THE STUDY OF PRESENT POLYGONAL PONDS OF ARCTIC ECOSYSTEMS (YAKUTIA) IN PALAEOLIMNOLOGY

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DATABASES OF THE NORTHERN LAKES AS A BASIS FOR ECOLOGICAL AIMS

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Climate and environmental changes of the Lategacial transition and Holocene in northeastern Siberia: Evidence from diatom oxygen isotopes and assemblage composition at Lake Emanda

Indexación ScopusA new dataset from Lake Emanda provides insights into climate and environmental dynamics in an extreme continental setting in northeastern Siberia. The δ18Odiatom record is supported by diatom assemblage analysis, modern isotope hydrology and atmospheric circulation patterns. The data reveal a relatively cold oligotrophic freshwater lake system persisting for the last ∼13.2 cal ka BP. Most recent δ18Odiatom (+21.5‰) combined with present-day average δ18Olake (−16.5‰) allows calculating Tlake (∼21 °C), reflecting summer conditions. Nonetheless, the δ18Odiatom variability is associated with changes in δ18Olake rather than with Tlake. An obvious shift of ∼2‰ in the δ18Odiatom record at 11.7–11.5 cal ka BP accompanied by significant changes in diatom assemblages reflects the onset of the Holocene. Relatively high δ18Odiatom during the Early Holocene suggests relatively warm and/or dry climate with associated evaporation effects. The absolute maximum in δ18Odiatom of +27.7‰ consistent with high values of diatom indices at ∼7.9–7.0 cal ka BP suggests a Mid Holocene Thermal Maximum. A continuous depletion in δ18Odiatom since ∼5.0 cal ka BP is interpreted as Middle to Late Holocene cooling reaching the absolute minimum at 0.4 cal ka BP (i.e. the Little Ice Age). An overall cooling trend (∼0.3‰ 1000 yr−1) throughout the Holocene follows decreasing solar insolation. The pattern of the Lake Emanda δ18Odiatom record is similar to that obtained from Lake El'gygytgyn suggesting a common “eastern” regional signal in both records, despite their hydrological differences. Presently, atmospheric moisture reaches the study region from the west and east with ∼40% each, as well as ∼20% from the north. © 2021 The Author(s)https://www-sciencedirect-com.recursosbiblioteca.unab.cl/science/article/pii/S0277379121001128?via%3Dihu

THE STUDY OF PRESENT POLYGONAL PONDS OF ARCTIC ECOSYSTEMS (YAKUTIA) IN PALAEOLIMNOLOGY

59-6

DATABASES OF THE NORTHERN LAKES AS A BASIS FOR ECOLOGICAL AIMS

86-8

Late Quaternary Climate Reconstruction and Lead-Lag Relationships of Biotic and Sediment-Geochemical Indicators at Lake Bolshoe Toko, Siberia

Millennial-scale climate change history in eastern Siberia and relationships between diatom diversity, paleoclimate, and sediment-geochemical lake system trajectories are still poorly understood. This study investigates multi-proxy time series reaching back to the Late Pleistocene derived from radiocarbon dated Lake Bolshoe Toko sediment cores, southeastern Yakutia, Russia. We analyzed diatoms, elements (XRF), minerals (XRD), grain-size, organic carbon, and included chironomid analyses and published pollen-data for quantitative paleoclimate reconstruction. Changes in diatom species abundances reveal repeated episodes of thermal stratification indicated by shifts from euplanktonic Aulacoseira to Cyclotella species. Chironomid and pollen-inferred temperature reconstruction reveal that the main shift between these diatom species is related to the onset of Holocene Thermal Maximum (HTM) at 7.1 cal ka BP. Comparison to other paleoclimate records along a north-south transect through Yakutia shows that the HTM was delayed as far south as the Stanovoy mountains. Relationships between sediment-geochemistry, paleoclimate variability and diatom species richness (alpha diversity) was tested in a moving temporal offset approach to detect lead-lag relationships. Sediment-geochemical data, mainly uniform during the Holocene, revealed strongest positive or negative correlations ahead of species richness changes. Mean July air temperature (TJuly) reconstructions correlate with both Hill numbers and relative assemblage changes indicated by sample scores of multidimensional scaling analysis (MDS) over the entire time series. We found that sediment organic carbon revealed distinct positive correlations, i.e., centennial-scale delay to increases in diatom effective richness (Hill numbers N0 and N2). We conclude that a lag of deposited organic carbon concentrations behind changes in diatom alpha diversity reveals that species richness can augment the production and thus sequestration of organic matter in comparable lake systems