华南地区二叠纪-三叠纪界线酸性火山灰的源区与规模

华南地区二叠纪-三叠纪之交(Permian-Triassic Boundary,简称PTB)火山灰与生物灭绝事件在地层层位上高度相关,可能是灭绝事件的触发因素之一,对其成因、来源和规模的研究具有重要科学意义。本研究在对广西来宾地区蓬莱滩剖面大隆组顶部凝灰质砂岩岩相学研究的基础上,通过碎屑锆石年代学、Hf同位素及微量元素的分析,结合华南地区PTB凝灰岩和火山粘土岩时空分布特征对其源区和规模进行讨论和限定。蓬莱滩剖面大隆组顶部2个凝灰质砂岩样品中81%的碎屑锆石U-Pb年龄集中在235±2.7Ma~258±4.8Ma之间,呈现出~252Ma的单一峰值;11%的锆石年龄为260±3.2Ma~276±3.6Ma;年龄为294±5.8Ma~561±6.9Ma的锆石6颗;元古宙锆石5颗,最老年龄为2063±13.4Ma。样品中晚二叠世碎屑锆石的Hf同位素表现出地壳来源特征,除一颗锆石值为+10.3外,其余均落在-16.5~-5.0之间,与华南PTB典型剖面基本一致。碎屑锆石U-Th-Hf-Nb微量元素特征显示其具有来源于大陆岩浆弧的属性。蓬莱滩剖面凝灰质砂岩中存在大量粒径0.5~2mm的晶屑,部分粒径甚至达到3mm,这些粗粒火山碎屑物暗示该剖面距离火山口源区较近。蓬莱滩剖面火山碎屑物的锆石U-Pb年龄和地层位置与华南PTB火山灰基本一致,并具有相似的锆石Hf同位素和微量元素特征,表明两者可能来自同一源区。在空间分布上,华南地区PTB附近的火山碎屑沉积岩和较粗的凝灰岩仅出现在华南的西南部,而华南北部主要分布粒度小于0.3mm的细粒火山灰,火山碎屑粒度由西南向东北逐渐减小的规律表明火山物质来源于华南西南缘。近年来,包括海南岛二叠纪花岗岩及桂西南酸性火山岩在内的众多证据表明华南板块西南缘存在一个二叠纪大陆岩浆弧。因此,本文提出华南PTB火山灰可能来源于华南板块西南缘古特提斯大陆岩浆弧。PTB火山灰仅分布在华南地区,在华北、西北等地区均未发现或报道同时期的火山灰,说明与这次俯冲作用相关的弧岩浆火山喷发规模有限,推测其不是触发全球性PTB生物灭绝事件的主要原因。     

丽江高美古的大气消光系数测定

１９９６年１－２月，我们用光电方法测定了丽江高美古在Ｂ、Ｖ两个波段的大气消光系数。为便于比较，在同一时期还测定了云南天文台凤凰山台址的大气消光系数。本文给出了观测结果，同时也列出了世界上一些天文台站的数据以供参考。     

2007年冬季大连市区气溶胶垂直剖面特征

选用2007年1月8—30日期间8个无云天的激光雷达资料进行分析。基于Fernald方法反演得到气溶胶消光系数廓线,结合无线电探空资料分析了边界层内气溶胶时空分布,并将反演的激光雷达最低观测高度处(180 m)的气溶胶消光系数与地面PM10、能见度资料进行对比分析。结果表明：冬季大连市区气溶胶主要分布在2 km以下区域,早晨和夜间在0.5 km以下区域经常存在一个气溶胶层;气溶胶消光系数廓线与探空资料较吻合;反演激光雷达最低观测高度处(180 m)的气溶胶消光系数与地面的PM10浓度呈正相关,与能见度呈负相关,相关性较好。     

Intrabasin variability of the carbon-isotope record across the Permian–Triassic transition, Sverdrup Basin, Arctic Canada

A major late Paleozoic depocentre, the Sverdrup Basin, Canadian High Arctic, has been largely left out of the latest Permian extinction debate, as early workers presumed Middle to Late Permian strata were absent. Basin-scale sequence-stratigraphic and chemostratigraphic correlations indicate Late Permian strata are only missing on the basin margins, where they were removed by sub-Triassic erosion, whereas continuous deposition is recorded in the basin centre. The varying degree of sub-Triassic erosion has significant impact on the carbon-isotope record across the Latest Permian Extinction event, where both the apparent rate and magnitude of carbon-isotope shift vary as a function of basin position. The intrabasin variability in apparent δ¹³C_org shift across the event is equivalent to that observed globally. In contrast to the abrupt isotope shifts recorded on the basin margin, similar to many records reported globally, the basin centre section shows a systematic shift associated with the Latest Permian Extinction. The Earth likely underwent a prolonged period of increasing environmental stress leading up to the event.     

省级MODIS植被指数序列的建立与应用

本文采用安德森分级采样直接获得的大气气溶胶质量密度换算成数密度。在此基础上,根据气溶胶数密度谱分布,验证了大气气溶胶的Junge谱与分段三参数谱相结合的谱模式。并且在得出气溶胶粒子谱基础上计算了大气气溶胶的散射、消光、吸收系数。     

Phylogeny, diet, and habitat of an extinct ground sloth from Cuchillo Curá, Neuquén Province, southwest Argentina

Advancements in ancient DNA analyses now permit comparative molecular and morphological studies of extinct animal dung commonly preserved in caves of semiarid regions. These new techniques are showcased using a unique dung deposit preserved in a late glacial vizcacha (Lagidium sp.) midden from a limestone cave in southwestern Argentina (38.5° S). Phylogenetic analyses of the mitochondrial DNA show that the dung originated from a small ground sloth species not yet represented by skeletal material in the region, and not closely related to any of the four previously sequenced extinct and extant sloth species. Analyses of pollen and plant cuticles, as well as analyses of the chloroplast DNA, show that the Cuchillo Curá ground sloth browsed on many of the same herb, grass, and shrub genera common at the site today, and that its habitat was treeless Patagonian scrub-steppe. We envision a day when molecular analyses are used routinely to supplement morphological identifications and possibly to provide a time-lapse view of molecular diversification.     

Latest Pleistocene paleoecology of Jefferson's ground sloth (Megalonyx jeffersonii) and elk-moose (Cervalces scotti) in northern Illinois

New records of Jefferson's ground sloth (Megalonyx jeffersonii) and elk-moose (Cervalces scotti) from Lang Farm provide the first precise temporal correlation of these taxa with the specific environments inhabited by them near the time of their extinction. Six AMS ¹⁴C measurements establish an age of 11,405 ± 50 ¹⁴C yr B.P. for Lang Farm Cervalces and an age of 11,430 ± 60 or 11,485 ± 40 ¹⁴C yr B.P. for the Megalonyx. These measurements represent the youngest ¹⁴C dates for these two genera based on direct dating. Comparison of the dates with pollen data from northern Illinois indicates that these species inhabited a nonanalog environment that was transitional from mid-latitude tundra to mixed conifer and deciduous woodland. Although spruce (Picea sp.) was dominant, it was less abundant than prior to 12,500 ¹⁴C yr B.P. The presence of black ash (Fraxinus nigra) and fir (Abies sp.) indicates a wet climate and heavy winter precipitation. This may have been the preferred habitat for Cervalces because of its narrow geographic range. However, this habitat type was only one of many occupied by Megalonyx as indicated by its broad geographic distribution.     

Contemporary management issues confronting fisheries science

Stock collapses have occurred worldwide. The most frequently cited cause is over-fishing, suggesting that fisheries management has been ineffective in controlling exploitation rates. The progression of a fishery from an over-exploited to a collapsed state involves impairment of the reproductive capacity of the target species, i.e. recruitment over-fishing. In many cases, this occurs by reduction of the spawning stock biomass (SSB) through the systematic elimination of spawning components within a stock complex. While operational definitions of minimum levels of SSB have been developed, they have seldom been applied and never adopted in a Canadian groundfish management context. The answer to the question of how much is enough to perpetuate a stock under exploitation has been illusive. Serebryakov [J. Cons. Int. Explor. Mer, 47 (1990) 267] has advocated definition of critical levels of SSB based on survival rates (R/SSB). We review his method and discuss the utility of the approach. An alternative approach to the problem of estimating minimum SSB is through a fundamental revision of the traditional stock and recruitment relationship. Explicit theoretical SSB thresholds below which reproduction/recruitment is severely impaired based upon density-dependent mating success (or Allee effects) is considered a superior approach to the question of how much is enough because of its ecological grounding. However, the successful application of this approach will require re-definition of the space/time scales of the management unit. Finally, support is growing for the establishment of closed areas or “no-take zones” as an alternative approach to managing the problems of fishing a stock complex by enabling sub-populations to escape fishing. While the expected benefits of areas protected from fishing are numerous, clear demonstrations of benefits of such areas in marine temperate ecosystems are lacking. In fact, unintended negative consequences may result from such actions.     

Airborne Laser Sensing of Scottish Coastal Waters

An Nd:YAG-based airborne lidar system has been used to measure the optical properties of littoral waters off the northwest Scottish coast. The small-scale structure of subsurface scattering layers was also investigated. Methods of solving the Lidar Sensing Equation in the single scattering approximation are described and the values of the derived extinction indices presented. The extinction index averaged over a series of five flights to the northeast of the Gulf Stream was ε= 0.224 m -1 with a standard deviation of 0.212 m -1 . Further, it was demonstrated that, in coastal waters, optical inhomogeneities with dimensions between 50 m and 200 km obey the power law Sp ε ~ k -P with the parameter P close to two. In turbid or transparent areas, the water extinction index can change by several tenths of a percent with respect to the surrounding water mass. This suggests that the observed nonmonotonic behavior of the power spectra of the water extinction index fluctuations is caused by the outer scale of turbulence, in particular, by the bottom depth at the measurement site.