Abstract
A radiocarbon and tephra-dated sediment core from Lifebuoy Lake, located on the north-east coast of Kamchatka Peninsula, was analysed for pollen, spores, diatoms, chironomids and tephra in order to uncover regional environmental history.The 6500-year environmental history of Lifebuoy Lake correlates with the broad regional patterns of vegetation development and climate dynamics with both diatoms and chironomids showing near-synchronous changes.Between ca. 6300 and 3900calyrBP, the lake ecosystem was naturally enriched, with several Stephanodiscus species dominating the diatom plankton. This natural eutrophication state is likely to be due to a combination of the base-rich catchment geology, the fertilisation effect of several fires in the catchment, silica input from tephra layers and, possibly, nitrogen input from seabirds. The substantial tephra deposit at about 3850calyrBP might have stopped sedimentary phosphorus from entering the lake water thus decreasing the trophic state of the lake and facilitating the shift in diatom composition to a benthic Fragiliariaceae complex.Both diatoms and chironomids showed simultaneous compositional changes, which are also reflected by statistically significant changes in their rates of change 300–400years after the arrival of Pinus pumila in the lake catchment. The rapid increase in both total diatom concentration and the percentage abundance of the large heavy species, Aulacoseira subarctica might be a response to the change in timing and intensity of lake spring turn-over due to the changes in the patterns of North Pacific atmospheric circulation, most notably westward shift of the Aleutian Low.The two highest peaks in A. subarctica abundance at Lifebouy Lake occurred during opposite summer temperature inferences: the earlier peak (3500–2900calyrBP) coincided with warm summers and the latter peak (300calyrBP–present) occurred during the cold summer period. These imply that A. subarctica shows no direct response to the changes of summer air temperature. Instead, it appears to thrive during the periods of increased winter precipitation, thicker ice and late spring turn-over periods, i.e., shows indirect response to climate.The clearest effect of tephra deposition on the lake ecosystem is above 908cm (ca. 3800calyrBP) where the tephra deposit might have caused the shift from Stephanodiscus-dominated planktonic assemblages to the Fragilariaceae complex of benthic species. Tephra deposits might have also contributed towards the development of eutrophic plankton from about 6300calyrBP. It is not certain if several tephra deposits influenced diatom and chironomid changes during the last 300years.
Highlights
The climate model experiments suggest that mid-Holocene climatic changes were time-transgressive in the Kamchatka Peninsula with the Holocene thermal maximum (HTM) being delayed in southern and central Kamchatka by about 2000 years in comparison with northern Kamchatka, Alaska and NE Siberia
This study presents the Holocene environmental history of the north-eastern coastal area of the Kamchatka Peninsula based on diatom, pollen and chironomid records from the sediment succession of a small coastal lake near the town of Ossora (Fig. 1a)
11 bulk sediment samples were 14C dated. These dates were rejected as they exhibited consistent reservoir effects in the range of 200–1200 years when compared with four visible tephra layers, which were geochemically identified
Summary
The climate model experiments suggest that mid-Holocene climatic changes were time-transgressive in the Kamchatka Peninsula with the Holocene thermal maximum (HTM) being delayed in southern and central Kamchatka by about 2000 years in comparison with northern Kamchatka, Alaska and NE Siberia (e.g., see Fig. 3 in Renssen et al, 2009). It is especially important to provide better insight into Holocene environmental and climate dynamics in northern Kamchatka since there is still little palaeoenvironmental evidence from this region, whereas the Holocene history of Alaska and NE Siberia are comparatively well-documented (e.g., Anderson et al, 2002; Edwards and Barker, 1994; Lozhkin et al, 2001, 2007). Quaternary diatom records were studied by Braitseva et al (1968)
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