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1.
A high-resolution Younger Dryas–late Holocene record of climate and environment from the Malangen fjord has been established on the basis of two marine sediment cores. Five pollen-spore assemblage zones have been defined covering the period c . 11 500 cal. yr BP (10 200 14C yr BP) to c . 1600 cal. yr BP (1600 14C yr BP) with a hiatus of c . 2000 cal. years between c . 10 200 and 8100 cal. yr BP (9000 and 7300 14C yr BP). The Holocene vegetation development from pioneer vegetation to forest development, identified in the marine pollen record, correlates well with pollen records from terrestrial sections of northern Norway. The marine pollen record was also correlated directly with marine proxy records of the bottom water temperature investigated in the same sediment cores. Correlation between the marine and terrestrial proxies suggests that changes in the influx of warm Atlantic Water to the fjord led to an instant change in the vegetation of the surrounding land area. The results thus support a strong link between marine and atmospheric mean climatic states in the North Atlantic region throughout the Holocene.  相似文献   

2.
Paludification intensity and peat deposition on Haukkasuo bog in southeastern Finland were studied with peat stratigraphic investigations by taking 79 samples for 14C carbon dating and 164 volumetric samples. Peat formation of Haukkasuo, a concentric raised bog, began about 10 400 cal. BP. Lateral expansion has been largely controlled by the flat clayey floor, which has favoured rapid growth of the bog. During the first 400 years of its existence the bog covered one-fifth, and in the following 2000 years one-half, of its present extent. The long-term carbon accumulation rate averages 22.3 g C/m2/yr in the central part of Haukkasuo and 16.7 g C/m2/yr in its margins. The highest rates of carbon accumulation over 500-year periods were recorded in the central part of the bog in 6500–5500, 3500–2500 and 1500–0 cal. BP. The rate of vertical peat increment was higher than average in these periods, and the peat was mainly slightly humified and, when close to the surface, un compacted. The rate of carbon accumulation was lowest in 5500–3500 and 2500–2000 cal. BP, when the rate of vertical growth was lower than average and the peat was more humified than average. The formation of peat, the rate of vertical peat increment and the succession of peat types in Haukkasuo have mainly been controlled by hydrological changes caused by local factors, although climatic factors might also be important. In particular, the formation of slightly humified peat in 3300–2700 cal. BP and during the last 1300 years can be related to humid climate.  相似文献   

3.
The laminated sediments at Pudozh in eastern Karelia are generally assumed to have been deposited between 13 000 and 16 000 14C yr BP and have been used to date the recession of the active ice margin. However, 17 AMS 14C measurements performed on terrestrial plant macrofossils contained in these sediments show that deposition began during the late Allerφd, when the ice margin had already receded to the northern part of Lake Onega. Based on an age model, we assume that the 1933-year-long varved sequence covers the time period between c. 12 900 and 11 000 calendar years BP. During this period, which comprises the later part of the Late Weichselian and the early Holocene, the local vegetation consisted of open, tree-less dwarf shrub heaths. Increased soil erosion may have occurred before 12 550 calendar years BP.  相似文献   

4.
Comparatively few Icelandic tephra horizons dated to the early part of the Holocene have so far been detected outside Iceland. Here, I present several tephra horizons that have been recorded in a Holocene peat sequence on the Faroe Islands. Geochemical analyses show that at least two dacitic and one rhyolitic tephra layers were erupted from the Katla volcanic system on southern Iceland between ca. 8000 and 5900 cal. yr BP. The upper two layers can be correlated with the SILK tephras described from southern Iceland, whereas the third, dated to ca. 8000 cal. yr BP, has a geochemistry virtually identical to the rhyolitic component of the Vedde Ash. The results suggest that the Late Weichselian and early Holocene eruption history of the Katla volcano was probably more complex than inferred from Iceland. A new, early Holocene rhyolitic tephra dated to ca. 10 500 cal. yr BP probably originates in the Snæfellsnes volcanic centre in western Iceland. These new findings may play an important role in developing a Holocene tephra framework for northwest Europe. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

5.
Deglaciation took place in eastern Jämtland and Ångermanland in central Sweden c . 10 500–10 200 cal. yr BP. In the present study, vegetation development and shore displacement during the earliest ice-free period are investigated by 14C dating of sediment from six isolated lake basins and by pollen analysis. A brief but distinct peak in Hippophaë occurs in all pollen diagrams coincident with basin isolation, followed by up to 500 years (varying locally) by an Alnus rise. The Alnus curve does not display a synchronous rise in the area. Its expansion below the highest shore level is time-transgressive and controlled mainly by the timing of basin isolation. The relationship between regional Alnus expansion and changes in hydrology and climate is discussed. The pollen diagrams show Pinus predominance with Corylus to the east (more coastal areas) and Betula predominance (though less pronounced) to the west during the period 10 200–9000 cal. yr BP. However, comparisons between sites suggest marked variability in the forest development. Shore displacement in easternmost Jämtland c . 10 300–9000 cal. yr BP is equal to or slightly more rapid than that of SE Ångermanland, contrary to the present pattern of isostatic recovery. A rapid shore level regression c . 10 300–10 000 cal. yr BP may be related to drainage of the Ancylus Lake.  相似文献   

6.
Rundgren, M., Ingólfsson, Ó., Björck, S., Jiang, H. & Haflioason, H. 1997 (September): Dynamic sea-level change during the last deglaciation of northern Iceland. Boreas , Vol. 26, pp. 201–215. Oslo. ISSN 0300–9483.
A detailed reconstruction of deglacial relative sea-level changes at the northern coast of Iceland, based on the litho- and biostratigraphy of lake basins, indicates an overall fall in relative sea level of about 45 m between 11300 and 9100 BP, corresponding to an isostatic rebound of 77 m. The overall regression was interrupted by two minor transgressions during the late Younger Dryas and in early Preboreal, and these were probably caused by a combination of expansions of local ice caps and readvances of the Icelandic inland ice-sheet margin. Maximum absolute uplift rates are recorded during the regressional phase between the two transgressions (10000–9850 BP), with a mean value of c . 15 cm 14C yr-1 or 11–12 cm cal. yr-1. Mean absolute uplift during the regressional phase following the second transgression (9700–9100 BP) was around 6 cm 14C yr-1, corresponding to c . 3 cm cal. yr-1, and relative sea level dropped below present-day sea level at 9000 BP.  相似文献   

7.
Studies of Late Quaternary sediments in south and central Sweden have yielded a detailed tephrochronology for the Last Glacial–Interglacial transition (LGIT; ca. 15,000–10,000 cal. yr BP) and the Holocene. More than ten tephra layers have been detected and geochemically characterised. The most widespread tephra from the LGIT is the rhyolitic phase of the Vedde Ash (ca. 12,000 cal. yr BP) which has been found in lacustrine sediments and marine clays south of the Younger Dryas moraines in south Sweden. Other horizons from the LGIT identified to date include the Borrobol tephra (ca. 14,400 cal. yr BP), the Hässeldalen tephra (ca. 11,500 cal. yr BP), the 10-ka Askja tephra (ca. 11,300 cal. yr BP) and the Högstorpsmossen tephra (ca. 10,200 cal. yr BP). The most significant Holocene isochrones are Hekla-4 (ca. 4260 cal. yr BP), Hekla-Selsund/Kebister (ca. 3750 cal. yr BP), Hekla-3 (ca. 3000 cal. yr BP) and Askja-1875. Two new Late Holocene tephra horizons (the Stömyren tephra, ca. 2100 cal. yr BP and the Gullbergby tephra; ca. 2700 cal. yr BP) were identified in single sites and are so far less valuable as marker horizons, but are potentially important for the future.  相似文献   

8.
Sillasoo, Ü., Mauquoy, D., Blundell, A., Charman, D., Blaauw, M., Daniell, J. R. G., Toms, P., Newberry, J., Chambers, F M. & Karofeld, E. 2007 (January): Peat multi‐proxy data from Männikjärve bog as indicators of late Holocene climate changes in Estonia. Boreas, Vol. 36, pp. 20–37. Oslo. ISSN 0300–9483. As part of a wider project on European climate change over the past 4500 years, a 4.5‐m peat core was taken from a lawn microform on Männikjärve bog, Estonia. Several methods were used to yield proxy‐climate data: (i) a quadrat and leaf‐count method for plant macrofossil data, (ii) testate amoebae analysis, and (iii) colorimetric determination of peat humification. These data are provided with an exceptionally high resolution and precise chronology. Changes in bog surface wetness were inferred using Detrended Correspondence Analysis (DCA) and zonation of macrofossil data, particularly concerning the occurrence of Sphagnum balticum, and a transfer function for water‐table depth for testate amoebae data. Based on the results, periods of high bog surface wetness appear to have occurred at c. 3100,3010–2990,2300, 1750–1610, 1510, 1410, 1110, 540 and 310 cal. yr BP, during four longer periods between c. 3170 and 2850 cal. yr BP, 2450 and 2000 cal. yr BP, 1770 and 1530 cal. yr BP and in the period from 880 cal. yr BP until the present. In the period between 1770 and 1530 cal. yr BP, the extension or initiation of a hollow microtope occurred, which corresponds with other research results from Mannikjarve bog. This and other changes towards increasing bog surface wetness may be the responses to colder temperatures and the predominance of a more continental climate in the region, which favoured the development of bog micro‐depressions and a complex bog microtopography. Located in the border zone of oceanic and continental climatic sectors, in an area almost without land uplift, this study site may provide valuable information about changes in palaeohydrological and palaeoclimatological conditions in the northern parts of the eastern Baltic Sea region.  相似文献   

9.
A little goes a long way: discovery of a new mid-Holocene tephra in Sweden   总被引：1，自引：0，他引：1  
This pilper reports the presence of a volcanic ash layer in western Sweden which is geochemically identiticd as the Kebister tephra. This tephrdpresenceof (dated c . 3600 14C BP) was discovered at Kebister, Shetland and thc rcsults presented here indicate that the deposit may have a greater geographical distribution than previously thought. The geochemistry of the volcanic glass was analysed by using discrete grain electron probe microanalysis (EPMA). Thc SiO2 content of the glass ranges from 66.19 to 71.96%, FeO content 2.73 to 6.07% and MgO content 0.15 to 0.57%˜ The tephra can he distinguished from the more widespread Hekla 4 tephra ( c . 3800 14C BP) on the basis of calcium and magnesium contents.  相似文献   

10.
Tree-ring and peat stratigraphy data were examined back to 5000 BC in order to identify and compare humidity changes in Fennoscandia. The temporal variation in distribution of Scots pine ( Pinus sylvestris L.) was used as a measure of past lake-level fluctuations in central Sweden. The chronology, which spans 2893 BC–AD 1998 with minor gaps in AD 887–907 and 1633–1650 BC and with additional floating chronologies back to 4868 BC, was cross-dated and fixed to an absolute timescale using a chronology from Torneträsk, northern Sweden. The peat stratigraphy from the Stömyren peat bog, south-central Sweden, was transformed into humification indices to evaluate humidity changes during the past 8000 years. The peat chronology is established by four tephra datings and eight 14C datings. Synchronous periods of drier conditions, interpreted from regeneration and the mortality pattern of pine, tree-ring chronology and peat humification, were recognized at c. 4900–4800 BC, 2400–2200 BC, 2100–1800 BC, 1500–1100 BC, AD 50–200, AD 400–600 and AD 1350–1500. Possible wetter periods were encountered at 3600–3400 BC, 3200–2900 BC, 2200–2100 BC, 1700–1500 BC, 1100–900 BC, 100 BC-AD 50, AD 200–400, AD 750–900 and AD 1550–1700. The wet and dry periods revealed by the tree rings and peat stratigraphy data indicate considerable humidity changes in the Holocene.  相似文献   

11.
Tephra-fall deposits from Cook Inlet volcanoes were detected in sediment cores from Tustumena and Paradox Lakes, Kenai Peninsula, Alaska, using magnetic susceptibility and petrography. The ages of tephra layers were estimated using 21 14C ages on macrofossils. Tephras layers are typically fine, gray ash, 1-5 mm thick, and composed of varying proportions of glass shards, pumice, and glass-coated phenocrysts. Of the two lakes, Paradox Lake contained a higher frequency of tephra (0.8 tephra/100 yr; 109 over the 13,200-yr record). The unusually large number of tephra in this lake relative to others previously studied in the area is attributed to the lake's physiography, sedimentology, and limnology. The frequency of ash fall was not constant through the Holocene. In Paradox Lake, tephra layers are absent between ca. 800-2200, 3800-4800, and 9000-10,300 cal yr BP, despite continuously layered lacustrine sediment. In contrast, between 5000 and 9000 cal yr BP, an average of 1.7 tephra layers are present per 100 yr. The peak period of tephra fall (7000-9000 cal yr BP; 2.6 tephra/100 yr) in Paradox Lake is consistent with the increase in volcanism between 7000 and 9000 yr ago recorded in the Greenland ice cores.  相似文献   

12.
Zhu, C., Ma, C., Yu, S.-Y., Tang, L., Zhang, W. & Lu, X. 2009: A detailed pollen record of vegetation and climate changes in Central China during the past 16 000 years. Boreas , 10.1111/j.1502-3885.2009.00098.x. ISSN 0300-9483.
Detailed pollen analyses, along with magnetic and loss-on-ignition (LOI) measurements, were conducted on a 3 m long peat sequence recovered from the Dajiuhu Basin, the Shennongjia Mountains in Central China. Ten AMS 14C dates provide a firm age control on this pollen record in terms of vegetation changes governed essentially by the rise and fall of the Asian summer monsoon during the past 16 000 years. Between 16 000 and 12 700 cal. yr BP, pollen assemblages were dominated by coniferous and broad-leaved trees, indicating a mixed forest landscape corresponding to the initial establishment of the monsoonal climate after the Last Glaciation. The progressive increases in percentages of evergreen tree pollen after 12 700 cal. yr BP point to a steady enhancement of the summer monsoon, which was episodically weakened during the Younger Dryas stadial. From 11 000 to 6000 cal. yr BP, values of coniferous and deciduous tree pollen decreased, while evergreen broad-leaved tree pollen increased substantially, implying a stronger than normal monsoonal climate condition corresponding to the Holocene Hypsithermal Interval. A great reduction in the values of evergreen tree pollen at about 4000 cal. yr BP indicates a sudden retreat of the summer monsoon from this area.  相似文献   

13.
Due to a lack of visible tephras in the Dead Sea record, this unique palaeoenvironmental archive is largely unconnected to the well-established Mediterranean tephrostratigraphy. Here we present first results of the ongoing search for cryptotephras in the International Continental Drilling Program (ICDP) sediment core from the deep Dead Sea basin. This study focusses on the Lateglacial (~15–11.4 cal. ka BP), when Lake Lisan – the precursor of the Dead Sea – shrank from its glacial highstand to the Holocene low levels. We developed a glass shard separation protocol and counting procedure that is adapted to the extreme salinity and sediment recycling of the Dead Sea. Cryptotephra is abundant in the Dead Sea record (up to ~100 shards cm-3), but often glasses are physically and/or chemically altered. Six glass samples from five tephra horizons reveal a heterogeneous geochemical composition, with mainly rhyolitic and some trachytic glasses potentially sourced from Italian, Aegean and Anatolian volcanoes. Most shards likely originate from the eastern Anatolian volcanic province and can be correlated using major element analyses with tephra deposits from swarm eruptions of the Süphan Volcano ~13 ka BP and with ashes from Nemrut Volcano, presumably the Lake Van V-16 volcanic layer at ~13.8 ka BP. In addition to glasses that match the TM-10-1 from Lago Grande di Monticchio (15 820±790 cal. a BP) tentatively correlated with the St. Angelo Tuff of Ischia, we further identified a cryptotephra with glass analyses which are chemically identical with those of the PhT1 tephra in the Philippon peat record (13.9–10.5 ka BP), and also a compositional match for the glass analyses of the Santorini Cape Riva Tephra (Y-2 marine tephra, 22 024±642 cal. a BP). These first results demonstrate the great potential of cryptotephrochronology in the Dead Sea record for improving its chronology and connecting the Levantine region to the Mediterranean tephra framework.  相似文献   

14.
Foraminifera, sedimentology, and tephra geochemistry in core 93030-006 LCF from the southwestern Iceland shelf were used to reconstruct paleoenvironments between 12.7 and 9.4 14C ka BP. Seismic-reflection profiles place the core in glacial-marine and marine sediments within one meter of the underlying glacial till. Foraminifers in the earliest glacial-marine sediments provide a record of ice-distal conditions and immigration of slope species onto the shelf in association with warm Atlantic water. Meltwater increased during the Allerød under a weakened Atlantic water influence. Arctic conditions began by 11.14 14C ka BP with an abrupt increase in meltwater and near exclusion of boreal fauna from the shelf. Meltwater diminished in the early Younger Dryas, coinciding with sea-surface cooling between 11.14 and 10.5 14C ka BP. A slight warming recorded in the uppermost glacial-marine sediments was interrupted by an inferred jökulhlaup event emanating from glacier ice on the Western Volcanic Zone. Retreat of the ice margin from the sea sometime between c. 10.3 and 9.94 14C ka BP coincided with this event. The onset of postglacial marine sedimentation occurred along with increasing evidence of Atlantic water c. 9.94 14C ka BP and was interrupted by a short-lived Pre-boreal cooling of the Irminger Current c. 9.91 14C ka BP. Conditions similar to those today were established by 9.7 14C ka BP.  相似文献   

15.
A total of 45 subfossil reindeer (Rangifer tarandus) antlers and bones - artefacts excluded - have been found over the years in the Baltic countries of Estonia, Latvia and Lithuania. The relatively high number of specimens suggests a stable residence of the species in the eastern Baltic region. For the first time, 12 of these finds were radiocarbon-dated. The ages of the samples range between 12 085 and 9970 14C yr BP (14 180-11 280 cal. yr BP), and cover the Lateglacial and early Holocene, a time period during which climatic conditions shifted from periglacial to temperate. The dates suggest a rapid colonization of the area during the deglaciation period and a local extinction around the Pleistocene-Holocene boundary. The results of the study do not support the theory that the recent wild reindeer populations of northern Europe had their origin in the Late Weichselian reindeer populations of the eastern Baltic region.  相似文献   

16.
Pollen and plant macrofossil analyses from Svanåvatnet in northern Norway provide records of past vegetation and climate in this region from c . 8700 cal. yr BP until the present. Pollen accumulation rates and the presence of plant macrofossils indicate that Betula pubescens (birch) was present from c . 8600 cal. yr BP and Pinus sylvestris (pine) from c . 8200 cal. yr BP. Quantitative climate is reconstructed using modern pollen-climate transfer functions based on weighted-averaging partial least squares regression. A rapid increase in mean July temperature (Tjul) and mean annual precipitation (Pann) is inferred for the early Holocene. At times when tree abundance is at its highest and most diverse, inferred Tjul indicates maximum temperatures during the mid-Holocene of about 2°C warmer than at present. During the same time period, inferred Pann is 200–300 mm above present-day conditions until c . 3000 cal. yr BP. Mean January temperatures (Tjan) are reconstructed to be about 2°C warmer than today from 8000 to 3500 cal. yr BP. After 3500 cal. yr BP until today, a gradual decrease is seen in all the reconstructed climate parameters, together with a reduction in tree abundance and the development of a mosaic of open vegetation with grasses, dwarf shrubs and wet areas, and of woodland containing B. pubescens , P. sylvestris and Picea abies (spruce).  相似文献   

17.
Sediments from two small lakes distal to the Tromsø–Lyngen moraine at Tromsø, northern Norway, indicate that the area was deglaciated prior to c. 11.7 14C ka BP. The earliest vegetation was dominated by calciphilous and heliophilous pioneer plants on unstable soils; this changed to a vegetation reflecting a dry continental climate until c. 10.7 14Cka BP. A phase (10.7–10.5 14Cka BP) with snow-bed communities was followed by one with a mosaic of plant communities. This was succeeded by Empetrum heaths c. 10.3 14Cka BP, then by an open forest with Betula pubescens after 10.0 14Cka BP. Ice-front oscillations in the Tromsø area are evaluated. The main part of the Younger Dryas glacial readvance, the Tromsø–Lyngen event, probably occurred between 10.7 and 10.3 14Cka BP.  相似文献   

18.
One of the early problems with the Storegga tsunami deposit was how to distinguish it from deposits of the midHolocene (Tapes) transgression. An excavation on Harøy, an island on the outermost western coast of Norway, shows a distinct, clean sand bed embedded in peat and clearly separated from the overlying Tapes beach deposits. This sand bed continues in the peat landwards of the beach ridge for at least 60 m. Radiocarbon dates of the peat show that the sand was deposited some time between 6900 and 7700 yr BP. The sedimentary structures of the bed, the 14C dates, and the fact that this is the only sand bed in the peat, suggest that the sand bed was deposited by a short-lived event, the Storegga tsunami. On the neighbouring island, Fjørtoft, a Stone Age settlement, dated to 7500 yr BP, was discovered in the early 1970s. The settlement was found underneath a sand bed that later had been covered by the Tapes beach ridge deposits. When discovered, the sand covering the settlement was inferred as eolian sand. However, this investigation shows that the Storegga tsunami deposited a widespread sand bed on the land surface around this time with a similar grain size distribution to eolian sand. It is therefore suggested that the sand bed covering this settlement was deposited from the Storegga tsunami. Both the stratigraphy and 14C dates demonstrate that the Tapes transgression maximum was reached well after the Storegga tsunami on Harøy, between 6500 and 6100 yr BP.  相似文献   

19.
A multiproxy study of palaeoceanographic and climatic changes in northernmost Baffin Bay shows that major environmental changes have occurred since the deglaciation of the area at about 12 500 cal. yr BP. The interpretation is based on sedimentology, benthic and planktonic foraminifera and their isotopic composition, as well as diatom assemblages in the sedimentary records at two core sites, one located in the deeper central part of northernmost Baffin Bay and one in a separate trough closer to the Greenland coast. A revised chronology for the two records is established on the basis of 15 previously published AMS 14C age determinations. A basal diamicton is overlain by laminated, fossil-free sediments. Our data from the early part of the fossiliferous record (12 300–11 300 cal. yr BP), which is also initially laminated, indicate extensive seasonal sea-ice cover and brine release. There is indication of a cooling event between 11 300 and 10 900 cal. yr BP, and maximum Atlantic Water influence occurred between 10 900 and 8200 cal. yr BP (no sediment recovery between 8200 and 7300 cal. yr BP). A gradual, but fluctuating, increase in sea-ice cover is seen after 7300 cal. yr BP. Sea-ice diatoms were particularly abundant in the central part of northernmost Baffin Bay, presumably due to the inflow of Polar waters from the Arctic Ocean, and less sea ice occurred at the near-coastal site, which was under continuous influence of the West Greenland Current. Our data from the deep, central part show a fluctuating degree of upwelling after c . 7300 cal. yr BP, culminating between 4000 and 3050 cal. yr BP. There was a gradual increase in the influence of cold bottom waters from the Arctic Ocean after about 3050 cal. yr BP, when agglutinated foraminifera became abundant. A superimposed short-term change in the sea-surface proxies is correlated with the Little Ice Age cooling.  相似文献   

20.
The timing of the extinction of the Australian Megafauna and whether it was simultaneous and widespread has been a much researched topic in Quaternary geoscience. The Black Creek Swamp Megafauna site on Kangaroo Island was thought to be a refugium for Megafauna; however, recent and multidiscipline age determinations have established that the fossils are considerably older than the well-quoted extinction age of 45 kyr. Further radiocarbon age determinations, δ13C isotope analysis and 13C-NMR spectroscopy of the fossil containing organic matter demonstrates that it is highly soluble and accumulated as recently as 31–18 cal. kyr BP. These radiocarbon ages are much younger than the 100–50 kyr age bracket ascertained for the fossil material itself, implying separate episodes of death, deposition and burial. The soluble nature of the organic matter and increasing radiocarbon ages with depth suggests lateral accumulation, probably transported by subsurface waters from elevated areas proximal to the low-lying swamp. Such depositional conditions and 14C age range implies that the site may have experienced an unusually wet Last Glacial Maximum, due maybe to its proximity to the continental shelf and thus to maritime conditions. C3 vegetation dominates the Black Creek Swamp and its organic matter (δ13C; −30‰ and −23‰); however, variations in δ13C may indicate climatic shifts. 13C-enrichment and an abundance of salt-tolerant gastropods within the site's final phase of sediment accumulation (<6 cal. kyr BP) suggest that conditions during this most recent period were not as wet as those of the Last Glacial Maximum.  相似文献   

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