| 1. |
- Felde, Vivian A., et al.
(författare)
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Compositional turnover and variation in Eemian pollen sequences in Europe
- 2020
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Ingår i: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 29:1, s. 101-109
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Tidskriftsartikel (refereegranskat)abstract
- The Eemian interglacial represents a natural experiment on how past vegetation with negligible human impact responded to amplified temperature changes compared to the Holocene. Here, we assemble 47 carefully selected Eemian pollen sequences from Europe to explore geographical patterns of (1) total compositional turnover and total variation for each sequence and (2) stratigraphical turnover between samples within each sequence using detrended canonical correspondence analysis, multivariate regression trees, and principal curves. Our synthesis shows that turnover and variation are highest in central Europe (47-55 degrees N), low in southern Europe (south of 45 degrees N), and lowest in the north (above 60 degrees N). These results provide a basis for developing hypotheses about causes of vegetation change during the Eemian and their possible drivers.
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| 2. |
- Van Meerbeeck, C. J., et al.
(författare)
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The nature of MIS 3 stadial-interstadial transitions in Europe : New insights from model-data comparisons
- 2011
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 30:25-26, s. 3618-3637
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Tidskriftsartikel (refereegranskat)abstract
- 15 abrupt warming transitions perturbed glacial climate in Greenland during Marine Isotope Stage 3 (MIS 3, 60-27 ka BP). One hypothesis states that the 8-16 degrees C warming between Greenland Stadials (GS) and Interstadials (GI) was caused by enhanced heat transport to the North Atlantic region after a resumption of the Atlantic Meridional Overturning Circulation (AMOC) from a weak or shutdown stadial mode. This hypothesis also predicts warming over Europe, a prediction poorly constrained by data due to the paucity of well-dated quantitative temperature records. We therefore use a new evidence from biotic proxies and a climate model simulation to study the characteristics of a GS-GI transition in continental Europe and the link to enhanced AMOC strength. We compare reconstructed climatic and vegetation changes between a stadial and subsequent interstadial - correlated to GS15 and GI14 (similar to 55 ka BP) - with a simulated AMOC resumption using a three-dimensional earth system model setup with early-MIS 3 boundary conditions. Over western Europe (12 degrees W-15 degrees E), we simulate twice the annual precipitation, a 17 degrees C warmer coldest month, a 8 degrees C warmer warmest month, 1300 degrees C-day more growing degree days with baseline 5 degrees C (GDD5) and potential vegetation allowing tree cover after the transition. However, the combined effect of frequent killing frosts, <20 mm summer precipitation and too few GDD5 after the transition suggest a northern tree limit lying at similar to 50 degrees N during GI14. With these 3 climatic limiting factors we provide a possible explanation for the absence of forests north of 48 degrees N during MIS 3 interstadials with mild summers. Finally, apart from a large model bias in warmest month surface air temperatures, our simulation is in reasonable agreement with reconstructed climatic and vegetation changes in Europe, thus further supporting the hypothesis.
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| 3. |
- Alexanderson, Helena, et al.
(författare)
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Optical dating of a Late Quaternary sediment sequence from Sokli, northern Finland
- 2008
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Ingår i: Geochronometria. - : Walter de Gruyter GmbH. ; 32, s. 51-59
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Tidskriftsartikel (refereegranskat)abstract
- Interstadial and non-glacial stadial sediments collected in boreholes from Sokli in northeastern Finland have been dated by optically stimulated luminescence on quartz and feldspar grains. The quartz OSL ages follow stratigraphic order, with one exception, and support the litho- and biostratigraphical correlation with the NW European mainland climate-stratigraphy and the marine oxygen-isotope stages. Feldspar IRSL dates generally overestimate the age, probably due to incomplete bleaching. The data show that during the last glacial cycle northeastern Finland was not glaciated until MIS 5b, around 90 ka. Interstadial conditions occurred around ~94 ka (MIS 5c), ~74-80 ka (MIS 5a) and 42-54 ka (MIS 3). The OSL ages have large standard errors mainly due to small sample sizes, relatively poor luminescence characteristics and uncertainties in dose-rate determinations.
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| 4. |
- Bos, Johanna A. A., et al.
(författare)
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Flora, vegetation and climate at Sokli, northeastern Fennoscandia, during the Weichselian Middle Pleniglacial
- 2009
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 38:2, s. 335-348
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Tidskriftsartikel (refereegranskat)abstract
- A 2 m thick laminated lacustrine deposit of silt and clay recovered from the high-latitudinal site at Sokli (northern Finland) provides a unique mid-Weichselian fossil record for Fennoscandia. High-resolution botanical and zoological analyses of the lacustrine deposit allow detailed reconstruction of the regional vegetational development and of the history of the lake and the wetland ecosystem within the Sokli basin during the early part of the Weichselian Middle Pleniglacial (=equivalent to Marine Isotope Stage (MIS) 3). The inferred terrestrial vegetation represented by the Sokli MIS 3 sequence (so-called Tulppio Interstadial) was probably low-arctic tundra, treeless but with shrub elements including juniper, willow, dwarf birch, ericoids, lycopods and a rich herb flora with a variety of arctic-alpine taxa and heliophilous, pioneer elements. The presence of herbs such as Rubus chamaemorus, Epilobium palustre, Potentilla palustris and Sphagnum, Drepanocladus and other mosses suggests that the lake was fringed by wet meadows and peatlands or peaty telmatic communities. The distributional ranges of pine and tree birch were probably only a few hundred kilometres south or southeast of Sokli. This is concordant with evidence for the presence of boreal tree taxa during the MIS 3 in the Baltic countries and further east in Europe, but contradicts with the commonly inferred treeless tundra or grass-dominated steppe conditions in central Europe.
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| 5. |
- Engels, Stefan, et al.
(författare)
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A comparison of three Eurasian chironomid-climate calibration datasets on a W-E continentality gradient and the implications for quantitative temperature reconstructions
- 2014
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 51:4, s. 529-547
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Tidskriftsartikel (refereegranskat)abstract
- Multiple regional chironomid-climate calibration datasets are available to reconstruct quantitatively July air temperatures from fossil chironomid assemblages. We examined the relationship between July air temperature and the 40 most common chironomid taxa in three independent Eurasian calibration (training) sets. The estimated temperature optimum of each chironomid taxon is systematically lower (by similar to 1-2 A degrees C) in a Norwegian calibration set compared to Finnish and Russian calibration sets. This result might partly be explained by the fact that the Norwegian calibration set extends further at the cold end of the temperature gradient. A difference in continentality between the Russian sites and the European sites might also contribute to this pattern. The number of taxa that show a statistically significant unimodal response to temperature is higher in the Norwegian calibration set (34 out of 40 taxa) compared to the modern Finnish (11 of 37 taxa; 3 common taxa absent) and the Russian calibration set (20 of 40 taxa), probably due to the longer temperature gradient incorporated in the Norwegian calibration set. We applied all three calibration sets to fossil chironomid assemblages from the high-latitude study site of Sokli (northeast Finland), a site with a unique series of lacustrine deposits covering (amongst others) the Holocene, part of early MIS 3 (at similar to 53 ka) and MIS 5d-c (at similar to 110-95 ka) and with independent proxy-records for comparison. In the early Holocene and during MIS 5c, the chironomid-based temperature inferences from all three inference models had similar values. Temperature reconstructions based on the Norwegian calibration set are 2-4 A degrees C lower for the late Holocene, early MIS 3 and MIS 5d than the inferred temperatures based on the other calibration sets. Although the lakes included in the Finnish calibration set are located closest to the site of Sokli, evaluation tests and a comparison with independent proxy data suggests that the Norwegian calibration set provides the most suitable analogues for reconstruction purposes for most of the fossil assemblages. Our results imply that when choosing a calibration set for quantitative climate reconstructions on glacial timescales, regional proximity of the fossil site may not be a sufficient basis, and the length of the temperature gradient of the calibration dataset and factors such as the continentality gradient covered by the calibration set must also be considered.
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| 6. |
- Engels, Stefan, et al.
(författare)
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Early Weichselian (MIS 5d and 5c) temperatures and environmental changes in northern Fennoscandia as recorded by chironomids and macroremains at Sokli, northeast Finland
- 2010
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 39:4, s. 689-704
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Tidskriftsartikel (refereegranskat)abstract
- A 25-m-long sediment record spanning the time from the Eemian to the Holocene was recovered from Sokli, northeast Finland. This study focuses on a 6-m-long sediment interval that is dated to the Early Weichselian period (MIS 5d and 5c) and consists of lacustrine and fluvial deposits. Using chironomid remains, botanical and zoological macroremains as well as sediment lithology, we were able to reconstruct past changes in the environment, including climate. The results indicate that the site was situated on a flood-plain during the latter stages of MIS 5d (Herning Stadial) and that summer temperatures might have been similar to 6 degrees C lower than at present. Although this value should be treated with caution, as numerical analysis shows that it has a very poor fit-to-temperature, this low reconstructed value concurs with several other reconstructions that are available from western Europe. During MIS 5c (Brorup interstadial), the depositional environment changed into a lake system, initially with stratification of the water and subsequently with complete mixing and a strong influence of streams. Both chironomid-based and macroremain-based temperature inferences indicate past July air temperatures that were significantly higher than at present. This result is in contrast to other (low-resolution) reconstructions from northern Fennoscandia that indicate past temperatures 6-7 degrees C lower than present using fossil coleopteran assemblages. However, several central European sites indicate that there was a phase during the Brorup interstadial that was characterized by high summer temperatures, and a comparison between the high-resolution reconstructions from western Europe and the results presented in this study suggests that the north south July air temperature gradient between the mid- and high-latitudes was much weaker during the Brorup interstadial than it is at present. High solar insolation values (particularly the obliquity) during the Brorup interstadial might explain the low summer temperature gradient over the European continent. A return to fluvial conditions occurred in the upper parts of the sediment sequence, and, after a brief interval of gyttja deposition under cooling conditions, the site became glaciated during MIS 5b.
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| 7. |
- Finné, Martin, et al.
(författare)
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Last Interglacial Climate in Northern Sweden-Insights from a Speleothem Record
- 2019
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Ingår i: Quaternary. - : MDPI AG. - 2571-550X. ; 2:3
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Tidskriftsartikel (refereegranskat)abstract
- Continental records with absolute dates of the timing and progression of climatic conditions during the Last Interglacial (LIG) from northern Europe are rare. Speleothems from northern Europe have a large potential as archives for LIG environmental conditions since they were formed in sheltered environments and may be preserved beneath ice sheets. Here, we present delta C-13 and delta O-18 values from speleothem Kf-21, from Korallgrottan in Jamtland (northwest Sweden). Kf-21 is dated with five MC-ICPMS U-Th dates with errors smaller than similar to 1 ka. Kf-21 started forming at similar to 130.2 ka and the main growth phase with relatively constant growth rates lasted from 127.3 ka to 124.4 ka, after which calcite formation ceased. Both delta C-13 and delta O-18 show rapid shifts but also trends, with a range of values within their Holocene counterparts from Korallgrottan. Our results indicate an early onset of the LIG in northern Europe with ice-free conditions at similar to 130 ka. Higher growth rates combined with more negative delta O-18 values between similar to 127.3 and 126.8 ka, interpreted here as warmer and more humid conditions, as well as indications of a millennial-scale cold spell centered at 126.2 ka, resemble findings from speleothem records from other parts of Europe, highlighting that these were regional scale climatic patterns.
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| 8. |
- Helmens, Karin F., et al.
(författare)
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Ice-free conditions in eastern Fennoscandia during early Marine Isotope Stage 3 : lacustrine records
- 2010
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 39:2, s. 399-409
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Tidskriftsartikel (refereegranskat)abstract
- The traditional notion that Fennoscandia was glaciated throughout Marine Isotope Stages (MIS) 4-2, from c. 70 kyr BP to the deglaciation 15-10 kyr BP ago, has been challenged during the last decade. Recent studies have shown that climate and environmental settings during MIS 3 were more dynamic than previously assumed, and lacustrine sediment bodies indicate open-water conditions for several sites in eastern Fennoscandia. In this study, three sediment sequences from western, eastern and northeast Finland are compared in detail with respect to their chronology, vegetation reconstruction and climatic inferences. OSL-dating places the sediments in early MIS 3. Pollen evidence suggests the presence of isolated birch trees and open birch forest close to the retreating ice margin, in contrast to vegetation reconstructions from central Europe, which indicate tree-less vegetation. Furthermore, reconstructions of climate using transfer functions have yielded surprising results, indicating present-day summer temperatures in northeast Finland. The combined results suggest ice-free and warm conditions in major parts of eastern Fennoscandia in early MIS 3, possibly during Greenland Interstadial (GIS) 14 around 53 kyr BP ago.
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| 9. |
- Helmens, Karin F., et al.
(författare)
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Large shifts in vegetation and climate during the early weichselian (mis 5d c) inferred from multi proxy evidence at Sokli (Northern Finland)
- 2012
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 41, s. 22-38
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Tidskriftsartikel (refereegranskat)abstract
- For decades, detailed studies on Early Weichselian deposits have been made in central Europe. In contrast, these studies are rare in Fennoscandia in northern Europe. We here integrate an extensive multi-proxy data set obtained on sediments of MIS 5d-c age that form part of a long sediment record preserved at Sokli in northern Finland. We make a detailed interpretation of the vegetation and depositional history for MIS 5d-c using pollen, macrofossils, diatoms and other siliceous microfossils, insect remains, and sediment characteristics, and combine these data with recently published estimates on July temperatures based on chironomids and selected plant indicator species in order to make inferences of paleo-climate regimes. The fossil record obtained on the seven meter thick MIS 5d-c deposit at Sokli is exceptionally rich in species due to the large variety of habitats associated with an overall fluvial depositional environment. A braided river system flanked by steppe-tundra vegetation is inferred for MIS 5d. Mean July temperatures of at least 12-14 degrees C are indicated by chironomids and plant indicator species and are in agreement with the presence of conifers and birch trees as recorded by macrofossils. The reconstructed environmental conditions suggest strong continental climate conditions at Sokli during MIS 5d. The gradual infilling of an oxbow lake and subsequent return to stream channel deposition is traced in great detail in the overlying gyttja and gravelly sediment of MIS 5c age. The terrestrial pollen and plant macrofossil record from the gyttja shows the establishment of birch forest followed by the spread of pine and then spruce. Rich plant indicator species assemblages indicate that the boreal environment at Sokli during MIS 5c experienced July temperatures several degrees higher than the present-day value of 13 degrees C. The high summer temperatures and presence of larch suggest more continental conditions. More open vegetation returned at Sokli during late MIS 5c and was followed by glaciation by the Fennoscandian Ice Sheet (MIS 5b). Despite the major differences in zonal vegetation types during MIS 5d-c, differences in reconstructed July temperatures are minor and suggest that winter temperatures combined with precipitation values mostly determined the stadial-interstadial climate variability. The most compelling conclusion from our study is that forest development during MIS 5c was remarkably similar to that recorded for the Eemian (MIS 5e) and Holocene Interglacials at the high-latitude site Sokli, and also to that inferred from MIS 5c sediments on the northern European mainland. Our results question the definition of MIS 5c in the terrestrial record of Europe as an interstadial interval of the last glacial cycle and suggest inclusion of MIS 5c together with the Eemian (MIS 5e) in an interglacial complex.
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| 10. |
- Helmens, Karin F., et al.
(författare)
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Major cooling intersecting peak Eemian Interglacial warmth in northern Europe
- 2015
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 122, s. 293-299
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Tidskriftsartikel (refereegranskat)abstract
- The degree of climate instability on the continent during the warmer-than-present Eemian Interglacial (around ca. 123 kyr ago) remains unsolved. Recently published high-resolution proxy data from the North Atlantic Ocean suggest that the Eemian was punctuated by abrupt events with reductions in North Atlantic Deep Water formation accompanied by sea-surface temperature cooling. Here we present multiproxy data at an unprecedented resolution that reveals a major cooling event intersecting peak Eemian warmth on the North European continent. Two independent temperature reconstructions based on terrestrial plants and chironomids indicate a summer cooling of the order of 2-4 degrees C. The cooling event started abruptly, had a step-wise recovery, and lasted 500-1000 yr. Our results demonstrate that the common view of relatively stable interglacial climate conditions on the continent should be revised, and that perturbations in the North Atlantic oceanic circulation under warmer-than-present interglacial conditions may also lead to abrupt and dramatic changes on the adjacent continent.
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