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1.
With accelerated melting of alpine glaciers, understanding the future state of the cryosphere is critical. Because the observational record of glacier response to climate change is short, palaeo‐records of glacier change are needed. Using proglacial lake sediments, which contain continuous and datable records of past glacier activity, we investigate Holocene glacier fluctuations on northeastern Baffin Island. Basal radiocarbon ages from three lakes constrain Laurentide Ice Sheet retreat by ca. 10.5 ka. High sedimentation rates (0.03 cm a?1) and continuous minerogenic sedimentation throughout the Holocene in proglacial lakes, in contrast to organic‐rich sediments and low sedimentation rates (0.005 cm a?1) in neighbouring non‐glacial lakes, suggest that glaciers may have persisted in proglacial lake catchments since regional deglaciation. The presence of varves and relatively high magnetic susceptibility from 10 to 6 ka and since 2 ka in one proglacial lake suggest minimum Holocene glacier extent ca. 6–2 ka. Moraine evidence and proglacial and threshold lake sediments indicate that the maximum Holocene glacier extent occurred during the Little Ice Age. The finding that glaciers likely persisted through the Holocene is surprising, given that regional proxy records reveal summer temperatures several degrees warmer than today, and may be due to shorter ablation seasons and greater accumulation‐season precipitation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

2.
In this paper, we show the potential of combining multi‐proxy analysis of lake sediments with catchment geomorphology to better understand palaeoenvironmental changes. Previous studies have suggested that alpine lakes in N Sweden may be highly sensitive to variations in catchment erosion and precipitation, and that this sensitivity may influence ecologically based reconstructions of past temperature changes. We analysed lake sediments covering the last 5100 years from the alpine Lake Vuoksjávrátje in NW Sweden in order to identify different erosional regimes in the lake catchment, sediment sources and lake sedimentary processes, which ultimately affect the palaeoecological record. The measured proxies include elemental geochemistry from XRF core scanning, grain size, sediment accumulation rates, fraction of terrestrial organic carbon and geomorphological mapping, supported by previously published chironomid and total organic carbon data. From the integrated results we identified time intervals when increased intensity of precipitation altered sedimentation and lake catchment erosional processes. The most prominent event occurred c. 2900 cal. a BP and is interpreted to be the result of excessive precipitation, possibly related to the climatic shift towards cooler and wetter conditions referred to as the 2.8 ka event.  相似文献   

3.
《Sedimentology》2018,65(5):1413-1446
Turbidites within Holocene lacustrine sediment cores occur worldwide and are valued deposits that record a history of earthquakes or storms. Without sedimentary architecture, however, interpretation of the cause, provenance and behaviour of their parent turbidity currents are speculative. Here, these interpretations are made from two‐dimensional ground‐penetrating radar images of ‘shore to shore’ architecture beneath three, previously cored lakes within the low seismicity New England (USA ) region. Shallow depths, low water and sediment conductivities, and signal sensitivity to density contrasts uniquely provided up to 30 m of sediment signal penetration. Core comparisons and signal analysis reveal that most horizons represent multidecimetre‐thick clusters of Holocene turbidites, which are denser than their organic‐rich silt matrix. Some horizons also represent erosional unconformities and sediment bypass interfaces. The key, common, architectural consequences of turbidity current activity include limited foreset progradation, conformably pinched or unconformable layers of organic‐rich sediment onlapped against slopes beneath 5 to 6 m of water, and mounded stratified sediments beneath rises. These features indicate that turbidity currents repeatedly bypassed the same slope without deposition and regardless of dip, and then simultaneously armoured and bypassed inter‐turbidite sediment along rises and basins to provide basinward, generally age‐conformable accumulation. The mounding precludes significant basinward focusing. Variable horizon amplitude suggests metre‐scale changes in armouring density. Unconformities localized near breaks in dip beneath slopes suggest erosive hydraulic jumps. One lake shows evidence of historically maintained channels associated with specific deltas. Shelf strata indicating inland current generation, similar key architecture in other, uncored lakes, countable, lake‐wide horizons, and absent slumps, slides and faults are consistent with storm‐driven turbidity currents, and with previous, core‐based conclusions that severe, Holocene storms were episodic throughout this region. The results generalize marine bypass and armouring to lacustrine settings, and so probably occur worldwide in lakes subject only to storms, including lakes where ground‐penetrating radar may locate core sites.  相似文献   

4.
A sediment core from Chuna Lake (Kola Peninsula, northwest Russia) was studied for pollen, diatoms and sediment chemistry in order to infer post‐glacial environmental changes and to investigate responses of the lake ecosystem to these changes. The past pH and dissolved organic carbon (DOC) of the lake were inferred using diatom‐based transfer functions. Between 9000 and 4200 cal. yr BP, slow natural acidification and major changes in the diatom flora occurred in Chuna Lake. These correlated with changes in regional pollen, the arrival of trees in the catchment, changes in erosion, sediment organic content and DOC. During the past 4200 yr diatom‐based proxies showed no clear response to changes in vegetation and erosion, as autochthonous ecological processes became more important than external climate influences during the late Holocene. The pollen stratigraphy reflects the major climate patterns of the central Kola Peninsula during the Holocene, i.e. a climate optimum between 9000 and 5400/5000 cal. yr BP when climate was warm and dry, and gradual climate cooling and an increase in moisture during the past 5400/5000 yr. This agrees with the occurrence of the north–south humidity gradient in Fennoscandia during the Holocene. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

5.
Thermokarst lakes are a widespread feature of the Arctic tundra, in which highly dynamic processes are closely connected with current and past climate changes. We investigated late Quaternary sediment dynamics, basin and shoreline evolution, and environmental interrelations of Lake El'gene‐Kyuele in the NE Siberian Arctic (latitude 71°17′N, longitude 125°34′E). The water‐body displays thaw‐lake characteristics cutting into both Pleistocene Ice Complex and Holocene alas sediments. Our methods are based on grain size distribution, mineralogical composition, TOC/N ratio, stable carbon isotopes and the analysis of plant macrofossils from a 3.5‐m sediment profile at the modern eastern lake shore. Our results show two main sources for sediments in the lake basin: terrigenous diamicton supplied from thermokarst slopes and the lake shore, and lacustrine detritus that has mainly settled in the deep lake basin. The lake and its adjacent thermokarst basin rapidly expanded during the early Holocene. This climatically warmer than today period was characterized by forest or forest tundra vegetation composed of larches, birch trees and shrubs. Woodlands of both the HTM and the Late Pleistocene were affected by fire, which potentially triggered the initiation of thermokarst processes resulting later in lake formation and expansion. The maximum lake depth at the study site and the lowest limnic bioproductivity occurred during the longest time interval of ～7 ka starting in the Holocene Thermal Maximum and lasting throughout the progressively cooler Neoglacial, whereas partial drainage and an extensive shift of the lake shoreline occurred ～0.9 cal. ka BP. Correspondingly, this study discusses different climatic and environmental drivers for the dynamics of a thermokarst basin.  相似文献   

6.
Large amounts of carbon in alpine sediments have been expected to be sensitive to climate change, but how carbon accumulation responds to climate change remains unclear. Thus, we explored the impact of different factors on the carbon accumulation rate (CAR) of alpine sediments by combining a variety of climatic variables, vegetation data and erosion indicators based on two alpine sediment successions on Taibai Mountain, the highest peak in central and eastern mainland China. One succession is near the modern treeline (Paomaliang Swamp, PML) and the other is located at the upper forest line (Sanqing Chi, SQC, a small lake). We used our previously published organic carbon content data and for the first time calculated the CAR, and further used pollen and physicochemical indicators to quantify the contributions from climate, vegetation and soil. We found that their contributions varied during different periods and between the two sediment successions. For the PML succession, from 5850 to 4000 calendar years before present (cal. a BP), the CAR was low, which was related to low annual temperatures, low vegetation cover and strong soil erosion. From 4000 to 2400 cal. a BP, a high CAR coincided with high annual temperatures, high vegetation cover and weak soil erosion. From 2400 to 200 cal. a BP, the CAR decreased, mainly attributed to low vegetation cover. Local vegetation cover had major impacts on the CAR in the SQC succession during the Middle–Late Holocene. In general, the local factor interpretation rate in SQC (83%) was higher than that of PML (47%), related to the vegetation stability of continuous forest and the treeline. This study highlights the important role of the local environment in determining carbon accumulation in the alpine region.  相似文献   

7.
Glaciers show a sensitive and rapid response to climate shifts. Associated changes in ice extent drive variations in the production of rock flour, the suspended product of glacial erosion. These glacigenic sediments may accumulate in downstream lakes, continuously recording glacier history. Consequently, the lacustrine sediment records of such glacier‐fed lakes represent valuable palaeoenvironmental archives that help constrain past climate variability. In this paper, we discuss the multi‐disciplinary methodological toolbox that is applied to fingerprint a glacier signal from such lake sediments. Special emphasis is placed on dating methods, which transform stratigraphical data into climate time series, allowing us to distinguish leads and lags between archives. We also elaborate on techniques that are used to validate sediment‐based glacier signals and resolve their climate signature. Finally, we conclude with a brief outlook on new research avenues such as proxy data–climate model comparisons.  相似文献   

8.
Jiang, S., Liu, X., Sun, J., Yuan, L., Sun, L. & Wang, Y. 2011: A multi‐proxy sediment record of late Holocene and recent climate change from a lake near Ny‐Ålesund, Svalbard. Boreas, Vol. 40, pp. 468–480. 10.1111/j.1502‐3885.2010.00198.x. ISSN 0300‐9483 The Arctic constitutes a unique and important environment with a significant role in the dynamics and evolution of the earth system. Arctic lake sediments, which accumulate slowly over time, contain abundant information about the biological communities that lived within the water body, as well as in the surrounding catchment. In this study, we collected a sediment core from Ny‐Ålesund, Svalbard, performed multi‐proxy analyses on sediment pigments, mineral magnetic susceptibility, various sediment quality (i. e. organic matter content, CaCO3 content, carbon and nitrogen isotope), and diatom composition, and reconstructed the history of ecosystem responses to environmental variations, especially regarding aquatic productivity and lake catchment surface processes. Ny‐Ålesund has undergone distinct ecological and climatic changes. During the Little Ice Age, the cold climate was unfavourable for the growth of lake algae, and therefore the lake primary productivity declined. After about AD 1890 and during the 20th century, the warming climate and reduced ice cover led to rapid lithological change and growth of lake algae, enhanced lake primary productivity, and increased input of nutrients derived from increased chemical weathering into the lake. The lake ecosystem on Ny‐Ålesund has had rapid responses to climatic and environmental changes in the Arctic.  相似文献   

9.
Lake Chalco (99.0°W, 19.5°N) in the Basin of Mexico, was formed during the Pleistocene after the emplacement of the Chichinautzin volcanic field that closed the former drainage system. The lake sediment record has been influenced by a number of factors, including glacial–interglacial cycles, local volcanism, erosion of soils and anthropogenic disturbances. The magnetic properties of the lake sediments and the associated tephra layers of the last 16500 yr have been studied. It is found that the magnetic properties of the Lake Chalco sediments are very distinctive. Magnetic concentration varies by a factor of 1000 and magnetic stability also varies over an extremely wide range. The predominant magnetic mineral is titanomagnetite in addition to an imperfect antiferromagnetic phase, possibly goethite. An unusually large range of coercivities is found in certain of the tephras. Down‐core variations in magnetic properties closely follow climatic/environmental changes previously established by other proxy methods. The late Pleistocene and late Holocene lake sediments display a higher concentration of magnetic minerals than the early–middle Holocene sediments. In the non‐volcanic sediments, fluctuations in the magnetic concentration reflect changes in both the intensity of erosion, as represented by ferrimagnetic and paramagnetic minerals, and by the maturing of soils, as represented by geothite. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

10.
The Sisimiut area was deglaciated in the early Holocene, c. 11 cal. ka BP. At that time the lowlands were inundated by the sea, but the isostatic rebound surpassed the global sea‐level rise, and the lowlands emerged from the sea. The pioneer vegetation in the area consisted of mosses and herbaceous plants. The oldest remains of woody plants (Empetrum nigrum) are dated to c. 10.3 cal. ka BP, and remains of Salix herbacea and Harrimanella hypnoides are found in slightly younger sediments. The maximum occurrence of statoblasts of the bryozoan Plumatella repens from c. 10 to 4.5 cal. ka BP probably reflects the Holocene thermal maximum, which is also indicated in geochemical proxies of the lake sediments. A maximum in organic matter accumulation in one of the three studied lakes c. 3 cal. ka BP can probably be ascribed to a late Holocene short‐duration temperature maximum or a period of increased aridity. Cenococcum geophilum sclerotia are common in the late Holocene, implying increased soil erosion during the Neoglaciation. A comparison with sediment and macrofossil records from inland shows similar Holocene trends and a similar immigration history. It also reveals that there has been a significant gradient throughout the Holocene, from an oceanic and stable climate at the outer coast to a more continental and unstable climate with warmer summers and drier conditions close to the margin of the Greenland ice sheet, where the buffer capacity of the sea is lower.  相似文献   

11.
High resolution sampling of sediment cores covering approximately the last 4000 yr from Lochan Uaine, a small corrie loch in the Scottish Cairngorm Mountains, show quasi‐periodic cycles in organic matter (measured as percentage loss on ignition). Analysis of these cycles show correspondences between loss on ignition, δ13C values and chironomid head capsule abundance. We interpret the changes as reflecting changes in lake productivity and hypothesise that they are driven by climate variability. However, it is not yet clear whether the periods of relatively high organic matter production and preservation are associated with colder or with warmer conditions. Nevertheless the results indicate the value of using sediments from remote, undisturbed mountain lakes as recorders of Holocene climate variability. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

12.
Ian Snowball 《地学学报》1993,5(3):258-270
A mineral magnetic study of lacustrine sediments and soils from the Kårsa valley in Lappland, Sweden was undertaken to estimate the potential of mineral magnetic techniques in elucidating the variability of climate, recorded by glacier fluctuations and soil development. Sediment cores from two lake basins receiving sediment input from a glacial outflow stream, and their respective catchments, show a mineral magnetic record that can be interpreted in terms of glacial activity and soil development. Dissolution of magnetite is indicated during periods of climatic amelioration and causes a high S-ratio. During periods of glacial advance (and colder, wetter climate) the minerogenic sediment supply is increased and magnetite is preserved in the sediment, resulting in a low S-ratio. Variations in the S-ratio can then be used as a proxy-climate indicator.  相似文献   

13.
早全新世降温事件的湖泊沉积证据   总被引：12，自引：1，他引：12  
我国华北干旱－半干旱区封闭湖泊流域化学风化历史记录了全新世以来次级的气候环境波动过程。高精度的沉积物地球化学、物理及生物参数变化表明，在全新世早－中期过渡阶段存在一次强降温气候事件，具体表现为流域化学风化减弱（高Rb/Sr比）、湖泊产生力减弱（低有机碳）以及湖泊水位下降。虽然该事件的寒冷程度比Younger Dryas弱，但是其与来自湖沼（包括北极、非洲、北美、西欧、青藏高原、祁连山等）、海洋（比北大西洋、地中海、加勒比海等）、欧－美大陆生物组合、极地冰芯等在内的环境记录的冷事件发生时间基本一致，集中发生于8.0-8.5ka B.P.之间。  相似文献   

14.
Holocene lacustrine sediments from two isolated lakes in north China are investigated. Based on palaeoclimatic significance of independent proxies in lake sediments, Holocene chemical weathering, and hence climate change, has been reconstructed for dated sediment cores from Daihai Lake and Aibi Lake. During early to mid-Holocene, higher weathering intensity occurred in the Daihai catchment under warm and humid climate conditions, and this reached a maximum at ∼5 kyr BP. However, synchronous proxy shifts from the two widely separated, isolated lake sediments indicate that there was a cool climate event during the early to mid-Holocene transition. This is characterized by reduced weathering in each catchment, low δ 13 C and δ 18 O of authigenic carbonate, and by lake level fluctuations. These might correspond to a global cooling signal identified in lakes, oceans, mollusc sequences, and polar ice cores, typically centred between ∼8.0 and 8.5 kyr BP. Dry conditions were experienced in Greenland, the North Atlantic and surrounding regions, and in broad monsoonal regions including Daihai at this time. However, recent extensive evidences as well as our data from the Aibi Lake sediments show that cool but wet conditions occurred in the central Eurasian continent at this time. After ∼2.5 kyr BP, a significant shift of independent sediment proxies indicates the beginning of the Neoglaciation with a higher frequency of fluctuations, including both the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Our continental records provide new evidence of the Holocene climate variability with global significance and highlight the different spatial nature of the response to oscillations associated with different climate patterns.  相似文献   

15.
《Quaternary Science Reviews》2007,26(13-14):1838-1860
The degree to which different lakes within a landscape respond coherently (in unison) to external drivers such as climate change and soil development is uncertain. Presentation of multi-proxy, geochemical and palaeoecological data from individual lakes in the form of fluxes minimizes distortions resulting from variable sedimentation rates and changes in sediment composition. We use the accumulation rates of magnetic minerals, total organic C and N, terrestrial and aquatic biomarkers, graminoid epidermis, pollen, green algae, diatoms and diatom C in four small lakes, situated between 2350 and 4595 m a.s.l. on the NE flank of Mt. Kenya, East Africa, to reconstruct changes in C cycling over the last 38 ka. The results conflict with earlier models of landscape and lake development, showing: (1) that glacial–interglacial changes in vegetation cannot be interpreted as simple, altitudinal shifts in the modern vegetation belts; and (2) that limnological changes were not coherent. Rapid variations in climate, water level, erosion and nutrient input overwhelmed long-term, successional trends in lake sedimentation and C accumulation since the Last Glacial Maximum. The results also reveal previously unrecognized features of the palaeoenvironmental record, such as the rapid degradation of organic matter in diatoms and the occurrence of a productive, fire-prone montane grassland during the highly seasonal, monsoonal climate of the Lateglacial and early Holocene.  相似文献   

16.
An early Holocene lake sediment record from central Nova Scotia contains a minerogenic oscillation that is closely correlative with the 8.2 kyr event (ca. 8200 cal. yr BP), an event that has not been reported elsewhere in Atlantic Canada. A variety of biological and sedimentological indicators have been examined to characterise autochthonous and allochthonous changes that occurred during this time. The minerogenic upper oscillation (UO, ca. 8400 cal. yr BP) is marked by an increase in the chrysophyte:diatom ratio. Following the oscillation, the diatom community reflects a shift to more productive, less acidic conditions. The pollen record shows no major response to this short‐lived event. Lithostratigraphic analyses indicates that the UO is characterised by an increase in clastic content, magnetic susceptibility and mean sediment grain size, all indicators of changing environmental conditions, most likely the result of regional cooling. The Taylor Lake record adds to a growing body of evidence for a widespread, hemispheric climate oscillation at 8.2 kyr. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

17.
Glaciated alpine landscapes are sensitive to changes in climate. Shifts in temperature and precipitation can cause significant changes to glacier size and terminus position, the production and delivery of organic mass, and in the hydrologic energy related to the transport of water and sediment through proglacial environments. A sediment core representing a 12,900-yr record collected from Swiftcurrent Lake, located on the eastern side of Glacier National Park, Montana, was analyzed to assess variability in Holocene and latest Pleistocene environment. The spectral signature of total organic carbon content (%TOC) since ~ 7.6 ka matches that of solar forcing over 70-500 yr timescales. Periodic inputs of dolomite to the lake reflect an increased footprint of Grinnell Glacier, and occur during periods when sediment sinks are reduced, glacial erosion is increased, and hydrologic energy is increased. Grain size, carbon/nitrogen (C/N) ratios, and %TOC broadly define the termination of the Younger Dryas chronozone at Swiftcurrent Lake, as well as major Holocene climate transitions. Variability in core parameters is linked to other records of temperature and aridity in the northern Rocky Mountains over the late Pleistocene and Holocene.  相似文献   

18.
The Holocene environmental history of South Georgia is important because of the island's location in the Southern Westerlies in an oceanic zone of the world devoid of high resolution terrestrial records. This is the first attempt to interpret a palaeoenvironmental record from lake sediments in South Georgia. It is based on a wide variety of analyses undertaken on cores from two lakes. Both are in the same, unglaciated, drainage basin, but one is at 80 m above sea-level and near the altitudinal limit for vegetation growth, whereas the other is at 25 m and within the zone of continuous vegetation cover. Results from both lakes indicate shifts of vegetation boundaries, which, together with evidence for changing biotic productivity within the lakes themselves, are interpreted as indicating climatic changes. Radiocarbon dates on the main changes identify a climatic optimum, beginning before 5620 ± 290 14C yr BP, and ending at around 4815 ± 330 14C yr BP, when conditions in the upper part of the catchment were more conducive to plant growth than they are today. The record obtained from the lower lake was shorter, but indicates two periods of harsher climate relative to the present since 4000 yr BP. This interpretation of the lake evidence agrees with other dated evidence of environmental change from peat sections, glacial stratigraphy and geomorphology in South Georgia. Together the work allows an overall reconstruction of environmental change in the Holocene.  相似文献   

19.
The development of a glacial lake impounded along the retreating, northeastern ice margin of the Fennoscandian Ice Sheet during the last deglaciation and environmental conditions directly following the early Holocene deglaciation have been studied in NE Finland. This so‐called Sokli Ice Lake has been reconstructed previously using topographic and geomorphologic evidence. In this paper a multiproxy approach is employed to study a 3‐m‐thick sediment succession consisting of laminated silts grading into gyttja cored in Lake Loitsana, a remnant of the Sokli Ice Lake. Variations in the sediment and siliceous microfossil records indicate distinct changes in water depth and lake size in the Loitsana basin as the Sokli Ice Lake was drained through various spillways opening up along the retreating ice front. Geochemical data (XRF core‐scanning) show changes in the influence of regional catchment geochemistry (Precambrian crystalline rocks) in the glacial lake drainage area versus local catchment geochemistry (Sokli Carbonatite Massif) within the Lake Loitsana drainage area during the lake evolution. Principal component analysis on the geochemical data further suggests that grain‐size is an additional factor responsible for the variability of the sediment geochemistry record. The trophic state of the lake changed drastically as a result of morphometric eutrophication once the glacial lake developed into Lake Loitsana. The AMS radiocarbon dating on tree birch seeds found in the glaciolacustrine sediment indicates that Lake Loitsana was deglaciated sometime prior to 10 700 cal. a BP showing that tree Betula was present on the deglaciated land surrounding the glacial lake. Although glacial lakes covered large areas of northern Finland during the last deglaciation, only few glaciolacustrine sediment successions have been studied in any detail. Our study shows the potential of these sediments for multiproxy analysis and contributes to the reconstruction of environmental conditions in NE Finland directly following deglaciation in the early Holocene.  相似文献   

20.
A 6.5 m long sediment succession (18.5-2.2 ka BP) from the northern sub-basin of lake Endletvatn was analysed lithologically, palynologically and chemically. The chemical analyses were performed at about 10 cm depth intervals for the following parameters: total organic C, N, P, Fe, Mn, Mg, Na, K, Ca and S, in addition to water content, dry density, and pH. Two main lithostratigraphical units can be distinguished, which also differ substantially in chemical characters. Five chemostratigraphical main units were distinguished. The two lowermost units 1-2 (18.5-12.9 ka BP) correspond to the lower lithostratigraphical main unit and are characterized by minerogenous sediments with low C and N, and high Fe, Mg and K. P is low, partly because of a scarcity of P in parent rocks. Chemostratigraphical unit 3 (12.9-9.6 ka BP) is characterized by increasing C and N and a high N/P ratio (10-20) culminating in the early part of the Younger Dryas, indicating abundant N available for bio-production. The Fe, Mg, and K content is still high, but decreasing, indicating decreasing glacial and kryogenic erosion and allogenic deposition until c. 10.5 ka BP. A hiatus represented by a sand layer covers most of the time-span 10.5-9.6 ka BP. Chemostratigraphical unit 4 (9.6-5.3 ka BP) represents the Holocene thermal optimum in three subunits. In the time interval 9.6-9.1 ka BP, Fe, Mg and K decrease to a minimum and P shows a pronounced increase. The megathermal period c. 8200-5300 BP, is characterized by maxima of C, N and P and a minimum of Fe. The katathermal period after 5.3 ka BP is characterized primarily by increased Fe precipitation, increasing Fe/Mn ratio, and P, C and N at a constantly lower level than during the megathermal. A stable C/N ratio of about 10, of the sediment interval younger than 12.9 ka BP characterizes the sediments as transitional between gyttja and dy. The Holocene lake type varied between weakly oligohumic and mesohumic. Stagnant bottom waters (reducing conditions) occur in the periods 12.9-11.5 ka BP and c. 7.5-5.3 ka BP. The climatic development and other environmental implications of the joint chrono-, chemo-, litho- and biostratigraphical data set are discussed.  相似文献   

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