During the ARK-X/2 expedition 1994 with the polar research vessel "Polarstern", more than 15 m of sediment cores were recovered from two lakes in the outer coastal region of East Greenland. Based on sub-bottom profiling by a Chirp sediment echosounder, sampling was carried out using gravity and piston corers. The comparison of the recieved sediment core data with the results of glaciological investigations from ice cores and geological investigations from the continental margin allows the reconstruction of the Late Quaternary climatic and environmental history of East Greenland. Sub-bottom profiling in Basalt Lake (N 72°43.4´, W 22°27.9´) indicates a rather simple basin in W-E-direction with more or less homogenous sediment fill. The thickest lacustrine sediment fill, comprising about 10 m occurs in the central eastern part of the basin. From the uppermost three meters, representing most of the Holocene, four samples of plant remains were 14C-AMS dated and calibrated (cal. yrs. BP). The lowermost 7 - 8 m of lacustrine sediments, overlaying a basal moraine, point to a rapid ice retreat, associated with high sedimentation rates. In a smaller Lake about 1 km south of Basalt Lake, here called Lake B 1, further eight AMS-dated samples of plant remains point to a glacier retreat in the outer fjords of East Greenland between 10 100 and 10 400 cal. yrs. BP. Combining geochemical and sedimentological analysis as biogenic opal, CNS-analysis and palynological information from sediments of both lakes, an early climatic optimum with continental conditions from 8 500 to 5 500 cal. yrs. BP is indicated. Winter precipitation increased at about 7 000 cal. yrs. BP, reaching a maximum between 5 500 and 3 500 cal. yrs. BP, indicated by a trend towards coarser sediments and a shift in the vegetation association from a Betula nana shaped dwarf shrub heath to a Salix arctica-Cassiope association. Parameters for bioproductivity dropped during this period. Caused by a futher cooling birches dissappeared rather completely in the following centuries. Only a short increase in temperature at about 1 000 cal. yrs. BP gives reason for a renewed but weak increase in geochemical parameters as well as in arboreal pollen concentration until the Little Ice Age startet in the time intervall between 600 and 500 cal. yrs. BP.
Reconstructing environmental change at regional and continental scales from the investigation of lake sediments requires an holistic approach and multiple lake and multiple parameter studies (Oldfield, 1977). In addition, accurate and precise independent chronologies are required for each sediment sequence if short-term variations in environmental (climate) change are to be revealed (Renberg, 1982). Excellent environmental archives are preserved in annually laminated (varved) lake sediment sequences in Fennoscandia (e.g. Renberg, 1982; Petterson et al. 1993; Snowball et al. 1999). These continuous sediment sequences posses an inherent calendar year chronology against which the variations of a considerable number of physical, chemical and biological parameters can be compared. Such parameters (e.g., mineral content, organic carbon, diatoms and pollen) form independent records of, for example, catchment erosion, lake productivity and regional vegetation dynamics. As part of the ELDP, two varved lake sediment sequences in close proximity to each other (15 km) in northern Sweden have been subjected to detailed mineral (environmental) magnetic measurements. There is excellent agreement between the two sites in the short term (<103 years) trends of detrital mineral erosion and deposition over the past 9,000 years, which is controlled to a large extent by the intensity of the spring melt-water flood (which reflects winter precipitation in the form of snow). After lake formation a major period of erosion (increased snow) occurred in both sites between 8,100 and 7,500 cal. BP, which was followed by very low erosion rates until 3,700 cal. BP. The late Holocene (until human influence at c. 200 cal. BP) is characterised by an increase in the intensity and frequency of erosion events, and reflects a more unstable (possibly more oceanic) climate regime. On the other hand, the long-term trends (>103 years) differ somewhat and indicate that long term development of the ecosystems plays an important role in determining the sediment characteristics.
Oldfield F, Progress in Physical Geography, 3, 460-504, (1977).
Petterson G, Renberg I, Geladi P, Lindberg A, & Lindgren F, Journal of Paleolimnology, 9, 195-208, 9, 195-208, (1993).
Renberg I, Geologiska Föreningens i Stockholm Förhandlingar, 104, 85-90, (1982).
Snowball IF, Sandgren P & Petterson G, The Holocene, 9, 000-000, (1999).
Lake Steißlingen is a small hardwater lake 5 km west of Lake Constance; its maximum depth is 20.5 m. The lake is feeded by submerged springs and precipitation. Sediment cores from the deepest part of the lake cover the complete late- and postglacial history and are dominated by annually laminated sediments, thus climatic and anthropogenic induced changes are recorded with high temporal resolution. Stratigraphy and absolute ages are constrained by pollen analysis, 14C-AMS-dating on terrestrial organic detritus as well as important marker layers, such as Laacher See- and Vasset-Kilian tephras, and known historic events. A variety of methods is applied in the analysis of the sediments such as inorganic and organic geochemistry, microfacies-analysis, pollen-analysis, diatom-analysis and O-isotope analyses on ostracodes, cellulose and molluscs. The aim of these analyses is the reconstruction of the lake's environmental and climate history and the gaining of a new standard profile for the western Lake Constance region.
Here the detailed late glacial history of the lake will be presented. A high resolution pollen diagram beginning in the Bølling shows that the vegetation development is typical for the Lake Constance region. The pollen stratigraphy of the late glacial allows a stratigraphical correlation with archives from the Swiss Plateau, Hessen and the Eifel. The late glacial sediments are partly laminated, but the establishment of an absolute varve chronology is difficult. Unfortunately 14C-Dates are not yet available for the late glacial. The LST allows at least absolute dating and varve counting of the Allerød. The Lake Steisslingen profile is thus a very important link between the prealpine Swiss Plateau and the more northerly archives and another step towards an independent, absolutely dated high resolution stratigraphy of the terrestrial late glacial.
Lake Holzmaar (6°53´E, 50°7´N) is a maar lake 425 m a.s.l. situated 90 km SE of Cologne in the West Eifel Volcanic Field. This region with elevations of up to 625 m a.s.l. is typical for montanuous landscapes of Western Europe and is characterised by a mean annual air temperature of 8.2°C (July mean: 16.0°C). The lake has a catchment area of 2.25 km2 with elevations of up to 475 m a.s.l. The trophic state of the modern lake is eutrophic to mesotrophic. Recent profundal sediments of Lake Holzmaar show carbon isotope values in organic matter of about -27.5 permille.
The Holocene part of the Holzmaar record comprises 11.5 m of varved sediments. They were sampled in 1 cm blocks resulting in a time resolution of approx. 5-30 years. Here, attention will mainly be paid to stable carbon isotope values of bulk organic matter (13Corg). However, a variety of other parameters and analyses (e. g. sediment accumulation rate, total organic carbon, biogenic silica, pollen) are available for a comprehensive interpretation.
The overall variability of carbon isotope ratios covers a bandwidth of 10 permille, ranging from -27.0 to -37.0 permille. The Laacher See Tephra event, however, is characterised by a 13Corg value of -23.3 permille. The record shows a number of prominent features supposedly indicating different states of the ecosystem. Presumably the system was controlled by different key variables. In a first attempt the record may be divided into three time slices with specific patterns and possibly different functional modes.
1); 13,500 - 10,200 varve years BP: "high variability" mode with high frequency but low amplitude oscillations (c. 4 permille). 2); 9,650 - 5,000 varve years BP: "single cycle" mode showing a smooth increase of carbon isotope values finally followed by a massive decrease. 3); 3,400 varve years BP - Present: "flip-flop" mode with rapid changes between high and low carbon isotope values with minor noise; changes from high to low values take place within periods of 50-100 years.
The possible variables controlling each mode will be discussed and compared with evidences of other sediment parameters to identify the mechansims of changes of the lake's ecosystem.
Acknowledgement: We thank A. Hemman for performing the isotope analyses.
An 8.7 m core was taken from a depth of 186 m in the western basin of Lake Constance. Ostracod species assemblages and their valve stable oxygen and carbon isotope values were analyzed. The core has been dated by combined C-14 analyses (organic macrofossils), correlation to other dated cores, and by varve counting. Modeled absolute ages yield a core base date of around 16,3 kyr BP.
As in most deep lakes, the profundal ostracod community is comparatively simple; being composed of a few benthonic species living in and on the sediment (Leucocythere, Limnocythere, Candona, Fabaeformiscandona, and Cytherissa) and bentho-nektonic species that swim above it (Cypria). The lowermost 2.5 m (approx. 16 - 14,5 kyr BP) are characterized by yellowish brown to grey rhythmites and contain low numbers of Leucocythere mirabilis and Cytherissa lacustris. Limnocythere sanctipatricii, Candona sp. and Fabaeformiscandona sp. appear after 14,5 kyr BP, coincident with the change from rhythmites to massive brownish-beige muds. During this period, temporary landslide-dammed lakes upstream of Lake Constance entrapped some of the detrital sediment load of the River Rhine. The final in-filling of these lakes led to a direct inflow of the Rhine into Lake Constance, and deposition of brownish-grey, finely laminated clayey silts after approx. 6 kyr BP.
Oxygen and carbon stable isotopic ratios were analyzed from adult specimens of two ostracod species: L. mirabilis and L. sanctipatricii. Oxygen isotope profiles for both species are similar. Late Glacial oxygen isotope values vary between -11 and -8 per mil, and include negative excursions for both the Older and Younger Dryas; values for the Holocene are around -8 per mil. The carbon isotopic values of both species are similar, and show an overall decrease from around -4 per mil in the Late Glacial to about -7 per mil during the early Holocene. After approx. 6 kyr BP the carbon isotope signals from L. mirabilis and L. sanctipatricii diverge. Limnocythere sanctipatricii carbon isotope values remain at around -7 per mil, whilst those from L. mirabilis decrease sharply to around -11 per mil. This change coincides with the aftermath of the Flims rockslide.
We postulate that this divergence is caused either by (1) changes in the pattern of seasonal production in the lake, or (2) divergence in food-substratum utilization (plant-based vs. detritus) between ostracod species. Both are likely to be the product of increased within-basin productivity, presumably in response to increased environmental temperatures after approx. 9,5 kyr BP.
Isotope records from lakes and tree rings provide important archives of continental climatic change from which long, high-resolution proxy records may be reconstructed. Additionally, the improvement in the temporal and spatial network of continental archives will undoubtedly improve our understanding of interhemispheric climate relationships. However, before longer records can be exploited, calibration of isotopic responses in modern hydrologic settings must be conducted to facilitate accurate paleoclimate interpretations. By developing realistic models of modern precipitation records, it is possible to back-calculate the isotopic composition of precipitation, beyond the existing Global Network of Isotopes in Precipitation (GNIP) initiated in 1961.
Here we compare oxygen isotope calibrations from two precipitation archives: A varved lake sequence from Baldeggersee, a small eutrophic lake located in Central Switzerland, and a tree ring cellulose record from a tree located in the lake's watershed, within 1 km of the lake. Laminated records such as tree rings and varved sediments provide the advantage of annual resolution such that sub-decadal changes can be directly compared between both archives. Oxygen isotopic values of lacustrine bio-induced calcite represent an integrated record of the isotopic composition of precipitation feeding the lake, modulated by the lake's residence time. Trees record the isotopic composition of precipitation utilized during photosynthesis, occurring from May to September in our study area.
Using new analytical procedures, we have constructed an alpha-cellulose stable oxygen isotope time series (1913 to 1995) from yearly rings in four spruce trees. A modified plant-water model, incorporating annual meteorological data and the alpha-cellulose oxygen isotope record generates annual isotopic composition of precipitation utilized by the plant. Model results are in good agreement with directly measured isotope data from the GNIP station at Bern for the period when the two records overlap (1973-1995). With this extended record of isotopic composition of precipitation, it is now possible to directly compare the two archives and evaluate the signal recorded in the lacustrine calcite record. After 1930, both records display the same first-order trends. In particular, both records record a 2‰ enrichment-depletion cycle from 1930 to 1980 with maximum isotope values recorded during the late 1940s - early 1950s. Good agreement of the major isotope features of these two proxy data sets indicates a similar climatic forcing, i.e. a change in the regional isotopic composition of precipitation in response to temperature change and/or a change in the dominant synoptic atmospheric circulation patterns. This novel comparison of oxygen records from two independent continental high-resolution proxies validates both approaches to paleo-isotopic reconstruction, thus making them useful for longer geologic records.
The Lac du Bouchet and Praclaux maars, located in the Velay region (French Massif Central), contain long records of paleoclimatic archives. The pollen contents and the magnetic records of these two continental sequences have been investigated over the last 15 years by french teams. These sedimentary sequences contain three tephra layers: the LDB tephra, located at the bottom of the Lac du Bouchet sequence, and the PCX-I and PCX-II tephra, situated at the top and bottom of the Praclaux sequence, respectively. A detailed petrographic and geochemical study suggests that the LDB and PCX-I tephra originated from a same eruptive event. Nine 40Ar/39Ar analyses on sanidine and biotite grains were performed on these tephra, using a continuous argon ion laser. Six total fusions on sanidine grains and one biotite single grain analysed by step-heating, from PCX-I tephra, displayed concordant ages ranging from 262 ± 17 ky to 303 ± 21 ky. Two total fusions on sanidine grains from LDB tephra yielded concordant ages of 283 ± 23 and 300 ± 27 ky. The weighted mean age of 274 ± 6 ky is similar to the correlation diagram (36Ar/40Ar vs 39Ar/40Ar) age of 275 ± 11 ky (initial 40Ar/36Ar ratio = 297.5 ± 25, MSWD=0.7). Thus, these tephra represent a high quality chronological marker which allows to correlate these two sequences. From the top (Holocene) to the bottom of this composite sequence, five main warm episodes alternating with five cold periods have been identified. The presence of the LDB-PCX-I tephra in the "Amargiers interstadial" allows to date accurately this paleoclimatic event and to correlate it with the last warm oscillation of the isotopic stage 9 (9a). Thus, the second (Eemian) and third (Le Bouchet I, II and III) warm episodes described in this sequence might be correlated with the isotopic stages 5e and 7a, 7c, 7e, respectively. Assuming a continuous infilling in these maars, the fourth ("Landos") and fifth ("Praclaux") interglacial episodes have been assigned to the isotopic stages 9e and 11, respectively. To test that interpretation, 40Ar/39Ar analyses were performed on the PCX-II tephra which is interbedded in the sediments representing the "Praclaux interglacial" episode. Five total fusions on sanidine single crystals, yielded concordant ages between 600 ± 11 ky and 631 ± 24 ky, with a weighted mean of 606 ± 6 ky, concordant with the age of 580 ± 20 ky measured on a Mont Dore pumice flow (Lo Bello et al., 1987). These ages do not fit with the isotopic stage 11; they could rather correspond to the isotopic stage 15, according to Karner and Marra (1998). This suggests a gap in the Praclaux sequence either between the "Amargiers" and "Landos" interstadials or between the "Landos" and "Praclaux" interstadials.
Lo Bello, P, feraud, G, Hall, CM, York, D, Lavina, P & Bernat, M, Chemical Geology, 66, 61-71, (1987).
Karner, DB & Marra, F, Geological Society of America, 110, 748-758, (1998).
Lago Grande di Monticchio (LGM), a maar lake in the Monte Vulture volcanic district (southern Italy), is located 120 km east of Naples. Several sediment cores were recovered for interdisciplinary palaeoclimatic and palaeoenvironmental investigations. The partly laminated sediment record of 73 m length includes more than 300 tephra layers ranging in thickness from 0.1 mm to 33 cm. Therefore, in addition to radiocarbon and Ar/Ar dates, detailed tephrochrochronological studies have been initiated in order to confirm the varve- and sedimentation rate chronology of the >100,000 year record. Fourteen of the thickest tephra layers have already been correlated with explosive events from Campanian volcanoes (Newton & Dugmore, 1993; Negendank & Zolitschka, 1994; Narcisi, 1996). Microscopic studies of all 330 tephra layers and geochemical investigations on glass shards using microprobe technique are in progress to specify the petrology. With that, at least 33 tephra layers can be correlated with Plinian as well as Interplinian eruptions from Somma-Vesuvius (<27 ka). Most tephras belong to eruptions of Ischia (including Y-7 "Mt. Epomeo Green Tuff", 56 ka) and the Phlegrean Fields (including Y-5 "Campanian Ignimbrite", 33-37 ka), as well as Alban Hills (>25 ka) and Sabatini in earlier times. Only one tephra layer has been related to the explosive eruption of Etna (Y-1 "Biancavilla Ignimbrite", 16.5 ka). Two tephras, occurring close to the onset of the LGM sediment profile, have been correlated with the marine X-5 and X-6 tephra layers (Campanian province, Ischia?), which are dated by Ar/Ar at 105 ka and 107 ka, respectively (Kraml, 1997). Therefore, studies of the tephrochronological record of Lago Grande di Monticchio will contribute both to a better knowledge of explosive activities of the Campanian volcanoes (eg. paleowind pattern) and to correlations with isochronous tephra markers of other lacustrine and of marine sediments from the Mediterranean (teleconnections).
Kraml M, Dissertation, University of Freiburg i.Br., 216p., (1997).
Narcisi B, Quaternary Science Reviews, 15, 155-165, (1996).
Negendank JFW & Zolitschka B, Terra Nostra, 1/94, 70-75, (1994).
Newton AJ & Dugmore AJ, Lecture Notes in Earth Sciences, 49, 333-348, (1993).
The Belomorian depression lake drilling project started in 1997. In this abstract we summarize the current data resulting from the field and laboratory work.
The key aims of these investigations are to restore the environmental history of the Belomorian (White Sea) depression. For this purpose the stratigraphy of raised coastal basins in the Umba area (66°41°, 34°28°), Lesozavod area (66°40°, 32°50°) and Chapoma area (66°06°;, 38°54°) was studied in order to identify and date lacustrine-marine-lacustrine transitions (isolation contacts) and construct relative sea-level curves for the Late Weichselian and Holocene. Nine lakes situated between 12 and 65 m a.s.l in the Umba area, ten lakes between 3 and 104 m a.s.l. in the Lesozavod area, and two lakes between 13 and 24 m a.s.l. in the Chapoma area, were cored. In addition, the altitude of beach ridges and terraces was measured in several places along the White Sea coast.
Various facies types and facies sequences, controlled by sea-level changes and influenced also by climatic factors, are recognized in cores. Main facies types are: (I) Postglacial lake (non-laminated clay), (II) Mixed (silt and sand with plant detritus), (III) Marine (silt, sand, shell fragments), (IV) Transitional (laminated gyttja or gittja and silt), (V) Lacustrine (gyttja, plant detritus). Diatom complexes corresponding to each facies type were determined. Cores from different investigated areas show a complicated facies sequence comprising either all facies types or only a few facies types. The lithostratigraphic investigation and C14 dating of the sections suggest that basins development in the Belomorian depression during the Late Weichselian and Holocene time proceeded in a complicated way from the postglacial lake stage through the salting stage, stages of normal sea salinity to contemporary freshwater lakes on the coast. The precise relationship of these stages with deglaciation, climatic variability and relative sea-level changes is under review.
This study is addressed to the glacial and climate history on the Severnaya Zemlya Archipelago, a key region for the still controversial discussed extension of the late Weichselian glaciation of Western Siberia. Two sediment cores (10.4 and 12.7 m) were recovered from the 10.6 km2 large and up to 18 m deep Changeable Lake (79°07`N, 95°07`E) on October Revolution Island. The lake is situated 4 km to the SW of the glacier edge and is fed by glacial melt water. The sediment cores were sampled in the central parts of two different basins, showing comparable lithological sequences. A highly consolidated diamicton at the base of the cores is overlain by fine-grained sediments, succeeding in colour from greenish-grey at the base via black to reddish-brown in the near-surface sediments.
Sediment lithology combined with AMS-14C-ages from different organic fractions (Foraminifera, humic acids, insect and plant fragments) implies the following paleoenvironmental history. The diamicton at the base is interpreted as a till, derived from the last glaciation of the Changeable Lake area. It is overlain by a homogenous marine sediment, formed during marine transgression which is AMS-14C-dated to >48.000 yrs. BP. on Foraminifera, indicating an even older age for the till. After this period, drying up of the basins caused a hiatus in the sediment sequence of about 10.000 yrs. The following laminated greenish-grey sediment resembles reworked marine sediment where insect and plant fragments are dated between 20.000 and 30.000 yrs. BP. This section is succeeded by a lithological unit which is characterized by fine lamination due to the lack of sediment input or a low sedimentation rate. First palynological studies show that the Holocene lake history starts with the deposition of the reddish-brown sediment.
The results indicate that the last greater glaciation on October Revolution Island happened prior to 48.000 yrs. BP. This supports the theory that during the late Weichselian only separated ice caps existed on the Islands.
In the areas of low mountain range of Central Europe, a great number of isolated Paleogeneous sediments exists, which are characterized by a small lateral extent (up to 3000 m), but show a considerable continuation to depth (up to 500 m). Most of them consist of laminated black shale sediments, which are famous for their fossil wealth. The main occurences are Eckfeld, Kunksköpfe (Eifel), Rott (Siebengebirge), Enspel (Westerwald), Messel, Prinz von Hessen (Sprendlinger Horst), Beuern (Vogelsberg), Sieblos (Rhön), Seifhennersdorf, and Kleinsaubernitz (Oberlausitz). Very often, isolated Paleogeneous sediments are the only tool to reconstruct the paleoenvironment and the paleoecology in the low mountain range of the Tertiary time.
Since 1990 we have mapped the three occurences of Eckfeld, Enspel, and Messel. We compared data taken from shallow and deep drillings with calculated geophysical field measurements. At the same time, we compared these results with data from maar volcanoes of the Eifel. From these investigations we concluded that the isolated Paleogeneous sediments of Central Europe generally can be interpreted as crater sediments of maar volcanoes. This result considerably influences the interpretation of the paleoecology and the reconstruction of the paleotopography in the vicinity of these isolated Paleogeneous sediments.
In order to improve the accurancy of this interpretation, we have started to study maar volcanoes located in a region with a climate similar to the climate in Europe in Tertiary times. For this purpose we selected an area of maar volcanoes in Eastern Java. In this region, the stratovolcano Gunung Lamongan, about 1670 m high, is concentrically surrounded by 30 maars, 40 scoria cones, and 20 ash cones. A lake is present at 10 of these maars. The others are bogs or dry maars. So far we have gathered geodetic, geomagnetic and gravity data at several maars. Additionally, geological and volcanological mapping campagnes started. Taking the Ranu Agung maar volcano as an example, we will present, climatical, limnological, sedimentological, volcanological, and geophysical data, correlated with the results of the isolated Paleogenoeous sediments of Central Europe.
The global Late Pliocene cooling, leading to the onset of Northern Hemisphere glaciation, is well expressed in the clay mineral distribution of marine sediment cores. In continental records, in contrast, respective clay mineral evidence for changes in the weathering conditions is lacking. This is due to the limited number of continental records with continuous, fine-grained sediment accumulation in Late Pliocene time and its preservation. An exception is Lake Baikal, the oldest and deepest fresh-water body of the world. Since ca. 30 Ma, Lake Baikal functions as a trap for fine-grained sediments in the interior of the Asian continent, far away from any marine influences. Hence, its more than 7 km thick sediment filling is expected to be a unique archive for the continental climate evolution in Asia, which at least partly is related to the uplift of the Himalayan system. The BDP-96-1 drill hole at Academician Ridge penetrated to ca. 200 m below lake floor. According to paleomagnetic data, the core base corresponds to ca. 5 Ma and sedimentation was widely constant at a rate of ca. 4 cm/ka. Williams et al. (1997) proofed that the hydrologic regime of Lake Baikal had reacted sensitive to climate changes throughout the time interval documented in the BDP-96 cores. Here, we present and discuss clay mineral data of core BDP-96-1 in the light of climate changes at Lake Baikal during the onset of Northern Hemisphere glaciation. An earlier clay mineral study on BDP-93 cores had shown that clay minerals in Lake Baikal sediments are a useful proxy for reconstructing both climatic history and source area changes (Melles et al., 1995; Yuretich et al., in press). XRD analysis of core BDP-96-1 were performed on 130 oriented samples of the 2 µm fraction, taken in steps of 20 cm in the depth interval 90 to 120 m. This corresponds with 2.1 to 3.3 Ma, in a time resolution of 5 to 10 ka. The results indicate that cooling started at about 2,9 Ma and change of source area around 2,7 Ma B.P. This findings are supported by other paramaters such as the heavy mineral distribution (Eckert et al. 1998) and palynological data (Demske et al. in press). Furthermore first geochemical data of the fraction 2 - 32 µm will be discussed Based on these data it should be possible to quantify the eolien input into the lake as an indicator for changes of the monsoon circulation in SE Siberia.
Williams DF, Kuzmin MI, Kawai T, Oberhänsli Het al, Eos. Trans, 78, 597-604, (1997).
Melles M, Grobe H & Hubberten H-W, IPPCCE Newsletter, 9, 17-22, (1995).
Yuretich R, Melles M, Sarata B & Grobe H Journal of Sedimentary Geology, (in press).
Eckert C, Müller J, Oberhänsli H & Hubberten H-W, Joint Int. Symp. Baikal Abs, Poster, (1998).
Demske D, Müller J, Eckert C, IPPCCE Newsletter, 12, (in press).
Reconstructing past global changes through the recognition of variability within environmental systems, is fundamental goal in earth science. Annually laminated lake sediments are natural archives that record the modes and mechanisms of palaeoclimatic variability. Applying the recently developed digital sediment colour analysis technique (DCSA), colour change (expressed as greyvalues) within annually laminated lake sediments from European lakes is used as a proxy indicator. In order to extract palaeoclimatic information from greyvalue time series (GTS) its basic structure is quantified through time series analysis (TSA). A common assumption in TSA is stationarity (of the GTS statistical moments) and independence, which is actually rare in palaeoclimatic data. Non-stationarity is a result of trends and/or abrupt changes. The identification, and subsequent treatment of such features is dependent on the definitions, differentiating between variability and change. Trends are both global and local, and are removed by detrending, using a polynomial equation or differencing; both of which allow the GTS to remain intact and analysed using classical Fourier analysis. Abrupt changes lead to the subdivision of the GTS into stationary sub-sets, that are analysed using evolutionary power spectra. The significance of spectral peaks is tested using both white and red noise backgrounds.
A feature of all the computed power spectra is the white noise-like structure (flat) at short timescales, and red noise like structure (exponential curve) at longer time scales, regardless of the GTS length. The cut off point typically occurs between 150-250 years, and possibly represents the response to a change in the dominant forcing mechanism. The broad interannual and interdecadal scale variability within the white noise like section is a common feature of palaeoclimatic time series, and arises through internal forcing mechanisms, and/or modulation of fixed period external forcing by internal mechanisms. The occurrence of peaks within the 11 (sunspot cycle) and 22 (hale) year period may indicate the influence of solar variability, common in many diverse palaeoclimatic proxies. However, such peaks have appeared in climate models where intra- and interannual forcing is the only forcing mechanism. This suggests that interdecadal variability may not necessarily be caused by processes operative on interdecadal scales, but may reflect the inherent fluctuations, due to the variability of the annual cycle. Furthermore, the evolutionary power spectra reveal a varying strength in the interdecadal signals, which together with a high signal-to-noise ratio, complicates the assignment of an explicit cause. Therefore, the application of the DCSA technique, in unison with spectral analysis can yield useful information on the timescales and variability over which earths climate system operates, and also can indicate the process responsible for such variability.
Lake Baikal is the oldest and deepest lake of the earth. It is situated in the center of the Baikal rift system, the largest extensional zone of the eurasian continent. Since late Oligocene (about 30 Ma ago) continous sedimentation lead to more than 7 km of sediment accumulation - an ideal archive to reconstruct paleoclimatic and paleoenvironmental evolution of the asian continent. Of special interest is the time, in which global climate underwent drastic changes, e.g. the Intensification of Northern Hemisphere glaciation. This climate change, which occured in the time interval between 2,5 and 3,1 Ma, can be seen in the sediments of BDP-96-1 (200 m length, 5 Ma), looking at different parameter. One of this parameters is the content of heavy minerals in the sediment. Heavy mineral and clay mineral data (Mueller, J. 1999) indicate changes in sediment input in the time between 2,9 and 2,7 Ma B.P. Heavy mineral analysis of core BDP-96-1 were performed on 68 samples of the >32 µm fraction, taken in steps of 40 cm in the depth interval 90 to 120 m. This corresponds with 2.1 to 3.3 Ma, in a time resolution about 10 ka. The results shows, that a relatively constant heavy mineral distribution until ca. 2,85 Ma B.P. can be established. From this time on higher variations are seen in all heavy mineral groups, but especially in the minerals apatite, titanite and zirconium. The amphibole and pyroxene distribution stays until 2,6 Ma B.P. relatively stable, after the amphiboles increase slightly wheras the pyroxenes decrease. The garnets shows an interesting evolution in the time interval between 3,0 and 2,4 Ma B.P.; here an increase occures until 2,8 Ma to about 4%, after decreasing again; additional EDX analysis on selected samples show, that before 2,8 Ma almandine dominates, after 2,8 Ma andradite.The question, if the heavy mineral distribution is dependent on climate, cannot be answered clearly; however changes in the catchment area can be pointed out; this can also maybe due to changing wind directions. Summarising the heavy mineral analysis can be said, that a climatic dependence, as seen in the clay mineral data, is can not be proofed. However, changes in the catchment area are clearly seen in the time intervall between 2,9 and 2,7 Ma B.P. This can be due to tectonical movements or due to changing wind directions; but it is probably a combination of both.
Mueller, J. Conf. Abs., 4, (1999)
The accumulation of organic matter in peat bogs potentially constitutes a continuous and high-resolution record of continental climate for the Holocene period. Few studies, however, have attempted to calibrate the relationships between environmental parameters (such as temperature, humidity, pCO2, light intensity...) and the isotopic ratios of plants in modern ombrotrophic bogs. For that purpose, we studied 8 species of modern peat bog plants (including vascular plants and mosses) at 14 sites along an altitudinal transect. The sites range from 500 to almost 2000 masl into the Jura Mountains and the Bernese Alps in Switzerland.
After chemical extraction of <alpha>-cellulose, carbon isotope ratios were measured by on-line combustion/continuous-flow methods. For comparison, the same analysis was performed on total plant C. We observe three different altitude-13C relationships depending on plant type. For cellulose from shrubs (Vaccinium and Calluna) the 13C-values increase linearly with altitude from -27 to -24 per mil. For annual plants (Andromeda and Carex) more complex relationships between altitude and 13C are observed, with values initially increasing with altitude to around 1600 masl and then decreasing. In contrast to the other vascular plants, Eriophorum 13C-values show no clear relationship with altitude. Sphagnum species also show generally increasing 13C with altitude, though the response of individual species may vary greatly depending on habitat. For S. magellanicum, a hummock specie, values range from -28 to -23 per mil. Again the values increase until 1600 masl and then decrease for the highest sites. In contrast, generally higher values are found in S. cuspidatum, a hollow specie, with no clear relationship to altitude.
Comparison of the isotopic data to meteorological data along the same transect allow us to rule out variations in humidity or water availability as causes for the observed trends in cellulose from the vascular plants. Instead, the decrease in the temperature and in the partial pressure of CO2 with altitude, but also the net increase of light intensity received by plants appear to be potential important parameters responsible for changes in the 13C-values. The larger response of hummock Sphagnum species may be due to their inability to regulate internal pCO2 through stomatal response to decreased external pCO2. Furthermore, the moss species seems to be more sensitive to changes in water availability.
The classic structure of a sublacustrine delta is described as a fan formed by a delta front, characterized by coarser-grained matter deposition, and a prodelta area where the comparatively fine particles are transported by the plume of river water entering into the lake. Depending on the density differences between the lake and the river water, interflows or underflows currents can form. In Lake Geneva, this model of deposition fits well on the two largest deltas, Rhône and Dranse, characterized by several adjacent canyons covered by turbidity currents.
In the Western part of Lake Geneva (Petit-Lac), the detritic sediment is brought into the lake by small river systems. In this study the geometry of two small deltas (Promenthouse and Asse) was investigated in order to understand their influence on lacustrine sedimentation during the Holocene period.
To observe and quantify the sequence stratigrafy of Promenthouse and Asse deltaic fans, an echosounding survey was carried out using a subbottom 12 kHz echosounder. A narrow spaced net of very high resolution profiles shows several Holocene deltaic sequences prograding offshore above the ancient glaciolacustrine and glacial deposits. The presence of important and still active slump movements is revealed on the slope by upward curved reflections. Eleven gravity cores of 1 m have been collected at the intersection of seismic profiles. In spite of the wide lateral extension (10 km2), the sediment discharge of the rivers is rather small and isotopic dating on the first centimeter of core sediments does not show important sedimentation rates. Bathymetric investigations and core analysis indicate a low sand and gravel deposition rate limited to the mouth of the rivers on the littoral shelf. The fine matter is transported offshore by an interflow current and settles down by rain out process into the lacustrine plain.
Sedimentation in the lake appears to be very sensitive to environmental changes in the catchment areas and is therefore a valid tool to reconstruct climatic fluctuation.
Swiss Science Foundation (grants 2000-042108.94 et 2000-52432-97)
Since the last glaciation climatic changes and geological events (floods, earthquakes) have been recorded in lake sediments. Sedimentological patterns reflecting this evolution can be found in the different parts of a lake basin (shelf, slope, lake bottom). These lacustrine structures were studied in the Hauts-Monts area (Western Lake Geneva, Switzerland).
12 kHz echosounding and very high-resolution seismic surveys were carried out to analyse the 3-D sedimentary sequences of the studied area. The chronology of the seismic sequences was dated with palynological analysis on gravity cores.
Three depositional environments show interesting records of sedimentological processes:
A 0.25 km2 erosional surface is present on the lake bottom. This structure is interpreted as due to deep currents. The geometry of the seismic sequence shows that this phenomenon started during the Boreal or Atlantic and it is still present today.
Seismic profiles of the lake slope show a great structure (1 km wide) with curved and chaotic reflections that is in discordance with the underlying and overlapping layers. This gravity flow occurred during the Boreal and is probably related to important seismic or flooding events that may have happened during that period.
Lake-level fluctuations controlled the deposition and the erosion of the sediments on the shelf and on the slope of the lake floor. A few transgression/regression cycles have been recognised on the seismic profiles:
1. lowering of the lake-level in 3 steps (?- Alleríd);
2. rise of the lake-level (Younger Dryas- Boreal);
3. lowering of the lake-level and coastal erosion of the previous sedimentary layers (Atlantic);
4. rise of the lake-level (Subboreal);
5. lowering to the today lake-level. Erosion and transport of the coastal sediments by the waves and coastal currents (Subatlantic).
The sedimentary environments, the structure and age of the sediments give a new and very time continuous information on past climatic and hydrologic changes that influenced the Late Glacial and Holocene history of Western Lake Geneva and its catchment area.
Swiss Science Foundation (grants 2000-042108.94 and 2000-52432-97)
In the framework of a multidisciplinary study, two cores (S2; S6), representing a composite section about 65 meters thick, have been drilled in the fluvio-lacustrine basin of Ripa Sottile (Conca di Rieti, Central Italy). The depositional history of the basin during the last glacial-interglacial cycle is controlled by the development of a tufa sill within the drainage plain. Here we present the paleo-climatic/environmental evolution of the basin by combining sedimentological and rock-magnetic analyses integrated with other proxies such as pollen, 14C dating and total organic carbon (TOC). The results suggest that the hydrological balance of the basin during the Late Pleistocene-Holocene was characterized by alternating phases of lacustrine and fluvial conditions. Concentration-related magnetic parameters (susceptibility, anhysteretic and isothermal remanence) as well as interparametric ratios, reflect the lower content of ferrimagnetic minerals occurring during the lacustrine phases. Whithin these lacustrine intervals, some levels exhibit a higher coercivity of the remanence coupled with increasing values of SIRM/K which testify the presence of diagenetic greigite formed during sub-oxic/anoxic conditions of the basin. The presence of poorly oxigenated waters, also shown by ostracods and mollusc associations, marks the boundaries between lacustrine and alluvial plain conditions. The lacustrine sediments prevailed until the middle of the Holocene, when a quick decline in lacustrine conditions, related to a progressive climatic deterioration, led to the demolition of the tufa sill.
A coring campaign in 1997 along the western shore of the Dead Sea recovered a continuous sediment record of the last 10,000 years. We obtained sediments from the locations Ein Gedi and Ein Feshkha which represent coastal environment, and from two different fan deltas Zeelim and Hever.
The cores mostly consist of laminated sediments, sometimes intercalated by slumping layers, with presumable earthquake-induced structures. Fine layers of detrital clay alternate with layers of authigenic aragonite of some mm thickness, sporadic with layers of silt or gypsum. The longest profile (21 m) shows coarse grained, idiomorphic halite crystals at its bottom. Additionally, the cores from fan deltas partly contain sand-layers with cross-bedding and clastic carbonates.
Selected plant relicts have been dated by AMS14C method. According to this, the top of the section has an age of 690 cal BP (calendar years BP). The resulting age model calculates the average sedimentation rate to 2.5 mm per year, except for a time interval between 6300 and 7500 cal BP which yields a doubling of the sediment influx and refers to a more humid climate. The halite base of the sequence has an age of around 10,000 cal BP and can therefore be related to a transition period after the shrinking of Lake Lisan at its final stage (Yechieli et al., 1993).
The sequences show deformed sections of some cm thickness. We suggest the deformed sequences of the Holocene sediments are of the same type of mixed layers described for Pleistocene sediments of the Lisan Formation by Marco et al. (1996). One of these mixed layers from the Zeelim profile was dated between 225 AD and 49 BC, presumably correlating to the severe earthquake of 31 BC in the Dead Sea region.
Marco S, Stein M, Agnon A & Ron H, J. Geophys. Res, 101, 6179-6191, (1996).
Yechieli Y, Magaritz M, Levy Y, Weber U, Kafri U, Woelfli W & Bonani G, Israel. Quat. Res, 39, 59-67, (1993).
Paleomagnetic investigations of Lake Baikal sediments and outcrops around the lake have been provided from 70-th years until present (Kravchinsky and Mats, 1982). We present magnetic studies of, gravity cores and deep holes obtained in 1993 at Buguldeika isthmus (Peck et al., 1994), and in 1992, 1996 (Peck et al., 1996; Kravchinsky et al., 1998) and 1998 at Academic Ridge, and preliminary studies of loess-like sediments around the lake. Whole-core magnetic susceptibility (K) of all cores was measured at a 3 cm interval. Magnetic susceptibility measurements provides accurate core correlation for Academician Ridge. More over we may report about good correlation of magnetic propitious throw over long distance with upper part of Buguldeyka isthmus hole cores. Variations in magnetic concentration and mineralogy is used to construct age model for sediments of lake Baikal and estimate rate of sedimentation. Magnetic concentration parameters correlate with diatom opal dilution during the more productive interglacial periods. Magnetic mineralogy variations indicate maximum eolian transport during glacial-interglacial cycles. This method enabled us to correlate K profiles of lake Baikal cores to the global ice volume record (SPECMAP curve) (King et al., 1993; Willaims et al., 1997). K-logging has especially priority using for correlation of boreholes obtaining of complete composite sediment profile. Oriented top-bottom samples were taken at an interval 2-30 cm for paleomagnetic investigations of hole cores sediments. All samples were stepwise alternated field demagnetised, and illustrate stable primary magnetisation. All depths samples show presence of one or two components for sediments magnetisation. Magnetostratigraphic age model of BDP-96 geomagnetic profile shows to the last 5 MA polarity scale. This data enabled to determine some of age boundaries, such as Brunhes-Matuyama, Matuyama-Gauss, Gauss-Gilbert, and number of new minor geomagnetic events. This events should be confirmed by BDP-98 analysing.The Lake Baikal inclination analysed after studying of BDP-93 and BDP-96 holes record displays presence of excursions behaviour. Age of the excursions is supported by climate proxy age model based on correlation of magnetic susceptibility to the marine oxygen-isotope record and absolute dating. Age estimation of 100 m of Baikal Drilling Project of 1993 year is 500 - 530 ka.First magnetic studies of loess-like sediments around the lake illustrate good perspective for magnetostratigraphy and paleoclimate investigations.
Kravchinsky AYa & Mats VD, Pliocene and Plaistocene of Central Baikal, Nauka, Novosibirsk, 129-152, (1982).
Peck J, King JW, Colman SM & Kravchinsky VA, Earth and Planetary Science Letters, 122, 221-238, (1994).
Peck J, King JW, Colman SM & Kravchinsky VA, Journal of Geophysical Research, 101, B5, 11365-11385, (1996).
Kravchinsky VA, Peck J, Sakai H, King JW, Nomura S, Tanaka A, Kuzmin MI, Williams D & Kawai T, Russian Journal of Geology and Geophysics, 11/12, in press, (1998).
King JW, Peck J, Gangemi P & Kravchinsky VA, Russian Journal of Geology and Geophysics, 10/11, 174-191, (1993).
Williams DF, Peck J, Karabanov EB, Prokopenko AA, Kravchinsky V, King J & Kuzmin MI, Science, 278, 1114-1117, (1997).
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