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Quantifying the relative influences of anthropogenic activities and climate change on soil erosion and deposition during the Holocene, when both forces have been interacting is a complex problem. Analysis of long-term patterns in soil erosion and lake deposition in a basin can provide the basis for untangling the complexities of climate and anthropogenic forcings. In this paper, sedimentary sequences from Xingyun Lake are compared with simulated soil erosion rates in the basin to explore the relationship between river basin soil erosion and lake deposition during the Holocene in Yunnan, China. Modern soil erosion rates are calculated using RUSLE, while Holocene soil erosion rates are estimated using modern rates with reconstructed precipitation and vegetation cover sequences. Through this investigation, we found the following results. First, Holocene vegetation in the lake basin was mainly affected by climate change, and the vegetation experienced the same pattern of changes as the climate. Soil erosion and lake deposition rates, along with changes to vegetation cover, were synchronous with precipitation trends during the Holocene. Second, soil erosion and lake deposition have been exacerbated by human activities, such as deforestation and land reclamation in the Xingyun Lake basin. Finally, this study provides new insights into the effects by anthropogenic impacts and climate forcing on the processes of soil erosion and lake deposition on the millennium scale. [ABSTRACT FROM AUTHOR]

This paper presents the results of pollen, diatom, charcoal, and sediment analyses from Lake Bol'shoye Zavetnoye, situated between the Gulf of Finland and Lake Ladoga on the Karelian Isthmus, north-western Russia. The main goal is to contribute to the discussion of Neolithic land use in north-eastern Europe. The article aims to answer questions related to Stone Age hunter-gatherer economy, ecology, and anthropogenic environmental impact through a comprehensive combination of multiple types of palaeoecological data and archaeological material. According to diatom data, Lake Bol'shoye Zavetnoye was influenced by the water level oscillations of Ancient Lake Ladoga during much of the Holocene. Intensified human activity and prolonged human occupation become visible in the Lake Bol'shoye Zavetnoye pollen data between 4480 BC and 3250 BC. During the final centuries of the Stone Age, a new phase of land use began, as several anthropogenic indicators, such as Triticum, Cannabis, and Plantago lanceolata appear in the pollen data and a decrease in Pinus values is recorded. In general, the results indicate that socio-cultural transformations could have taken place already from the mid-5th millennium BC onwards, including new ways of utilizing the environment, perhaps also in the field of subsistence, even though the livelihood was based on foraging throughout the period. [ABSTRACT FROM AUTHOR]

Micro x-ray fluorescence (µXRF) core scanning is capable of measuring the elemental composition of lake sediment at sub-millimetre resolution, but bioturbation and physical mixing may degrade environmental signals at such fine scales. The aim of this research is to determine the maximum possible resolution at which meaningful environmental signals may be reconstructed from lake sediments using this method. Sediment from a coastal lake in the Outer Hebrides, Scotland, has been analysed using calibrated element measurements to reconstruct storminess since AD 200. We find that a Ca/K ratio in lake-core sediments reflects the presence of fine calcium carbonate shell fragments, a constituent of sand in the catchment that is washed and blown into the lake. Variations in this ratio are significantly correlated with instrumental records of precipitation and low pressures, suggesting it is a proxy for storminess. Furthermore, identification of a c. 60-year cycle supports a climatic influence on Ca/K, as this cycle is frequently identified in reconstructions of the North Atlantic Oscillation and North Atlantic sea-surface temperature. Comparison with weather records at different resolutions and spectral analysis indicate that µXRF data from Loch Hosta can be interpreted at sub-decadal resolutions (equivalent to core depth intervals of 3–5 mm in this location). Therefore, we suggest that sub-centimetre sampling using µXRF core scanning could be beneficial in producing environmental reconstructions in many lake settings where sediments are not varved. [ABSTRACT FROM AUTHOR]

We present results from a multidisciplinary project using lake sediment as a natural archive in combination with archaeology to investigate the earliest history of the Gladhammar mining area, southeastern Sweden. The aim was to identify and trace human impacts on the landscape, specifically in connection with settlement and metal production. Sediment records from two lakes linked to different processes in metal production were analyzed; Tjursbosjön down-slope of the mining area and Hyttegöl situated downstream of an excavated blast furnace, 1.8 km from the mines. The sediment analyses included multi-element geochemistry (WD-XRF), stable lead isotopes, pollen, and charcoal. Although historical documents record activities beginning in AD 1526, the archaeological study found indications that mining and metal production likely predated this period. The known historical period is well reflected in the sediment records, such as a 500-fold increase in copper, stream erosion, loss of forest cover and an expansion in agriculture. More importantly, already in the 12th–13th centuries, there was a 2- to 10-fold increase in lead, copper, and charcoal particles and evidence of erosion linked to the establishment of a blast furnace. Lead isotopes reveal a change from natural conditions to an input of lead from regional ores as early as the 9th–10th centuries. Settlement in the form of agriculture can be seen from 2000 BP. This sediment evidence of early mining or metallurgy during the 9th–15th centuries is supported by a few radiocarbon dates from the excavated mining fields, which on their own were considered as vague or improbable outliers by archaeologists. [ABSTRACT FROM AUTHOR]

Quantitative records of pre-industrial temperature changes are fundamental for understanding long-term natural climate variability. We used visible reflectance spectroscopy to measure chlorophyll content (and its derivatives) in a sediment core from Kurupa Lake, north-central Brooks Range, Alaska, to reconstruct summer temperature and the number of annual non-freezing days over the past 5.7 ka. A calibration-in-time approach was used to convert downcore changes in chlorophyll content to the climate variables, and an ensemble approach was used to integrate age and calibration uncertainties. The strongest correlation (rmedian = 0.69, pmedian = 0.02, RMSEP = 1.9°C) is for summer (June through September) temperature using the 20th Century Reanalysis Project dataset. The chlorophyll-inferred 3-year-mean summer temperature shows that the warmest century (3.0–2.9 ka BP) was about 3.0°C (90% range of the ensemble members = 2.3–4.0°C) higher and that the coldest century (1.4–1.3 ka BP) was about 5.5°C lower (90% range = −7.6°C to −5.0°C) than during the reference period (AD 1961–1990). Century-to-century temperature changes over the past 5.7 ka at Kurupa Lake have been large (90% range = −2.8°C to 3.1°C shifts in centennial mean), including the shift between the 19th and 20th centuries, which was above the 90th percentile of temperature changes across all representations of the reconstruction. In contrast to most Northern Hemisphere temperature reconstructions, Kurupa Lake shows no overall millennial-scale cooling trend. We suggest that increased summer duration (by 4.3 days during the last 6 ka) along with no long-term increase in sea-ice cover over the adjacent Chukchi Sea counter-balanced the influence of decreased insolation intensity on the aquatic productivity in Kurupa Lake. [ABSTRACT FROM PUBLISHER]

High-resolution seismic profiling has been combined with geochemical analyses of both watershed samples and five lacustrine cores retrieved from two natural lacustrine basins of glacial origin: Lake Majeur and Lake Sigriou (1630 m a.s.l. and 1995 m a.s.l., respectively, Eastern French Pyrenees). Identifying specific minerogenic and organic markers of autochthonous and allochthonous supply, data allow documenting past climatic and anthropogenic pressures. Over the past century, the lacustrine sediment of Lake Majeur has been essentially composed of algae, drastically contrasting with the natural sedimentary infill of the basin, mainly resulting from soil erosion from the mid–late Holocene. Since ad 1907, the Lake Majeur has been used for hydroelectricity production. Human-induced lake-level regulations, affecting up to 37% of the lacustrine surface, have increased by fourfold the accumulation rate of the lake and favoured water enrichment. Rubidium abundance within the lacustrine sediments of the two lakes reflects the mid–late Holocene palaeohydrology. After dam construction in ad 1907, greater quantities of rubidium found in Lake Majeur sedimentary infills indicate drier climatic periods, such as from ad 1975 to ad 1982, during which water reservoirs were particularly in demand. Inversely, before the dam was built, rubidium fluctuations were correlated with wetter conditions and hydrological events were recorded as sandy layers deposited by canyon reactivation, synchronous with European climatic deterioration phases. We notably document that the Mediaeval Climate Anomaly was interrupted by some humid periods dated c. ad 940, ad 1080, ad 1100 and ad 1250. We also date the onset of the ‘Little Ice Age’ c. ad 1360 and identify that this period was wetter after c. ad 1500. [ABSTRACT FROM AUTHOR]

Holocene paleoclimate records from Greenland help us understand the response of the Greenland Ice Sheet and regional oceanic and atmospheric circulation systems to natural climate variability in order to place recent changes in a longer-term perspective. Here biogeochemical analysis of a lake sediment core from southeast Greenland is used to define changes in moisture balance and runoff during the Holocene in a catchment near the margin of the Greenland Ice Sheet. A 1.6 m sediment core that spans the last 8.8 ka was recovered from Flower Valley Lake on Ammassalik Island. Magnetic susceptibility, diatoms, bulk biogeochemical properties (TOC, C/N, δ13Corg), and lipid biomarkers (n-alkanes; C16–C31) reveal changes in clastic sedimentation and the relative input of terrestrial- and aquatic-derived organic matter. Hydrogen isotope values (δD) of mid- (n-C25) and long-chain (n-C29, n-C31) n-alkanes allow reconstruction of δD of precipitation and summertime evaporation of lake water. Following a period of early lake ontogeny and landscape stabilization after deglaciation from 8.4 to 7.0 ka, the mid Holocene, 8.4–4.1 ka, is characterized by greater evaporative enrichment of the lake water as indicated by δD records. After 4.1 ka, there is a decrease in evaporative enrichment of the lake water. There is also an abrupt transition to more variable sedimentation marked by sharp increases in magnetic susceptibility, C/N, δ13Corg, and the concentration of long-chain n-alkanes, showing periodic delivery of terrestrial organic matter and clastic sediment to the lake. Higher insolation during the mid Holocene resulted in a warmer and drier climate with longer ice-free periods in the summer and enhanced evaporation of lake water. The reduction in insolation and colder temperatures during the late Holocene caused a reduction in evaporation of lake water over the last 4.1 ka and was accompanied by periodic increases in surface runoff, which correspond with intervals of cold Greenland Ice Sheet surface temperatures. [ABSTRACT FROM PUBLISHER]

A detailed understanding of decadal to millennial-scale climate changes requires seasonal-scale (summer-winter) reconstructions of past precipitation and temperature fluctuations. Comparing seasonally resolved varve records with pollen-based sum of growing degree-days (GDD) reconstructions from Lake Nautajärvi, we examined the intra-annual nature of climate variability in central southern Finland during the Holocene. The organic varve record and the GDD reconstruction show roughly comparable trends supporting the interpretation that both proxies predominantly reflect summer temperatures in the study area. The records suggest low but rising early-Holocene (9500 to 8500 cal. yr BP) summer temperatures. The Holocene Thermal Maximum (HTM) in the GDD record dates to about 7500 to 4500 cal. yr BP, but the organic varve record along with reconstructed changes in vegetation composition, notably a peak of Tilia pollen percentages, indicate that during the HTM there was a trend towards a more continental climate with maximum mid-summer temperatures reached at 6500 to 4500 cal. yr BP. Both records reflect the start of the post-HTM cooling at about 4500 cal. yr BP, simultaneously with an increase of the amount of catchment erosion and mineral matter influx into the lake, suggesting gradually colder and/or longer winters with high net accumulation of snow. The organic varve record and the GDD record start to diverge at 2000 cal. yr BP, possibly owing to the human influence on catchment processes. The reconstructed mid-Holocene summer temperature peak deviates from the regional climate model outputs, which suggest highest summer temperatures during the early Holocene. [ABSTRACT FROM AUTHOR]

Reconstruction of soil weathering is one of the more difficult problems for palaeoecologists interested in landscape-scale environmental changes. Here we use scanning electron microscopy and energy dispersive x-ray analysis (SEM/EDS) to study the pitting of feldspars in soils and lake sediments at two sites in the Great Lakes region, USA. A semi-quantitative feldspar weathering index (FWI) allows description of the weathering status for large numbers of individual grains, and reveals differences among soil horizons and strata of lake sediment as well as between the two sites. Feldspars in upper soil horizons generally have greater FWI than those in lower horizons, but analyses also suggest considerable weathering in the soil C horizon at the site with more rapid water infiltration. At one site, the FWI of upper soil horizons and surface lake sediment are similar, implying that lake sediments have the potential to record changes in soil over time. However, differences between upper soil horizons and surface sediment at the other site highlight the need to examine more sites and more profiles within sites to better relate catchment and sediment characteristics. We interpret increases in the FWI over time within lake sediments as evidence of progressive weathering of soils and conclude that the sites had different histories of soil development. However, the complexities of sediment deposition in lakes and the paucity of information relating FWI to soil characteristics prevent straightforward reconstruction of soil development. Variability within each record appears tied to initial grain chemistry, depositional environment, changes in lake level and progressive degradation of grains. As more information relating micromorphology to soil characteristics becomes available, this technique should become a more useful complement to chemical studies of lake sediment. [ABSTRACT FROM AUTHOR]

Ten peat cores were taken from the catchment of Lochnagar, a remote mountain lake in the Cairngorms region of Scotland. Organic content, measured as loss-on-ignition (LOI), profiles of most of the cores are high (_90%) throughout. As the movement of spheroidal carbonaceous particles (SCPs) is insignificant, with steady accumulation, the peats can be used as an archive for reconstructing the historical records of SCP deposition. The SCP profiles of these cores were matched to the SCP dating features of a Lochnagar lake-sediment core so that the catchment peats could be dated. The results show that the start of SCP record is a good dating feature. The applicability of the rapid increase in SCP concentration for dating depended on the stability of peat accumulation, whereas the subsurface peak may be a useful future dating horizon. [ABSTRACT FROM AUTHOR]

A fine-resolution analysis of pollen, charcoal, magnetic susceptibility, sediment fractions and total carotenoids was used to investigate the last 2000 years of environmental history at Lake Keilambete, in western Victoria, Australia. The chronology of sedimentation was based on three radiocarbon dates, supplemented by inferences from 22 previous radiocarbon ages from the site, spanning approximately the last 7500 years. Changes in the analysed parameters infer a relatively higher effective moisture from approximately 2000 to 1800 cal. BP. Increased instability in the Lake Keilambete catchment from 1750 to 1425 cal. BP may reflect a decreased moisture availability and cooler temperatures. At about 1450 cal. BP a period of considerable environmental change is suggested at Lake Keilambete. Warmer temperatures or an increased moisture supply seem likely between 1415 and 1320 cal BP. From around c. 1150 until 800 cal. BP, overlapping the 'Medieval Warm Period', a series of changes in the composition of the Lake Keilambete sediment suggests temperature variability. Changes in some vegetation indices and in charcoal may provide evidence for the 'Little Ice Age', but this evidence is not conclusive. [ABSTRACT FROM PUBLISHER]

AMS-radiocarbon dating of specific organic fractions is used to evaluate sources of errors in dating of organic-poor lake sediment from Linnévatnet, a proglacial arctic lake. Dates on un differentiated (bulk) organic matter are much too old because of contamination from detrital coal. Attempts to remove coal from other organic matter were only partially successful, a consequence of the wide grain-size distribution of the coal. Even if coal contamination is fully removed, the bulk of the remaining organic matter is of aquatic origin and is unsuitable for 14C dating because the lake waters are depleted in 14 C due to dissolution of carbonate minerals. Terrestrial plant macrofossils provide the only reliable material to date the lake sediment; however, this material is present in sufficient quantity for AMS-radiocarbon dating only in cores proximal to the main inlet streams. Paired dates on terrestrial plants and aquatic insects from the same core level and paired dates on modern aquatic and terrestrial vegetation indicate differences in carbon reservoir activities of 1000 and 3000 years. In hard-water lakes, coring is recommended in inlet-proximal areas where inwashed terrestrial vegetation is most concen trated. Chronologies established in proximal cores can be transferred to central-basin cores using litho or chemo-stratigraphic indices. [ABSTRACT FROM PUBLISHER]

Sediments deposited during the last 5400 years in two Danish, closed, oligotrophic lakes have been analysed for pollen, dark-coloured hyphae and microscopic charred particles. Chronologies are provided by numerous radiocarbon datings. Redundancy analysis is used to develop a model for the relationship between concentrations of sedimentary charred particles and pollen at Lake Solsø. The only pollen type which is significantly correlated with charred particles is Calluna. The model is used to predict charred particle concentrations in the sediments of lake Skånsø from the Calluna-concentrations and the predicted values are compared to the observed. The results indicate that: (1) the source area and the means of transportation for microscopic charred particles and pollen are approximately identical; (2) charred particles and pollen may be focused differentially in a lake; and (3) high fire intensities triggered heathland expansion and heaths were maintained by fires through millennia. [ABSTRACT FROM PUBLISHER]