A method for the selective removal of inorganic ash particles from lake sediments

Inorganic ash particles are formed by the fusing of inorganic material present during the high temperature combustion of fossil fuels. As they accumulate in lake sediments, they record the history of atmospheric contamination produced from such sources. A technique has been developed for concentrating these particles from lake sediments involving the stepwise removal of unwanted components of the sediment, including organic material and biogenic silica.When applied to a sediment core taken from Loch Tinker, central Scotland, a particle concentration profile, very similar to that of the carbonaceous particle profile (the other component of fossil-fuel combustion ash) is produced. The concentration of the inorganic ash spheres in the sediment is approximately an order of magnitude higher than the carbonaceous particles and there appears to be a continuous pre-industrial background value. This seems to imply a similar source (i.e. coal combustion rather than oil) for both inorganic ash and carbonaceous particles. This method has also been used with success on peat cores.     

Radiometric dating of recent lake sediments from a highly eroded area in semiarid Tanzania

Semiarid regions are vulnerable environments with a series of important and often discussed problems such as land degradation, water scarcity and desertification. These regions are dynamic and respond quickly to climatic and environmental changes. Unlike lakes in temperate zones, lakes in semiarid regions are yet poorly utilized as climatic and environmental indicators. In this study aquatic deposits are used to uncover the environmental history of a severely degraded area in central Tanzania. The ²¹⁰Pb and ¹³⁷Cs chronologies date a 360 cm long sediment sequence to 155 years. The sediments show that lake Haubi basin changed from a seasonally waterlogged depression to a lake at the turn of the century. Calculated sedimentation rates show that the catchment of the lake has been subject to varied and enhanced soil erosion during the last 155 years.     

The siliceous sediments of Lake Cantara South,a saline lake in South Australia

A textural analysis of the siliceous sediments component of a small saline lake in south-eastern South Australia (Lake Cantara South) was undertaken. The data indicated periods of marine incursion, lagoonal dominance and elevated freshwater inputs. Lake Cantara originated as a marine embayment; then followed periods of intermittent marine connection; finally, the lake became athalassic (mostly saline but with occasional freshwater inundations). This history accords well with that derived from an examination of mollusc fossils (marine, estuarine, athalassic saline, and freshwater forms) and with previously published mineralogical, geochemical and geomorphological evidence.     

The landscape factor in the formation of pollen records in lake sediments

Comprehensive paleobotanical and geochemical methods have been used to study the relationship between the spatial scale of landscape development and values of pollen influx to take the bog sediments. The spatial-temporal history of the four lakes and a bog was established in NE Estonia and pollen analyses of thier sediment were made. It was found that the influx of total arboreal pollen directly corresponds with the sizes of the sites studied, and varies with thier expansion or reduction.     

Four thousand years of atmospheric lead pollution in northern Europe: a summary from Swedish lake sediments

This paper presents a large palaeolimnological study of the pre-industrial and industrial history of atmospheric lead pollution deposition in Sweden. Both lead concentrations and ²⁰⁶Pb/²⁰⁷Pb ratios have been analysed in 31 lakes covering most of Sweden, plus one lake in north-west Russia. Four of the lakes have varved (annually-laminated) sediments. Isotope analysis is a sensitive and effective method to distinguish pollution lead from natural catchment lead and to detect early pollution influence, because the ²⁰⁶Pb/²⁰⁷Pb ratio in unpolluted background sediments in Sweden was > 1.3, while that of lead from pollution, derived from ores and coal, was < 1.2. The sediments show a consistent picture of past temporal changes in atmospheric lead pollution. These changes include: the first traces of pollution 3,500-3,000 yrs ago; a pollution peak in Greek-Roman Times (about 0 AD); lower lead fall-out between 400 and 900 AD; a significant and permanent increase in atmospheric lead fall-out from about 1000 AD; an increase with the Industrial revolution; a major increase following World War II; the maximum peak in the 1970s; and decreasing fall-out over the last decades. The four varved sediments provide high-resolution records of atmospheric pollution. They reveal pollution peaks about 1200 and 1530 AD which match the history of metal production in Europe. According to the varve records the lead pollution level in the late 1990s had decreased beneath the level of the 1530s. The pollution level 1200 AD was about 35% of the 1980s, when lead pollution was still near its all time high. About 50% of the total accumulated atmospheric lead pollution deposition through time was deposited in the pre-industrial period. The sediments also show a consistent picture of the geographic distribution of atmospheric lead deposition over time, with higher deposition in south Sweden and declining levels to the north, which supports the hypothesis that the main sources of pre-industrial atmospheric lead pollution in Sweden were cultural areas in mainland Europe and Great Britain.     

Climate change inferred from aeolian sediments in a lake shore environment in the central Tibetan Plateau during recent centuries

Studies of the past climate variation on the Tibetan Plateau(TP) are currently limited in number and low in density and temporal resolution. We investigated the climate condition from about 400 years before present(B.P.) in the central TP at the shore of Co(means "lake") Nag using aeolian sediments. A 2.7-m sand profile with 57 sediment samples and six optically stimulated luminescence(OSL) samples were studied through grain-size analysis, geochemical elements and parameters, and depositional rate estimation. A previous assumption was verified that sand deposition at the shore of Lake Co Nag originated from hills to the east. Two significant wet periods between 90–140 and about 380 years B.P. were indicated by the variation of element profiles and sediment depositional rates. Aeolian activity is sensitive to variations from different seasonal changing patterns of climate factors in the study area, and aeolian sediments respond differently to climate conditions during the cold little ice age(LIA) and the warm 20 th century. Present day dry seasons of winter and spring might be much warmer and drier compared to seasons of 400 years ago although summer precipitation has increased, resulting in significantly more aeolian activity and higher depositional rate(about 6 times compared to 380–240 years ago) of sandy sediments. Aeolian problems like blown-sand deposition and desertification may be worse in a projected warming future in the central TP as well as other cold and high altitude regions. Our results suggest an agreement with environmental evolution during the little ice age and the 20 th century in a broader scale on the TP.     

Climate of the past millennium inferred from varved proglacial lake sediments on northeast Baffin Island,Arctic Canada

This study uses ^239+240Pu-dated varved sediments from Big Round Lake, a proglacial lake on northeast Baffin Island, Arctic Canada to generate a 1000-year-long, annual-resolution record of past climate. Varve thickness is positively correlated with July–August–September temperature measured at Clyde River, 70 km to the north of the lake (r = 0.46, p < 0.001). We therefore interpret the variability and trends in varve thickness to partially represent summer temperature. The coolest Little Ice Age temperatures occurred in this record from 1575 to 1760 AD and were approximately 1.5°C cooler than today (average from 1995 to 2005 AD) and 0.2°C cooler than the last millennium (average from 1000 to 2000 AD). Pre-twentieth-century warmth occurred during two intervals, 970–1150 AD and 1375–1575 AD; temperatures were approximately 1.2°C cooler than today, but 0.1°C warmer than the last millennium. The Big Round Lake varve-thickness record contains features similar to that reconstructed elsewhere in the eastern Canadian Arctic. This high-resolution quantitative record expands our understanding of arctic climate during the past millennium.

Sciaridae in lake sediments: indicators of catchment and stream contribution to fossil insect assemblages

The larval head capsules of Sciaridae (black fungus gnats) are transported into lakes from terrestrial habitats, in most cases via streams or rivers, and preserve well in lake sediments. The abundance of sciarid remains can provide information on the importance of terrestrial and running-water input into fossil insect assemblages in lake sediments if examined in relation to the number of fossils of aquatic insects such as the Chironomidae, Thaumaleidae, Ceratopogonidae, or Simuliidae. Here we describe fossil head capsules of sciarid larvae and provide an example of how these remains can be used to constrain past changes in taphonomic processes that influence fossil chironomid records.     

Radiometric dating of lake sediments from Signy Island (maritime Antarctic): evidence of recent climatic change

Sediment cores from three lakes (Moss, Sombre and Heywood) in the maritime Antarctic (Signy Island, South Orkney Islands) have been successfully dated radiometrically by²¹⁰Pb and¹³⁷Cs. The core inventories of both fallout radionuclides are an order of magnitude higher than that which can be supported by the direct atmospheric flux at this latitude. The elevated values may be explained by fallout onto the catchment during the winter being delivered directly to the lakes during the annual thaw. Two of the lakes (Sombre and Heywood) show marked increases in sediment accumulation afterc. 1950. This appears to be associated with a documented rise in temperature in the South Orkney Islands, which has caused extensive deglaciation at Signy Island.This is the tenth of a series of papers to be published by this journal following the 20 ^th anniversary of the first application of²¹⁰Pb dating of lake sediments. Dr P.G. Appleby is guest editing this series.     

AMS 14C dating of tundra lake sediments using chironomid head capsules

Radiocarbon dating of late-Quaternary sediments from high-latitude lakes is often complicated by the influx of old carbon, reservoir effects, or both. If terrestrial plant macrofossils are also absent, the dating of bulk sediment often provides the only means to establish chronologies for these problematic sediment sequences. Given that chironomid (non-biting midge) remains are sufficiently abundant in many northern lakes to be ¹⁴C-dated via the accelerator mass spectrometry (AMS) method, we decided to explore their utility in age-model development. Five age determinations based on chironomid material were obtained from a lake sediment core sampled in the shrub tundra of northern Québec. These results were compared to six AMS bulk sediment ages, as well as to a date obtained from Drepanocladus spp. The chironomids yielded consistently younger ages (with increasing age offset upcore), confirming both the presence of a reservoir effect and the value of chironomids in establishing more reliable ¹⁴C chronologies.     

Seasonal trends in the uranium-series istopic signatures of lake waters and sediments: Hawes Water, north-west England

Potential seasonal variation in the U-series radioisotopic signatures of lake and input waters was investigated in Hawes Water, north-west England, and the sedimentary record was examined to establish whether any observed seasonality is preserved in the sediment U and Th radioisotopic activity ratios. U-series disequilibrium in the waters is indicative of both surface and shallow sub-surface origins for the dissolved U, and that this supply is influenced by changes in the prevailing hydrological regime. However, the lake is buffered from this seasonality in that the ²³⁴U/²³⁸U activity ratio remains constant during the year, and the U content undergoes only a marginal decrease during summer. The change in the mechanism of lake sedimentation from allochthonous organic input during winter to autochthonous carbonate formation during summer has a more significant influence on the U-series radioisotopic characteristics of sedimentary record in that the proportion of organic and carbonate material both exhibit a strong control on the²³⁴U/²³⁸U activity ratio and U content. In addition, significant proportions of sediment U and Th are associated with ferromanganese oxyhydroxides. Given this seasonality, it is of some significance that the ²³⁴U/²³⁸U activity ratios of the bottom sediments preserve a reasonable record of lake U-series disequilibrium and are, therefore, potential indicators of long-term changes in catchment hydrology.     

柴达木盆地北缘湖泊表层沉积物炭屑特征及其环境意义

沉积物中的炭屑在探讨火(灾)的基本特征及其与植被和人类活动关系方面具有重要意义。采用孢粉学提取方法,对柴达木盆地北缘的湖泊表层沉积物进行了微体炭屑的分析工作,用以探讨其空间分布及其与区域植被和现代人类活动之间的关系。结果表明:不同粒径的炭屑浓度均呈现出自西向东升高的趋势,与区域植被覆盖度自西向东增加的趋势一致。其中,小粒径的炭屑以近圆形占多数,表明区域性火事件中燃烧的木本植被占主导地位;粒径较大的长条形炭屑在盆地东部区域占优势,表明地方性火事件向东增加,草本植物燃烧逐渐增多,与自西向东草本植物的增多相吻合,且燃烧由区域向近源转换。此外,该地区人口数量也有自西向东增加的趋势,推测人类生产生活用火对炭屑浓度有很大的贡献量,与大颗粒炭屑浓度向东升高有较好的对应关系。表层沉积物炭屑的空间变化特征不仅很好地反映了相应地区的火的信息,还对区域植被和人类活动等要素具有较好的指示意义。     

Hydrogen isotope ratios of individual lipids in lake sediments as novel tracers of climatic and environmental change: a surface sediment test

We determined hydrogen isotope ratios of modern lake-waters and individual lipids from surface sediments of 36 lakes in the eastern North America. The lakes selected lie on two transects (south–north transect from Florida to Ontario and east–west transect from Wisconsin to South Dakota) and encompass large temperature and moisture gradients, and a wide range of lake water δD values (>100‰). The study allows a rigorous test of the applicability of using δD values of sedimentary lipids as paleoclimatic and paleoenvironmental proxies. We examined a range of lipids including C₁₇ n-alkane, straight chain fatty acids, phytol and sterols in both free extracts and ester-bound fractions in the solvent extracted sediments. Useful isotopic indicators are expected to show a linear correlation and constant fractionation factor between their δD values in surface sediments and modern lake water. Our results demonstrate that several lipid compounds, free and ester-bound palmitic acid (16:0), C₁₇ n-alkane, and phytol are useful candidates for paleoclimate reconstructions, in addition to two sterols that have been suggested previously (. Compound-specific D/H ratios of lipid biomarkers from sediments as a proxy for environmental and climatic conditons. Geochim. Cosmochim. Acta 65: 213–222). Authigenic or biogenic carbonate in sediments is conventional material for paleoclimatic study using ocean and lake sediments. However, because majority of lake sediments do not contain suitable carbonate materials for isotopic study, hydrogen isotope ratios of these lipids provide invaluable new sources of paleoclimatic and paleoenvironmental information.     

Environmental changes during modern period from the record of Gaoyou Lake sediments, Jiangsu

Based on analysis of parameters of cores taken from Gaoyou Lake, including magnetic susceptibility, grain-size characteristics and sedimentary rate, environmental changes during the modern period were examined with the assistance of historical records and Gaoyou Lake water level materials. It is concluded that during the modern period a higher value of magnetic susceptibility and a lower sediment grain size coincided with a wet climate, while a lower value of magnetic susceptibility and a higher grain size were related with a dry climate. The results indicate that the climate in the 123 years period from 1880 to 2003AD can be divided into four stages: two low water level stages (1880–1915AD, 1948–1981AD) and two high water level stages (1915–1948AD, 1981–2003AD). It appears that the regional cli-mate generally underwent a dry–wet–dry–wet pattern in 30-year cycles. At present, it is at the end of a wet period, so the regional climate is expected to become dry in the near future. This conclusion corresponds with the climate records in the historical literature of the Gaoyou area, and it also matches with the climatic changes in North Jiangsu area.