CHIRONOMID FAUNA OF CENTRAL YAKUTIAN LAKES (NORTHERN RUSSIA) IN PALAEOENVIRONMENTAL INVESTIGATION

-

CHIRONOMID FAUNA OF CENTRAL YAKUTIAN LAKES (NORTHERN RUSSIA) IN PALAEOENVIRONMENTAL INVESTIGATION

-

Quantitative estimates of Mid- to late Holocene climate variability in Siberia inferred from chironomids in lake sediments

The reconstruction of the dynamic elements of past environments is extremely important for understanding both the present state and evolutionary trends in future climate development. Since long-term measurements on climate variability very rarely go back more than about 100 years, palaeoclimate and environmental reconstructions based on proxy indicators must be used to validate the output of global climate models. Especially important such reconstructions are in climatologically sensitive and pristine regions such as polar areas, where any small global climate change results in distinct regional variations of temperature, precipitation, and other climate-induced changes. There are few examples of quantitative palaeoclimate studies in Siberia. The obtained environmental reconstructions have to be tested by further quantitative studies from other sites in this region, using numerical proxy data that are based on regional calibration datasets and temperature models, which were not available until now. At the present state of knowledge, biological indicators from aquatic and terrestrial environments are the most reliable proxies, because they react sensitively to climate change and define different aspects of environments, which should be assessed together for reliable reconstructions. The basis of all quantitative reconstruction approaches are regional calibration datasets from which the empirical reconstruction models (i.e. the transfer function) will be established. New calibration dataset and based on it chironomid-climate inference models for reconstructing palaeoclimate variables were established along latitudinal temperature gradients in northeastern Siberia. Previous application of non-regional models for temperature reconstruction causes difficulty in their interpretation and makes results sometimes controversial. Reconstructions of the ecological conditions of the Holocene were made using the new models and have shown fluctuations in the lake level and other climate dependant parameters. Strong faunistic changes take place after 4500 yBP. T july went down up to 2oC below modern temperature. These observations confirm end of Holocene climate optimum at this time

Quantitative estimates of Mid- to late Holocene Climate Variability in northeastern Siberia inferred from chironomids in lake sediments

Yakutia (Russia, northeastern part of Eurasia) represents one of Earths most extreme climatic settings in the worldwith deep-reaching frozen ground and a semiarid continental climate with highest seasonal temperature contrastsin the northern hemisphere. The amplitude of temperature variations around the year sometimes exceeds 100oC.There are few examples of quantitative palaeoecological studies in Siberia and these data have to be tested byquantitative studies from other sites in this region, inferred from different proxies and using regional calibrationdatasets and temperature models that are still lacking. Chironomid midges (Insecta, Diptera, Chironomidae) havebeen widely used to reconstruct past climate variability in many areas of Western Europe and North America. Achironomid-mean July air temperature inference model has been developed, based on a modern calibration set of200 lakes sampled along a transect from 110° to 159° E and 61° to73° N in northern Russia. The inference modelwas applied to sediment cores from 2 lakes in the Central Yakutia in order to reconstruct past July air temperatures.The lacustrine records span mid- to late Holocene. The downcore variability in the chironomid assemblages and thecomposition of organic matter give evidence of climate-driven and interrelated changes in biological productivity,lacustrine trophic states, and lake-level fluctuations. Three phases of the climate development in Central Yakutiacan be derived from the geochemical composition of the lake cores and according to the inferred from chironomidassemblages mean July air ToC. Content of organic matters reached maximal values in the period between 7000-4500 yBP. Sedimentation rate is especially high, numerous molluscs shells are found in sediments. All this alongwith the reconstructed air temperature confirmed that Mid Holocene optimum in Central Yakutia took place in thisperiod with the maximal temperatures up to 4oC above present day ToC. Strong faunistic changes take place after4500 yBP. Temperature reconstruction has shown that around 4500 ka BP air temperature went down up to 2oCbelow modern temperature. These observations confirm end of Holocene climate optimum at this time. The lakestatus record reveals a long-term trend towards lake-level lowering in the course of climate deterioration after 4.2cal. ka BP and reduced evaporation as well as progressive sediment infill. This long-term trend is overprinted byshort-term fluctuations at centennial time scales with high lake levels and decreased biological productivity duringcool climate spells with reduced evaporation, as also observed in modern thermokarst lakes of Central Yakutia