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| 2. |
- Hammarlund, Dan, et al.
(författare)
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Late Holocene expansion of Siberian dwarf pine (Pinus pumila) in Kamchatka in response to increased snow cover as inferred from lacustrine oxygen-isotope records
- 2015
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 134:SI, s. 91-100
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Tidskriftsartikel (refereegranskat)abstract
- Holocene records of cellulose-inferred lake-water δ18O were produced from two lake-sediment sequences obtained in central and northern Kamchatka, Russian Far East. The sediment records share similar fluctuations in δ18O during the interval of ca. 5000-800calyr BP that correspond (inversely) with changes in K+ content of the GISP2 ice-core record from Greenland, a proxy for the relative strength of the Siberian High, suggesting control by climate-related variability in δ18O of regional precipitation. The dramatic expansion of Siberian dwarf pine (Pinus pumila) in northern and central Kamchatka between ca. 5000 and 4000calyr BP, as inferred from pollen records from the same and neighbouring sites, appears to have occurred at a time of progressively declining δ18O of precipitation. This development is interpreted as reflecting a regional cooling trend accompanied by increasing winter snowfall related to gradual intensification of the Siberian High from ca. 5000 to ca. 3000calyr BP. A thicker and more long-lasting snow cover can be assumed to have favoured P. pumila by providing a competitive advantage over other boreal and subalpine tree and shrub species in the region during the later part of the Holocene. These results, which are the first of their kind from Kamchatka, provide novel insight into the Holocene vegetational and climatic development in easternmost Asia, as well as long-term atmospheric circulation dynamics in Beringia.
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| 3. |
- Andrén, Elinor, et al.
(författare)
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The relative influences of climate and volcanic activity on Holocene lake development inferred from a mountain lake in central Kamchatka
- 2015
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 1872-6364 .- 0921-8181. ; 134, s. 67-81
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Tidskriftsartikel (refereegranskat)abstract
- A sediment sequence was taken from a closed, high altitude lake (informal name Olive-backed Lake) in the central mountain range of Kamchatka, in the Russian Far East. The sequence was dated by radiocarbon and tephrochronology and used for multi-proxy analyses (chironomids, pollen, diatoms). Although the evolution of Beringian climate through the Holocene is primarily driven by global forcing mechanisms, regional controls, such as volcanic activity or vegetation dynamics, lead to a spatial heterogeneous response. This study aims to reconstruct past changes in the aquatic and terrestrial ecosystems and to separate the climate-driven response from a response to regional or localised environmental change. Radiocarbon dates from plant macrophytes gave a basal date of 7800 cal yr BP. Coring terminated in a tephra layer, so sedimentation at the lake started prior to this date, possibly in the early Holocene following local glacier retreat. Initially the catchment vegetation was dominated by Betula and Alnus woodland with a mosaic of open, wet, aquatic and semi-aquatic habitats. Between 7800 and 6000 cal yr BP the diatom-inferred lake water was pH 4.4-53 and chironomid and diatom assemblages in the lake were initially dominated by a small number of acidophilic/acid tolerant taxa. The frequency of Pinus pumila (Siberian dwarf pine) pollen increased from 5000 cal yr BP and threshold analysis indicates that P. pumila arrived in the catchment between 4200 and 3000 cal yr BP. Its range expansion was probably mediated by strengthening of the Aleutian Low pressure system and increased winter snowfall. The diatominferred pH reconstructions show that after an initial period of low pH, pH gradually increased from 5500 cal yr BP to pH 5.8 at 1500 cal yr BP. This trend of increasing pH through the Holocene is unusual in lake records, but the initially low pH may have resulted directly or indirectly from intense regional volcanic activity during the midHolocene. The chironomid-inferred July temperature reconstruction suggests cool periods between 32002800 cal yr BP and 1100-700 cal yr BP and a warmer period between 2800 and 1100 cal yr BP. Chironomid and diatom DCA scores decline from ca. 6000 cal yr BP, indicating compositional changes in these aquatic assemblages. In comparison declines in pollen PCA scores are delayed, starting ca. 5100 cal yr BP. The results suggest that while catchment vegetation was responding primarily to climate change, the biota within the lake and lake water chemistry were responding to localised environmental conditions. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.
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| 5. |
- Leavitt, Peter R., et al.
(författare)
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Paleolimnological evidence of the effects on lakes of energy and mass transfer from climate and humans
- 2009
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 54:6, s. 2330-2348
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Forskningsöversikt (refereegranskat)abstract
- The premise of this article is that climate effects on lakes can be quantified most effectively by the integration of process-oriented limnological studies with paleolimnological research, particularly when both disciplines operate within a common conceptual framework. To this end, the energy (E)-mass (m) flux framework (Em flux) is developed and applied to selected retrospective studies to demonstrate that climate variability regulates lake structure and function over diverse temporal and spatial scales through four main pathways: rapid direct transfer of E to the lake surface by irradiance, heat, and wind; slow indirect effects of E via changes in terrestrial development and subsequent m subsidies to lakes; direct influx of m as precipitation, particles, and solutes from the atmosphere; and indirect influx of water, suspended particles, and dissolved substances from the catchment. Sedimentary analyses are used to illustrate the unique effects of each pathway on lakes but suggest that interactions among mechanisms are complex and depend on the landscape position of lakes, catchment characteristics, the range of temporal variation of individual pathways, ontogenetic changes in lake basins, and the selective effects of humans on m transfers. In particular, preliminary synthesis suggests that m influx can overwhelm the direct effects of E transfer to lakes, especially when anthropogenic activities alter m subsidies from catchments.
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| 6. |
- Solovieva, N., et al.
(författare)
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The Holocene environmental history of a small coastal lake on the north-eastern Kamchatka Peninsula
- 2015
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 1872-6364 .- 0921-8181. ; 134, s. 55-66
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Tidskriftsartikel (refereegranskat)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 3900 cal yr BP, 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 3850 cal yr BP 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 300-400 years 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 turnover 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 (3500-2900 cal yr BP) coincided with warm summers and the latter peak (300 cal yr BP-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 908 cm (ca. 3800 cal yr BP) 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 6300 cal yr BP. It is not certain if several tephra deposits influenced diatom and chironomid changes during the last 300 years. (C) 2015 The Authors. Published by Elsevier B.V.
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| 7. |
- Andrén, Elinor, et al.
(författare)
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Holocene climate and environmental change in north-eastern Kamchatka (Russian Far East), inferred from a multi-proxy study of lake sediments
- 2015
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 134, s. 41-54
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Tidskriftsartikel (refereegranskat)abstract
- A sediment record from a small lake in the north-eastern part of the Kamchatka Peninsula has been investigated in a multi-proxy study to gain knowledge of Holocene climatic and environmental change. Pollen, diatoms, chironomids and selected geochemical parameters were analysed and the sediment record was dated with radiocarbon. The study shows Holocene changes in the terrestrial vegetation as well as responses of the lake ecosystem to catchment maturity and multiple stressors, such as climate change and volcanic eruptions. Climate change is the major driving force resulting in the recorded environmental changes in the lake, although recurrent tephra deposition events also contributed. The sediment record has an age at the base of about 10,000 cal yrs BP, and during the first 400 years the climate was cold and the lake exhibited extensive ice-cover during winter and relatively low primary production. Soils in the catchment were poor with shrub alder and birches dominatingthe vegetation surrounding the lake. At about 9600–8900 cal yrs BP the climate was cold and moist, and strong seasonal wind stress resulted in reduced ice-cover and increased primary production. After ca. 8900 cal yrs BP the forest density increased around the lake, runoff decreased in a generally drier climate resulting in decreasedprimary production in the lake until ca. 7000 cal yrs BP. This generally dry climate was interrupted by a brief climatic perturbation, possibly attributed to the 8.2 ka event, indicating increasingly windy conditions with thick snow cover, reduced ice-cover and slightly elevated primary production in the lake. The diatom record shows maximum thermal stratification at ca. 6300–5800 cal yrs BP and indicates together with the geochemical proxies a dry and slightly warmer climate resulting in a high productive lake. The most remarkably change in the catchment vegetation occurred at ca. 4200 cal yrs BP in the form of a conspicuous increase in Siberian dwarf pine (Pinus pumila), indicating a shift to a cooler climate with a thicker and more long-lasting snow cover. Thisvegetational change was accompanied by marked shifts in the diatom and chironomid stratigraphies, which are also indicative of colder climate and more extensive ice-cover.
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| 8. |
- Jones, V. J., et al.
(författare)
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The influence of Holocene tree-line advance and retreat on an arctic lake ecosystem : a multi-proxy study from Kharinei Lake, North Eastern European Russia
- 2011
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Ingår i: Journal of Paleolimnology. - : Springer. - 0921-2728 .- 1573-0417. ; 46:1, s. 123-137
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Tidskriftsartikel (refereegranskat)abstract
- A consequence of predicted climate warming will be tree-line advance over large areas of the Russian tundra. Palaeolimnological techniques can be used to provide analogues of how such changes in tree-line advance and subsequent retreat affected lake ecosystems in the past. A Holocene sediment core taken from Kharinei Lake (Russia) was dated radiometrically and used for multi-proxy analyses with the aim of determining how climate and tree-line dynamics affected the productivity, community structure, carbon cycling and light regime in the lake. Pollen and macrofossil analyses were used to determine the dates of the arrival and retreat of birch and spruce forest. C:N ratios and percent loss-on-ignition were used to infer past changes in sediment organic matter. Visible-near-infrared spectroscopy and diatom analysis were used to infer past changes in lake-water carbon. Algal pigments and aquatic macrophytes were used to determine changes in lake productivity and light. Chironomids together with remains of the aquatic flora and fauna were used to provide information on past July temperature and continentality. Lake sedimentation was initiated shortly before 11,000 cal. years BP, when both chironomid- and pollen-inferred temperature reconstructions suggest higher summer temperatures than present, between 1 and 2 degrees C warmer, and lake productivity was relatively high. A few trees were already present at this time. The spruce forest expanded at 8,000 cal. year BP remaining in the vicinity of the lake until 3,500 cal. year BP. This period coincided with a high concentration of organic material in the water column, and relatively high benthic productivity, as indicated by a high benthic: planktonic diatom ratio. After tree-line retreat, the optical transparency of the lake increased, and it became more open and exposed, and was thus subject to greater water-column mixing resulting in a higher abundance of diatom phytoplankton, especially heavily silicified Aulocoseira species. The colder climate resulted in a shorter ice-free period, the lake was less productive and there was a loss of aquatic macrophytes. Increased wind-induced mixing following forest retreat had a greater influence on the lake ecosystem than the effects of decreasing organic matter concentration and increased light penetration.
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