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.     

The postglacial environmental development of Raffles Sø, East Greenland: inferences from a 10,000 year diatom record

A 341 cm long sediment sequence was recovered from the unofficially named Raffles Sø on Raffles Ø, outer Scoresby Sund region, East Greenland. The sediment sequence consists in the upper part (0–230 cm) of a stratified gyttja enriched in organic carbon and biogenic silica whereas the lower core part (235–341 cm) is composed of terrigenous, consolidated glacio-limnic sediments. ¹⁴C-AMS measurements indicate that the sediment sequence represents the entire Holocene lake history from 10,030 calibrated radiocarbon years.The geochemical parameters (opal, total organic carbon (TOC), total nitrogen (TN)) and the total diatom concentration show similar developments during the Holocene, and reflect changes in biological production and nutrient input into the lake. These records clearly reveal a broad Holocene TOC-opal-maximum interval between 5200 and 1800 cal. yrs BP.The diatom flora consisted of 66 taxa representing 20 genera but only seven taxa were abundant and, sometimes, these were monospecifically dominant during the Holocene. In the sediment core from Raffles Sø four successive stratigraphical zones can be distinguished. Accumulation of diatom valves began at 9900 cal. yrs BP with a Stephanodiscus minutulus (Kütz.) Cleve and Möller dominated assemblage (stratigraphic zone 1) followed by a diatom flora dominated by Cyclotella pseudostelligera Hustedt and, less frequently, by Diatoma tenuis Agardh (9400 until 5900 cal. yrs BP, zone 2). Cyclotella sp. A, a taxon which belongs to the Cyclotella rossii-comensis-tripartita-complex, was the dominant floral element between 5200 and 1800 cal. yrs BP (zone 3). From 1800 cal. yrs BP, the periphytic taxa Fragilaria capucina var. gracilis (Østr.) Hustedt and F. capucina var. rumpens (Kütz.) Lange-Bertalot attained highest relative abundances, also almost monospecifically (zone 4).The distribution and composition of the diatom assemblages in the sediment record from Raffles Sø probably reflect past variations in the extent of the lake-ice cover during the growing season. More or less ice-free conditions during summer may have prevailed during the early Holocene until ca. 1800 cal. yrs BP, which allowed growth of planktonic diatoms (Cyclotella taxa) in the pelagic lake region. From 1800 cal. yrs BP, colder conditions lead to a perennial lake-ice cover with a small ice-free moat in summer which favored the growth of periphytic, littoral species (Fragilaria capucina varieties).     

Textural attributes, mineralogy and provenance of sand dune fields in the greater Al Ain area, United Arab Emirates

Sand dunes and interdune sediments around Al Ain city have markedly high carbonate contents which increase towards Jabal Hafit mountain and the Arabian Gulf coast. The dunes are composed predominantly of well-sorted fine sands, consisting of unstrained quartz and carbonate grains together with minor proportions of chert and feldspars. Scanning electron microscope (SEM) examination reveals that quartz grains display various mechanically- and chemically-formed surface textures. The heavy minerals are dominated by opaques and pyroxenes with minor tourmaline, garnet, rutile, epidote, monazite, zircon, hornblende and staurolite.Interdune sediments consist of fine and very fine, poorly- to extremely poorly-sorted sands together with small concentrations of gravel, silt and clay. The light sand fractions compositionally resemble those of dunes but contain, in addition, gypsum, anhydrite, halite and celestite. Percentages of pyroxenes are higher whereas those of zircon, tourmaline and rutile are lower than in dunes. X-ray diffractometry reveals that the clay fractions consist solely of palygorskite. Generally, interdune sediments are much less mature texturally and mineralogically than dune sands; the maturity of both types of sediments decreases toward the NE of the study area.Sand dunes in the various districts of the greater Al Ain area are genetically related. Also, there is a partial genetic relationship between the dunes and interdune sediments; both are mainly multicyclic. Their major parts were brought mainly by the dominant north-west (El Shamal) winds from older dune fields in other localities in U.A.E., Qatar and El-Rub El-Khali. Local contributions to the dune fields from Jabal Hafit mountain, the Oman Mountains and the calcareous coast of the Arabian Gulf were, in cases, significant. Also, authigenesis by groundwater under highly evaporitic conditions played a major role in the formation of interdune sediments through the genesis of the clay and some nonclay minerals.     

东太平洋中国开辟区沉积物中热水活动的矿物学及地球化学证据

通过对东太平洋多金属结核中国开辟区表层沉积物和短柱状沉积物的系统观察和分析，首次根据矿物学和地球化学两方面的证据，发现中国开辟区沉积物中热水活动及其产物的存在。X射线衍射分析表明，沉积物样品中普遍含有重晶石，部分样品中含量高达10％以上，扫描电镜观察发现，重晶石均为完整自形晶，并与同为自形的石英及钠长石共生。根据本区重晶石的地质背景及结晶形态，可以认为它的形成环境与加利福尼亚湾瓜伊马斯盆地（Guaymas)相似，属热水成因，伴生的石英和钠长石亦为常见的热水矿物，。这一共生组合的形成温度不低于70℃。地球化学研究发现，在柱状沉积物剖面上，Ba的垂向分布有两种类型，一种为平稳型，在一定深度范围内无明显变化。另一种为跃升型，并伴有其他活泼组分的同步变化，跃升型可视为热水活动在沉积历史上的记录，迄今为止，热水矿物组合主要见于东区的表层沉积物，而在西区，Ba在沉积物中的富集主要见于10cm以下层位，根据沉积速率推算，在中国开辟区西区的热水化活动记录比东区至少早0．1Ma。     

中国白垩纪沙漠中的戈壁沉积

戈壁是广义沙漠体系的一个组成部分，然而在沙漠研究尤其在古沙漠研究中未得到充分的重视。笔者根据近年来的古今沙漠的研究，讨论了戈壁的形成作用、中国白垩纪沙漠戈壁沉积和风磨石的形成和分布特征，以便引起广大同行的重视。     

ON THE NUMBER OF FRACTIONS TO COMPUTE TRANSPORT OF SEDIMENT MIXTURES

1 INTRODUCTIONMany hydro-momhological mathematical models neglect the innuence of river bed maerialheterogeneity and its time and space changes during transport and related erosion/dePosition processes. Inthese models a rePresentative diameter of the river bed grain-size distribution (for examPle d5o) isspecified as initial data in each comPutational point of the modeled domain. Different d5o can be assignedto each ghd point but temPoral changes in bed material gradation cannot be simula…     

新疆岩石·岩屑·水系沉积物元素背景平均值

论证了中国丰度及地壳表层物质成分研究的必要性和重要性，利用区域地球化学勘查所提供的高精度分析数据，经严格统计计算，发表新疆地区其一级构造单元表层岩石、岩屑、水系沉积物的39种元素背景平均值。     

Pollution vulnerability of the Quaternary aquifer near Cairo, Egypt, as indicated by isotopes and hydrochemistry

The present study was conducted to delineate the pollution vulnerability of the Quaternary aquifer in two areas, Imbaba and Shobra El-Khima, near Cairo, Egypt. Environmental isotopes combined with hydrochemistry were used for this purpose. The groundwater in the Imbaba area (average total dissolved solids about 900 mg/L; sodium/chloride, sulfate, and bicarbonate water types) is more mineralized than groundwater in the Shobra El-Khima area (average total dissolved solids 500 mg/L; calcium and sodium/bicarbonate water type). A high nitrate content and significant mineralization in the groundwater are probably due to contamination of recharge to the aquifer by irrigation drainage, deteriorated sewage networks, and septic tanks. The deuterium and oxygen-18 compositions of the groundwater are depleted compared to Nile River water, which is the main source of aquifer recharge. This less isotopically enriched water probably represents older Nile water recharge that flooded the region before construction of the Aswan High Dam in 1963, or it is a mixture of a young water and originally deposited paleowater that was in deeper horizons at a time of cooler and more humid climate. Intensive pumping has moved the paleowater higher in the aquifer. Groundwater in the Shobra El-Khima area has higher residence time, based on the tritium concentration, than groundwater in the Imbaba area. The percentage of the isotopically depleted water equals 75% in the Shobra El-Khima and 35% in Imbaba, and the thickness of the clay cap above the aquifer is 38 m in Shobra El-Khima and 20 m in Imbaba. These factors are indicative of the rate of recharge to the aquifer and were used to evaluate the pollution vulnerability in the two areas. Electronic Publication     

Suspended sediment transport and deposition in a high arctic meromictic lake

A study of sedimentary processes and sediment yields in a high arctic meromictic lake (Lake C2, Taconite Inlet, Northern Ellesemere Island, Canada) was undertaken from May 1990 through August 1992 to understand the links between climatic controls, hydrology, and the laminated sediment record preserved in the lake. Understanding the relationships between processes and the sediment record is critical for interpreting the climatic significance of the laminated sediments in a region where high resolution climate proxy records are quite limited.Sediment transport to Lake C2 is dominated by fluvial processes. During the early part of the melt season slushflows transport sediment to the lake surface. Subsequently, suspended sediment is delivered to the lake by the main inlet stream and distributed lakeward by a plume emanating the main inlet channel. Due to the strong density stratification of the water column the plume distributes sediment downlake by overflows and interflows in the epilimnion. In general, overflows are generated by lower discharge events whereas interflows penetrate to the halocline during high discharge with increased suspended sediment concentration.Sediment trap analysis demonstrates that suspended sediment transport and deposition responds to diurnal through annual changes in stream discharge. Seasonal and annual sediment trap yields agree with average accumulation rates determined from varve thickness measurements and cumulative suspended sediment discharge from the main inlet stream indicating a close link between climatological, hydrological, and sedimentological controls and varve deposition.This is the fourth in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.