| 1. |
- Andrén, Thomas, et al.
(författare)
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Correlation of Swedish glacial varves with the Greenland (GRIP) oxygen isotope record
- 1999
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Ingår i: Journal of Quaternary Science. - 0267-8179 .- 1099-1417. ; 14:4, s. 361-371
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Tidskriftsartikel (refereegranskat)abstract
- A mean varve thickness curve has been constructed for a part of the Swedish varve chronology from the northwestern Baltic proper. The mean varve thickness curve has been correlated with the delta(18)O record from the GRIP ice-core using the Younger Dryas-Preboreal climate shift. This climate shift was defined by pollen analyses. The Scandinavian ice-sheet responded to a warming at the end of the Younger Dryas, ca. 10 995 to 10 700 clay-varve yr BP. Warming is recorded as a sequence of increasing mean varve thickness and ice-rafted debris suggesting intense calving of the ice front. The Younger Dryas-Preboreal climatic shift is dated to ca. 10 650 clay-varve yr BP, about 40 yr after the final drainage of the Baltic Ice Lake. Both the pollen spectra and a drastic increase in varve thickness reflect this climatic shift. A climate deterioration, correlated with the Preboreal oscillation, is dated to ca. 10 440 to 10 320 clay-varve yr BP and coincides with the brackish water phase of the Yoldia Sea stage. The ages of the climatic oscillations at the Younger Dryas-Preboreal transition show an 875 yr discrepancy compared with the GRIP record, suggesting a large error in the Swedish varve chronology in the part younger than ca. 10 300 clay-varve yr BP.
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| 2. |
- Coope, G.R., et al.
(författare)
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Temperature gradients in northern Europe during the last glacial-Holocene transition (14-9 14C kyr BP) interpreted from coleopteran assemblages.
- 1998
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Ingår i: Journal of Quaternary Science. - 0267-8179 .- 1099-1417. ; 13:5, s. 419-433
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Tidskriftsartikel (refereegranskat)abstract
- Late-glacial and early Holocene climatic conditions have been reconstructed for northern Europe using the mutual climatic range (MCR) palaeoclimate method based on fossil coleopteran assemblages. Altogether, beetle faunas from 77 sites have been analysed ranging from Ireland in the west to Poland and Finland in the east, and MCR estimates calculated. The results are plotted on 16 maps, each representative of a selected time-slice covering the period from 14.5 C-14 kyr BP to 9.0 C-14 kyr BP. Eight of the maps show the MCR estimates of T-max (mean temperature of the warmest month) derived from each site for which data are available, while the remainder show estimated T-max isotherms interpolated from these values. It can be demonstrated that at times the thermal climate was fairly uniform throughout the study area, whereas at others temperature gradients were much steeper than they are in the region today. There also appears to be a distinct contrast between cold periods, when contours trended NW-SE, and warmer periods, when contours trend W-E or even NE-SW. The pattern of climatic changes that emerges is shown to be very different from the traditional view that has been used up to now as a template for classifying Late-glacial climatic events on a wide, even global, scale. The suddenness and intensity of changes in the thermal climate may have been partially responsible for an apparent lack of equilibrium between the flora and fauna of the time and the physical environment in which they lived.
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| 3. |
- Björck, S., et al.
(författare)
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An event stratigraphy for the Last Termination in the North Atlantic region based on the Greenland Ice-core record: a proposal by the INTIMATE group.
- 1998
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Ingår i: Journal of Quaternary Science. - 0267-8179 .- 1099-1417. ; 13:4, s. 283-292
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Tidskriftsartikel (refereegranskat)abstract
- It is suggested that the GRIP Greenland ice-core should constitute the stratotype for the Last Termination. Based on the oxygen isotope signal in that core, a new event stratigraphy spanning the time interval from ca. 22.0 to 11.5 k GRIP yr BP (ca. 19.0-10.0 k C-14 yr BP) is proposed for the North Atlantic region. This covers the period from the Last Glacial Maximum, through Termination 1 of the deep-ocean record, to the Pleistocene-Holocene boundary, and encompasses the Last Glacial Late-glacial of the traditional northwest European stratigraphy. The isotopic record for this period is divided into two stadial episodes, Greenland Stadials 1 (GS-1) and 2 (GS-2), and two interstadial events, Greenland Interstadials 1 (GI-1) and 2 (GI-2). In addition, GI-1 and GS-2 are further subdivided into shorter episodes. The event stratigraphy is equally applicable to ice-core, marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon-dated chronostratigraphy that has been used hitherto.
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| 4. |
- Witte, H.J.L., et al.
(författare)
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Regression coefficients of thermal gradients in northwestern Europe during the last glacial-Holocene transition using beetle MCR data.
- 1998
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Ingår i: Journal of Quaternary Science. - 0267-8179 .- 1099-1417. ; 13:5, s. 435-445
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Tidskriftsartikel (refereegranskat)abstract
- Palaeotemperature estimates obtained from 74 sites in northern Europe, and collectively spanning approximately the last 45 000 yr (radiocarbon time-scale), have been compiled as a major component of the EPECC project. The data presented here have been obtained using the mutual climatic range (MCR) method based on beetle assemblage data. The sites range across a transect from Ireland in the west to Poland and Finland in the east. Thermal gradients have been derived from the data using multiple linear regression. The regression models were solved for each of a series of 'time windows'. Each interval has a separate time-dependant trend, which was removed by detrending before solving the regression equations. The robustness and confidence intervals of the regression coefficients were estimated using the bootstrap method, with samples being selected from the data set by Monte Carlo simulation. The resulting palaeotemperature gradients were compared with modern temperature gradients over Europe. The data suggest that there were significant changes in the steepness of latitudinal temperature gradients over northern Europe during the past 45000 yr, although most attention in our compilations is focused on the last glacial-Holocene transition, the period for which the most abundant data are available so far. A significant delay in warming at the end of the last glacial stage in the northern part of the study area, by comparison with the southern sector, is also inferred. Reasons for these temporal and geographical variations and their possible palaeoclimatic implications are discussed.
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| 5. |
- Adrielsson, Lena, et al.
(författare)
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Interactions between the Greenland Ice Sheet and the Liverpool Land coastal ice cap during the last two glaciation cycles
- 2005
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Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 20:3, s. 269-283
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Tidskriftsartikel (refereegranskat)abstract
- The sedimentary record from the Ugleelv Valley on central Jameson Land, East Greenland, adds new information about terrestrial palaeoenvironments and glaciations to the glacial history of the Scoresby Sund fjord area. A western extension of a coastal ice cap on Liverpool Land reached eastern Jameson Land during the early Scoresby Sund glaciation (approximate to the Saalian). During the following glacial maximum the Greenland Ice Sheet inundated the Jameson Land plateau from the west. The Weichselian also starts with an early phase of glacial advance from the Liverpool Land ice cap, while polar desert and ice-free conditions characterised the subsequent part of the Weichselian on the Jameson Land plateau. The two glaciation cycles show a repeated pattern of interaction between the Greenland Ice Sheet in the west and an ice cap on Liverpool Land in the east. Each cycle starts with extensive glacier growth in the coastal mountains followed by a decline of the coastal glaciation, a change to cold and arid climate and a late stage of maximum extent of the Greenland Ice Sheet.
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| 6. |
- Alexanderson, Helena, et al.
(författare)
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Depositional history of the North Taymyr ice-marginal zone, Siberia - a landsystem approach
- 2002
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Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 17:4, s. 361-382
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Tidskriftsartikel (refereegranskat)abstract
- The sediment-landform associations of the northern Taymyr Peninsula in Arctic Siberia tell a tale of ice sheets advancing from the Kara Sea shelf and inundating the peninsula, probably three times during the Weichselian. In each case the ice sheet had a margin frozen to its bed and an interior moving over a deforming bed. The North Taymyr ice-marginal zone (NTZ) comprises ice-marginal and supraglacial landsystems dominated by thrust-block moraines 2-3 km wide and large-scale deformation of sediments and ice. Large areas are still underlain by remnant glacier ice and a supraglacial landscape with numerous ice-walled lakes and kames is forming even today. The proglacial landsystem is characterised by subaqueous (e.g. deltas) or terrestrial (e.g. sandar) environments, depending on location/altitude and time of formation. Dating results (OSL, C-14) indicate that the NTZ was initiated ca. 80 kyr BP during the retreat of the Early Weichselian ice sheet and that it records the maximum limit of a Middle Weichselian glaciation (ca. 65 kyr BP). During both these events, proglacial lakes were dammed by the ice sheets. Part of the NTZ was occupied by a thin Late Weichselian ice sheet (20-12 kyr BP), resulting in subaerial proglacial drainage. Copyright (C) 2002 John Wiley Sons, Ltd.
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| 7. |
- Ammann, B, et al.
(författare)
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The Würmian Late-glacial in lowland Switzerland
- 1994
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 9:2, s. 119-125
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Tidskriftsartikel (refereegranskat)abstract
- A synthesis is provided of Late-glacial (14-9 ka BP) environmental changes in lowland Switzerland (the 'Swiss Plateau'). The chronology of deglaciation and subsequent developments in vegetation cover in the area are summarised. The sequence of climatic variations experienced in the region during the Late-glacial is then described and a curve representing the main palaeotemperature variations is presented.
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| 8. |
- Andersson, Rina Argelia, et al.
(författare)
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Elemental and isotopic carbon and nitrogen records of organic matter accumulation in a Holocene permafrost peat sequence in the East European Russian Arctic
- 2012
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 27:6, s. 545-552
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Tidskriftsartikel (refereegranskat)abstract
- A peat deposit from the East European Russian Arctic, spanning nearly 10 000 years, was investigated to study soil organic matter degradation using analyses of bulk elemental and stable isotopic compositions and plant macrofossil remains. The peat accumulated initially in a wet fen that was transformed into a peat plateau bog following aggradation of permafrost in the late Holocene (similar to 2500 cal a BP). Total organic carbon and total nitrogen (N) concentrations are higher in the fen peat than in the moss-dominated bog peat layers. Layers in the sequence that have lower concentrations of total hydrogen (H) are associated with degraded vascular plant residues. C/N and H/C atomic ratios indicate better preservation of organic matter in peat material dominated by bryophytes as opposed to vascular plants. The presence of permafrost in the peat plateau stage and water-saturated conditions at the bottom of the fen stage appear to lead to better preservation of organic plant material. delta 15N values suggest N isotopic fractionation was driven primarily by microbial decomposition whereas differences in delta 13C values appear to reflect mainly changes in plant assemblages. Positive shifts in both delta 15N and delta 13C values coincide with a local change to drier conditions as a result of the onset of permafrost and frost heave of the peat surface. This pattern suggests that permafrost aggradation not only resulted in changes in vegetation but also aerated the underlying fen peat, which enhanced microbial denitrification, causing the observed 15N-enrichment.
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| 9. |
- Andersson, Sofia, 1975-, et al.
(författare)
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Late Holocene climate change in central Sweden inferred from lacustrine stable isotope data
- 2010
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Ingår i: Journal of Quaternary Science. - : John Wiley & Sons. - 0267-8179 .- 1099-1417. ; 25, s. 1305-1316
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Tidskriftsartikel (refereegranskat)abstract
- Stable isotopes (18O and 13C) of lacustrine carbonates (Chara spp algae and Pisidium spp molluscs) from a lake sedimentary sequence in central Sweden were analysed to infer changes in lake hydrology and climate during the late Holocene. Results from analysis of lake water isotopes (18O and 2H) show that Lake Blektjärnen water isotope composition is responsive to the water balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate, decreasing the relative importance of precipitation input. Under such conditions evaporation and atmospheric equilibration enrich lake water in 18O and 13C, respectively, which is reflected in the isotopic composition of the carbonates in the lake. From the relatively positive Chara 18O values we infer that conditions were dry and warm between 4400-4000 cal yr BP whereas more negative values indicate that conditions were wetter and probably cooler between 4000-3000 cal yr BP. A drier climate is inferred from more positive values between 2500-1000 cal yr BP. However, a successive depletion after ca 1750 cal yr BP, also detected in several other 18O records (carbonate and diatom), suggest increasingly wetter conditions in Scandinavia after that time, which is probably related to increased zonal flow.
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| 10. |
- Andersson, Sofia, 1975-, et al.
(författare)
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Late Holocene humidity changes inferred from stable isotopes in Chara encrustations and Pisidium shells in a lacustrine sediment sequence from central Sweden
- 2010
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 8:25, s. 1305-1316
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Tidskriftsartikel (refereegranskat)abstract
- Stable isotopes (δ18O and δ13C) of lacustrine carbonates (Chara spp. algae and Pisidium spp. molluscs) from a lake sedimentary sequence in central Sweden were analysed to infer changes in lake hydrology and climate during the late Holocene. Results from analysis of lake water isotopes (δ18O and δ2H) show that Lake Blektjärnen water isotope composition is responsive to the balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate, decreasing the relative importance of precipitation input. Under such conditions evaporation and atmospheric equilibration probably enrich lake water in 18O and 13C, respectively, which is reflected in the isotopic composition of the carbonates in the lake. From the relatively positive Chara δ18O values we infer that conditions were dry and warm between 4400 and 4000 cal. a BP, whereas more negative values indicate that conditions were wetter and probably cooler between 4000 and 3000 cal. a BP. A drier climate is inferred from more positive values between 2500 and 1000 cal. a BP. However, a successive depletion after ca. 1750 cal. a BP, also detected in several other δ18O records (carbonate and diatom), suggest increasingly wetter conditions in Scandinavia after that time, which is probably related to increased strength of the zonal flow.
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| 11. |
- Andresen, Camilla Snowman, et al.
(författare)
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Holocene climate changes in southern Greenland: evidence from lake sediments
- 2004
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Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 19:8, s. 783-795
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Tidskriftsartikel (refereegranskat)abstract
- A Holocene lake sediment record is presented from Lake N14 situated on Angissoq island 15 km off the main coast of southern Greenland. The palaeoclimatic development has been interpreted on the basis of flux and percentage content of biogenic silica, clastic material, organic material and sulphur as well as sedimentation rate, moss content and magnetic susceptibility. A total of 43 radiocarbon dates has ensured a reliable chronology. It is argued that varying sediment composition mainly reflects changing precipitation. By analogy with the present meteorological conditions in southern Greenland, Holocene climate development is inferred. Between 11550 and 9300 cal. yr BP temperature and precipitation increase markedly, but this period is climatically unstable. From 9300 yr BP conditions become more stable and a Holocene climatic optimum, characterised by warm and humid conditions, is observed from 8000 to 5000 cal. yr BP. From 4700 cal. yr BP the first signs of a climatic deterioration are observed, and from 3700 cal. yr BP the climate has become more dry and cold. Superimposed on the climatic long-term trend is climate variability on a centennial time-scale that increases in amplitude after 3700 cal. yr BP. A climatic scenario related to the strength and position of the Greenland high-pressure cell and the Iceland low-pressure cell is proposed to explain the Holocene centennial climate variability. A comparison of the Lake N14 record with a terrestrial as well as a marine record from the eastern North Atlantic Ocean suggests that the centennial climate variability was uniform over large areas at certain times.
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| 12. |
- Antonsson, Karin, et al.
(författare)
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Quantitative palaeotemperature records inferred from fossil pollen and chironomid assemblages from Lake Gilltjärnen, northern central Sweden
- 2006
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 21:8, s. 831-841
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Tidskriftsartikel (refereegranskat)abstract
- Palaeotemperature reconstructions based on radiocarbon-dated fossil pollen and chironomid stratigraphies obtained from Lake Gilltjarnen provide evidence of climate changes during the last 11 000 years in the boreal zone of northern central Sweden. The records show consistent trends during the early and mid-Holocene, indicating low temperatures at 11 000-10 000 cal. yr BP, followed by a rising trend and a period of maximum values from about 7000 to 4000 cal. yr BP. At 3000 cal. yrBP the chironomid-inferred temperature values rise abruptly, deviating from the late-Holocene cooling trend indicated by the pollen-based reconstruction and most of the other palaeotemperature records from central Scandinavia, probably as a result of local limnological changes in Lake Gilltjarnen and its catchment. Comparison of the present results with a lake-level reconstruction from Lake Ljustjarnen, ca. 100 km southwest of Lake Gilitjarnen, shows that the low early-Holocene temperatures were associated with high lake-levels at 10500-8500 cal. yrBP, whereas low lake-levels and dry conditions prevailed during the period of high temperatures at between 7500 and 5000 cal. yr BP, probably due to high summer evapotranspiration and lower precipitation.
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| 13. |
- Apolinarska, Karina, et al.
(författare)
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Multi-component stable isotope records from Late Weichselian and early Holocene lake sediments at Imiolki, Poland: palaeoclimatic and methodological implications
- 2009
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Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 24:8, s. 948-959
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Tidskriftsartikel (refereegranskat)abstract
- Late Weichselian and early Holocene climatic and environmental changes are inferred from stable carbon and oxygen isotope records obtained on bulk and biogenic carbonates from the sediment sequence of Lake Lednica, western Poland. Along with sediment and pollen stratigraphic data, a wide range of carbonate components occurring in the sediments was analysed for delta C-13 and delta O-18, including shells of several gastropod species and the bivalve genus Pisidium, carapaces of the ostracod subfamily Candoninae and oogonia of the aquatic macrophyte genus Chara. The development of catchment soils and the onset of authigenic carbonate production in response to the climatic amelioration during the Late Weichselian are clearly reflected by rising carbonate content, distinct isotopic shifts in bulk carbonates and decreasing delta C-13 values of bulk organic matter in the sediments. The GI-1/GS-1 (the Bolling-Allerod Interstadial complex/Younger Dryas Stadial) and the GS-1/Preboreal transitions are marked by significant shifts in delta O-18 values of 2-3 parts per thousand, as well as by distinct changes in carbonate content, indicative of a decrease and a subsequent increase in mean annual temperature. Corresponding delta C-13 records reflect primarily changes in aquatic productivity, with favourable conditions for phytoplankton and macrophytes during GI-1 and the Preboreal resulting in persistent C-13 enrichment. The Younger Dryas Stadial is characterised by depletions in C-13 and O-18, with indications of a climatic tripartition. Consistent offsets in delta C-13 and delta O-18 between records obtained on specific carbonate components reflect vital effects in combination with seasonal characteristics and habitat preferences of the respective carbonate-precipitating biota. Largely parallel first-order variations in delta C-13 and delta O-18 of the different carbonate components demonstrate that individual isotope records may provide important palaeoclimatic information, although more detailed reconstructions can be obtained from multi-component analysis. Copyright (C) 2009 John Wiley & Sons, Ltd.
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| 14. |
- Aradottir, N., et al.
(författare)
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Drumlin formation within the Bustarfell drumlin field, northeast Iceland: integrating sedimentological and ground-penetrating radar data
- 2022
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 38:3, s. 386-402
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Tidskriftsartikel (refereegranskat)abstract
- Drumlins are important bedforms of former glaciated landscapes as they demonstrate past ice-flow directions and elucidate processes that operated at the ice/bed interface. Recently mapped drumlins and other streamlined subglacial bedforms in northeast Iceland reveal the flow-sets of cross-cutting palaeo-ice streams that were active within the Iceland Ice Sheet (IIS) during and following the Last Glacial Maximum. Here we study the Bustarfell drumlin field within the Vopnafjorour-Jokuldalsheioi flow-set. The internal architecture of two drumlins was investigated using sedimentological analysis and ground-penetrating radar (GPR, 50 and 100 MHz) to illuminate subglacial processes that contributed to drumlin formation, as well as the history and dynamics of the IIS. On the stoss side of one of the drumlins, two subglacial traction till units were identified, separated by a thick unit of deformed glaciofluvial sand and gravel. The core of glaciofluvial material suggests that the drumlin formed around well-drained patches (sticky spots) in the subglacial bed that retarded the ice flow locally through increased basal drag and encouraged till deposition. Furthermore, our GPR data indicate a combination of erosional and depositional processes. We suggest that the glaciofluvial sediments were deposited as small ice-marginal fans on the Bustarfell plateau, possibly during the Bolling-Allerod interstadial, and that the drumlins were formed around these fans during a subsequent readvance during the Younger Dryas.
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| 15. |
- Balashova, Anna, et al.
(författare)
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The Lake Natron Footprint Tuff (northern Tanzania) : volcanic source, depositional processes and age constraints from field relations
- 2016
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 31:5, s. 526-537
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Tidskriftsartikel (refereegranskat)abstract
- The Engare Sero Footprint Site, situated on the southern shore of Lake Natron in northern Tanzania, has been reported to host one of the best preserved sets of fossilized hominid footprints in the world. However, until now there has been no detailed characterization and age determination of the footprint-bearing strata (the Footprint Tuff). Here, we combine field observations with geochemical and mineralogical analyses and measurements of the anisotropy of magnetic susceptibility to constrain depositional processes, the role of reworking and the volcanic source for the Footprint Tuff. We find that the footprint-bearing horizon consists of volcanic ash-fall that has been slightly reworked by water, and that this was produced during a voluminous eruption of the Oldoinyo Lengai volcano. The unit, which covered the footprints and helped to preserve them, consists of the wind-blown material from the same eruption, mixed together with locally derived detrital material. We can constrain the ash horizon to be of Holocene age, based on: (i) the location of the Footprint Tuff within the regional stratigraphy, (ii) previous age determination of an ash layer that can be correlated with the Footprint Tuff and (iii) the regional climatological history of the area. The ash horizon was probably deposited around 11000-10500 years ago, but could potentially be even younger than this.
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| 16. |
- 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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| 17. |
- Belle, Simon
(författare)
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Abrupt rise in the contribution of CH4-derived carbon to benthic secondary production of a shallow hemiboreal/boreal lake
- 2018
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 33, s. 969-976
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Tidskriftsartikel (refereegranskat)abstract
- Understanding long-term carbon flows through aquatic food webs is essential to assess impact of climatic and environmental changes on lake ecosystems. We reconstructed temporal changes in carbon sources fuelling chironomid biomass in a small and shallow hemiboreal/boreal lake over the last 11 000 years. Results were compared with temporal dynamics of known potential controlling factors: summer air temperature, human activities, phytoplankton assemblages and organic matter composition. We report an abrupt rise in the contribution of methane-derived carbon to chironomid biomass. However, this sudden increase was not the consequence of drastic changes in the composition of sedimentary organic matter, mean air temperature, lake trophic state or human activities in the catchment area. Our results suggest that shallowing of the lake caused by sedimentary infilling processes was a possible driver of the expansion of anoxic zones, enhancing CH4 cycling in lake sediments. However, complementary studies are needed to better understand the mechanisms by which lake shallowing could affect carbon flows to aquatic consumers, and then better assess the natural dynamics of past carbon processing in the benthic food web of shallow lakes.
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| 18. |
- Bennike, O, et al.
(författare)
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Chronology of the last recession of the Greenland Ice Sheet
- 2002
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Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 17:3, s. 211-219
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Tidskriftsartikel (refereegranskat)abstract
- A new deglaciation chronology for the ice-free parts of Greenland, the continental shelf and eastern Ellesmere Island (Canada) is proposed. The chronology is based on a new compilation of all published radiocarbon dates from Greenland, and includes crucial new material from southern, northeastern and northwestern Greenland. Although each date provides only a minimum age for the local deglaciation, some of the dates come from species that indicate ice-proximal glaciomarine conditions, and thus may be connected with the actual ice recession. In addition to shell dates, dates from marine algae, lake sediments, peat, terrestrial plants and driftwood also are included. Only offshore and in the far south have secure late-glacial sediments been found. Other previous reports of late-glacial sediments (older than 11.5 cal. kyr BP) from onshore parts of Greenland need to be confirmed. Most of the present ice-free parts of Greenland and Nares Strait between Greenland and Ellesmere Island were not deglaciated until the early Holocene. Copyright (C) 2002 John Wiley Sons, Ltd.
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| 19. |
- Berglund, Björn E., et al.
(författare)
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Late Weichselian environmental change in southern Sweden and Denmark
- 1994
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 9:2, s. 127-132
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Tidskriftsartikel (refereegranskat)abstract
- A synthesis is presented of the envronmental and climatic variations that are inferred to have occurred in southern Sweden (up to latitude 59°N) and Denmark during the Weichselian Late-glacial (14-9 ka BP). The chronology and characteristics of the main phases of deglaciation, sea-level change, periglacial activity, soil development, vegetation cover and climate change are summarised. A curve representing the main changes in temperature, including quantitative estimates based upon beetle data and using the ‘mutual climatic range’ method, is presented.
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| 20. |
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| 21. |
- Berglund, Mikael
(författare)
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The Holocene shore displacement of Gästrikland, eastern Sweden : A contribution to the knowledge of Scandinavian glacio-isostatic uplift
- 2005
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 20:6, s. 519-531
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Tidskriftsartikel (refereegranskat)abstract
- The shore displacement in Gästrikland, east-central Sweden, has been investigated by means of AMS radiocarbon dating of sediment cores from isolated basins. Twenty dates from 11 sites are presented. Pollen and diatom analyses, and archive material from the Geological Survey of Sweden, have been used to identify isolation intervals in the cores and as chronological support to the 14C dates. An important pollen stratigraphical time-marker is a distinct mid-Holocene increase in Tilia. For the mid-Holocene, pollen stratigraphy is used rather than the 14C dates for the age determination. The deglaciation of Gästrikland, according to the new 14C dates, took place ca. 11 000 cal. yr BP (ca. 9500 14C yr BP). Through the Holocene the shore displacement is regressive. The regression was initially rapid (on average ca. 3.5 m per 100 yr 11 000-7500 cal. yr BP, probably much more rapid at the earliest stage), then slowed down considerably and was from ca. 5000 cal. yr BP (probably already from 7000 cal. yr BP) relatively constant, ca. 0.8-0.9 m per 100 yr. There are important differences between the shore level curve from Gästrikland and curves from other areas, indicating some irregularities in the regional glacio-isostatic rebound.
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| 22. |
- Bergman, Jonas, et al.
(författare)
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Holocene tephra horizons at Klocka Bog, west-central Sweden: aspects of reproducibility in subarctic peat deposits
- 2004
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 19:3, s. 241-249
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents one of the most extensive Holocene tephra records found to date in Scandinavia. Microtephra horizons originating from Icelandic eruptions were recorded in two ca. 2 m thick peat profiles at Klocka Bog in west-central Sweden. Five of the microtephra horizons were geochemically correlated to the Askja-1875, Hekla-3, Kebister, Hekla-4 and Lairg A tephras respectively. Radiocarbon-based dating of these tephras broadly agree with previously published ages from Iceland, Sweden, Germany and the British Isles. The identification of the Lairg A tephra demonstrates a more widespread distribution than previously thought, extending the usefulness of Icelandic Holocene tephrochronology further north into west-central Scandinavia. Long-lasting snow cover and seasonal wind distribution in the lower stratosphere are suggested as factors that may be responsible for fragmentary tephra deposition patterns in peat deposits of subarctic Scandinavia.
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| 23. |
- Bigg, Grant R., et al.
(författare)
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Last glacial ice-rafted debris off southwestern Europe : the role of the British-Irish Ice Sheet
- 2010
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 25:5, s. 689-699
-
Tidskriftsartikel (refereegranskat)abstract
- Ice-rafted debris (IRD) seeded into the ocean from Northern Hemisphere ice sheets is found in ocean cores along the southwestern European margin through the last glacial period. It is known that the origin of this IRD, especially off Iberia, can vary between North America and western Europe during short-lived episodes of greatly enhanced iceberg flux, known as Heinrich events, although in most Heinrich events the IRD has a North American source. During the longer times of much lower IRD fluxes between Heinrich events, use of an intermediate complexity climate model, coupled to an iceberg dynamic and thermodynamic model, shows that background levels of IRD most likely originate from western Europe, particularly the British Irish Ice Sheet. Combining modelling with palaeoceanographic evidence supports reconstructions of a short-lived, but substantial, Celtic and Irish Sea Ice Stream around 23 ka.
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| 24. |
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| 25. |
- Björck, Svante, et al.
(författare)
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A magnetostratigraphic comparison between 14C years and varve years during the late Weichselian, indicating significant differences between the time-scales
- 1987
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 2:2, s. 133-140
-
Tidskriftsartikel (refereegranskat)abstract
- A 14C-dated magnetostratigraphy of absolute declination and inclination between 12500 and 10000 14C yr BP was recently developed for southern Sweden. Recently also the Swedish geochronological time-scale, based on c. 11 500 annually deposited clay-varves, was connected with the present. It should therefore be possible to compare the two chronologies with a reliable magnetostratigraphic record in an appropriate clay-varve section. We have found such a site within the Middle Swedish end-moraine zone. Statistical correlations between the two independently dated time-scales suggest that at 10500–10200 14Cy r BP the varve chronology exceeds the 14C chronology by the order of 500-600 varve yr. Other correlations indicate that the difference between the two chronologies was less at 11000 14C yr BP, and further correlations between the time-scales at 12000 14C yr BP suggest that the difference between the chronologies increased steadily from 12000 to 10000 14C yr BP. If these correlations are correct they imply that the 14C production rate increased steadily during the Late Weichselian.
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| 26. |
- Blaauw, M., et al.
(författare)
-
Were last glacial climate events simultaneous between Greenland and France?
- 2010
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 25:3, s. 387-394
-
Tidskriftsartikel (refereegranskat)abstract
- Several large abrupt climate fluctuations during the last glacial have been recorded in Greenland ice cores and archives from other regions. Often these Dansgaard–Oeschger events are assumed to have been synchronous over wide areas, and then used as tie-points to link chronologies between the proxy archives. However, it has not yet been tested independently whether or not these events were indeed synchronous over large areas. Here, we compare Dansgaard–Oeschger-type events in a well-dated record from southeastern France with those in Greenland ice cores. Instead of assuming simultaneous climate events between both archives, we keep their age models independent. Even these well-dated archives possess large chronological uncertainties that prevent us from inferring synchronous climate events at decadal to multi-centennial time scales. If possible, comparisons between proxy archives should be based on independent, non-tuned time-scales.
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| 27. |
- Bordiga, Manuela, et al.
(författare)
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Coccolithophore carbonate during the last 450 ka in the NW Pacific Ocean (ODP site 1209B, Shatsky Rise)
- 2014
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 29:1, s. 57-69
-
Tidskriftsartikel (refereegranskat)abstract
- This study focuses on Pleistocene-Holocene sediments from the Shatsky Rise (Ocean Drilling Program Site 1209B, NW Pacific Ocean). We quantify the contribution of calcite made by coccoliths in oceanic sediments, investigating the role of calcareous nannoplankton during the last 450 ka. Coccolith carbonate constitutes 60-90% of bulk carbonate. Coccolith carbonate accumulation rates (CARs) and CaCO3 fine fraction confirm that coccolithophores are major contributors to the carbonate export and accumulation. Primary productivity shows highest values from marine isotope stage (MIS) 12 to 8. Thereafter, although coccolith calcite content remains high, other sediment components, such as as foraminifera and biogenic opal, seem to be favored, perhaps related to an increase in fertilization by eolian dust. Our results demonstrate the important role of coccolithophore production and sedimentation on the regulation of ocean carbonate chemistry on time scales >1000-100 000 years. On glacial-interglacial scales, coccolithophore productivity could have affected deep-water saturation by buffering deep-sea CO2 through increased carbonate dissolution episodes. Spectral and wavelet analyses are consistent with CARs primarily driven by glacial-interglacial variability and obliquity-controlled changes. Coccolith-based paleoceanographic reconstructions allow us to establish that during the last 450 ka the mid-latitudes of the NW Pacific are controlled by the dynamics of the El Nino Southern Oscillation perturbations and Boreal Monsoon system.
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| 28. |
- Borgmark, Anders, et al.
(författare)
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A comparative study of peat proxies from two eastern central Swedish bogs and their relation to meteorological data
- 2006
-
Ingår i: Journal of Quaternary Science. - : John Wiley & Sons. - 0267-8179 .- 1099-1417. ; 21:2, s. 109-114
-
Tidskriftsartikel (refereegranskat)abstract
- Analyses of peat humification, testate amoebae, carbon and nitrogen content have been carried out on a peat sequence from Ältabergsmossen. At Gullbergbymossen testate amoebae and peat humification were analysed. Both bogs are located in eastern central Sweden. The longest sequence, Ältabergsmossen, covers the last 150 yr and the data from Gullbergbymossen covers the last 60 yr, both with a time resolution of ca. 2–4 yr cm−1. The different proxies were compared to each other and were also compared to instrumental meteorological data. Correlation between peat humification and C/N ratios is high whereas the correlation is low between these physical/chemical parameters and reconstructed water tables inferred from the testate amoebae assemblages. High peat humification values and C/N ratios greater than 50 indicate aerobic decay and are thought to reflect the thickness of the acrotelm. High humification values and low C/N ratios are recorded in peat deposited between 1965 and 1980, whereas the dry period starts in the early 1970s according to instrumental meteorological data and inferred water-table depth. The difference in the timing of the onset of a dry-shift between the physical/chemical proxies and meteorological data and testate amoebae derived water table changes is interpreted as renewed decay of already deposited peat. The term secondary decomposition is used for this process. The secondary decomposition process has implications for interpreting physical/chemical and biological parameters in peat as they may be out of phase during the beginning of a dry-shift.
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| 29. |
- Boston, Clare M., et al.
(författare)
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Topographic controls on plateau icefield recession : insights from the Younger Dryas Monadhliath Icefield, Scotland
- 2019
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 34:6, s. 433-451
-
Tidskriftsartikel (refereegranskat)abstract
- Plateau icefields are a common form of mountain ice mass, frequently found in mid-latitude to high-arctic regions and increasingly recognized in the Quaternary record. Their top-heavy hypsometry makes them highly sensitive to changes in climate when the equilibriaum line altitude (ELA) lies above the plateau edge, allowing ice to expand significantly as regional ELAs decrease, and causing rapid recession as climate warms. With respect to future climate warming, it is important to understand the controls on plateau icefield response to climate change in order to better predict recession rates, with implications for water resources and sea-level rise. Improving knowledge of the controls on glacier recession may also enable further palaeoclimatic information to be extracted from the Quaternary glacial record. We use the distribution of moraines to examine topographic controls on Younger Dryas icefield recession in Scotland. We find that overall valley morphology influences the style of recession, through microclimatic and geometric controls, with bed gradient affecting moraine spacing. Ice mass reconfiguration may occur as recession progresses because ice divide migration could alter the expected response based on hypsometric distribution. These results add to a growing body of research examining controls on glacier recession and offer a step towards unravelling non-linear ice mass behaviour.
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| 30. |
- Cartier, Rosine, et al.
(författare)
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Paleohydrological history of Lake Allos (2200 m a.s.l) since 13 500 cal a bp in the Mediterranean Alps inferred from an ostracod δ18O record
- 2022
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 37:6, s. 1044-1055
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the first Lateglacial/Holocene (the last 13 500 cal a bp) ostracod δ18O record to infer hydroclimate variability in the Southern French Alps. Cytherissa lacustris (δ18Osp) shells extracted from the sediments of Lake Allos allowed a reconstruction of δ18Olake water (δ18Olw) except for the interval 5800–2800 cal a bp. The shape of the Younger Dryas (YD) clearly differed from records documented in the northern Alps. First, δ18Olw values remained close to modern values before a marked drop ca. 12 000 cal a bp. Then, after several oscillations, δ18Olw values increased, reaching the highest value of the record ca. 6100 cal a bp during a thermal optimum for this latitude. Finally, low δ18Olw values occurred from 450 to 100 cal a bp during the Little Ice Age (LIA) following the Medieval Climate anomaly. At the beginning of the YD, δ18Olw probably reflected changes in local glacier dynamics and precipitation sources. The following decrease in δ18Olw values was associated with higher freshwater inputs during the second half of the YD. During the LIA, the low δ18O values are consistent with a higher torrential activity and lower air temperatures.
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| 31. |
- Chabangborn, Akkaneewut, 1977-, et al.
(författare)
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Climate over mainland Southeast Asia 10.5–5 ka
- 2014
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 29:5, s. 445-454
-
Tidskriftsartikel (refereegranskat)abstract
- We assembled and evaluated Holocene palaeo-vegetation records regarding semi-quantitative precipitation and temperature for mainland Southeast Asia and compared these with precipitation reconstructions for the Indian Ocean (IOM) and East Asian (EAM) monsoon sub-systems. Our results indicate that temperatures and precipitation in mainland Southeast Asia generally exceeded 18 °C and 1100 mm a−1 during the Holocene. Mainland Southeast Asia experienced cool/wet climatic conditions between 10.5 and 10 ka BP, a warmer/drier climate between 10 and 9 ka BP, cooler/wetter conditions between 9 and 7 ka BP, and moderately warmer/drier conditions since 7 ka BP. The reconstructed summer monsoon intensity compares well with the reconstructed hydroclimate for the EAM region, but diverges from that of the IOM region between 10.5 and 9 ka BP and 7–6.5 ka BP. This discrepancy is explained by differences in land–sea configuration, and regional sea-level history. A strengthening/weakening of the Asian summer monsoon between 9 and 7 ka BP and after 6.5 ka BP, respectively, is observed across the whole Asian monsoon region. Our new data sets support an asynchronous onset of the Asian summer monsoon optimum.
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| 32. |
- Coope, G.R., et al.
(författare)
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Regional differences in the Lateglacial climate of northern Europe based on coleopteran analysis.
- 1995
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 10:4, s. 391-395
-
Tidskriftsartikel (refereegranskat)abstract
- The termination of the Last Glaciation, the Lateglacial period, was characterised by highly unstable climates which, in northern Europe, oscillated between warm temperate and arctic conditions. Different indicators of past climate have provided contrasting views an the timing and intensity of these climatic changes. Here we present preliminary reconstructions of the thermal climate interpreted from subfossil coleopteran assemblages from Britain, Norway, Sweden and Poland, in which regional differences can be ascribed to the varying influence of, (a) the North Atlantic surface water temperatures, (b) the proximity of the Fennoscandian ice sheet and (c) the ice free continent. Quantification of the thermal climate enables these local differences to be resolved.
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| 33. |
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| 34. |
- Davies, Siwan M, et al.
(författare)
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Identification of the Fugloyarbanki tephra in the NGRIP ice-core: a key tie-point for marine and ice-core sequences during the last glacial period
- 2008
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 23:5, s. 409-414
-
Tidskriftsartikel (refereegranskat)abstract
- A visible tephra horizon in the NGRIP ice core has been identified by geochemical analysis as the Fugloyarbanki Tephra, a widespread marker horizon in marine cores from the Faroe Islands area and the northern North Atlantic. An age of 26 740 ± 390 yr b2k (1σ uncertainty) is derived for this tephra according to the new Greenland Ice Core Chronology (GICC05) based on multi-parameter counting of annual layers. Detection of this tephra for the first time within the NGRIP ice core provides a key tie-point between marine and ice-core records during the transition between MIS 3 and 2. Identification of this volcanic event within the Greenland records demonstrates the future potential of using tephrochronology to precisely correlate palaeoarchives in widely separated localities that span the last glacial period, as well as providing a potential method for examining the extent of the radiocarbon marine reservoir effect at this time.
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| 35. |
- de Jong, Rixt, et al.
(författare)
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Storminess variation during the last 6500 years as reconstructed from an ombrotrophic peat bog in Halland, southwest Sweden
- 2006
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 21:8, s. 905-919
-
Tidskriftsartikel (refereegranskat)abstract
- Cores taken from an ombrotrophic peat bog in the coastal zone of Halland, southwest Sweden, were examined for wind transported mineral grains, pollen and humidity indicators. The core covers the period from 6500 cal. yr BP to present. Ombrotrophic conditions existed from ca. 4200 cal. yr BP onwards. Bog surface wetness fluctuated strongly until ca. 3700 cal. yr BP, with an apparent dominance of dry summer conditions from 4800-4500 cal. yr BP. Local wet shifts occurred around 4300, 2800, 2400 and 1500 cal. yr BP, whereas the most recent 600 years of the record show increasingly dry conditions. Mineral grain content, interpreted as aeolian sand influx (ASI), was used as a proxy for (winter) storm frequency and intensity until ca. 1500 cal. yr BP, after which increasing human impact, as reconstructed by pollen analysis, became a second important potential cause for increased sand drift. Strongly increased storminess occurred at 4800, 4200, 2800-2200, 1500, 1100 and 400-50 cal. yr BP, indicating a dominance of cold and stormy winters during these periods. Many of these storm periods apparently coincide with storm events in other sites in southwestern Scandinavia, suggesting that our ASI record reflects a regional scale climatic signal. Furthermore these stormy periods correlate to well-known cold phases in the North Atlantic region, suggesting a link to large-scale fluctuations in atmospheric circulation patterns.
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| 36. |
- Delmonte, Barbara, et al.
(författare)
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Aeolian dust in the Talos Dome ice core (East Antarctica, Pacific/Ross Sea sector) : Victoria Land versus remote sources over the last two climate cycles
- 2010
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 25:8, s. 1327-1337
-
Tidskriftsartikel (refereegranskat)abstract
- A new ice core (TALDICE) drilled at Tabs Dome (East Antarctica, Ross Sea sector) preserves a ca. 250 ka long record of palaeoclimate and atmospheric history. We investigate dust variability and provenance at the site during glacial periods and the Holocene through the Sr-Nd isotopic composition of ice core dust and potential source areas (PSA). We provide new isotopic data on dust sources from Victoria Land such as regoliths, glacial drifts, aeolian sands and beach deposits. Some of these sources are located at high altitude and are known to have been ice free throughout the Pleistocene. The major features of the TALDICE dust record are very similar to those from central East Antarctica. During glacial times, South America was the dominant dust supplier for Tabs Dome as well as for the entire East Antarctic plateau. Conversely, during the Holocene the principal input of mineral dust at Tabs Dome probably derives from proximal sources which are the ice-free areas of northern Victoria Land, located at similar altitude with respect to the drilling site. Atmospheric mobilisation of dust from these neighbouring areas and transport inland to Tabs Dome can be ultimately associated with advection of maritime air masses from the Pacific/Ross Sea region. Copyright (C) 2010 John Wiley & Sons, Ltd.
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| 37. |
- Dowling, Thomas, et al.
(författare)
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Rapid subglacial streamlined bedform formation at a calving bay margin
- 2016
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 31:8, s. 879-892
-
Tidskriftsartikel (refereegranskat)abstract
- Using the LiDAR-derived Swedish national height model we have identified previously undescribed shallow streamlined glacial bedforms, small-scale drumlins, on the Närke plain in south-central Sweden. These drumlins could only be detected with high-resolution LiDAR, due to both their subtle size and forest cover. In this area the ice margin receded in a subaqueous environment with a proglacial water depth in the order of 100 m during the last deglaciation. As indicated by the configuration of marginally formed De Geer moraine ridges draping the drumlinoids, the receding ice margin formed deeply indented calving bays. These were located around subaqueous outlets of the subglacial melt-water drainage, with their apex position marked geomorphologically by beaded esker ridges. The mapped small-scale drumlins are aligned perpendicular to the reconstructed ice sheet margin and suggest formation along flow lines adjusted to the configuration of these calving embayments as they propagated up-flow with ice margin retreat. Based on these geometric relationships we argue that the emplacement of the drumlins was near-marginal, ∼7.7–1 km from the margin, on a short timescale (∼5–35 years).
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| 38. |
- Drobyshev, Igor, et al.
(författare)
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A 700-year record of large fire years in northern Scandinavia shows large variability and increased frequency during the 1800s
- 2015
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 30:3, s. 211-221
-
Tidskriftsartikel (refereegranskat)abstract
- Years with climatically mediated increases in boreal forest fire activity, referred to as large fire years (LFYs), contribute to a disproportionally large portion of the burned area over centuries, and are important drivers of ecosystem processes by affecting forest structure, biodiversity, and carbon balance at regional and continental scales. We analysed changes in LFY return intervals in northern Sweden (the area above 60°N) over 1273-1960 using a network of 29 sites with dendrochronologically reconstructed fires, complemented by documentary records of fires available from forestry statistics. We observed large variability in return intervals of LFYs, an increase in LFY frequency during the 1800s, and consistent associations between LFY occurrence and 500-hPa pressure anomalies over the European sub-continent over 1800xps2#1960. An increase in LFY frequency during the 1800s might be climatically driven, and would thus long precede the period of likely human-induced climatic changes of the 1900s. Long-term variability in climatically driven LFYs may present a challenge in partitioning the effects of human-related and human-independent components of climatic forcing upon forest fire activity. © 2015 John Wiley & Sons, Ltd.
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| 39. |
- Edvardsson, Johannes, et al.
(författare)
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Holocene peatland development and hydrological variability inferred from bog-pine dendrochronology and peat stratigraphy - a case study from southern Sweden
- 2012
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 27:6, s. 553-563
-
Tidskriftsartikel (refereegranskat)abstract
- Dendrochronological analysis was applied to subfossil remains of Scots pine (Pinus sylvestris L.) buried in a South Swedish peat deposit. In combination with peat stratigraphy, this approach was explored for its potential to provide information on the local hydrological and depositional history at the site, forming the basis for a regional palaeohydrological analysis. A 726-year ring-width chronology was developed and assigned an absolute age of 7233-6508cal a BP (5284-4559 BC) through cross-dating with German bog-pine chronologies, whereas two short additional records of older ages were radiocarbon dated. Registration of growth positions of individual trees allowed assessment of the spatial dynamics of the pine population in response to hydrological changes and peatland ontogeny. Annually resolved growth variability patterns in the pine population reveal several establishment and degeneration phases, probably reflecting fluctuations in bog-surface wetness. A major establishment phase at 7200-6900?cal a BP reflects the onset of a period of lowered groundwater level, also indicated by increased peat humification, and a development consistent with regional temperature and lake level reconstructions revealed from other proxies. This study demonstrates that subfossil bog-pine populations may provide annually to decadally resolved reconstructions of local groundwater variability, which are highly relevant in a long-term palaeoclimatic context. Copyright (c) 2012 John Wiley & Sons, Ltd.
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| 40. |
- Edvardsson, Johannes
(författare)
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Mid- to Late Holocene climate transition and moisture dynamics inferred from South Swedish tree-ring data
- 2016
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 31:3, s. 254-256
-
Tidskriftsartikel (refereegranskat)abstract
- A 1561-year tree-ring width (TRW) chronology covering the period 2668–1108 BC (4617–3057 BP) has been developed from 159 moisture-sensitive peatland pines (Pinus sylvestris L.) sampled at Åbuamossen, southern Sweden. Tree population dynamics and annual growth responses of the trees were shown to reflect and give absolute age to regional hydro-climatological changes. The main wet-shifts recorded in the TRW data were precisely dated to 2150–2100, 1550 and 1230–1150 BC (4100–4050, 3500 and 3180–3000 BP) and are likely to be related to the stepwise Mid- to Late Holocene climate transition, during which the condition changed from relatively warm and dry towards cold and moist in the northern hemisphere. The tree-colonization phase was ended by several long-lasting periods showing depressed annual tree growth and an abrupt dying-off phase, possibly caused by increasing water level in the peatland as well as the adjacent river Helge Å. This study demonstrates that TRW data obtained from subfossil peatland trees can provide detailed information and exact age control on moisture variability in peatlands associated with regional hydroclimatic changes. Moreover, the combined information from the stratigraphical and the TRW analyses enabled a detailed temporal and spatial site development reconstruction.
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| 41. |
- Ely, Jeremy C., et al.
(författare)
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Recent progress on combining geomorphological and geochronological data with ice sheet modelling, demonstrated using the last British-Irish Ice Sheet
- 2021
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 36:5, s. 946-960
-
Tidskriftsartikel (refereegranskat)abstract
- Palaeo-ice sheets are important analogues for understanding contemporary ice sheets, offering a record of ice sheet behaviour that spans millennia. There are two main approaches to reconstructing palaeo-ice sheets. Empirical reconstructions use the available glacial geological and chronological evidence to estimate ice sheet extent and dynamics but lack direct consideration of ice physics. In contrast, numerically modelled simulations implement ice physics, but often lack direct quantitative comparison with empirical evidence. Despite being long identified as a fruitful scientific endeavour, few ice sheet reconstructions attempt to reconcile the empirical and model-based approaches. To achieve this goal, model-data comparison procedures are required. Here, we compare three numerically modelled simulations of the former British–Irish Ice Sheet with the following lines of evidence: (a) position and shape of former margin positions, recorded by moraines; (b) former ice-flow direction and flow-switching, recorded by flowsets of subglacial bedforms; and (c) the timing of ice-free conditions, recorded by geochronological data. These model–data comparisons provide a useful framework for quantifying the degree of fit between numerical model simulations and empirical constraints. Such tools are vital for reconciling numerical modelling and empirical evidence, the combination of which will lead to more robust palaeo-ice sheet reconstructions with greater explicative and ultimately predictive power.
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| 42. |
- Esper, Jan, et al.
(författare)
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Northern European summer temperature variations over the Common Era from integrated tree-ring density records
- 2014
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 29:5, s. 487-494
-
Tidskriftsartikel (refereegranskat)abstract
- Tree-ring chronologies of maximum latewood density are most suitable to reconstruct annually resolved summer temperature variations of the late Holocene. The two longest such chronologies have been developed in northern Europe stretching back to the 2nd century BC, and the 5th century AD. We show where similarities between the two chronologies exist, and combine portions of both into a new summer temperature reconstruction for the Common Era. To minimize the transfer of potential biases, we assess the contribution of the candidate reconstructions' measurements, and exclude data (i) from exceptionally young and old trees, and (ii) produced by different laboratory technologies. Our new composite reconstruction reveals warmer conditions during Roman, Medieval and recent times, separated by prolonged cooling during the Migration period and Little Ice Age. Twentieth century warmth, as indicated in one of the existing density records, is reduced in the new reconstruction, also affecting the overall, millennial-scale, cooling trend over the late Holocene (-0.30 degrees C per 1000 years). Due to the reduced biological memory, typical for tree-ring density measurements, the new reconstruction is most suitable for evaluating the rate and speed of abrupt summer cooling following large volcanic eruptions.
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| 43. |
- Fang, Keyan, et al.
(författare)
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How robust are Holocene treeline simulations? A model-data comparison in the European Arctic treeline region
- 2013
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 28:6, s. 595-604
-
Tidskriftsartikel (refereegranskat)abstract
- Treeline encroachments and retractions can provide global-scale feedbacks to the climate system, and treeline dynamics are therefore of great relevance for understanding global climate variability. To assess the accuracy of long-term treeline simulations based on the generalized dynamic vegetation model LPJ-GUESS, we simulate European Arctic treeline dynamics over the past 9000 years and compare the results with fossil-based reconstructions. The results show that while LPJ-GUESS is limited in its ability to capture species-level current treeline patterns and past dynamics, it is generally able to realistically simulate the Holocene coniferous treeline changes with a cutoff biomass carbon of 2 C kg m(-2). The model captures the northward expansion of the boreal forest during the mid Holocene and correctly simulates a treeline retreat in response to climate cooling during the last 3000 years. However, there are data-simulation disagreements particularly during the early Holocene, which mainly result from the differences between the two palaeoclimate model scenarios used to drive the simulations. We suggest that the spatial accuracy of the model could be improved by incorporating the influence of topographic features, the extent of the Arctic peatlands, the tree species life-history characteristics, microclimate and other ecological factors. Copyright (c) 2013 John Wiley & Sons, Ltd.
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| 44. |
- Feurdean, A., et al.
(författare)
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Late Quaternary palaeocological and paleoclimatological reconstruction in the Gutaiului Mountains, NW Romania
- 2004
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 19:8, s. 809-827
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Tidskriftsartikel (refereegranskat)abstract
- Macrofossil, pollen, lithostratigraphy, mineral magnetic measurements (SIRM and magnetic susceptibility), loss-on-ignition, and AMS radiocarbon dating on sediments from two former crater lakes, situated at moderate altitudes in the Gutaiului Mountains of northwest Romania, allow reconstruction of Late Quaternary climate and environment. Shrubs and herbs with steppe and montane affinities along with stands of Betula and Pinus, colonised the surroundings of the sites prior to 14 700 cal. yr BP and the inferred climatic conditions were cold and dry. The gradual transition to open Pinus-Betula forests, slightly higher lake water temperatures, and higher lake productivity, indicate more stable environmental conditions between 14 700 and 14 100 cal. yr BP. This development was interrupted by cooler and drier climatic conditions between 14 100 and 13 800 cal. yr BP, as inferred from a reduction of open forests to patches, or stands, of Pinus, Betula, Larix, Salix and Populus. The expansion of a denser boreal forest, dominated by Picea, but including Pinus, Larix, Betula, Salix, and Ulmus started at 13 800 cal. yr BP, although the forest density seems to have been reduced between 13 400 and 13 200 cal. yr BP. Air temperature and moisture availability gradually increased, but a change towards drier conditions is seen at 13 400 cal. yr BP. A distinct decrease in temperature and humidity between 12 900 and 11 500 cal. yr BP led to a return of open vegetation, with patches of Betula, Larix, Salix, Pinus and Alnus and individuals of Picea. Macrofossils and pollen of aquatic plants indicate rising lake water temperatures and increased aquatic productivity already by ca. 11 800 cal. yr BP, 300 years earlier than documented by the terrestrial plant communities. At the onset of the Holocene, 11 500 cal. yr BP, forests dominated by Betula, Pinus and Larix expanded and were followed by dense Ulmus forests with Picea, Betula and Pinus at 11 250 cal. yr BP. Larix pollen was not found, but macrofossil evidence indicates that Larix was an important forest constituent at the onset of the Holocene. Moister conditions were followed by a dry period starting about 10 600 cal. yr BP, which was more pronounced between 8600 and 8200 cal. yr BP, as inferred from aquatic macrofossils. The maximum expansion of Tilia, Quercus, Fraxinus and Acer between 10 700 and 8600 cal. yr BP may reflect a more continental climate. A drier and/or cooler climate could have been responsible for the late expansion (10 300 cal. yr BP) and late maximum (9300 cal. yr BP) of Corylus. Increased water stress, and possibly cooler conditions around 8600 cal. yr BP, may have caused a reduction of Ulmus, Tilia, Quercus and Fraxinus. After 8200 cal. yr BP moisture increased and the forests included Picea, Tilia, Quercus and Fraxinus.
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| 45. |
- Filipsson, Helena, et al.
(författare)
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Relationships between primary productivity and bottom-water oxygenation off northwest Africa during the last deglaciation
- 2011
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Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 26:4, s. 448-456
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedThe upwelling region off northwest Africa is one of the most productive regions in the world ocean. This study details the response of surface-and deep-water environments off Mauritania, northwest Africa, to the rapid climate events of the last deglaciation, especially the Bolling-Allerod (15.5-13.5 ka BP) and Younger Dryas (13.5-11.5 ka BP). A high accumulation rate gravity core GeoB7926-2, recovered at similar to 20 degrees N, 18 degrees W, was analysed for the grain size distribution of the terrigenous sediment fraction, the organic carbon content, diatom and benthic foraminifera communities. Humid conditions were observed during the Bolling-Allerod with a high contribution of fluvial sediment input. During the Younger Dryas intensified trade winds caused a larger sediment input of aeolian dust from the Sahara and more intense upwelling with higher primary productivity, as indicated by high diatom concentrations. The abrupt and large increase of organic matter caused low oxygen conditions at the sea floor, reflected by the poor benthic foraminiferal fauna and the dominance of the low-oxygen-tolerant foraminiferal species Bulimina exilis. This is surprising since low-oxygen conditions have not been recorded during modern times at the sea floor in this region, despite present-day intensive upwelling and high primary productivity. After the Younger Dryas, more humid conditions returned, diatom abundance decreased and B. exilis was replaced by typical deep-sea species as found in the region today, indicating the return of more oxygenated conditions at the sea floor.
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| 46. |
- Fransner, O., et al.
(författare)
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Glacial landforms and their implications for glacier dynamics in Rijpfjorden and Duvefjorden, northern Nordaustlandet, Svalbard
- 2017
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 32:3, s. 437-455
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Tidskriftsartikel (refereegranskat)abstract
- Observations of subglacial landforms yielding the configuration and dynamics of former ice-flows have for the first time been made in Rijpfjorden and Duvefjorden, Nordaustlandet, Svalbard, using sub-bottom acoustic, swath-bathymetric data and sediment cores. Five acoustic-stratigraphic units were distinguished suggesting the presence of a complete glacial-postglacial succession in the central fjord basins. C-14 ages from the sediments indicate that the inner Rijpfjorden and central Duvefjorden were deglaciated before ca. 10.6 cal ka BP and 11.0 cal ka BP, respectively. Maximum sediment thickness in Rijpfjorden and Duvefjorden is 26 m, resulting in sediment accumulation rates of ca. 66 cm ka(-1). The landform record suggests that the ice streaming in both fjords was topographically controlled. The considerably deeper basin and higher elongation ratios of the crag-and-tails in Duvefjorden are linked to the faulted bedrock and possibly to somewhat larger ice stream and/or more focused ice-flow compared to that in Rijpfjorden. De Geer moraines suggest slower retreat of a grounded ice margin from shallow areas of Rijpfjorden. In deeper areas of the fjords, the glaciers were probably floating, resulting in the lack of ice-marginal transverse landforms. The ice margin retreat from these areas was probably relatively rapid and dominated by calving.
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| 47. |
- Fritz, Sherilyn C., et al.
(författare)
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Caribbean hydrological variability during the Holocene as reconstructed from crater lakes on the island of Grenada
- 2011
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Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 26:8, s. 829-838
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Tidskriftsartikel (refereegranskat)abstract
- Contemporary precipitation patterns in the Caribbean region are spatially variable, and the small number of Holocene paleoclimatic records may not adequately capture patterns of variation in the past. The hydrological history of Grenada was inferred from paleolimnological analyses of sediment cores from two crater lakes on the island. The basins were formed by volcanic activity some time during the Last Termination, but were dry between ca. 13 000 and ca. 7200 cal. a BP. After filling, the lakes were initially very shallow, and sedimentation was interrupted by a hiatus ca. 6300-5500 cal. a BP, followed by deposition of a thick tephra in both sites. After 5500 cal. a BP, lake level shows considerable multi-centennial variability, superimposed upon a long-term trend of generally higher lake level after 3200 cal. a BP. The pattern of lake-level variation in Grenada shows some similarity with other Caribbean paleoclimatic records in terms of the timing of transitions, but differs from several classic studies in the sign of inferred precipitation change. The differences among records may reflect spatially variable precipitation patterns in the past in response to the position of the Intertropical Convergence Zone and to sea surface temperature influences on the trade winds and Caribbean low-level jet. Copyright (C) 2011 John Wiley & Sons, Ltd.
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| 48. |
- Gayantha, Kasun, et al.
(författare)
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Reconstruction of the Late Holocene climate and environmental history from North Bolgoda Lake, Sri Lanka, using lipid biomarkers and pollen records
- 2020
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Ingår i: Journal of Quaternary Science. - : WILEY. - 0267-8179 .- 1099-1417. ; 35:4, s. 514-525
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Tidskriftsartikel (refereegranskat)abstract
- The catastrophic impact and unpredictability of the Indian Ocean Monsoon (IOM) over South Asia are evident from devastating floods, mudslides and droughts in one of the most densely populated regions of the globe. However, our understanding as to how the IOM has varied in the past, as well as its impact on local environments, remains limited. This is particularly the case for Sri Lanka, where erosional landscapes have limited the availability of well-stratified, high-resolution terrestrial archives. Here, we present novel data from an undisturbed sediment core retrieved from the coastal Bolgoda Lake. This includes the presentation of a revised Late Holocene age model as well as an innovative combination of pollen, source-specific biomarkers, and compound-specific stable carbon isotopes of n-alkanes to reconstruct the shifts in precipitation, salinity and vegetation cover. Our record documents variable climate between 3000 years and the present, with arid conditions c. 2334 and 2067 cal a bp. This extreme dry period was preceded and followed by more wet conditions. The high-resolution palaeoenvironmental reconstruction fills a major gap in our knowledge on the ramifications of IOM shifts across South Asia and provides insights during a time of major redistribution of dense human settlements across Sri Lanka.
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| 49. |
- Githumbi, Esther N., et al.
(författare)
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Late Pleistocene and Holocene Afromontane vegetation and headwater wetland dynamics within the Eastern Mau Forest, Kenya
- 2021
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 36:2, s. 239-254
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Tidskriftsartikel (refereegranskat)abstract
- The Mau Forest Complex is Kenya's largest fragment of Afromontane forest, providing critical ecosystem services, and has been subject to intense land use changes since colonial times. It forms the upper catchment of rivers that drain into major drainage networks, thus supporting the livelihoods of millions of Kenyans and providing important wildlife areas. We present the results of a sedimentological and palynological analysis of a Late Pleistocene–Holocene sediment record of Afromontane forest change from Nyabuiyabui wetland in the Eastern Mau Forest, a highland region that has received limited geological characterization and palaeoecological study. Sedimentology, pollen, charcoal, X-ray fluorescence and radiocarbon data record environmental and ecosystem change over the last ~16 000 cal a bp. The pollen record suggests Afromontane forests characterized the end of the Late Pleistocene to the Holocene with dominant taxa changing from Apodytes, Celtis, Dracaena, Hagenia and Podocarpus to Cordia, Croton, Ficus, Juniperus and Olea. The Late Holocene is characterized by a more open Afromontane forest with increased grass and herbaceous cover. Continuous Poaceae, Cyperaceae and Juncaceae vegetation currently cover the wetland and the water level has been decreasing over the recent past. Intensive agroforestry since the 1920s has reduced Afromontane forest cover as introduced taxa have increased (Pinus, Cupressus and Eucalyptus).
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| 50. |
- Greisman, Annica, et al.
(författare)
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The role of climate variability and fire in early and mid Holocene forest dynamics of southern Sweden
- 2009
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 24:6, s. 593-611
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to investigate the possible links between regional climate, fire and vegetation at the small spatial scale during the early and mid Holocene in southern Sweden using pollen, plant macrofossil and charcoal records from a small bog. The fire history was compared with climate reconstructions inferred from various proxy records in the study region. High fire activity is related to dry and warm climate around 8550, 7600, 5500-5100 and 4500 cal. a BC. Low fire activity ca. 6500-6000 and 4750 BC may correspond to the widespread '8.2 k event' (ca. 6200 BC) recorded across the North Atlantic region, and a later, brief period of increased precipitation, respectively. The decrease in broadleaved trees Culminating ca. 6500-6000 BC correlates with the '8.2 k event'. A long mid Holocene period with low fire activity (ca. 4350-1000 BC) agrees with the pattern emerging for Europe from the global charcoal database, and may correspond to generally wetter and cooler conditions. High fire activity ca. 8550 BC probably triggered the local establishment of Corylus. Warmer and drier conditions (and high fire activity) ca. 7600 BC might have favoured the establishment of Alnus, Quercus and Tilia. The fire-adapted Pinus maintained important populations throughout the early and mid Holocene.
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