A high-resolution paleoclimate record spanning the past 25,000 years in southern East Africa

High-resolution profiles of the mass accumulation rate of biogenic silica and other geochemical proxies in two piston cores from northern Lake Malawi provide a climate signal for this part of tropical Africa spanning the past 25,000 years. The biogenic silica mass accumulation rate was low during the relatively dry late Pleistocene, when the river flux of silica to the lake was suppressed. Millennial-scale fluctuations, due to upwelling intensity, in the late Pleistocene climate of the Lake Malawi basin appear to have been closely linked to the Northern Hemisphere climate until 11 thousand years ago. Relatively cold conditions in the Northern Hemisphere coincided with more frequent north winds over the Malawi basin, perhaps resulting from a more southward migration of the Intertropical Convergence Zone.     

Ecological consequences of a century of warming in Lake Tanganyika

Deep tropical lakes are excellent climate monitors because annual mixing is shallow and flushing rates are low, allowing heat to accumulate during climatic warming. We describe effects of warming on Lake Tanganyika: A sharpened density gradient has slowed vertical mixing and reduced primary production. Increased warming rates during the coming century may continue to slow mixing and further reduce productivity in Lake Tanganyika and other deep tropical lakes.     

Critical depth for the survival of coral islands: effects on the hawaiian archipelago

Coral islands drown when sea level rise exceeds the maximum potential of coral reefs to grow upward (about 10 millimeters per year). During the Holocene transgression (18,000 years ago to present) sea levels rose at rates of up to 10 to 20 millimeters per year, and most coral island reefs situated deeper than a critical depth of30 to 40 meters below present day sea level drowned. Coral islands that did not drown during the Holocene transgression apparently all developed on antecedent foundations shallower than critical depth. During low stands in sea level during the Pleistocene, these islands were elevated and subject to subaerial erosion. Today, in the Hawaiian Archipelago, the depth of drowned banks is inversely related to summit area; smaller banks are progressively deeper, evidently because of erosional truncation during low sea level stands. Bank summit area may therefore be an important factor determining the failure or success of coral islands.     

滇池流域农业沟渠系统景观特征分析

近年来,随着沟渠生态功能退化,导致区域生态质量不断恶化。根据景观生态学的廊道理论和尺度格局原理,在现状调查的基础上,利用地理信息系统技术对滇池流域农业沟渠进行空间格局分析和网络分析。结果表明,高级别沟渠多数为混凝土或砖石衬砌结构,其缓冲带植被覆盖度低,沟渠断面宽度与植被带宽度比值较小;通过网络结构分析,发现滇池流域农业沟渠网络结构相似,连通度和环度较低,滇池东南岸和南岸研究区沟渠分维数大,沟渠分布较均匀。     

Geomicrobiology of subglacial ice above Lake Vostok, Antarctica

Data from ice 3590 meters below Vostok Station indicate that the ice was accreted from liquid water associated with Lake Vostok. Microbes were observed at concentrations ranging from 2.8 x 10(3) to 3.6 x 10(4) cells per milliliter; no biological incorporation of selected organic substrates or bicarbonate was detected. Bacterial 16S ribosomal DNA genes revealed low diversity in the gene population. The phylotypes were closely related to extant members of the alpha- and beta-Proteobacteria and the Actinomycetes. Extrapolation of the data from accretion ice to Lake Vostok implies that Lake Vostok may support a microbial population, despite more than 10(6) years of isolation from the atmosphere.     

More than 200 meters of lake ice above subglacial Lake Vostok, Antarctica

Isotope studies show that the Vostok ice core consists of ice refrozen from Lake Vostok water, from 3539 meters below the surface of the Antarctic ice sheet to its bottom at about 3750 meters. Additional evidence comes from the total gas content, crystal size, and electrical conductivity of the ice. The Vostok site is a likely place for water freezing at the lake-ice interface, because this interface occurs at a higher level here than anywhere else above the lake. Isotopic data suggest that subglacial Lake Vostok is an open system with an efficient circulation of water that was formed during periods that were slightly warmer than those of the past 420,000 years. Lake ice recovered by deep drilling is of interest for preliminary investigations of lake chemistry and bedrock properties and for the search for indigenous lake microorganisms. This latter aspect is of potential importance for the exploration of icy planets and moons.     

滇池流域农业沟渠系统景观特征分析

近年来,随着沟渠生态功能退化,导致区域生态质量不断恶化。根据景观生态学的廊道理论和尺度格局原理,在现状调查的基础上,利用地理信息系统技术对滇池流域农业沟渠进行空间格局分析和网络分析。结果表明,高级别沟渠多数为混凝土或砖石衬砌结构,其缓冲带植被覆盖度低,沟渠断面宽度与植被带宽度比值较小;通过网络结构分析,发现滇池流域农业沟渠网络结构相似,连通度和环度较低,滇池东南岸和南岸研究区沟渠分维数大,沟渠分布较均匀。     

Long-term sea-level fluctuations driven by ocean basin dynamics

Earth's long-term sea-level history is characterized by widespread continental flooding in the Cretaceous period (approximately 145 to 65 million years ago), followed by gradual regression of inland seas. However, published estimates of the Late Cretaceous sea-level high differ by half an order of magnitude, from approximately 40 to approximately 250 meters above the present level. The low estimate is based on the stratigraphy of the New Jersey margin. By assimilating marine geophysical data into reconstructions of ancient ocean basins, we model a Late Cretaceous sea level that is 170 (85 to 270) meters higher than it is today. We use a mantle convection model to suggest that New Jersey subsided by 105 to 180 meters in the past 70 million years because of North America's westward passage over the subducted Farallon plate. This mechanism reconciles New Jersey margin-based sea-level estimates with ocean basin reconstructions.     

Paleoearthquakes in the puget sound region recorded in sediments from lake washington, u.s.a

Holocene sediments in Lake Washington contain a series of turbidites that were episodically deposited throughout the lake. The magnetic signatures of these terrigenous layers are temporally and areally correlatable. Large earthquakes appear to have triggered slumping on the steep basin walls and landslides in the drainage area, resulting in turbidite deposition. One prominent turbidite appears to have been deposited about 1100 years ago as the result of a large earthquake. Downcore susceptibility patterns suggest that near-simultaneous slumping occurred in at least three separate locations, two of which now contain submerged forests. Several other large earthquakes may have occurred in the last 3000 years.     

Human occupations and climate change in the Puna de Atacama,Chile

Widespread evidence for human occupation of the Atacama Desert, 20 degrees to 25 degrees S in northern Chile, has been found from 13,000 calibrated 14C years before the present (cal yr B.P.) to 9500 cal yr B.P., and again after 4500 cal yr B.P. Initial human occupation coincided with a change from very dry environments to humid environments. More than 39 open early Archaic campsites at elevations above 3600 meters show that hunters lived around late glacial/early Holocene paleolakes on the Altiplano. Cessation of the use of the sites between 9500 and 4500 cal yr B.P. is associated with drying of the lakes. The mid-Holocene collapse of human occupation is also recorded in cave deposits. One cave contained Pleistocene fauna associated with human artifacts. Faunal diversity was highest during the humid early Holocene.     

Northern hemisphere controls on tropical southeast African climate during the past 60,000 years

The processes that control climate in the tropics are poorly understood. We applied compound-specific hydrogen isotopes (deltaD) and the TEX(86) (tetraether index of 86 carbon atoms) temperature proxy to sediment cores from Lake Tanganyika to independently reconstruct precipitation and temperature variations during the past 60,000 years. Tanganyika temperatures follow Northern Hemisphere insolation and indicate that warming in tropical southeast Africa during the last glacial termination began to increase approximately 3000 years before atmospheric carbon dioxide concentrations. deltaD data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial-scale events recorded in Northern Hemisphere monsoonal climate records. This implies that precipitation in tropical southeast Africa is more strongly controlled by changes in Indian Ocean sea surface temperatures and the winter Indian monsoon than by migration of the Intertropical Convergence Zone.     

土地利用变化与社会经济因素对湖南典型水库水质变化的影响

东江湖、水府庙水库和大通湖是湖南典型水库,以上述3个流域为研究对象,在土地利用类型遥感解译结果、社会经济统计数据以及水质监测数据的基础上,采用主成分分析和灰色关联度分析对研究区水质变化驱动力进行比较分析,为探究土地利用变化与社会经济发展对水库水质的影响。结果表明,东江湖流域的土地利用类型以林地为主,大通湖流域以耕地为主,水府庙水库流域内耕地和林地比例差异较为相似。土地利用类型和人类活动对3个水库的影响程度存在差异,东江湖水质变化的主要驱动因子为经济因素、林地及建设用地的面积比例。水府庙水库的水质变化主要驱动力为经济因素、建设及耕地面积比例的变化。大通湖水质变化的主要驱动力是经济因素、人口因素以及建设用地面积比例变化。湖泊受污染情况是大通湖水府庙水库东江湖。     

Isotopic composition of old ground water from lake agassiz: implications for late pleistocene climate

A uniform oxygen isotope value of -25 per mil was obtained from old ground water at depths of 20 to 30 meters in a thick deposit of clay in the southern part of the glacial Lake Agassiz basin. The lake occupied parts of North Dakota and southern Manitoba at the end of the last glacial maximum and received water from the ice margin and the interior plains region of Canada. Ground water from thick late Pleistocene-age clay deposits elsewhere, a till in southern Saskatchewan, and a glaciolacustrine deposit in northern Ontario show the same value at similar depths. These sites are at about 50 degrees N latitude, span a distance of 2000 kilometers, and like the Lake Agassiz sites, have a ground-water velocity of less than a few millimeters per year. The value of -25 per mil is characteristic of meltwater impounded in the southern basin of Lake Agassiz. This value corresponds to an estimated air temperature of -16 degrees C, compared with the modern temperature of 0 degrees C for this area.     

青海湖流域蒸发皿蒸发量及其影响因素的变化特征

[目的]研究青海湖流域1961～2007年蒸发皿蒸发量及其影响因素的变化特征。[方法]采用气候倾向率方法,对青海湖流域1961～2007年20 cm小型蒸发皿蒸发量及其影响气候因子的变化趋势进行了分析。[结果]近47年来,青海湖流域的蒸发皿蒸发量呈现出减少的趋势,倾向率为-47.75 mm/10a。各季节的蒸发量除秋季没有变化外,其他各季以7.33～19.57 mm/10a的速率减小,其中春季减幅最大,冬季减幅最小;就变化趋势的空间特征而言,青海湖流域各站的年蒸发皿蒸发量除刚察站外,其他各站均表现为不同程度的减少趋势,减幅为32.36～75.63 mm/10a。蒸发皿蒸发量的减少幅度随着经度的增加而减少。影响蒸发皿蒸发量的日照时数呈显著下降趋势,夏季降水量显著增加,平均气温显著升高,平均最低气温的升高速率比平均最高气温的升高速率大,导致气温日较差减小,对蒸发也会产生影响。[结论]该研究对更好地了解青海湖流域对气候变化的响应以及该区域的水资源管理均具有十分重要的意义。     

静脉河道负荷削减工程及其效果分析

在分析太湖流域入湖河流水环境现状的基础上,通过负荷削减工程的实施,使河网水质达到功能区要求,削减入湖河流的污染物排放总量,从而降低太湖污染负荷。以武进港流域的建华河、跃进河、红旗河等8条河为研究对象,开展了静脉河道负荷削减技术研究,对8个负荷削减工程的运行效果进行比较,研究出适用于流域河网地区的负荷削减技术,包括垂向移动式生态床技术、生物接触氧化技术、生态浮岛技术等。负荷削减效果表明,该技术可有效去除静脉河道低中度污染水中的N、P等污染物质,并具有良好的生态景观效果。通过进一步优化,可形成适合于太湖流域河网地区水环境质量改善和生态修复的关键技术。太湖流域的污染负荷主要来自入湖河流,开展入湖河流水环境综合治理对太湖流域水环境和湖体富营养化改善具有重要的意义。     

Deposit from a giant wave on the island of lanai, hawaii

Limestone-bearing gravel, the newly named Hulopoe Gravel, blankets the coastal slopes on Lanai. The deposit, which reaches a maximum altitude of 326 meters, formerly was believed to have been deposited along several different ancient marine strandlines, but dated submerged coral reefs and tide-gauge measurements indicate that the southeastern Hawaiian Islands sink so fast that former worldwide high stands of the sea now lie beneath local sea level. Evidence indicates that the Hulopoe Gravel and similar deposits on nearby islands were deposited during the Pleistocene by a giant wave generated by a submarine landslide on a sea scarp south of Lanai.     

开县蔬菜基地土壤对汉丰湖水质的影响

为了解三峡水库蓄水后被淹没的肥沃土壤对"汉丰湖"水质的影响,结合2007年开县环境监测站对开县156～175m水位线以下的蔬菜基地的调查监测数据,对"汉丰湖"存在的污染贡献和成库后潜在的环境风险进行研究。结果表明,部分监测点总汞、总镍超标;部分监测点总磷和化学需氧量达到清库标准要求,为政府制定措施提供技术参考和理论依据。     

Holocene sea-level curves for santa monica shelf, california continental borderland

A curve is constructed showing changes in sea level at the Santa Monica shelf over the past 18,000 years. The curve is based on radiocarbon dates, sedimentologic data, and high-resolution seismic stratigraphic analysis of late Quaternary terrace deposits. Sea level was 117 meters below its present position about 18,000 years ago. During the first 8000 years of the Flandrian transgression, sea level rose to at least 24 meters, fell to about 46 meters, and then rose to 20 meters, all below present sea level. Subsequently, sea level rose more slowly and without discernible interruption to its present position.     

Evidence for Glacial Control of Rapid Sea Level Changes in the Early Cretaceous

Lower Cretaceous bulk carbonate from deep sea sediments records sudden inputs of strontium resulting from the exposure of continental shelves. Strontium data from an interval spanning 7 million years in the Berriasian-Valanginian imply that global sea level fluctuated about 50 meters over time scales of 200,000 to 500,000 years, which is in agreement with the Exxon sea level curve. Oxygen isotope measurements indicate that the growth of continental ice sheets caused these rapid sea level changes. If glaciation caused all the rapid sea level changes in the Cretaceous that are indicated by the Exxon curve, then an Antarctic ice sheet may have existed despite overall climatic warmth.     

小兴安岭不同年龄林分对气候变化的潜在响应

应用林窗模型LINKAGES分别对小兴安岭原始林不同年龄林分在5种气候变暖情景下的未来演替动态进行了模拟预测.5种气候变暖情景分别为:OSU、GISS、GFDL、UKMO和CGCM2.不同年龄林分的运行结果均表明:在OSU、GISS情景下,温度升高较平缓,小兴安岭的主要树种分布基本保持现有状态,总生物量有升高趋势;在GFDL、UKMO温度大幅度升高情景下,小兴安岭森林不能适应生态环境的急剧改变,存在全部衰退的可能;而CGCM2情景下,红松生物量先上升后下降,红松针阔混交林将逐渐演替为以色木槭和蒙古栎占优势的阔叶混交林.不同年龄林分间比较发现:当增温幅度未超过红松的耐受范围时,过熟林对气候变化的抗干扰能力显著优于其他林龄类型,但总生物量水平略低;中幼林对气候变化的适应能力最强,能够在气候变化过程中朝着最有利于充分利用光照、养分等环境因子的方向演替,树种组成达到稳定后的总生物量水平通常最高.反之,当超过红松的耐受范围时,过熟林的抗干扰能力和恢复能力均下降,表现为林分的迅速衰退及总生物量的明显波动;中幼林对气候变化的适应能力仍然较强,演替动态最平稳.