In the scope of the Russian-German KALMAR project, our subproject deals with the reconstruction of lateQuaternary land environments, inferred from lake-sediment records and peat sections. The study follows amulti-proxy approach, using fossil bioindicators, such as diatoms (see Hoff et al.), pollen (see Dirksen, V. etal.) and chironomids, as well as geochemistry, radiocarbon dating, and tephra stratigraphy (see Dirksen, O. etal.). In addition to available peat samples from former field work, lacustrine sediment cores were taken during alimnogeological expedition to Kamchatka in September 2007. Promising mid- to late Holocene sediment recordswere obtained from Two-Yurts Lake, situated in a former proglacial basin of the central Kamchatka mountainchain. The hydrology of Two-Yurts Lake is characterized by an open system with three major riverine inflows andone outflow. Lake waters reveal neutral pH values, fresh-water conditions, and slight oxygen undersaturation insummer. The lake basin morphology is characterized by a flat profundal plain at 21-27 m water depth. A terraceat 2 m above present level and another subaquatic terrace at 16 m water depth give evidence of former lake-levelfluctuations. Sediment core PG1857 was taken from the central part of the lake basin. Radiocarbon dating andtephra stratigraphy suggest a basal age of 7.5 ka BP, consistent with dating results from an offshore peat sectionthat covers a glacial moraine to the east of the lake (see Dirksen, O. et al.).Above a basal clay, the lake sediments consist of diatomaceous oozes with interspersed ash layers. Fossil diatomassemblages are dominated by planktonic cold-water forms indicating low to intermediate trophic lake status (seeHoff et al.), as also indicated by low concentrations of total organic matter (TOC) and low TOC/TN ratios. Inaddition to diatoms, the lake sediments include abundant fossil chironomid head capsules, exhibiting a higherbiodiversity than in temperate climate zones. Changes in chironomid assemblages give insight into changesin lake ecology, water depth and temperature. The lacustrine pollen records point to vegetation changes in thecatchment. On the basis of preliminary data, the variability of proxy data in sediment core PG1857 suggest ahigher than present biological productivity, lower lake level and higher temperature before 3.7 ka BP. Subsequentlake-deepening and cooling appeared in conjunction with increased detrital sediment supply, possibly pointing toenhanced fluvial run-off. The observed environmental changes towards the late Holocene are consistent with theonset of neoglacial climate deterioration on Kamchatka.
Helmholtz Research Programs > PACES I (2009-2013) > TOPIC 3: Lessons from the Past > WP 3.3: Proxy Development and Innovation: the Baseline for Progress in Paleoclimate Research