Holocene freshwater diatoms: palaeoenvironmental implications from southKamchatka,Russia

Abstract

Holocene palaeolimnological conditions were reconstructed by analysing fossil diatom assemblages within a lacustrine sediment core fromLakeSokoch, southernKamchatka (Russia). Sediments of this proglacial lake cover the past 9400 years and hence represent almost the wholeHolocene history. The biosiliceous muddy sample material was analysed for several geochemical and biological parameters, such as the total organic carbon and biogenic silica content, and the diatom community (quantitative and qualitative changes). Based on changes in the relative abundances of the most frequent speciesAulacoseira subarctica,Staurosira martyiandStephanodiscus alpinusand a depth‐constrained cluster analyses (CONISS), five diatom assemblage zones could be identified. The oldest stage recovered lies between 9400 and 9000 cal. aBPand reflects the initial lake stage after the retreat of local glaciers, with a high detrital sediment supply, shallow‐water conditions and a high diatom diversity. The next zone (9000–6200 cal. aBP) shows a more mature lake system with accumulating biogenic remains and higher water levels during climate amelioration. This is followed by the most obvious change in the diatom assemblage, delineated by an occurrence ofS. alpinus, between 6200 and 2700 cal. aBP. Wet conditions in spring probably led to an enhanced fluvial runoff and eutrophic to hypertrophic conditions. The end of this period might reflect climate deterioration related to theNeoglacial epoch of theHolocene. Between 2700 and 1600 cal. aBPthe sediments ofLakeSokoch reveal oligotrophic water conditions in a windy high‐energy environment. The youngest interval, between 1600 cal. aBPand thePresent, indicates shallow‐water conditions and a very short growing season, which might reflect theLittleIceAge. The results may offer a baseline for the interpretation ofHolocene palaeoenvironmental changes inKamchatka and their relation to regional climate change from a palaeoecological perspective.