Fallout of pyroclastic debris from submarine volcanic eruptions

Volcanic fallout deposits on land, being widespread and accessible for study, have received much attention and have revealed a great deal about subaerial eruption mechanisms. In contrast, virtually nothing is known about equivalent deposits produced by submarine volcanoes, despite the probable abundance of such material in today's oceans and in accreted volcanic arc terrains. Many submarine deposits may form by the fallout of debris to the sea floor downcurrent from the umbrella region of submarine eruption columns. Experiments on water-saturated pumice and pieces of rock (lithics) show that particles settling to the sea floor at terminal velocities of 10 to 50 centimeters per second will display conspicuous bimodality of particle diameters: pieces of pumice may be five to ten times as large as codeposited lithic fragments. Similar material, erupted into the air and deposited on land, displays less well-developed bimodality; pumice diameters are generally two to three times as large as associated lithics. Submarine fallout deposits are therefore distinctive and may be used to indicate a subaqueous origin for some of the great thicknesses of nonfossiliferous volcanic debris contained in ancient volcanic terrains worldwide whose environment of deposition has been uncertain.     

Three-dimensional splay fault geometry and implications for tsunami generation

Megasplay faults, very long thrust faults that rise from the subduction plate boundary megathrust and intersect the sea floor at the landward edge of the accretionary prism, are thought to play a role in tsunami genesis. We imaged a megasplay thrust system along the Nankai Trough in three dimensions, which allowed us to map the splay fault geometry and its lateral continuity. The megasplay is continuous from the main plate interface fault upwards to the sea floor, where it cuts older thrust slices of the frontal accretionary prism. The thrust geometry and evidence of large-scale slumping of surficial sediments show that the fault is active and that the activity has evolved toward the landward direction with time, contrary to the usual seaward progression of accretionary thrusts. The megasplay fault has progressively steepened, substantially increasing the potential for vertical uplift of the sea floor with slip. We conclude that slip on the megasplay fault most likely contributed to generating devastating historic tsunamis, such as the 1944 moment magnitude 8.1 Tonankai event, and it is this geometry that makes this margin and others like it particularly prone to tsunami genesis.     

沿海半城市化地区特征及土地利用变化分析——以福建省厦门市集美区为例

以福建省厦门市集美区为例,分析集美区人口、经济、产业、用地景观等方面所表现出来的半城市化现象基本特征。并基于研究区1987～2007年5期TM／ETM＋遥感影像数据分析其20年土地利用时空动态变化特征及土地利用存在的问题。结果表明,集美区具有典型的半城市化地区的特征,20年间建设用地大量增加,耕地面积急剧减少。城市建设用地增长最快,其扩展主要是通过侵占耕地和未利用地;未利用地的增加主要来自耕地的转化。耕地主要流向建设用地、未利用地和林地。淡水水域被转化为建设用地和未利用地。耕地是在城市化过程中最容易受到侵占的土地利用类型。随着快速城市化的发展,半城市化地区的耕地、湿地（包括滩涂和近海海域）面积明显减少,致使其提供的生态系统服务功能降低,必将引起一系列生态环境问题,生态环境的恶化反过来又制约着经济的进一步发展．因此应重视半城市化地区土地利用的规划与管理,促进区域的可持续发展。     

基于GIS的北京市海淀区土地利用强度三维定量评价

城市土地利用强度定量研究是我国土地利用规划中的重要内容与难点。在此提出了一套基于层次分析法,以GIS技术为支撑,以建筑密度与建筑容积率、土地利用现状、交通密度、人口密度为主要指标的新方法,用于城市土地利用强度的三维定量评价,并以北京市海淀区东区为例进行了实证分析。研究结果表明,这套方法可以快速、便捷、准确的定量评价城市土地利用强度,并为城市土地利用规划决策提供科学有效的基础数据。     

Freshwater peat on the continental shelf

Freshwater peats from the continental shelf off northeastern United States contain the same general pollen sequence as peats from ponds that are above sea level and that are of comparable radiocarbon ages. These peats indicate that during glacial times of low sea level terrestrial vegetation covered the region that is now the continental shelf in an unbroken extension from the adjacent land areas to the north and west.     

Satellite observations of lightning

Analysis of the positions of nighttime thunderstorms as determined from the detection of optical radiation by satellite OSO-B reveals that ten times as many lightning storms occur over land areas as over the sea.     

海域使用权变换为土地使用权若干问题探索

阐述了"海变地"海域使用权的性质、权能及公法难题,分析了海域使用权变换登记的类型、效力及要件:《海域使用管理法》和《物权法》明确了海域使用权是一项物权,把海域变成土地并在其上开展建设活动,是"海变地"海域使用权的前后相继、不可分割的两项权能;新出台的《不动产登记暂行条例》规定,海域使用权和林权、建设用地使用权等都将登记在不动产登记簿上,海域使用权和土地使用权都将由国土部门统一登记。     

区域容积率对基准地价的影响及修正研究—以河北省滦县为例

容积率是影响地价的重要因素之一,容积率修正系数直接关系到基准地价的评估与应用精度。在综合分析文献的基础上,以河北省滦县为例,分析了区域容积率对地价及基准地价的影响规律,利用高光谱遥感和实地校正等方法确定标准容积率,并找出容积率与其修正系数的关系,建立容积率修正体系的对数模型;验证了容积率对地价的影响规律,同时建立了容积率与土地集约利用程度的关系。     

Insular erosion, isostasy, and subsidence

Organic reefs and shore erosion record the intersection of sea level with islands. From this record it is possible to reconstruct the history of vertical movement of the islands and the adjacent deep sea floor, including midplate swells. As judged by coral thickness, islands with barrier reefs sink as though they were on thermally youthful crust regardless of the actual age. Reefless islands do not sink until truncated by erosion. Apparently, thermal subsidence is balanced by isostatic uplift in response to erosion. Barrier reefs prevent wave erosion of encircled volcanoes and capture products of stream erosion so that isostatic uplift is eliminated. Insular shelves widen initially at rates of 0.6 to 1.7 kilometers per million years; the rates decrease with time. Thus the subsidence of islands depends on the size of the is land and the presence of reefs, and it may not always be the same as that of the surrounding oceanic crust.     

Extending the sub-sea-floor biosphere

Sub-sea-floor sediments may contain two-thirds of Earth's total prokaryotic biomass. However, this has its basis in data extrapolation from ~500-meter to 4-kilometer depths, whereas the deepest documented prokaryotes are from only 842 meters. Here, we provide evidence for low concentrations of living prokaryotic cells in the deepest (1626 meters below the sea floor), oldest (111 million years old), and potentially hottest (~100 degrees C) marine sediments investigated. These Newfoundland margin sediments also have DNA sequences related to thermophilic and/or hyperthermophilic Archaea. These form two unique clusters within Pyrococcus and Thermococcus genera, suggesting unknown, uncultured groups are present in deep, hot, marine sediments (~54 degrees to 100 degrees C). Sequences of anaerobic methane-oxidizing Archaea were also present, suggesting a deep biosphere partly supported by methane. These findings demonstrate that the sub-sea-floor biosphere extends to at least 1600 meters below the sea floor and probably deeper, given an upper temperature limit for prokaryotic life of at least 113 degrees C and increasing thermogenic energy supply with depth.     

工业化、城镇化背景下农村居民点内部土地利用演变

为分析工业化、城镇化背景下农村居民点用地演变规律,以河北省东马营村为例,采用参与式农村评估、ArcGIS矢量化等方法,分析其工业化发展历程,并选取扩展强度指数、容积率、吉布斯-马丁多样化指数等指标,在微观尺度上对农村居民点内部土地利用动态演变及其驱动过程进行研究分析。结果表明:1)1985—2015年,东马营村箱包工业的发展导致当地经济非农化、农户从业结构非农化,当地纯农型农户所占比例不足1%,其显然已经不是传统意义上的农村;2)东马营村农村居民点的用地规模、扩展强度、多样性、建设面积与建筑面积等持续增长,其动态演变是与工业化发展历程相适应的。研究认为,未来应借助村级土地利用规划编制工作,通过农村土地整理、复垦等缓解快速工业化农村地区的建设用地供需矛盾,同时应做好耕地流转,提高耕地利用效率。     

Geothermal convection through oceanic crust and sediments in the Indian ocean

Closely spaced heat flow surveys at four sites on the flanks of the Central Indian Ridge and the Southeast Indian Ridge delineate a pattern of oscillatory heat flow which can only result from cellular convection of oceanic bottom water through the oceanic crust and overlying sediment. These cells have a wavelength of 5 to 10 kilometers and are presently active in sea floor 18 x 10(6), 25 x 10(6), and 45 x 10(6) years old of the Crozet Basin and in sea floor 55 x 10(6) years old of the Madagascar Basin. The precise measurement of nonlinear temperature profiles makes it possible to calculate the conductive and convective heat transfer components through the sea floor. Even in the oldest sites, geothermal convection is still a major component of heat transfer through both the crust and sedimentary layers. These observations coupled with the results of earlier oceanwide geothermal studies indicate that more than one-third of the entire surface area of the world's ocean floor contains presently active geothermal convection that is cellular in plan form.     

Deep-sea erosion and manganese nodule development in the southeast Indian ocean

Features exhibited by a large number of sea floor photographs together with the dating of 187 sediment cores from the southeast Indian Ocean have revealed extensive manganese nodule development and sediment erosion in deep basinal areas. The most extensive nodule field, with an area of 10(6) square kilometers, occurs in the northwestern sector of the South Australian Basin and is named the Southeast Indian Ocean Manganese Pavement. The crests and flanks of the adjacent mid-ocean ridge are, in contrast, free of nodules and marked by much less dynamic bottom water conditions.     

Atmospheric carbon dioxide levels over phanerozoic time

A new model has been constructed for calculating the level of atmospheric CO(2) during the past 570 million years. A series of successive steady states for CO(2) is used in order to calculate CO(2) level from a feedback function for the weathering of silicate minerals. Processes considered are: sedimentary burial of organic matter and carbonates; continental weathering of silicates, carbonates, and organic matter; and volcanic and metamorphic degassing of CO(2). Sediment burial rates are calculated with the use of an isotope mass-balance model and carbon isotopic data on ancient seawater. Weathering rates are calculated from estimates of past changes in continental land area, mean elevation, and river runoff combined with estimates of the effects of the evolution of vascular land plants. Past degassing rates are estimated from changes in the rate of generation of sea floor and the shift of carbonate deposition from platforms to the deep sea. The model results indicate that CO(2) levels were high during the Mesozoic and early Paleozoic and low during the Permo-Carboniferous and late Cenozoic. These results correspond to independently deduced Phanerozoic paleoclimates and support the notion that the atmospheric CO(2) greenhouse mechanism is a major control on climate over very long time scales.     

Molecular fossil record of elevated methane levels in late Pleistocene coastal waters

Accumulating evidence suggests that methane has been released episodically from hydrates trapped in sea floor sediments during many intervals of rapid climate warming. Here we show that sediments from the Santa Barbara Basin deposited during warm intervals in the last glacial period contain molecular fossils that are diagnostic of aerobic and anaerobic methanotrophs. Sediment intervals with high abundances of these compounds indicate episodes of vigorous methanotrophic activity in methane-laden water masses. Signals for anaerobic methanotrophy in 44,100-year-old sediment are evidence for particularly intense methane emissions and suggest that the basin's methane cycle can profoundly affect oxygen budgets in the water column.     

Sediment distribution on the mid-ocean ridges with respect to spreading of the sea floor

An abrupt change in sediment thickness between the crests and flanks of the mid-ocean ridges can be interpreted as a major discontinuity in the rates either of spreading of the sea floor or of accumulation of sediment. The preferable interpretation of the data is that the process of spreadig of the sea floor is intermittent and that the present cycle of spreading commenced around 10 million years ago. following a long period Of quiescence during which most of the observed sediments were deposited.     

Recent emerged beach in eastern Mexico

A bluff on the eastern coast of Mexico reveals a cross section through an ancient beach deposit now lying 4 meters above sea level. Radio-carbon dates on the shells within the deposit reveal an age of 1940 years. The deposit appears to be valid evidence for submergence greater than that of the present, but whether that submergence was due to a higher eustatic stand of the sea or whether there has been an uplift of the land since that time cannot yet be determined.     

租佃制是具有活力的土地流转方式

历来中国农村自始至终存在着两种经济成分：一种是自给自足的小农经济,即所谓“编户齐民”似“汪洋大海”的小农经济。另一种是地主经济,他们依靠其社会政治、经济地位优势,占有超常的土地,控制劳动力,用剥削方式从事生产经营。地主土地的经营方式归纳起来大致有三种：蓄养农奴耕作、雇工耕作和出租给佃户耕作。宋代以后广泛实行的租佃制是历史选择的结果。租佃制促进了土地权属的流转,目前土地租赁在农业经营中依然存在活力。     

Alteration of oceanic volcanic glass: textural evidence of microbial activity

The subsurface biosphere may constitute as much as 50 percent of Earth's biomass. Direct and indirect evidence suggests that an extensive biosphere exists in the rocks below the sea floor. This survey of basalts of the Atlantic, Pacific, and Indian Oceans supports the hypothesis that bacteria have colonized much of the upper oceanic crust, which has a volume estimated at 10(18) cubic meters. Although this is the largest habitat on Earth, its low abundance of bacteria constitutes much less than 1 percent of Earth's biomass.     

In situ measurements of chemical distributions in a deep-sea hydrothermal vent field

Large changes in the concentration of sulfide around a hydrothermal vent in the Galápagos Rift provide direct evidence for the consumption of sulfide by the organisms of the vent community. These changes were detected with a new chemical analyzer capable of measuring silicate, sulfide, oxygen, and temperature on the sea floor at depths of 2500 meters. More than 10,000 measurements showed systematic variations in the sulfide and oxygen concentrations due to biogenic oxidation of sulfide in the hydrothermal solutions. Silicate concentration was highly correlated with temperature, but different trends were observed at different locations.