The paleolimnology of North Pond: watershed-lake interactions

We examined the stratigraphic record of North Pond, a small, oligotrophic lake in western Massachusetts, U.S.A. to describe late and post-glacial watershed-lake interactions. In particular we investigated the effects of two similar vegetation changes in the watershed on lake biogeochemistry. There was a transient (about 100 years) decline in hemlock ca. 7500 yr B.P. that has not been recorded in other pollen stratigraphies in the northeast. The second event was the classical hemlock decline that occurred ca. 4800 yr B.P. and lasted about 2000 years. This decline occurred throughout the range of hemlock and is thought to have been caused by a pathogen. As the climate began to warm ca. 10 000 yr B.P., a spruce dominated boreal woodland was established in the watershed. Sediment chemistry data showed that as soils became more acidic, the lake also acidified as evidenced by diatom-inferred (DI) pH. Hemlock was established in the watershed by about 8000 yr B.P. This was accompanied by a slight decrease in DI pH. The transient hemlock decline ca. 7500 yr B.P. was associated with an increase in sedimentary charcoal particles, that suggested fire was responsible for its demise. The diatom stratigraphy indicated a brief, slight, increase in productivity and alkalinity and a brief decrease in lakewater dissolved organic carbon concentrations. Aquatic microfossil data indicated a decrease in the area of the littoral zone ca. 7500 yr B.P. Following the transient decline the lake became more acidic. There were only brief, subtle changes associated with the classical hemlock decline, including a slight decline in DI pH. Although the two disturbances involved a similar vegetation shift, the timing and mechanisms of the disturbances had a greater impact on lake biogeochemistry.     

Late Pleistocene-Holocene paleolimnology of three north-western Russian lakes

The vegetation history and development of three different types of lakes, lakes Valday, Kubenskoye and Vishnevskoye (northwest of the East European Plain) were reconstructed using paleolimnological techniques. Watershed vegetation demonstrates a close connection with climate fluctuations: gradual expansion of the southern broad-leaved trees to the North during the Holocene with the maximum extent during the climate optimum (8000–5000 BP); and their subsequent retreat afterwards; followed by the extension of spruce during the cold and dry Subboreal time; and dominance of pine-spruce-birch forests in the Subatlantic time. The Late Pleistocene and Holocene climate changes resulted in lake-level fluctuations and other ecosystem changes. Valday Lake was formed ca. 12,500 BP as an oligotrophic, deep water basin. The lake level decreased during the dry Boreal, then increased again during the humid Atlantic period. The large shallow Kubenskoye Lake was formerly a part of an ice margin lake, which was then separated (ca. 13,000 BP) and developed into the Sukhona Basin with an outflow to the northwest. During the Atlantic, the outflow direction changed to the east. As a result, the ancient Sukhona Lake disappeared and Kubenskoye Lake formed in its modern size and shape. Vishnevskoye Lake, on the Karelian Isthmus, was formed at the beginning of the Preboreal after the disappearance of the Baltic Ice Lake. It was flooded by waters of the Boreal Ancylus transgression of the Baltic Basin and had become a small eutrophic lake by the time.     

Five thousand years of sediment transfer in a high arctic watershed recorded in annually laminated sediments from Lower Murray Lake,Ellesmere Island,Nunavut, Canada

Sediments in Lower Murray Lake, northern Ellesmere Island, Nunavut Canada (81°21′ N, 69°32′ W) contain annual laminations (varves) that provide a record of sediment accumulation through the past 5000+ years. Annual mass accumulation was estimated based on measurements of varve thickness and sediment bulk density. Comparison of Lower Murray Lake mass accumulation with instrumental climate data, long-term records of climatic forcing mechanisms and other regional paleoclimate records suggests that lake sedimentation is positively correlated with regional melt season temperatures driven by radiative forcing. The temperature reconstruction suggests that recent temperatures are ~2.6°C higher than minimum temperatures observed during the Little Ice Age, maximum temperatures during the past 5200 years exceeded modern values by ~0.6°C, and that minimum temperatures observed approximately 2900 varve years BC were ~3.5°C colder than recent conditions. Recent temperatures were the warmest since the fourteenth century, but similar conditions existed intermittently during the period spanning ~4000–1000 varve years ago. A highly stable pattern of sedimentation throughout the period of record supports the use of annual mass accumulation in Lower Murray Lake as a reliable proxy indicator of local climatic conditions in the past.

长江三峡及江汉平原地区全新世环境考古与异常洪涝灾害研究

根据对长江三峡及江汉平原地区新石器文化遗址的分布、文化间断、埋藏古树和历史资料探讨了本区全新世异常洪水频率的变化，共划分出４个洪水频率发期：第Ⅰ洪水期（８０００ａＢＰ－５５００ａＢＰ）共发生特大洪水９次；第Ⅱ洪水期（４７００ａＢＰ－３５００ａＢＰ），至少发生特大洪水９次；第Ⅲ洪水期（２２００ａＢＰ－７００ａＰＢ），共发生特大洪水５２次，其中在小冰期最冷期（３００ａＢＰ－１００ａＢＰ）就有４０次。前     

The late-glacial and early-Holocene palaeoecology of cladoceran microfossil assemblages at Kråkenes, western Norway, with a quantitative reconstruction of temperature changes

Cladoceran microfossil remains were analysed from a sediment core taken from a lake basin at Kråkenes, western Norway. The sequence included immediate post-glacial conditions (ca. 12,300 ¹⁴C BP), the Allerod, Younger Dryas, and early Holocene to approximately 8,500 ¹⁴C BP. The interpretation of changes in the cladoceran assemblages is based on the known ecology of the taxa, the documented environmental history of the study sequence, the variations in the organic content of the sediment, the radiocarbon dates, and the results of analyses of other biotic groups, including diatoms, macrophytes, and chironomids. In addition, a quantitative reconstruction of changes in air temperature is presented for the study period. This reconstruction is based on transfer functions developed from a separate Swiss surface-sediment cladoceran data set.The cladoceran assemblages throughout the sequence are dominated by littoral chydorid taxa. Bosmina, Daphnia, and Simocephalus represent the open-water component of the zooplankton. Chydorus piger and Daphnia were the only immediate post-glacial pioneer taxa. A rapid proliferation of the open-water and littoral cladoceran taxa began with the onset of the Allerod and persisted for approximately 1,000 yrs. At the start of the Younger Dryas a local glacier formed and drained into the lake, causing a sudden decline in chydorid diversity, with only Chydorus sphaericus and Acroperus harpae persisting throughout this period. Chydorid diversity started to recover in the upper Younger Dryas and continued in the early Holocene. Progressive acidification and oligotrophication are also discernible from the cladoceran assemblages present in the Holocene.The reconstructed mean summer air temperature was from 8-21 °C, with prediction errors of 1.8-2.5 °C. The Allerod was only slightly warmer than the Younger Dryas period, but a progressive increase in temperature is apparent during the early Holocene. In conclusion, the results of this study provide a further demonstration of the value of cladocera as indicators of a variety of palaeoenvironmental parameters, including temperature.     

Influence of late holocene pyroclastic eruptions on the sedimentary geochemistry of Lake Rotoiti,North Island,New Zealand

Lake Rotoiti in Taupo Volcanic Zone was formed by damming of the drainage system through the floor of Okataina Caldera. Basin sediments are predominantly silt or sand, with mineralogy consistent with derivation from local silicic rocks and airfall tephras. Sandy lithofacies around the shoreline are wave worked deposits. Sand and gravel lithofacies in deeper water and on steep slopes are largely relict or airfall tephras, or both. Profundal sediments are diatomaceous silts. Organic-rich diatomaceous silts also accumulate in near-shore wave-damped zones under weed beds.Short cores penetrated the Tarawera (1886 AD) and Kaharoa (1180 AD) Tephras, identified by their stratigraphic position, geochemistry and mineralogy. Localised slumping is evidenced from secondary tephras interbedded and redeposited within the basin silts. Sedimentation rates in the basins, estimated from the age of bounding tephras, are 0.9 to 4.0 mm y^-1, and are highest under the influence of inflowing water from adjacent Lake Rotorua. For several hundred years prior to the Tarawera eruption sediment accumulation rates and the sediment geochemistry remained unchanged; deposition was predominantly biogenic opaline silica with a small terrestrial component. The Tarawera eruption deposited a terrestrial-silica, aluminum-rich primary tephra across the lake, which was followed by reworked tephra from within the catchment, the effects of which were progressively diluted by biogenic opaline silica as conditions stabilised. While the major effects of the eruption have been rapidly absorbed the lake has not returned to pre-eruption background conditions. A new equilibrium has been attained in which Tarawera Tephra continues to be eroded into the lake and is the principal source for a doubling of sedimentation rates following the eruption. High arsenic levels in some diatomaceous silts are attributed to episodic venting of hydrothermal fluids or gases into the water column.     

西辽河流域全新世以来人地系统演变历史的重建

考古研究表明，西辽河流域是我国古代文明的起源地之一，全新世以来先后演绎了多期古文化，文明一直延续至今。利用野外考古材料和已有考古研究成果，系统地梳理了本区文化景观的演变历史；利用土壤剖面、古土壤年代数据、文化遗址中的碳屑显微结构等证据，结合前人的研究成果，系统地复原了本区自然景观的演变历史；详细探讨了全新世以来本区人地系统的耦合演变进程，揭示了本区人地系统演变的时历史规律和内在机制。     

绿洲沉积特征及沉积模式

绿洲沉积是指在绿洲生物发育、演化的环境中无机和有机物在地表和近地表层的沉积或沉淀作用。绿洲沉积是绿洲物质循环过程的重要环节,其沉积物不仅记录了物源组成、介质性质、能量状态及动力特征等,还记录了绿洲环境变化的大量信息。沉积物的颜色、组构、组成等方面表明绿洲沉积是可识别的。通过研究绿洲沉积,可以揭示绿洲物质循环、认识绿洲环境演变、解析绿洲对全球变化的响应,为绿洲低耗、高效、可持续发展理论模式的构建和技术创新提供科学依据。