Analysis Of Lake Sediments Research Articles

Late Holocene climate of the Eastern Mediterranean inferred from diatom analysis of annually-laminated lake sediments

Diatoms from the annually-laminated sediments of Nar crater lake in central Turkey are used to investigate climatic changes throughout the last 1720 years at decadal time resolution. A diatom-conductivity transfer function is employed to infer past water balance. Further information has been extracted from the palaeo-record through calculation of diatom biovolume, rarefaction (species diversity) and concentration, and through the identification of diatom bloom events in core thin sections. The Nar diatom sequence is compared with oxygen isotope (δ 18O) and pollen records from the same sediment cores in order to test the respective roles of changes in climate and land cover. Diatom-inferred (DI) conductivity excluding bloom taxa and δ 18O show very good correspondence for the first half of the record and demonstrate that this region experienced a period of century-scale drought prior to AD 540, with a subsequent rapid and simultaneous shift to fresher lake conditions and wetter climate. After a drier phase in the Nar record from AD 800–950, the period of the Medieval Climate Anomaly (AD 950–1400) was generally well watered. During the subsequent Little Ice Age (∼AD 1700–1900), DI-conductivity and δ 18O become decoupled. Thin sections reveal between 20 and 40 distinct diatom bloom events per century since AD 1100, with increasing frequency between AD 1700 and 2000. Human land-use changes evident in the pollen sequence may have influenced the diatom relationship with lake water conductivity in the later part of the record. None the less, diatom DCA axes do show a clear response to multi-decadal drought events within the last six centuries. Differences between the proxy-climate records from Nar Lake may be associated with the dissimilar thresholds to environmental fluctuations and non-stationarity in the response of different proxies through time. The palaeoclimate records from Nar show that arid periods occurred in the Eastern Mediterranean during the last two millennia that were more prolonged and extreme than those experienced in the last century.

Short-term fluctuations in vegetation and phytoplankton during the Middle Eocene greenhouse climate: a 640-kyr record from the Messel oil shale (Germany)

The Palaeogene was the most recent greenhouse period on Earth. Especially for the Late Palaeocene and Early Eocene, several superimposed short-term hyperthermal events have been described, including extremes such as the Palaeocene–Eocene Thermal Maximum. Major faunal and floral turnovers in the marine and terrestrial realms were recorded in association with these events. High-resolution palynological analysis of the early Middle Eocene maar lake sediments at Messel, near Darmstadt, Germany, provides an insight into the dynamics of a climax vegetation during the Middle Eocene greenhouse climate in a time span without significant climatic excursions. Numerical techniques like detrended correspondence analysis and wavelet analysis have been applied to recognize cyclic fluctuations and long-term trends in the vegetation through a time interval of approximately 640 kyr. Based on the numerical zoning of the pollen diagram, three phases in the development of the vegetation may be distinguished. Throughout these phases, the climax vegetation did not change substantially in qualitative composition, but a trend towards noticeably less humid conditions probably in combination with a drop of the water level in the lake may be recognized. A shift in algal population from the freshwater dinoflagellate cyst Messelodinium thielepfeifferae to a dominance of Botryococcus in the uppermost part of the core is interpreted as a response to changes in acidity and nutrient availability within the lake. Time series analyses of pollen assemblages show that variations in the Milankovitch range of eccentricity, obliquity and precession can be distinguished. In addition, fluctuations in the sub-Milankovitch range are indicated. This demonstrates that floral changes during steady depositional conditions in the Middle Eocene of Messel were controlled by orbital forcing.

Six millennia of summer temperature variation based on midge analysis of lake sediments from Alaska

Despite their importance for evaluating anthropogenic climatic change, quantitative temperature reconstructions of the Holocene remain scarce from northern high-latitude regions. We conducted high-resolution midge analysis on the sediments of the past 6000 years from a lake in south-central Alaska. Results were used to estimate mean July air temperature ( T July) variations on the basis of a midge temperature transfer function. The T July estimates from the near-surface samples are broadly consistent with instrumental and treering-based temperature data. Together with previous studies, these results suggest that midge assemblages are more sensitive to small shifts in summer temperature (∼0.5 °C) than indicated by the typical error range of midge temperature transfer functions (∼1.5 °C). A piecewise linear regression analysis identifies a significant change point at ca 4000 years before present (cal BP) in our T July record, with a decreasing trend after this point. Episodic T July peaks (∼14.5 °C) between 5500 and 4200 cal BP and the subsequent climatic cooling may have resulted from decreasing summer insolation associated with the precessional cycle. Centennial-scale climatic cooling of up to 1 °C occurred around 4000, 3300, 1800–1300, 600, and 250 cal BP. These cooling events were more pronounced and lasted longer during the last two millennia than between 2000 and 4000 cal BP. Some of these events have counterparts in climatic records from elsewhere in Alaska and other regions of the Northern Hemisphere, including several roughly synchronous with known grand minima in solar irradiance. Over the past 2000 years, our T July record displays patterns similar to those inferred from a wide variety of temperature proxy indicators at other sites in Alaska, including fluctuations coeval with the Little Ice Age, the Medieval Climate Anomaly, and the First Millennial Cooling (centered around 1400 cal BP). To our knowledge, this study offers the first high-resolution, quantitative record of summer temperature variation that spans longer than the past 2000 years from the high-latitude regions around the North Pacific.

Late-twentieth-century warming in Lake Tanganyika unprecedented since AD 500

Lake Tanganyika has become warmer, increasingly stratified and less productive over the past 90 years. Analyses of lake sediments show that this recent warming is unprecedented within the past 1,500 years.

Glacier and climate reconstruction at Tres Lagunas, NW Argentina, based on 10Be surface exposure dating and lake sediment analyses

We present 35 10Be surface exposure ages from quartzite moraine boulders at Tres Lagunas in the Sierra de Santa Victoria, NW Argentina. Additionally, an ~ 8 m sediment core from a glacial lake was investigated to provide independent radiocarbon age control. The oldest and most extensive glaciation occurred ≥ 116.3 ka and likely coincides with the lake transgression phase Ouki on the Altiplano. Maximum glaciation in phase with the global Last Glacial Maximum (LGM) is dated to 22–25 ka and documents a glacial mass-balance response to substantially lower temperatures and minor precipitation increase in phase with the Sajsi lake transgression phase. After initial deglaciation and formation of a small paleolake at Tres Lagunas, a glacial readvance is documented by an outwash diamict in the sediment core and radiocarbon dated to 19–17 ka, as well as by a moraine surface exposure dated to ~ 17 ka. The most prominent moraine was deposited at ≥ 14.5 ka coinciding with the lake transgression phase Tauca on the Altiplano. This Late Glacial advance reflects the massive intensification of the South American Summer Monsoon (SASM) in response to northern hemispheric cooling during Heinrich I and the resultant southward shift of the intertropical convergence zone (ITCZ) and La Niña like conditions in the eastern equatorial Pacific. Rapid deglaciation started after ~ 14.5 ka, interrupted only by minor glacial still stands at ~ 13.8 ± 1.5 ka and 12.0 ± 1.5 ka, the latter one correlating with the Coipasa transgression phase on the Altiplano and the Younger Dryas.

Testate amoeba analysis of lake sediments: impact of filter size and total count on estimates of density, species richness and assemblage structure

Testate amoebae are informative about palaeoecological conditions, but the methods generally used for their analyses in lake sediments differ from those used for their analyses in peats, making comparisons difficult. This study examines how filter mesh size and total number of individuals counted affect species richness, Shannon diversity, equitability, density and assemblage structure. We analysed the complete testate amoeba contents of six sediment samples from Lake Lautrey, France. The abundance of testate amoebae was high (1,403–10,870 shells cm−3), and species smaller than 63 μm in both length and width represented up to 89% of total abundance and 43% of species richness. A simulation showed that using 47- or 63-μm mesh-size filters reduced inter-sample differences and changed the patterns of abundance, species richness and assemblage structure, causing loss of information and leading to potential erroneous palaeoecological interpretation. Rarefaction analyses suggest that although 170 shells are sufficient to assess the general structure of assemblages, such small sample sizes can underestimate species richness by overlooking taxa with relative abundances <4%. Total counts of 400 shells yield better estimates of assemblage structure and recover at least 50% of total species richness, although species with absolute frequencies below 2% may still be missed. Higher counts are required to obtain reliable estimates of species richness and assemblage structure in samples that have high testate amoeba densities but are dominated by a few small taxa. Further studies should determine the bioindicator value and functional roles of small and/or rare species in lakes and thus to what extent overlooking them affects palaeoecological interpretations.

Assessing the Scale of Prehistoric Human Impact in the Neotropics Using Stable Carbon Isotope Analyses of Lake Sediments: A Test Case From Costa Rica

AbstractAnalyses of pollen and other terrestrial microfossils in sediment profiles from neotropical lakes can complement and extend archaeological studies by documenting the timing of prehistoric human disturbances within watersheds. However, assessing the scale of prehistoric human impact from sedimentary microfossil assemblages alone is often difficult. We explore here the utility of combining stable carbon isotope (δ13C) analyses of lake sediments and isotopie mixing models to improve our ability to gauge the extent of prehistoric human disturbance recorded in sediment profiles. Our test case involves the analysis o f a sediment core from Laguna Bonillita on the central Caribbean slope of Costa Rica that spans approximately the last 2,700 calendar years. Variations in the δ13C values of the Laguna Bonillita sediments suggest that human population growth and environmental impacts in the watershed were at their maximum ~cal yr 300 B.C. This finding is in keeping with archaeological evidence of rapid regional population growth at this time but differs from initial interpretations of the sediment record that were based on pollen and charcoal analyses alone. We believe that the use of stable carbon isotope data from sediment profiles can improve estimates of the scale of prehistoric human impact and in doing so improve the contributions of paleoecological research to archaeology.

The impact of environmental change and human land use on alluvial valleys in the Loess Plateau of China during the Middle Holocene

In recent years a growing number of studies have reported proxy evidence for Holocene climatic and environmental change on the Loess Plateau of north-central China. Pollen from lake cores and sediment analyses from loess sections firmly point to a warm-moist Mid-Holocene Climatic Optimum. Archaeological evidence indicates that at the same time, human agricultural settlements expanded into this area during the Middle Neolithic Period. A geoarchaeological study of sediment sections from several valleys within the catchment of the Yiluo River, Henan Province, indicates a sequence beginning with a stable landscape, soil development and high water tables in the Early Mid-Holocene, which was exploited by Early Neolithic millet farmers in the Peiligang Period. Subsequently, there was a rapid shift to episodes of hillslope erosion and increased valley alluviation in the later Mid-Holocene. The resulting alluvial sediments, dating from 5300/5010 cal. BC through 2130/1870 cal. BC, represent clay-rich water-logged deposits that contain sediment and phytolith evidence for the first rice paddy farming in this region. This coincides with the first migration of Neolithic rice farmers to the area in the Yangshao Period ca. 5500 cal. BC. These fills, temporally and stratigraphically linked to archaeological sites and human land-use practices, suggest that they originated as a direct result of human impact on the landscape. After ca. 2000 cal. BC, Holocene valley incision in this catchment led to narrowing floodplains, the disappearance of the valley wetland deposits, and a reduction in land available for paddy farming.

Quality control in the analysis of lake sediments for spheroidal carbonaceous particles

The use of spheroidal carbonaceous particles (SCPs) in environmental studies as a means to identify atmospherically deposited contamination, or as a technique to provide a chronology for lake sediment cores, is rapidly increasing. However, currently there are no internationally accepted quality controls for this methodology. No reference standard exists to provide inter‐calibration, and no standardized criteria for identification have been proposed. This paper addresses these issues. It is suggested that morphology (spheroidal but not spherical), color (black only), depth (i.e., three‐dimensional rather than disc‐like), and porosity (characteristic when present) should be used as criteria for SCP identification under the light microscope. A sediment reference material for SCP analysis has also been developed. Two hundred ten replicate analytical measurements were made on a homogenized sediment material resulting in a reliable estimate of the mean SCP concentration of 6005 ± 70 SCP per gram dry sediment (gDM−1). This material is available to SCP analysts for quality control purposes.

Holocene environmental change in the West African Sahel: sedimentological and mineral‐magnetic analyses of lake sediments from Jikariya Lake, northeastern Nigeria

AbstractPrevious studies have demonstrated long‐term changes in effective moisture in sub‐Saharan Africa. Here, we reconstruct Holocene environments using a ∼7 m lake‐sediment sequence recovered from the northeastern Nigerian Sahel and attempt to distinguish basin‐specific changes from regional climatic variations. The sequence was analysed for sedimentological properties, mineral magnetism and pollen, and dated by 137Cs, 210Pb excess and 14C. Extremely arid conditions of the terminal Pleistocene ended ca. 11 500 cal. BP (calendar years) when climate ameliorated and a lake developed until the occurrence of an arid event leading to lake desiccation at ∼11 200 cal. BP. Following this, climate ameliorated and a water body re‐emerged. Very wet conditions predominated 11 200–5600 cal. BP, followed by drought between 5600 and 5500 cal. BP and a return to moderate humidity from 5500 to 4000 cal. BP. After 4000 cal. BP, a marked deterioration occurred, culminating in lake desiccation at ca. 800 cal. BP. After this time the climate remained generally dry and the re‐emerging lake was shallow. Comparison of these results with other well‐dated sequences in the region demonstrates the importance of basin‐specific influences on the palaeolimnological records in addition to regional climatic controls. Disentangling these different controls, as well as the reconstruction of Holocene climate, therefore requires a multiple‐basin approach. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Determination of plutonium isotopes in freshwater lake sediments by sector-field ICP-MS after separation using ion-exchange chromatography

The determination of Pu isotopes in lake sediments is important for many studies, such as Pu pollution source identification, sediment mixing estimation, erosion evaluation and establishment of deposition chronology in lakes. In this paper, a simple analytical method using sector field inductively coupled plasma mass spectrometry (ICP-MS) combined with two-stage chromatographic separation and purification of Pu was developed based on the optimization and adaptation of the previously published method for marine samples with an emphasis on the study of the elimination of interferences for the analysis of freshwater lake sediments. A strong base anion-exchange resin (AG MP-1M) was used to purify Pu isotopes with concentrated HBr as the final eluent for Pu elution. The chemical yields were ca. 64% and the decontamination factor for U was ca. 10 5. The developed method was validated using a freshwater lake sediment reference material (SRM-4354) and a marine sediment reference material (IAEA-368), and applied to the determination of Pu isotopes in sediment samples of Lake Poyang, East China. For the analysis of certified reference materials, both 239+240Pu activity of 31.6 mBq g −1 and 240Pu/ 239Pu atom ratio of 0.033 for IAEA-368 were comparable to the certified value and/or literature values. As for SRM-4354, 239+240Pu activity of 3.90 mBq g −1 agreed well with the certified value. However, the mean 240Pu/ 239Pu atom ratio of 0.144 was lower than those reported by other laboratories. This difference suggested that this material may be isotopically inhomogeneous. 240Pu/ 239Pu atom ratios of Poyang Lake sediment samples ranged from 0.185 to 0.192 with a mean value of 0.187±0.004, indicating that plutonium pollution originated from global fallout.

Annually laminated Late Pleistocene sediments from Llangorse Lake, South Wales, UK: a chronology for the pattern of ice wastage

This paper presents the results of microfacies analysis of proglacial lake sediments from the Llangorse basin in South Wales. It is the first detailed micromorphological investigation of mineral-laminated lake sediments in the UK. Four microfacies of the mineral-laminated sequence are identified and subsequently compared to modern and palaeo-datasets. The laminated sediments are interpreted as glaciolacustrine varves, thereby validating previous interpretations. The total number of varves in the core indicates that Glacial Lake Llangorse existed for a minimum of 574 years. This sequence cannot be ‘fixed’ to a specific age other than the latter part of the Dimlington Stadial. The varve thickness decreases through the core, suggesting that the ice margin, which initially impounded the lake, became progressively more distal to the locus of sedimentation. These data, when related to Lewis' model of deglaciation in the area, imply that the ice margin retreated at an average rate of 5.2 m a −1 .

The Holocene history of George VI Ice Shelf, Antarctic Peninsula from clast-provenance analysis of epishelf lake sediments

The Antarctic Peninsula has experienced a dramatic increase in temperature and the loss of ca. 14,000 km 2 of ice-shelf area in recent years. During this time George VI Ice Shelf (GVIIS) has remained relatively intact, but it is now reaching its theoretical limit of viability. Epishelf lakes, formed when ice shelves dam the mouths of marine embayments, accumulate sediments that can be used to constrain past ice-shelf behaviour. They are stratified water bodies with an upper layer of fresh meltwater overlying a marine layer of water. Multi-proxy analysis of a sediment core from Moutonnée Lake, an epishelf lake dammed by GVIIS on the east coast of Alexander Island, has recently shown that it retreated to at least the Ablation Point area in the early Holocene, ca. 9600–7500 years BP, demonstrating its vulnerability to periods of atmospheric and oceanic warmth. This study tests this interpretation of ice-shelf collapse through detailed analyses of granulometric, geochemical and Sr and Nd isotope provenance data for > 8 mm clasts from the same cores. Clast data from Moutonnée Lake were compared with geological reference data from two further lakes on Alexander Island (Ablation Lake and Citadel Bastion Lake) and an extensive archive of rocks and isotope-geochemical provenance data from the Antarctic Peninsula region. Underpinning this provenance analysis is the contrast between the plutonic/igneous outcrops in Palmer Land on the western side and the predominantly sedimentary strata of Alexander Island on the eastern side of George VI Sound, and the different patterns in their deposition that would be expected at Moutonnée Lake during periods of ice-shelf presence and absence. Results show that changes in clast distribution and provenance reflect the early Holocene retreat and reformation of George VI Ice Shelf at Moutonnée Lake. The period of ice-shelf retreat was marked by the onset of marine conditions in the basin followed by a rapidly deposited zone of clasts whose provenance, distribution, varied lithology and larger than average clast size are indicative of a period of lake ice disintegration and ice-rafted debris deposition between ca. 9600–8450 years BP. Igneous clasts in the ice-rafted debris have a close affinity with the plutonic provinces of western Palmer Land suggesting transport to the site by icebergs or recycling through Alexander Island strata/moraines. When epishelf lake conditions returned after ca. 7500 years BP, the clasts were smaller, the number of lithologies more limited and the assemblage dominated by olive-green vitric tuff and pale-green rhyolitic clasts that isotope data link to Early Cretaceous volcanic activity in Palmer Land. Their dominance in the upper part of the core most likely relates to increased erosion of Palmer Land ash/tuffs from volcanic outcrops on the floor of Moutonnée Valley and implies a downturn in climate after ca. 7500 years BP and the reformation of George VI Ice Shelf.

Paleoecological analyses of lake sediments reveal prehistoric human impact on forests at Anthony Island UNESCO World Heritage Site, Queen Charlotte Islands (Haida Gwaii), Canada

Pollen and plant macrofossil analyses of lake sediments from Anthony Island in the southern Queen Charlotte Islands (Haida Gwaii), British Columbia, reveal 1800 yr of relatively stable temperate rainforest vegetation. Cupressaceae (cedar) pollen percentages and accumulation rates decline about 1000 cal yr BP, coincident with occupation of the island by Haida peoples, who use Thuja plicata (western red cedar) almost exclusively for house construction, dugout canoes, monumental poles, and many other items. Anthropogenic disturbance offers the most likely explanation for the decline of T. plicata.

Diatom responses to limnological and climatic changes at Ribains Maar (French Massif Central) during the Eemian and Early Würm

High-resolution diatom analysis was carried out to assess the limnological and climatic changes that took place at Ribains maar (French Massif Central) during the Late Pleistocene (∼131–∼105 ka BP), with a focus on the Eemian interglacial in particular. Numerical analyses were used to show that most of the variability in the fossil diatom assemblages was due to climate independently from the changes in the lake catchment vegetation (as represented by pollen data). Diatom-based quantitative reconstructions of the past limnological conditions, as well as a comprehensive literature review on the auto-ecological requirements for the principal diatom taxa, were used to interpret the record. An absolute time-scale for the sequence was derived by matching the major pollen shifts with the radiometrically dated changes in oxygen isotopes observed in Italian stalagmites. This study shows that at Ribains maar, the transition from the Riss (=Saalian) Glacial to the Eemian interglacial was marked by a gradual increase in the contribution of spring-blooming diatom species, indicating a longer growing season and milder winter/spring conditions at that time. A short cooling event interrupts this trend and may correspond to a stadial. At the start of the Eemian a peak in benthic taxa and the suppression of spring-blooming flora probably reflects the effects of deglaciation on the catchment. During the Eemian interglacial itself three main phases were distinguished within the diatom record. The first phase (∼8000 years in duration) was dominated by Stephanodiscus minutulus, which suggests that intense mixing in the water-column took place during spring. The pollen record was simultaneously dominated by Quercus and Corylus that typify this phase as the climatic optimum of the Eemian. The second phase, almost equal in duration to the first phase (∼7000 years), is generally dominated by Cyclotella taxa and suggests a less productive lake and much reduced period of spring mixing compared with the first phase. In the pollen diagram this corresponds to an interval dominated by Carpinus–Picea–Abies that indicates a cooler and wetter climate. The third and last phase of the Eemian, ∼2000 year long, saw the return to Stephanodiscus-dominated assemblages, indicating a warming that may correspond to the Dansgaard–Oeschger event 25 identified in the Greenland ice-core record. In the early stage of the Würm Glacial (=Weichselian), assemblages in the Melisey I stadial (∼3000 year long) were dominated by either Aulacoseira subarctica or Asterionella formosa, which suggest colder spring conditions than during the late Eemian, but not as cold as the ones indicated by the pollen record. Stephanodiscus spp. again dominate during the Saint-Germain Ia interstadial (∼5000 year long) suggesting a return to the conditions that prevailed before the Melisey stadial, in agreement with the pollen record. The record ends with the Montaigu cold event, which is characterised by a Pinus peak in the pollen record, and corresponds to a large abundance of A. subarctica in the diatom sequence. Throughout the Eemian the abundance of Stephanodiscus spp., which is thought to be driven by winter conditions, show cyclic fluctuations that most likely match the cooling events identified in a pollen record from Germany. Variation in insolation throughout the Eemian may have been the driving factor behind the species succession observed in the diatom sequence. While this study demonstrates that diatom analysis of lake sediment can provide very detailed information on long-term climate change, a review of the few other diatom investigations published on European Eemian deposits shows that this technique has been so far seldom used to its full potential in this context in central and southern Europe.

A preliminary record of the historical seabird population in the Larsemann Hills, East Antarctica, from geochemical analyses of Mochou Lake sediments

An 85‐cm long sediment sequence from Mochou Lake on Mirror Peninsula in the Larsemann Hills, East Antarctica, was investigated for elemental geochemistry, biogeochemistry and strontium (Sr) isotopic composition in the acid‐insoluble and acid‐soluble fractions. The biogeochemical data showed that the freshwater lacustrine sediment originated after 2750 BP. The element Zn, Cu, F, P and Se fluxes displayed almost the same vertical distribution patterns, and their ratios over loss on ignition had strong positive correlations with each other, indicating a common source, probably from seabird droppings. The Sr isotopic compositions provided further evidence of the influence of seabirds on the freshwater lacustrine sediments. The87Sr/86Sr ratios determined in the acid‐soluble fraction were remarkably lower than those of the acid‐insoluble fraction; with a bedrock87Sr/86Sr signature, they were close to those of the marine‐derived Sr and were negatively correlated with total amino acids. Using the ratio vs. depth profiles of P, Zn, Cu, Se, F, As, Cd and Ni fluxes over Al, we reconstructed the historical seabird population in the catchment area of Mochou Lake. During the past c. 2800 years, the seabird population has experienced substantial changes in the absence of human activity, and four troughs were identified. After comparison with the palaeoclimatic records and glacial advance and retreat history, the pronounced seabird population declines seem to be related to climatic deterioration.

A preliminary record of the historical seabird population in the Larsemann Hills, East Antarctica, from geochemical analyses of Mochou Lake sediments

A preliminary record of the historical seabird population in the Larsemann Hills, East Antarctica, from geochemical analyses of Mochou Lake sediments

Perceived and Measured Levels of Environmental Pollution: Interdisciplinary Research in the Subarctic Lowlands of Northeast European Russia

Using interdisciplinary field research in the Usa Basin, northeast European Russia, we compared local inhabitants' perception of environmental problems with chemical and remote-sensing signatures of environmental pollution and their local impacts. Extensive coal mining since the 1930s around Inta and Vorkuta has left a legacy of pollution, detected by measuring snowpack, topsoil, and lichen chemistry, together with remote-sensing techniques and analysis of lake water and sediments. Vorkuta and its environs suffered the worst impacts, with significant metal loading and alkalization in lakes and topsoils, elevated metals and cations in terricolous (reindeer) lichens, and changes in vegetation communities. Although the coal industry has declined recently, the area boasts a booming oil and gas industry, based around Usinsk. Local perceptions and concerns of environmental pollution and protection were higher in Usinsk, as a result of increased awareness after a major oil spill in 1994, compared with Vorkuta's inhabitants, who perceived air pollution as the primary environmental threat. Our studies indicate that the principal sources of atmospheric emissions and local deposition within 25 to 40 km of Vorkuta were coal combustion from power and heating plants, coal mines, and a cement factory. Local people evaluated air pollution from direct observations and personal experiences, such as discoloration of snow and respiratory problems, whereas scientific knowledge played a minor role in shaping these perceptions.

Holocene timber-line dynamics at Bachalpsee, a lake at 2265 m a.s.l. in the northern Swiss Alps

Palaeobotanical analysis and radiocarbon dating of lake sediments from Bachalpsee (2265 m a.s.l.), a small lake above the present-day timber-line in the northern Swiss Alps reveals that the region was already deglaciated during the Younger Dryas. The sediment record is dominated by long-distance transported pollen that originates from lowland vegetation but the plant macrofossils give evidence of the local vegetation development. Comparison with palaeobotanical results from three sites along an altitudinal transect permits the reconstruction of the regional timber-line history. Throughout the entire Holocene the catchment of Bachalpsee consisted of a mosaic of open meadows and dwarf shrubs (Salix, Vaccinium, Rhododendron). Chironomid and cladoceran assemblages suggest that the early to mid-Holocene was the warmest interval at Bachalpsee. Comparison of the palaeobotanical results with those from the mire “Feld” (2130 m a.s.l.) in the vicinity of Bachalpsee showed that during the mid-Holocene the timber-line was formed by Pinus cembra and Picea abies with some scattered Abies alba trees and was situated close to Bachalpsee but never reached its catchment. The maximum timber-line in the Northern Alps was reached between 6000 and 3000 cal b.p. which is several millennia later than in the Central Alps. The species composition of the tree-line (Abies alba, Pinus cembra and the absence of Larix decidua) points to less continental and moister climatic conditions compared with the central Alps during the early to mid-Holocene. From 3000 cal b.p. onwards the timber-line was lowered by human deforestation with the most intense pulses of human impact occurring since the Middle Ages. The catchment of Bachalpsee has been used as alpine pasture since the Bronze Age.

Late Holocene paleoenvironment in northern New Caledonia, southwestern Pacific, from a multiproxy analysis of lake sediments

Lithostratigraphic and palynological analysis of two cores recovered from the ‘Grand Lac’ (New Caledonia), combined with 35 14C AMS dates, yields a paleoenvironmental record spanning the last 2000 yr. The lithology is represented mainly by clayey or laminated layers. A catastrophic event, which is marked by very coarse deposits, occurred probably between ca 1070–960 cal yr B.P. and possibly is associated with an unusually severe La Niña event. Before and after this event, a similar combination of the two main sediment types is recorded. The repeated alternation of laminated and clayey layers is interpreted as the response to local hydrologic forcing, which may reflect a shift from relatively wet to relatively drier conditions, respectively. Variable amount of micro-charcoal is detected all along the profile. Without additional evidence, notwithstanding the initial local human settlement documented since ca 2900 14C yr B.P., micro-charcoal occurrence and variability cannot be linked directly to an anthropogenic origin. No distinct palynological zonations in relation to the lithology are observed, and the vegetation changes may only represent minor transitions across environmental limits.