SIBCLIMLAKE · Climate variability and associated limnological changes in the coldest region of Eurasia over the past millennium: chironomid-based reconstructions in NE Siberia

Climate variability and associated limnological changes in the coldest region of Eurasia over the past millennium: chironomid-based reconstructions in NE Siberia

The study was aimed at chironomid-based reconstructing climatic variability and climate impact on lakes in the Siberian Arctic. Chironomid fossils from sediment cores taken in littoral and the deepest part of three lakes were analysed. The analysis of data collected at the closest meteorological station pointed out a clear warming trend in the region since 1980. Geochronology of the cores covering time periods from circa 110 to circaa 950 years was based on radioisotope dating and age-depth modeling. Chironomid data in the cores over the past century were summarised by the detrended correspondence analysis (DCA) axis 1 sample scores, which indicated gradual changes in the assemblages since 1900 and much more rapid changes since the period 1975 - 1980. Analysis of changes in the littoral and deep-water assemblages over the past century included a comparison of recent chironomid responses to climate changes with instrumental records from the adjacent meteorological station. The chironomid responses to climate changes were evaluated by linking the DCA axis 1 sample scores to monthly temperatures by nonlinear partial least squares (PLS) regression. For the littoral assemblages, the strongest correlations were for DCA scores versus mean air temperatures for February or December. This may reflect the impact of winter temperatures on lake ice thickness, break-up dates, and duration of the ice-covered and ice-free seasons, which in turn direct and indirect affect the littoral communities. The deep-water assemblage DCA scores were most strongly correlated with temperatures in August, September, October or November. This suggests that the deep-water assemblage changes are mainly driven by direct and indirect effects of changes in temperatures of the end of the growing season and ice freeze-up dates. We used PLS regression to evaluate the responses of the assemblages to changes in the basic features of the ice-covered and ice-free seasons by linking the DCA axis 1 sample scores to annual sum of negative degree-days (NDD), annual sum of positive degree-days (PDD), and duration of time with negative mean daily temperatures (Dice). The analysis indicated statistically significant relationship between the deep-water assemblages and PDD whereas the littoral assemblages are related to NDD and Dice. For analysis of the assemblage changes through the past millennium, a principal component analysis (PCA) was applied to the chironomid records in two cores taken in littoral and deep water. The results from PCA reveal that compositional turnover of the littoral assemblages along PCA axis 2 and the deep-water assemblages along PCA axis 1 closely match the changes in proportion of the cold-stenothermic taxon Micropsectra, and these axes can be considered as temperature axes. Changes in both chironomid records clearly show the most significant climatic events of the past millennium: the medieval warm period (MWP) before circa 1400, the little ice age cooling (the coldest interval between circa 1550 - 1650 and circa 1900), and the recent warming of 20th century. The pattern of inferred climate changes, as represented by the PCA chironomid sample scores, is broadly similar to those found in other millennial records across the European and Western Hemisphere Arctic. Our reconstruction suggests that the recent warming is unusual in the context of the variability of the past century but is, within the millennial climate variability, comparable to the MWP. Detrended canonical correspondence analysis revealed that striking compositional shifts have occurred in the littoral chironomid assemblages during the recent period since 1980. These changes are much more pronounced than over the period 1900 - 1980 and almost comparable to the beta-diversity values for the period of circa 850 years (1050 - 1900). The obtained results contribute to our understanding of such a complex phenomenon as climate change, and its implications.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз