining under the ice throughout the ice-covered period during the later stage of palaeo-lake development. Chironomid record points to three successive stages during the water body evolution: (1) a peatland pool; (2) a pond (i.e., less deep than the maximum ice-cover thickness); and (3) a shallow lake (i.e., more deep than the maximum ice-cover thickness). The evolutionary trend of palaeo-lake points to intensive thermokarst processes occurring in the region during the Last Interglacial. Shrub tundra communities with Alnus fruticosa, Betula nana dominated the vegetation during the interglacial optimum that is evidenced by pollen record. The climate was relatively moist and warm. The results of this study suggest that quantitative chironomid-based temperature reconstructions from the Arctic thermokarst ponds/lakes may be problematic owing to other key environmental factors, such as prolonged periods of winter anoxia and local hydrological/geomorphological processes, controlling the chironomid assemblage