| 1. |
- Björck, Svante, et al.
(författare)
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Consistently large marine reservoir ages in the Norwegian Sea during the Last Deglaciation
- 2003
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Ingår i: Quaternary Science Reviews. - 0277-3791. ; 22:5-7, s. 429-435
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Tidskriftsartikel (refereegranskat)abstract
- With the exception of the GS-1/Younger Dryas cold period marine reservoir ages for the Last Deglaciation in the North Atlantic-Norwegian Sea are generally assumed to have been around 400-500 radiocarbon years in magnitude (Earth Planet. Sci. Lett. 126 (1994) 275; Radiocarbon 37 (1995) 53; Quat. Res. 52 (1999) 104; Nature 412 (2001) 724). By comparing the climate records obtained from the GRIP ice-core (Nature 359 (1992) 311; J. Quat. Sci. 13(4) (1998) 283) and from North Atlantic/Norwegian Sea cores (Quat. Res. 52 (1999) 104; Geology 23 (12) (1995) 1059; Nature 356 (1991) 757; Nature 356 (1992) 757; Paleoceanography 3(1) (1988) 1; Nature 343 (1990) 612; Earth Planet. Sci. Lett. 126 (1994) 275), with radiocarbon-dated European continental records, we show that marine reservoir ages in the Norwegian Sea were of the order of 1000 C-14 yr, including large uncertainties. This approach rests on the reasonable assumption that climate changes throughout the NE Atlantic and Europe were more or less synchronous at the centennial scale. Fairly large variations in reservoir ages over time may have been caused by changing atmospheric C-14 content. The results indicate that detailed land-sea correlations for the North Atlantic during the Last Deglaciation are not feasible using radiocarbon dating alone. (C) 2003 Elsevier Science Ltd. All rights reserved.
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| 2. |
- Björkman, Leif, et al.
(författare)
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Lateglacial and early Holocene vegetation development in the Gutaiului Mountains, northwestern Romania
- 2002
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Ingår i: Quaternary Science Reviews. - 0277-3791 .- 1873-457X. ; 21:8-9, s. 1039-1059
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Tidskriftsartikel (refereegranskat)abstract
- Pollen analyses and AMS C-14 measurements were performed on lacustrine sediments and peat sequences from two former crater lakes (Preluca Tiganului, Steregoiu) situated in the Gutaiului Mountains in northwestern Romania, in order to reconstruct the vegetation development during the Lateglacial and Early Holocene. Before c. 14,700 cal. years BP (GS-2) open vegetation with shrubs (Salix, Juniperus), grasses and herbs (e.g. Artemisia and Chenopodiaceae) prevailed in the area. Around c. 14,700 cal. years BP and coinciding with the beginning of GI-le, Pinus expanded, and patchy vegetation with scattered Pinus stands developed. The last 100 years of GI-le (14,150-14,050 cal. years BP) were characterised by an increase in Pinus and Betula and an expansion of open forest communities. This development was shortly interrupted between 14,050 and 13,800 cal. years BP (likely corresponding to the cold phase GI-ld), when the tree cover became reduced and open vegetation with scattered Pinus individuals became frequent. The period with a significant expansion of Betula and Picea and the formation of an open forest (including Pinus and Omits), which took place between 13,800 and c. 12,950 cal. years BP, is tentatively correlated with GI-lc-a. A renewed reduction in tree cover (decrease of Picea and Betula, disappearance of Ulms) started at similar to 12,950 cal. years BP and at 12,600 cal. years BP forest stands were rapidly replaced by open vegetation communities with low shrubs (Salix, Juniperus), grasses and herbs (e.g. Artemisia and Chenopodiaceae). The period between 12,900 and 11,500 is correlated with the cold phase GS-1. At 11,500 cal. years BP, most likely as a response to the warmer climatic conditions at the beginning of the Holocene, an expansion of Betula and Alnus and, slightly later, also of Ulmus can be observed. Between 11,500 and 11,250 cal. years BP, open forests with Betula, Pinus and Ulmus were widespread in the area. At 11,250 cal. years BP dense forests dominated by Ulmus replaced the open forest type. Around 10,700cal. years BP Quercus, Tilia and Fraxinus expanded strongly, and Acer and Corylus became established. Mixed deciduous forest with Picea dominated the upland vegetation between 10,700 and 10, 150 cal. years BP. At 10,150 cal. years BP Corylus increased significantly and between 10,150 and 8500 cal. years BP, dense mixed deciduous forests with Picea and Corylus were abundant in the area. Climatic fluctuations seem to have been the driving force behind vegetation changes during the Lateglacial period, while the forest development during the Early Holocene was mainly driven by migrational and successional processes.
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| 3. |
- Hammarlund, Dan, et al.
(författare)
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Rapid hydrological changes during the Holocene revealed by stable isotope records of lacustrine carbonates from Lake Igelsjon, southern Sweden
- 2003
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Ingår i: Quaternary Science Reviews. - 0277-3791. ; 22:2-4, s. 353-370
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Tidskriftsartikel (refereegranskat)abstract
- A Holocene sediment sequence from Lake Igelsjon, south central Sweden, was studied by stable oxygen- and carbon-isotope analyses of different carbonate components. The deposit, which covers the time-span from ca 11,500 cal BP to the present, was laid down in a small, kettle-hole lake, the hydrological balance of which is presently dominated by groundwater flow. Isotopic records obtained on bulk carbonates originating mainly from summer-produced, calcitic algal encrustations exhibit several rapid shifts of more than 2parts per thousand, likely reflecting pronounced hydrological variations. Corresponding isotopic data obtained on calcitic gastropod opercula from parts of the profile show subdued responses to major climatic shifts, probably related to an extended calcification season. The isotopic records were complemented by studies of modern isotope hydrology, and our interpretations are based on a simplistic climate-hydrology model in which variations in groundwater generation within the lake catchment produce changes in groundwater level and related adjustments of lake level and surface/volume ratio of the basin during the ice-free season. Assumed periods of decreased lake volume in a relatively dry climate (low lake level) are characterised by enrichment in O-18 and C-13 resulting from increased evaporation/inflow ratio and atmospheric equilibration, respectively. In clear contrast to this situation, intervals of more humid climatic conditions give rise to increased lake volume (high lake level), possibly surface over flow, and relatively depleted isotopic ratios. Relatively humid conditions, which may correlate to a wide-spread cooling event recorded by various proxies across the North Atlantic region, are indicated by distinct isotopic shifts at ca 8300 and 8000 cal BP, bracketing a period of O-18-depletion. The period between ca 8000 and 4000 cal BP was characterised by relatively dry and stable climatic conditions, whereas the subsequent part of the Holocene experienced a more humid and variable climate following marked and coherent depletions in O-18 and C-13 at ca 4000 cal BP. (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 4. |
- John Lowe, J., et al.
(författare)
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Inter-regional correlation of palaeoclimatic records for the last Glacial-Interglacial Transition : A protocol for improved precision recommended by the INTIMATE project group
- 2001
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Ingår i: Quaternary Science Reviews. - 0277-3791. ; 20:11, s. 1175-1187
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Tidskriftsartikel (refereegranskat)abstract
- The remit of the INTIMATE project of the INQUA Palaeoclimate Commission is to synthesise marine, terrestrial and ice-core data for the North Atlantic region during the Last Glacial-Interglacial Transition (LGIT: ca 13-1014C kyr BP; ca 15-11.5 ice-core kyr BP). A major problem, however, is the difficulty of effecting correlations at a temporal resolution that are adequate for defining 'leads' and 'lags' between the polar ice, terrestrial, marine, and atmospheric realms. The limitations of the dating and correlation methods currently employed are summarised, and new quality assurance protocols are proposed. These include recommendations on the contextual information that should accompany radiocarbon dates, procedures for radiocarbon calibration, the use of an event-stratigraphic approach in inter-regional correlations, and the more widespread use of time-parallel marker horizons (based on tephra layers, oxygen isotope stratigraphy, palaeomagnetic stratigraphy, and radiocarbon 'wiggle-matching') to underpin the geochronology and correlation of events during the LGIT. These protocols will be adopted by the INTIMATE project in future international, collaborative research and are recommended to other groups working on this important time period.
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| 5. |
- Kjaer, Kurt, et al.
(författare)
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What causes till thickness to change over distance? Answers from Myrdalsjokull, Iceland
- 2003
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Ingår i: Quaternary Science Reviews. - 0277-3791. ; 22:15-17, s. 1687-1700
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Tidskriftsartikel (refereegranskat)abstract
- Many explanations have been provided for variations of the spatial distribution and thickness of till sheets. This paper gives new insight into the architecture of a stratigraphically distinct till sheet as a function of the type of substratum and preadvance topography at a scale of similar to 10 km. This emphasises the sensitivity of the subglacial system to changes in the basal drainage conditions. The study area is the forefield of Slettjokull at the northern margin of the Myrdalsjokull ice cap, central south Iceland. Here, detailed lithostratigraphical and sedimento logical investigations, including mapping of the thickness for two till units, sediment logging, clast fabric and geotechnical measurements provide a basis for interpretations. The results show that the thickness of a stratigraphically distinct till sheet is directly correlated to the type of substratum. Where the substratum consists of sorted sediments the till is thin. Conversely, the till is thick where the substratum consists of till overlying sorted sediments. A sedimentological model is presented in which till thickness is tied to the variable hydraulic conditions experienced in a deforming subglacial bed. (C) 2003 Elsevier Ltd. All rights reserved.
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| 6. |
- Schomacker, Anders, et al.
(författare)
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An extensive late Holocene glacier advance of Kotlujokull, central south Iceland
- 2003
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Ingår i: Quaternary Science Reviews. - 0277-3791. ; 22:14, s. 1427-1434
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents data on an extensive late Holocene advance of Kotlujokull, a southeastern outlet glacier from the ice cap Myrdalsjokull, central south Iceland. During the advance, basal till was deposited on top of a volcanic ash layer resting on lava hummocks. Remnants of this landscape are now seen 3.5-5.5 km in front of Kotlujokull as a fragment surrounded by the Myrdalssandur. Electron microprobe analysis of the volcanic ash shows that it is silicic and originates from the volcano Katla underneath Myrdalsjokull. A C-14 AMS date on a twig fragment sampled in the upper part of the volcanic ash layer provides a maximum age of the till of 1610 +/- 40 yr BP, and this is supported by tephrochronological and geochemical analyses of the volcanic ash. It is concluded that Kotlujokull must have advanced more than 5.5 km from its present position after 1.6 kyr 13P. This advance is much more extensive than the Little Ice Age (LIA) advance and took place in a relatively cold period also identified in the Greenland ice cores and the diatom record in the seas surrounding Iceland. In the proglacial environment in front of the Icelandic ice caps, the preservation potential of older end-moraines is strongly restricted due to intense glaciofluvial erosion. Therefore, the LIA end-moraines have in many cases been interpreted as marking the outermost Holocene glacier front position. This study as well as other recent results stresses the fact that the "LIA glacial maximum" in Iceland may not be identical to the Holocene glacial maximum, and that far more case studies with well-constrained dating control are needed. (C) 2003 Elsevier Science Ltd. All rights reserved.
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| 7. |
- Thomas, PJ, et al.
(författare)
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Age limit and age underestimation using different OSL signals from lacustrine quartz and polymineral fine grains
- 2003
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Ingår i: Quaternary Science Reviews. - 0277-3791. ; 22:10-13, s. 1139-1143
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Tidskriftsartikel (refereegranskat)abstract
- As part of a systematic palaeohydrological reconstruction of lake level fluctuations during the Last Glacial Maximum, a transect of cores from ancient Lake Xinias in centra Greece has already been studied with respect to pollen, sediment and mineral magnetic analyses. The chronology was based on C-14 AMS dating of terrestrial plant macrofossil remains from peat and clayey peat (Palaeogeog. Palaeoclimatol. Palaeoecol. 158 (2000) 65). This site thus provides an opportunity for the comparison of fine grain optically stimulated luminescence (OSL) ages of water-lain sediments with an independent chronology. We present here infrared (IR), post-IR blue and blue OSL characteristics of the fine grain sediments from Lake Xinias and a preliminary comparison with independent ages. The equivalent doses based on the IR results are about 40% of those based on post-IR blue stimulation, which in turn are 10-15% below those based on quartz OSL. We discuss the ages derived from the 3 signals in terms of the independent chronology, and draw conclusions about initial bleaching of the quartz and feldspar components, and the reliability of the post-IR blue signal as a chronometer. (C) 2003 Elsevier Science Ltd. All rights reserved.
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| 8. |
- Zillén, Lovisa, et al.
(författare)
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Calendar year ages of three mid-Holocene tephra layers identified in varved lake sediments in west central Sweden
- 2002
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Ingår i: Quaternary Science Reviews. - 0277-3791. ; 21:14-15, s. 1583-1591
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Tidskriftsartikel (refereegranskat)abstract
- Three intermediate to rhyolitic Icelandic Holocene tephra horizons (Hekla-3, Kebister, and Hekla-4) have been identified in annually laminated (varved) lake sediments in the Province of Varmland, west central Sweden. Calendar year ages were obtained from varve counts and are supported by additional C-14 dating based on terrestrial plant macrofossils. The varve ages of the three tephras are 3295 +/- 95 cal. BP (Hekla-3), 4030 +/- 103 cal. BP (Kebister), and 4390 +/- 107 cal. BP (Hekla-4). The varve age of Hekla-3 refines the former calibrated 14 C age based on studies in the British Isles and Germany. Considering the age-error estimates associated with the varve chronology and calibrated C-14 ages, the ages of Kebister and Hekla-4 are in agreement with former studies. Thus, the age difference between Kebister and Hekla-4 is estimated to be ca 400 +/- 40 varve years (formally estimated to ca 200 C-14 years), between Hekla-3 and Hekla-4 to ca 1135 +/- 55 varve years (formally estimated to ca 1100 calibrated C-14 years) and between Hekla-3 and Kebister, 708 +/- 20 varve years.
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| 9. |
- Björck, Jonas, et al.
(författare)
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An event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden : results from investigations of varved clay and terrestrial sequences
- 2002
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Ingår i: Quaternary Science Reviews. - 0277-3791 .- 1873-457X. ; 21:12/13, s. 1489-1501
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden. The event stratigraphy for eastern middle Sweden comprises ten events and covers the time-span from ca 12,900 to 10,200 cal yr BP. The local event stratigraphy has been linked to the GRIP isotopic event stratigraphy by different correlations. The onset of the Younger Dryas is dated to 12,650 cal yr BP. This cold event lasted for ca 1125 cal yr in the area. The Vedde Ash (ca 12,000 cal yr BP) has been recorded in two terrestrial sequences, which makes it possible to exactly link the event stratigraphy to the GRIP ice-core and to marine cores in the North Atlantic region. The final drainage of the Baltic Ice Lake has been dated to ca 11,560 cal yr BP, which predates the Younger Dryas/Preboreal climatic boundary with ca 35 yr. An early Holocene cold event has been detected both in terrestrial and varved clay sequences at ca 11,305-11,185 cal yr BP. This cold event coincides almost exactly with a brackish water phase in the Baltic Sea. A previously unrecorded early Holocene tephra horizon has been found in lacustrine sediments at ca 10,200 cal yr BP.
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| 10. |
- Wohlfarth, B, et al.
(författare)
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Environment and Climate in Southwestern Switzerland during the Last Termination, 15-10 ka BP
- 1994
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 13:4, s. 361-394
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Tidskriftsartikel (refereegranskat)abstract
- Various records from sites ranging in altitude between 372 and 2290 m along a NW-SE transect through SW Switzerland were compiled and correlated within well defined chrono- and biostratigraphic units. Deglaciation of lowland areas is estimated at ca. 15,000-14,000 BP (minimum age), while the lower part of the Rhone valley and the Jura Mountains may have become ice free later. A significant climatic warming is clearly indicated by several palaeoecological records at ca. 12,600 BP. The compiled data give no clear evidence of a cooler phase between 12,200-12,000 BP. Oxygen isotope data point to a slight and progressive decrease in the deltaO-18 values between ca. 12,500-11,000 BP, which is followed by a marked drop at 11,000 BP. A very distinct change in lithology, rock glacier development and in mollusc and vegetation records characterises many low and high altitude sites ca. 300 years later, at 10,700 BP. Between 11,000 and 10,000 BP oxygen isotope records seem to respond more rapidly to the climatic shifts than the biostratigraphical records. Possible explanations for these time-lags are discussed. Our compilation shows that further multidisciplinary research in key sites would provide more precise palaeoclimatological information, both qualitatively and quantitatively. Higher time resolution and quantitative estimates of climatic parameters are needed to evaluate in detail the mechanisms and consequences of these rapid climatic changes in SW Switzerland.
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