| 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. |
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| 3. |
- Ivarsson, Magnus, et al.
(författare)
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Zygomycetes in Vesicular Basanites from Vesteris Seamount, Greenland Basin - A New Type of Cryptoendolithic Fungi
- 2015
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Ingår i: PLoS One. - : Public Library of Science (PLoS). ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- Fungi have been recognized as a frequent colonizer of subseafloor basalt but a substantial understanding of their abundance, diversity and ecological role in this environment is still lacking. Here we report fossilized cryptoendolithic fungal communities represented by mainly Zygomycetes and minor Ascomycetes in vesicles of dredged volcanic rocks (basa- nites) from the Vesteris Seamount in the Greenland Basin. Zygomycetes had not been reported from subseafloor basalt previously. Different stages in zygospore formation are documented in the studied samples, representing a reproduction cycle. Spore structures of both Zygomycetes and Ascomycetes are mineralized by romanechite-like Mn oxide phases, indicating an involvement in Mn(II) oxidation to form Mn(III,VI) oxides. Zygospores still exhibit a core of carbonaceous matter due to their resistance to degradation. The fungi are closely associated with fossiliferous marine sediments that have been introduced into the vesicles. At the contact to sediment infillings, fungi produced haustoria that penetrated and scavenged on the remains of fragmented marine organisms. It is most likely that such marine debris is the main carbon source for fungi in shallow volcanic rocks, which favored the establishment of vital colonies.
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| 4. |
- Klimaschewski, A., et al.
(författare)
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Holocene environmental changes in southern Kamchatka, Far Eastern Russia, inferred from a pollen and testate amoebae peat succession record
- 2015
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 134, s. 142-154
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Tidskriftsartikel (refereegranskat)abstract
- High resolution palaeoenvironmental records in Far-Eastern Russia are rare, and the Kamchatka Peninsula is among the least studied areas of the region. This paper describes a record spanning the last ca. 11,000 yr, obtained from a bog in the southern part of Kamchatka. The radiocarbon dated core was analysed for pollen, testate amoebae, charcoal and loss-on-ignition (LOI). The vegetation during the early Holocene was dominated by grasses (Poaceae), birch (Betula) and heath (Ericaceae p. p.). Around 10,300 cal yr BP there was a substantial change in the vegetation cover to shrub alder (Alnus viridis s.I.) stands with sedges and ferns (Polypodiophyta) as well as herbs such as meadow rue (Thalictrum) in the understory. In the surroundings of Utka peatlands started to form. The variations in the vegetation cover were most probably caused by climatic changes. At the beginning of sediment accumulation, before 10,300 cal yr BP, the composition of the vegetation points to cooler summers and/or decreased annual precipitation. Around 10,300 cal yr BP, changes in vegetation occurred due to rising temperatures and/or changed water regimes. Increased abundancies of dry indicating testate amoebae after 9100 cal yr BP point to intermediate to dry soil conditions. Between 8600 and 7700 cal yr BP tree alder (Alnus incana) was widely spread at the site which probably indicates optimal environmental conditions. The tephra layer at 381-384.5 cm (ca. 8500 cal yr BP) produces a strong impact on the testate amoebae assemblages. At 7700 cal yr BP there was a sudden drop of A. incana in the local vegetation. From this time on, A. incana and also A. viridis decrease continuously whereas Betula gradually increases. The upper part of the sequence (after 6300 cal yr BP) shows higher abundancies of meadowsweet (Filipendula) and sweet gale (Myrica) pollen. After 6300 cal yr BP, changes in testate amoebae demonstrate variable soil moisture conditions at the site. Between 3700 and 1800 cal yr BP, wet conditions dominate as dry indicating testate amoebae decrease. After 1800 cal yr BP soil conditions become more variable again but this time with dry dominating testate amoebae. In contrast to surrounding regions, there is no evidence of trees such as spruce or larch growing in the surroundings of the site even though those trees are characteristic of many eastern Siberian sites. This difference might be because of the maritime influence of the Okhotsk Sea. Even dwarf pine (Pinus pumila), which is currently widely dispersed in northern Kamchatka, became part of the local vegetation only during the last 700 yr.
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| 5. |
- van Helmond, Niels A G M, et al.
(författare)
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Seasonal hypoxia was a natural feature of the coastal zone in the Little Belt, Denmark, during the past 8 ka
- 2017
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Ingår i: Marine Geology. - : Elsevier. - 0025-3227 .- 1872-6151. ; 387, s. 45-57
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Tidskriftsartikel (refereegranskat)abstract
- The extent of the hypoxic area in the Baltic Sea has rapidly expanded over the past century. Two previous phases of widespread hypoxia, coinciding with the Holocene Thermal Maximum (HTM; 8–4 ka before present; BP) and the Medieval Climate Anomaly (MCA; 2–0.8 ka BP), have been identified. Relatively little is known about bottom water redox conditions in the coastal zone of the Baltic Sea during the Holocene, however. Here we studied the geochemical composition of a sediment sequence from a currently seasonally hypoxic site in the Danish coastal zone, the Little Belt, retrieved during Integrated Ocean Drilling Program Expedition 347 (Site M0059). The base of the studied sediment sequence consists of clays low in organic carbon (Corg), molybdenum (Mo) and iron sulfides (Fe-sulfides), and rich in iron oxides (Fe-oxides), indicative of a well-oxygenated, oligotrophic (glacial) meltwater lake. An erosional unconformity separates the glacial lake sediments from sediments that are rich in Corg. The absence of Mo, in combination with high Corg/S values, indicates that these sediments were deposited in a highly productive, well-oxygenated freshwater lake. The transition to modern brackish/marine conditions was very rapid, and subsequent continuous sequestration of Mo in the sediment and high ratios of reactive iron (FeHR) over total Fe (FeTOT) suggest (seasonal) hypoxia occurred over the last ~ 8 ka. Maxima in sediment Corg, Mo and FeHR/FeTOT ratios during the HTM and MCA suggest that the hypoxia intensified. Our results demonstrate that the Little Belt is naturally susceptible to the development of seasonal hypoxia. While periods of climatic warming led to increased deoxygenation of bottom waters, high nutrient availability in combination with density stratification were likely the main drivers of hypoxia in this part of the coastal zone of the Baltic Sea during the Holocene.
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| 6. |
- Vinogradova, Olena, et al.
(författare)
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3000 Years of past regional and local land-use and land-cover change in the southeastern Swedish coastal area : Early human-induced increases in landscape openness as a potential nutrient source to the Baltic Sea coastal waters
- 2024
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Ingår i: The Holocene. - : Sage Publications. - 0959-6836 .- 1477-0911. ; 34:1, s. 56-73
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Tidskriftsartikel (refereegranskat)abstract
- Reconstructions of past land use and related land-cover changes at local and regional scales are needed to evaluate the potential long-term impacts of land use on the coastal waters of the Baltic Sea. In this purpose, we selected the Gamleby area at the Swedish Baltic Sea coast for a case study. We use a new, high resolution pollen record from a small lake (Lillsjön) located 3.6 km NNW of the bay Gamlebyviken and detailed analysis of the available archeological data to reconstruct local land-use changes over the last 3000 years. To estimate land-cover change at local (2–3 km radius area) and regional (50 km radius area) scales we use four additional, published pollen records from two small and two large lakes (25–70 km S of Lillsjön) and the Landscape Reconstruction Algorithm, a pollen-vegetation modeling scheme. Results show that regional and local (small lakes Lillsjön and Hyttegöl) land-cover changes are comparable over the last 1500 years (Late Iron Age to present), and that landscape openness was much larger locally than regionally (difference of 20–40% cover over the last 500 years). The periods of largest potential impacts on the Gamlebyviken Bay from regional and local land use are 200–950 CE (Late Iron Age) and 1450 CE to present, and of lowest potential impacts 950–1450 CE. The question on whether the large landscape openness 1150–50 BCE and significant afforestation 50 BCE–200 CE reconstructed for Lillsjön’s area are characteristic of the Gamlebyviken region will require additional pollen records in the catchment area.
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| 7. |
- 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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| 8. |
- Andrén, Thomas, et al.
(författare)
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New insights on the Yoldia Sea low stand in the Blekinge archipelago, southern Baltic Sea
- 2007
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Ingår i: GFF. - 1103-5897 .- 2000-0863. ; 129, s. 277-285
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Tidskriftsartikel (refereegranskat)abstract
- One sediment core from the Jarnavik bay in Blekinge archipelago has been investigated for its content of pollen and diatoms and its chemical properties. Two levels were also dated by radiocarbon. Based on the results the sediment sequence analysed has been divided into three environmental units largely corresponding to the lithology of the sequence. A lowermost unit consisting of weakly varved and homogeneous clay was deposited during the end of the brackish phase of the Yoldia Sea at a moderate water depth. On top of this unit a gyttja-clay unit was deposited. The onset of the deposition of this unit has been dated to c. 11 100 cal. yrs. BP. An increasing organic production and increased terrestrial influence is recorded in the chemical data and a very shallow water depth is indicated in the pollen and diatom flora. These results point to conditions in a bay probably isolated from the Yoldia Sea. A local tentative shore displacement curve have been constructed and it is proposed that this unit represents the low stand at c. -18 m during the Yoldia Sea stage in this part of the Baltic Sea basin. The uppermost unit consists of homogeneous clay with a low content of organic carbon. An increasing water depth is indicated by the composition of both pollen and diatoms. The diatom flora also displays an increase in freshwater species. This environmental change was probably the result of a transgression in the beginning of the Ancylus Lake stage.
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| 9. |
- Green, P. F., et al.
(författare)
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Stratigraphic landscape analysis, thermochronology and the episodic development of elevated, passive continental margins
- 2013
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Ingår i: Geological Survey of Denmark and Greenland Bulletin. - : Geological Survey of Denmark and Greenland. - 1811-4598 .- 1604-8156 .- 1904-4666. ; :30, s. 4-150
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Tidskriftsartikel (refereegranskat)abstract
- The continental margin of West Greenland is similar in many respects to other elevated, passive continental margins (EPCMs) around the world. These margins are characterised by extensive regions of low relief at elevations of 1-2 kilometres above sea level sloping gently inland, with a much steeper, oceanward decline, often termed a 'Great Escarpment', terminating at a coastal plain. Recent studies, based on integration of geological, geomorphological and thermochronological evidence, have shown that the high topography of West Greenland was formed by differential uplift and dissection of an Oligo-Miocene peneplain since the late Miocene, many millions of years after continental break-up between Greenland and North America. In contrast, many studies of other EPCMs have proposed a different style of development in which the high plateaux and the steep, oceanward decline are regarded as a direct result of rifting and continental separation. Some studies assume that the elevated regions have remained high since break-up, with the high topography continuously renewed by isostasy. Others identify the elevated plains as remnants of pre-rift landscapes. Key to understanding the development of the West Greenland margin is a new approach to the study of landforms, stratigraphic landscape analysis, in which the low-relief, high-elevation plateaux at EPCMs are interpreted as uplifted peneplains: low-relief surfaces of large extent, cutting across bedrock of different age and resistance, and originally graded to sea level. Identification of different generations of peneplain (re-exposed and epigene) from regional mapping, combined with geological constraints and thermochronology, allows definition of the evolution leading to the formation of the modern-day topography. This approach is founded particularly on results from the South Swedish Dome, which document former sea levels as base levels for the formation of peneplains. These results support the view that peneplains grade towards base level, and that in the absence of other options (e.g. widespread resistant lithologies), the most likely base level is sea level. This is particularly so at continental margins due to their proximity to the adjacent ocean. Studies in which EPCMs are interpreted as related to rifting or break-up commonly favour histories involving continuous denudation of margins following rifting, and interpretation of thermochronology data in terms of monotonic cooling histories. However, in several regions, including southern Africa, south-east Australia and eastern Brazil, geological constraints demonstrate that such scenarios are inappropriate, and an episodic development involving post-breakup subsidence and burial followed later by uplift and denudation is more realistic. Such development is also indicated by the presence in sedimentary basins adjacent to many EPCMs of major erosional unconformities within the post-breakup sedimentary section which correlate with onshore denudation episodes. The nature of the processes responsible is not yet understood, but it seems likely that plate-scale forces are required in order to explain the regional extent of the effects involved. New geodynamic models are required to explain the episodic development of EPCMs, accommodating post-breakup subsidence and burial as well as subsequent uplift and denudation, long after break-up which created the characteristic, modern-day EPCM landscapes. © 2013 Pushpa Publishing House, Allahabad, India.
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| 10. |
- Jakobsson, Martin, et al.
(författare)
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Reconstructing the Younger Dryas ice dammed lake in the Baltic Basin: Bathymetry, area and volume
- 2007
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 1872-6364 .- 0921-8181. ; 57:3-4, s. 355-370
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Tidskriftsartikel (refereegranskat)abstract
- A digital 3D-reconstruction of the Baltic Ice Lake's (BIL) configuration during the termination of the Younger Dryas cold phase (ca. 11700 cal. yr BP) was compiled using a combined bathymetric-topographic Digital Terrain Model (DTM), Scandinavian ice sheet limits, Baltic Sea Holocene bottom sediment thickness information, and a paleoshoreline database maintained at the Lund University. The bathymetric-topographic DTM, assembled from publicly available data sets, has a resolution of 500 X 500 m on Lambert Azimuthal Equal Area projection allowing area and volume calculations of the BIL to be made with an unprecedented accuracy. When the damming Scandinavian ice sheet margin eventually retreated north of Mount Billingen, the high point in terrain of Southern central Sweden bordering to lower terrain further to the north, the BIL was catastrophically drained resulting in a 25 m drop of the lake level. With our digital reconstruction, we estimate that approximately 7800 km(3) of water drained during this event and that the ice dammed lake area was reduced by ca. 18%. Building on previous results suggesting drainage over 1 to 2 years, our lake volume calculations imply that the freshwater flux to the contemporaneous sea in the west was between about 0.12 and 0.25 Sv. The BIL reconstruction provides new detailed information on the paleogeography in the area of southern Scandinavia, both before and after the drainage event, with implications for interpretations of geological records concerning the post-glacial environmental development. (c) 2007 Elsevier B.V All rights reserved.
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