| 1. |
- Barnekow, Lena, et al.
(författare)
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Boreal forest dynamics in north-eastern Sweden during the last 10,000 years based on pollen analysis
- 2008
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Ingår i: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 17:6, s. 687-700
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Tidskriftsartikel (refereegranskat)abstract
- A pollen record obtained from a 2.2-m sediment succession deposited in a small lake in the province of Vasterbotten, north-eastern Sweden, reveals the presence of continuous forest cover since 8,500 calendar years before present (cal B.P.). Forest with abundant Pinus (pine) and Betula (birch) initially colonized the area, followed by a dominance of deciduous trees, primarily Betula, from ca. 8,000 to ca. 3,200 cal B.P. Pollen accumulation rates of Quercus (oak), Ulmus (elm) and Tilia (linden) suggest the possible local presence of these thermophilous tree species during this period. The climate gradually became colder and moister around 3,500 cal B.P. and an increased abundance of Sphagnum spores indicates paludification. Picea (spruce) became established around 3,200 cal B.P. and less than 500 years later this was the dominant tree species around the lake. The fire frequency as inferred from charcoal particles exhibits a general increase from ca. 3,000 cal B.P. with subsequent charcoal accumulation maxima at around 2,800 cal B.P., 1,700 cal B.P. and in recent time. The human influence on vegetation was significant during the last 200-300 years. Soil erosion increased substantially and fern spores amount to ca. 55% of the total pollen assemblage in the uppermost samples. These results suggest an extensive anthropogenic impact on the local forest ecosystem, with abundant logging, burning and ditching in the vicinity of the lake. Independent evidence of sub-recent human-induced environmental change is provided by historical accounts. Complementary information on catchment soil development and aquatic nutrient status was provided by records of magnetic susceptibility and elemental carbon, and nitrogen contents obtained from the same sediment core.
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| 2. |
- Barnekow, Lena
(författare)
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Holocene vegetation dynamics and climate changes in the Torneträsk area, northern Sweden
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this study was to reconstruct the Holocene vegetation history and the climate changes in a subarctic area. The results are based on pollen and macrofossil records from six lakes in the Torneträsk area. The lakes are situated at altitudes between 370 and 999 m a.s.l., along a transect from the boreal pine-birch forest to the alpine tundra with heath vegetation. The chronology in each lake is based on radiocarbon dated terrestrial plant macrofossils and combined with varve chronology in one of the lakes. Ages from radiocarbon dated plant macrofossils were compared with ages from radiocarbon dated bulk sediment samples in two of the lakes. The results show that radiocarbon dated bulk sediment samples give older ages compared to the macrofossil samples. The age differences varied between 550 and 2200 years in samples from a lake with calcareous rich sediment and between 250 and 800 years in samples from lake sediment with a low carbonate carbon content. Erroneous high ages from bulk sediment samples will not only effect the chronology, but will also lead to incorrect pollen-influx calculations. The results of this study also indicate that the tree-line, which consists of mountain birch (Betula pubescens ssp. tortuosa), was situated c. 300-400 m above the present tree-line during the early and the mid-Holocene. When land up-lift has been taken into account this higher tree-line corresponds to a summer temperature of 1.5-2°C higher than today. The climate was warm and moist during the early Holocene and warm and dry during the mid-Holocene. A pine-birch forest expanded first in the eastern part of the Torneträsk area at c. 8300 cal BP and about 700 years later to the western part at low altitudes. Optimal conditions for pine (Pinus sylvestris) occurred between 6300 and 4500 cal BP when the pine-birch forest reached its highest altitude at least 560 m a.s.l., i.e. 110 m above the present pine limit. During this time the pine limit reached 175 m above the present. Dry conditions during this interval are also supported from lake-level studies in one of the lakes, which show that the lake level was lowered c. 1-1.5 m. At 4500 cal BP the tree-line begun to descend and the lake-level rose again. The climate became both colder and more humid than before. As a result of this climate change the vegetation became more mosaic-like with sparse forests also at low altitudes and the heath vegetation increased.
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| 3. |
- Barnekow, Lena, et al.
(författare)
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Strong correlation between summer temperature and pollen accumulation rates for Pinus sylvestris, Picea abies and Betula spp. in a high resolution record from northern Sweden
- 2007
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Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 22:7, s. 653-658
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Tidskriftsartikel (refereegranskat)abstract
- Highly resolved pollen spectra analysed from a 47cm peat monolith recovered from a mire in northern Sweden exhibit climatic sensitivity in the pollen accumulation rates (PAR) of boreal treeline species. Robust temporal control, afforded through multiple AMS radiocarbon dating of the post atomic bomb-test period (AD1961-AD2002), provides a unique opportunity to compare pollen accumulation rates with the instrumental meteorological record. A series of strong correlations are observed between summer temperature and PAR for Pinus sylvestris, Picea abies and Betula spp. (excluding B. nana). Despite well constrained, contiguous (“annual”) sampling, the temporal resolution of the pollen signal preserved within each sample appears to be degraded to ca. 3-5 year resolution. This is likely to reflect processes occurring during peat accumulation and pollen deposition, as well as dating uncertainties and the effects of sub-sampling. These findings identify limitations to the maximum resolution that may realistically be recovered from the peat archive using high resolution sampling protocols and AMS 14C dating. We also identify the need for additional work to quantify the role of climate on peat accumulation and the resultant impact on assemblage based palaeoenvironmental reconstructions within mire sequences. The strongest climate association observed for Picea abies (r2adjusted = 0.53; n=36), was extended through the monolith beyond the 42 year period of “annual” sampling and the response successfully correlated with the Bottenviken historical instrumental record to AD1860. Although only presenting data from a single site, and requiring wider replication, we conclude that for sites close to the ecological limits of tree species, where levels of anthropogenic/non-climatic forcing on pollen production are low, well-dated records of PAR may potentially provide a proxy for reconstructing past summer temperature variability.
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| 4. |
- Berglund, Björn, et al.
(författare)
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Early Holocene history of the Baltic Sea, as reflected in coastal sediments in Blekinge, southeastern Sweden
- 2005
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Ingår i: Quaternary International. - : Elsevier BV. - 1873-4553 .- 1040-6182. ; 130:1, s. 111-139
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Tidskriftsartikel (refereegranskat)abstract
- Integrated palaeoecological studies of two fiord sediment sequences in the province of Blekinge, SE Sweden, covering the time span 11,000-5000 cal BP, reveal the timing and the environment for the Ancylus Lake/Littorina Sea transition 9800-8500 cal BP. The first ingression of saline water into the Baltic Sea through the Danish Straits occurred earlier than formerly assumed. New evidence, particularly mineral magnetic and palaeobotanical analyses, demonstrate that on the general trend of the eustatically caused Littorina transgression several minor fluctuations of the water level can be identified between 8500 and 5000 cal years BP. A distinct regression phase around 8 100 cal BP is correlated with the Greenland ice-core cold event dated to 8200 ice-core years BP. This is described as a regional climatic catastrophe for the Baltic Sea region. The coastal stratigraphy is compared with the offshore stratigraphy earlier studied. A tentative shore displacement curve for Early and Middle Holocene is presented.
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| 5. |
- Bergman, Jonas, et al.
(författare)
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Deglacial vegetation succession and Holocene tree-limit dynamics in the Scandes Mountains, west-central Sweden: stratigraphic data compared to megafossil evidence
- 2005
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Ingår i: Review of Palaeobotany and Palynology. - : Elsevier BV. - 0034-6667. ; 134:3-4, s. 129-151
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Forskningsöversikt (refereegranskat)abstract
- High-resolution records of plant macrofossils, magnetic susceptibility, and total carbon content, complemented by pollen data, were obtained from a postglacial lake sediment sequence at alpine Lake Stentjarn (987 m a.s.l.), in west-central Sweden. Holocene vegetational and environmental changes were reconstructed from the data, with particular emphasis on the deglacial establishment of terrestrial vegetation and subsequent tree-limit dynamics. A short-lived pioneer flora with Geum rivale, Dryas octopetala, Empetrum nigrum, Ledum palustre, Saxifraga sp., Salix spp., and Oxyria digyna established locally following deglaciation at c. 10,500 cat year BP. The pioneer flora was out-competed by establishing Betula pubescens and grasses at c. 10,300 cat year BP. Subsequent local expansions of B. pubescens at c. 9800 cat year BP and Pinus sylvestris at c. 9200 cal year BP were followed by a temporary retraction of the birch tree-limit and a permanent retreat of pine between 8500 and 8000 cat year BP, accompanied by declining aquatic productivity and increasing catchment erosion. A gradual decrease in forest density initiated at c. 6000 cat year BP led to a retreat of the birch tree-limit from the lake catchment at c. 3500 cat year BP, followed by persistence of scattered trees until c. 2000 cat year BP. A mosaic heath vegetation dominated by Empetrum nigrum and Betula nana developed at c, 3500 cat year BP. Comparison of the stratigraphic data from Lake Stenljiirn with records of radiocarbon-dated subfossil wood remains (megafossils) obtained from adjacent areas during recent decades revealed a high level of consistency of the inferred tree-limit variations for P. sylvestris, B. pubescens, and Alnus incana. Chronological control was established by radiocarbon dating of terrestrial macrofossils and geochemical identification of a tephra horizon originating from the Icelandic Askja- 1875 eruption.
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| 6. |
- Bigler, Christian, et al.
(författare)
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Holocene environmental history of Lake Vuolep Njakajaure (Abisko National Park, Northern Sweden) reconstructed using biological proxy indicators
- 2006
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Ingår i: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 15:4, s. 309-320
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Tidskriftsartikel (refereegranskat)abstract
- Holocene environmental and climatic changes are reconstructed using analyses of biological proxies in lake sediments from Vuolep Njakajaure, a lake located near the altitudinal treeline in northern Sweden (68 degrees 20' N, 18 degrees 47' E). We analysed biological proxy indicators from both aquatic and terrestrial ecosystems, including diatoms, pollen and chironomid head capsules, in order to reconstruct regional Holocene climate and the development of the lake and its catchment. During the early Holocene and after 2500 cal B.P., Fragilaria taxa dominated the diatom assemblages, whereas planktonic Cyclotella taxa prevailed during the major part of the Holocene (7800-2300 cal B.P.), indicating the importance of the pelagic habitat for diatom assemblage composition. The planktonic diatoms appeared at the same time as Alnus became established in the catchment, probably altering nutrient availability and catchment stability. The pollen record is dominated by mountain birch (Betula pubescens ssp. tortuosa) pollen throughout the Holocene, but high percentage abundances of Scots pine (Pinus sylvestris) pollen suggest the presence of a mixed pine-birch forest during the mid-Holocene (6800-2300 cal B.P.). Head capsules of Tanytarsini and Psectrocladius dominated the chironomid assemblage composition throughout the Holocene, in combination with Corynocera ambigua after 2300 cal B.P. A quantitative, diatom-based reconstruction of mean July air temperature indicated a relatively cold temperature during the early Holocene (9000-8000 cal B.P.) and after ca. 2300 cal B.P., whereas the mid-Holocene period is characterised by stable and warm temperatures. The overall patterns of Holocene climate and environmental conditions are similarly described by all biological proxy-indicators, suggesting relatively warm conditions during the mid-Holocene (ca. 7800-2300 cal B.P.), with a subsequent colder climate after 2300 cal B.P. However, the onset and magnitude of the inferred changes differ slightly among the proxies, illustrating different responses to lake development phases, land-uplift, and climate forcing (e.g., insolation patterns) during the Holocene in northern Sweden.
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| 7. |
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| 8. |
- Gaillard, Marie-José, 1953-, et al.
(författare)
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Holocene land-cover reconstructions for studies on land cover-climate feedbacks
- 2010
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 6, s. 483-499
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Tidskriftsartikel (refereegranskat)abstract
- The major objectives of this paper are: (1) to review the pros and cons of the scenarios of past anthropogenic land cover change (ALCC) developed during the last ten years, (2) to discuss issues related to pollen-based reconstruction of the past land-cover and introduce a new method, REVEALS (Regional Estimates of VEgetation Abundance from Large Sites), to infer long-term records of past land-cover from pollen data, (3) to present a new project (LANDCLIM: LAND cover – CLIMate interactions in NW Europe during the Holocene) currently underway, and show preliminary results of REVEALS reconstructions of the regional land-cover in the Czech Republic for five selected time windows of the Holocene, and (4) to discuss the implications and future directions in climate and vegetation/land-cover modeling, and in the assessment of the effects of human-induced changes in land-cover on the regional climate through altered feedbacks. The existing ALCC scenarios show large discrepancies between them, and few cover time periods older than AD 800. When these scenarios are used to assess the impact of human land-use on climate, contrasting results are obtained. It emphasizes the need for methods such as the REVEALS model-based land-cover reconstructions. They might help to fine-tune descriptions of past land-cover and lead to a better understanding of how long-term changes in ALCC might have influenced climate. The REVEALS model is demonstrated to provide better estimates of the regional vegetation/landcover changes than the traditional use of pollen percentages. This will achieve a robust assessment of land cover at regional- to continental-spatial scale throughout the Holocene. We present maps of REVEALS estimates for the percentage cover of 10 plant functional types (PFTs) at 200 BP and 6000 BP, and of the two open-land PFTs “grassland” and “agricultural land” at five time-windows from 6000 BP to recent time. The LANDCLIM results are expected to provide crucial data to reassess ALCC estimates for a better understanding of the land suface-atmosphere interactions.
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| 9. |
- Hammarlund, Dan, et al.
(författare)
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Holocene changes in atmospheric circulation recorded in the oxygen-isotope stratigraphy of lacustrine carbonates from northern Sweden
- 2002
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 12:3, s. 339-351
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Tidskriftsartikel (refereegranskat)abstract
- The oxygen-isotope composition of local precipitation (delta(18)O(P)) is reconstructed from carbonate lake-sediment components in a sediment core covering the last 10000 calendar years from Lake Tibetanus, a small, hydrologically open, groundwater-fed take in the Abisko area, northern Sweden. Comparison of the delta(18)O(P) history with a pollen-based palaeotemperature record from the same core clearly reveals pronounced deviations from the normally expected temporal delta(18)O(P)-temperature relation (so-called 'Dansgaard relation') that may be a function of changing oceanicity. The transition from relatively moist, maritime conditions in the early Holocene to a much drier climate after 6500 cal. BP is reflected by major changes in forest extent and composition as recorded by pollen and plant macrofossil data. At the time of maximum influence of westerly air-mass circulation (high zonal index) c. 9500 cal. BP, brought about by high summer insolation and enhanced meridional pressure gradients. delta(18)O(P) at Lake Tibetanus was about 2%, higher than would be predicted by the modem isotope-temperature relation, The occurrence of long-term changes in delta(18)O(P)-temperature relations, which are more sensitive measures of palaeoclimate than either delta(18)O(P) or temperature alone, needs to be taken into account when extracting palaeoclimatic information from continental oxygen-isotope records.
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| 10. |
- Hammarlund, Dan, et al.
(författare)
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Multi-component carbon isotope evidence of early Holocene environmental change and carbon-flow pathways from a hard-water lake in northern Sweden
- 1997
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Ingår i: Journal of Paleolimnology. - 0921-2728. ; 18:3, s. 219-233
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Tidskriftsartikel (refereegranskat)abstract
- A 9000-year carbonate-rich sediment sequence from a small hard-water lake in northernmost Sweden was studied by means of multi-component stable carbon isotope analysis. Radiocarbon dating of different sediment fractions provides chronologic control and reveals a rather constant hard-water effect through time, suggesting lake has remained hydrologically open throughout the Holocene. Successive depletion of C-13 in fine-grained calcite and carbonate shells during the early Holocene correlate with a change in catchment vegetation from pioneer herb communities to boreal forest. The vegetational change and associated soil development likely gave rise to an increased supply of C-13-depleted carbon dioxide in groundwater recharging the lake. This process is therefore believed to be the main cause of decreasing values of delta(13)C in dissolved inorganic carbon of the lake and thereby in limnic carbonates. Strongly C-13-depleted sedimentary organic matter may be related to enhanced kinetic fractionation during photosynthetic assimilation by means of proton pumping in Characean algae. This interpretation is supported by a substantial offset between delta(13)C of DIC as recorded by mollusc shells and delta(13)C Of fine-grained calcite.
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