| 1. |
- 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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| 2. |
- Kylander, Malin, et al.
(författare)
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A New Micro-Analytical Technique for the Identification of Tephra Layers in Sediments
- 2008
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Konferensbidrag (populärvet., debatt m.m.)abstract
- Tephrochronology uses material emitted during volcanic eruptions as isochronous markers for linking paleoclimatic records. Cryptotephra (i.e., those tephra not visible to the naked eye) layers can be as little as one to two shards thick while the shards themselves can be smaller than 10 m. The methods used to locate cryptotephra are often time consuming and laborious (e.g., sieving and point counting, density separation techniques) and in some cases may not be applicable (e.g., magnetic susceptibility of tephra may not differ from the sediment). XRF is a well-established analytical tool that has recently taken a new direction with the introduction of core scanning systems. The ITRAX XRF core scanning system is non-destructive, can acquire continuous data for a broad range of elements in situ in both marine and lacustrine sediments as well as take radiographic images. We test the possibility of screening sediment cores to flag the potential location of cryptotephra layers thereby eliminating lengthy laboratory work and saving on often precious sample. The method was tested by seeding a sediment core with tephra shards in layers of increasing thickness and then scanning the core with the ITRAX. The method was then further tested on sequences from two different sites: Hässeldala Port in Southern Sweden where up to 5 different cryptotephra have been detected and Lake Pechora from Russia which has several visible tephra layers. We show that using the ITRAX it is possible to locate most tephra layers without using any sample and within a minimal amount of time (a 1 m core can be analyzed reasonably in 12 hours and it requires essentially no sample preparation).
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| 3. |
- Plunkett, Gill, et al.
(författare)
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Distal tephrochronology in volcanic regions: Challenges and insights from Kamchatkan lake sediments
- 2015
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 1872-6364 .- 0921-8181. ; 134, s. 26-40
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Tidskriftsartikel (refereegranskat)abstract
- Kamchatka is one of the world's most active volcanic regions and has hosted many explosive eruptions during the Holocene. These eruptions had the potential to disperse tephra over wide areas, forming time-synchronous markers wherever those tephras are found. Recent research in Kamchatka has begun to focus on the geochemical analysis of individual glass shards in order to characterise tephra layers. We have applied this approach to the study of visible tephras from three lakes - one in central and two in northern Kamchatka - with the aim of identifying key tephras and potential issues in the application of distal (>100 km from an active volcano) tephra in volcanically complex regions. In total, 23 tephras from 22 tephra beds have been geochemically analysed, representing products from at least four volcanic systems in Kamchatka. We demonstrate that distal lake sediments in the region can yield reliable tephrostratigraphies, capturing tephra from eruptions that have the greatest potential to disperse volcanic ash beyond the region. We draw attention to issues relating to correlating and distinguishing key marker horizons from the highly active Shiveluch Volcano, namely the need to ensure inter-lab comparability of geochemical data and good chronological control of the proximal and distal tephras. Importantly, we have also extended the known distribution of two key tephra isochrons from the Ksudach volcano. Our work contributes valuable glass geochemical on data several key marker beds that will facilitate future tephra and palaeoenvironmental research within and beyond Kamchatka. (C) 2015 Elsevier B.V. All rights reserved.
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