| 1. |
- Bergman, Jonas, et al.
(författare)
-
Deglacial vegetation succession and Holocene tree-limit dynamics in the Scandes Mountains, west-central Sweden: stratigraphic data compared to megafossil evidence
- 2005
-
Ingår i: Review of Palaeobotany and Palynology. - : Elsevier BV. - 0034-6667. ; 134:3-4, s. 129-151
-
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.
|
|
| 2. |
- Blaauw, M., et al.
(författare)
-
Bayesian testing for synchrony of events in glacial proxy archives
- 2007
-
Ingår i: European Geosciences Union, 2007. ; , s. 00301-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Often chronological uncertainties are ignored in multi-site comparisons, resulting inpotentially wrong assumptions concerning (a)synchrony of events between archives.We explore this problem in a Bayesian framework, constructing millions of plausiblewiggle-match age-models in order to quantify the chronological uncertainties withinand between proxy archives. Using these data we can now calculate the statisticalprobability that events indeed coincided. The method is applied to a high-resolution14C and OSL dated lake core from south-eastern France which largely predates theIntCal04 14C calibration curve. Depending on the applied comparison curve, eventsin this core appear synchronous or asynchronous with events in the NGRIP ice core.
|
|
| 3. |
- Davies, SM, et al.
(författare)
-
Cryptotephra sedimentation processes within two lacustrine sequences from west central Sweden
- 2007
-
Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 17:3, s. 319-330
-
Tidskriftsartikel (refereegranskat)abstract
- Distal tephra horizons, particularly within lacustrine sequences, are increasingly being used as time-synchronous marker horizons within palaeoclimatic and palaeoenvironmental investigations. As sedimentary features marking the presence of these so-called cryptotephras are absent to the naked eye, it is of some importance that the stratigraphic position representing primary airfall, and likewise the timing Of the volcanic event, is accurately and consistently recorded amongst these deposits. Often tephra shards from a cryptotephra deposit can be found spanning several centimetres of sediments within lacustrine and peat sequences. Very few studies, however, have looked in detail at the sedimentation and vertical distribution of cryptotephra deposits within such sequences and, more importantly, the criteria for defining the correct stratigraphic position of the volcanic event. Two sediment cores from Lake Spaime and Lake Getvaltjarnen, west central Sweden are employed to investigate in detail the vertical distribution of the tephra shards derived from the AD 1875 eruption of the Askja volcano in Iceland. Detailed geochemical analysis of shards from both records indicate that products of the Askja eruption are present for at least 120 years and thus emphasize the importance of carefully identifying the correct horizon that marks the timing of the volcanic event rather than shards resulting from a period of reworking or downward migration. Both sites yield contrasting shard concentration profiles and thus raise a number of questions regarding the influence of site-specific processes on cryptotephra sedimentation, particularly the role of snow-beds acting as tephra traps, the possibility of reworking, and downward migration of shards in soft sediment. A second tephra is also identified at Lake Getvaltjarnen and is believed to originate from the AD 1477 Veidivotn eruption and represents the first occurrence of this tephra outside of Iceland.
|
|
| 4. |
|
|
