Natural variability of Greenland climate, vegetation, and ice volume during the past million years

The response of the Greenland ice sheet to global warming is a source of concern notably because of its potential contribution to changes in the sea level. We demonstrated the natural vulnerability of the ice sheet by using pollen records from marine sediment off southwest Greenland that indicate important changes of the vegetation in Greenland over the past million years. The vegetation that developed over southern Greenland during the last interglacial period is consistent with model experiments, suggesting a reduced volume of the Greenland ice sheet. Abundant spruce pollen indicates that boreal coniferous forest developed some 400,000 years ago during the "warm" interval of marine isotope stage 11, providing a time frame for the development and decline of boreal ecosystems over a nearly ice-free Greenland.     

Rapid variability of seawater chemistry over the past 130 million years

Fluid inclusion data suggest that the composition of major elements in seawater changes slowly over geological time scales. This view contrasts with high-resolution isotope data that imply more rapid fluctuations of seawater chemistry. We used a non-steady-state box model of the global sulfur cycle to show that the global δ(34)S record can be explained by variable marine sulfate concentrations triggered by basin-scale evaporite precipitation and dissolution. The record is characterized by long phases of stasis, punctuated by short intervals of rapid change. Sulfate concentrations affect several important biological processes, including carbonate mineralogy, microbially mediated organic matter remineralization, sedimentary phosphorous regeneration, nitrogen fixation, and sulfate aerosol formation. These changes are likely to affect ocean productivity, the global carbon cycle, and climate.     

Oxygen isotope constraints on the sulfur cycle over the past 10 million years

Oxygen isotopes in marine sulfate (delta18O(SO4)) measured in marine barite show variability over the past 10 million years, including a 5 per mil decrease during the Plio-Pleistocene, with near-constant values during the Miocene that are slightly enriched over the modern ocean. A numerical model suggests that sea level fluctuations during Plio-Pleistocene glacial cycles affected the sulfur cycle by reducing the area of continental shelves and increasing the oxidative weathering of pyrite. The data also require that sulfate concentrations were 10 to 20% lower in the late Miocene than today.     

The rise of oxygen over the past 205 million years and the evolution of large placental mammals

On the basis of a carbon isotopic record of both marine carbonates and organic matter from the Triassic-Jurassic boundary to the present, we modeled oxygen concentrations over the past 205 million years. Our analysis indicates that atmospheric oxygen approximately doubled over this period, with relatively rapid increases in the early Jurassic and the Eocene. We suggest that the overall increase in oxygen, mediated by the formation of passive continental margins along the Atlantic Ocean during the opening phase of the current Wilson cycle, was a critical factor in the evolution, radiation, and subsequent increase in average size of placental mammals.     

Role of seasonality in the evolution of climate during the last 100 million years

A simple climate model has been used to calculate the effect of past changes in the land-sea distribution on the seasonal cycle of temperatures during the last 100 million years. Modeled summer temperatures decreased over Greenland by more than 10 degrees C and over Antarctica by 5 degrees to 8 degrees C. For the last 80 million years, this thermal response is comparable in magnitude to estimated atmospheric carbon dioxide effects. Analysis of paleontological data provides some support for the proposed hypothesis that large changes due to seasonality may have sometimes resulted in an ice-free state due to high summer temperature rather than year-round warmth. Such "cool" non-glacials may have prevailed for as much as one-third of the last 100 million years.     

Lichen-like symbiosis 600 million years ago

The fossil record of fungi and lichens is scarce. Here we report the discovery of lichen-like fossils, involving filamentous hyphae closely associated with coccoidal cyanobacteria or algae, preserved in marine phosphorite of the Doushantuo Formation (between 551 and 635 million years old) at Weng'an, South China. These fossils indicate that fungi developed symbiotic partnerships with photoautotrophs before the evolution of vascular plants.     

Flood volcanism in the northern high latitudes of Mercury revealed by MESSENGER

MESSENGER observations from Mercury orbit reveal that a large contiguous expanse of smooth plains covers much of Mercury's high northern latitudes and occupies more than 6% of the planet's surface area. These plains are smooth, embay other landforms, are distinct in color, show several flow features, and partially or completely bury impact craters, the sizes of which indicate plains thicknesses of more than 1 kilometer and multiple phases of emplacement. These characteristics, as well as associated features, interpreted to have formed by thermal erosion, indicate emplacement in a flood-basalt style, consistent with x-ray spectrometric data indicating surface compositions intermediate between those of basalts and komatiites. The plains formed after the Caloris impact basin, confirming that volcanism was a globally extensive process in Mercury's post-heavy bombardment era.     

近62年来汉中市极端降水变化研究

【目的】对汉中市极端降水事件的变化趋势进行研究,为汉中地区防洪减灾和水资源调控决策提供参考依据。【方法】利用1951-2012年的汉中市逐日降水资料,采用百分位阈值划分极端降水事件,并通过滑动平均、Mann-Kendall检验、趋势分析等方法,对汉中市极端降水事件的变化趋势进行研究。【结果】近62年来,汉中市年极端降水量、年极端降水日数及年极端降水强度以年代际尺度波动变化,但总体略呈下降趋势,且年极端降水量的下降速率为-0.5mm/年。但在1987年之后,各项极端降水指标均呈明显增加趋势,年极端降水量和年极端降水日数呈显著的线性增加趋势,年极端降水量增加速率达7.52mm/年。2006-2008年,汉中市年最大日降水量、年极端降水量、年极端降水强度呈显著增多增强趋势。【结论】进入21世纪后,汉中市极端降水事件引发的自然灾害呈增加趋势,应加强调控及防治能力,预防洪涝灾害的发生。     

近10年中国土地评价研究进展

以土地评价为研究对象,通过查阅和分析近10年来中外学者发表的相关学术论文,介绍了土地评价的方法以及与GIS的综合应用,探讨了农用地评价、土地资源、适宜性和可持续性评价以及应用等方面的发展状况.     

Seven million years of glaciation in greenland

Glacial till, glaciomarine diamictites, and ice-rafted detritus found in marine cores collected off the shore of southeast Greenland record multiple Late Cenozoic glaciations beginning in the Late Miocene. Distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast Greenland margin. Glaciers advanced to the sea during several intervals in the Pliocene and Pleistocene. North Atlantic glaciation may have nucleated in southern Greenland rather than further north because of the high mountains and the high levels of precipitation in this region.     

Genome size in conodonts (chordata): inferred variations during 270 million years

DNA is too unstable to be preserved during fossilization, but it still seems possible to infer the genome content of fossils because in every group of organisms investigated cell size is proportional to quantity of DNA. Accordingly, information on macroevolutionary trends in genome size through millions of years is potentially available. This survey of inferred variation in genome content in fossils is based on measurements of epithelial cells in extinct conodonts over a period of 270 million years. Why genome size varies so widely amongst living organisms is a subject of continuing debate. Paleontology offers a distinct temporal perspective, but lack of data on conodont paleoecology make the proposed adaptive explanations for genome variation difficult to test.     

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.     

广西大豆育种四十年进展与展望

[目的]总结分析改革开放四十年以来广西大豆育种进展,并结合广西大豆生产需求和自身优势,对今后广西大豆育种提出相关建议,为广西大豆产业发展提供理论依据.[方法]根据公开发表文献资料及育种单位提供的内部材料,从遗传育种研发体系、新品种选育及推广、优异种质鉴评与育种亲本创制、育种方法与技术创新等方面,对改革开放开始—"八五"(S6.5-8.5)、"九五"—"十五"(S9.5-10.5)、"十一五"(S11.5)和"十二五"至今(S12.5-)4个时期的广西大豆育种进展进行总结分析,并提出今后广西大豆育种研究方向和侧重点.[结果]广西大豆育种项目、经费及其来源均迅速增加,其中项目由S6.5-8.5时期的2个增加至S12.5-的23个,经费由S6.5-8.5时期的5万元增加至S12.5-时期的1260万元,S11.5时期起建成5个大豆育种平台.至今,正式通过审定命名的大豆品种共39个,其中春大豆28个,夏大豆11个;通过国家农作物品种审定委员会和广西农作物品种审定委员会双审定品种3个,国家农作物品种审定委员会审定品种5个,广西农作物品种审定委员会审定品种31个;S6.5-8.5、S9.5-10.5、S11.5和S12.5-时期分别有4、10、12和13个品种通过审定;37个通过有性杂交选育而成,2个通过系统选育而成;高蛋白品种15个,高油品种2个,双高品种4个,菜用品种1个、高异黄酮品种2个、高抗镉金属品种2个.39个大豆品种共追溯到40个祖先亲本,平均每个育成品种有1.03个,高于全国平均水平(0.52个),且祖先亲本中,有11个是广西本地种质,占27.5%;有22个是我国其他省(区)种质,占55.0%;有7个是国外种质,占17.5%.春大豆育种骨干亲本9个,夏大豆育种骨干亲本6个.优良大豆新品种的育成及大面积推广,获省部级科技进步奖7项.广西大豆高产育种主要利用育成品种(祖先亲本含丰产性好的种质材料)或丰产性好的国外引种作为直接亲本.广西大豆种质资源丰富,至今收集保存有6000余份,但利用率低(地方种质资源利用率不足2%,野生大豆种质利用率为0).[建议]加大科研投入,丰富育种手段,加快大豆种质资源的挖掘、创新及利用,尤其是野生大豆种质资源的驯化和利用;在保持广西大豆高蛋白优势的同时,加强选育高产、优质、抗逆、耐荫、适宜机械化的绿色大豆新品种,尤其是夏大豆品种;加快特色专用型大豆新品种选育.     

Variations in terrigenous input into the deep equatorial atlantic during the past 24,000 years

Estimates of terrigenous fluxes at three different water depths at two sites in the equatorial Atlantic by normalization against excess (230)Th flux indicate that the flux of terrigenous material to the seafloor was significantly higher during the last glacial period than it is today. Fluxes started to decrease during deglaciation and reached minimal values in the middle of the Holocene. From 15,000 to 5,000 years ago, there was a substantial increase in flux with increasing water depth below 2,800 meters; this increase may reflect resuspension and lateral transport of slope and rise sediment, possibly because of intensification of deepwater circulation during that period.     

过去300年东北地区林地和草地覆盖变化

东北地区是我国森林、草场资源最为丰富的地区之一。近300年来,耕地扩张、森林砍伐、草地退化等所导致的显著土地覆盖变化会通过对陆-气之间碳通量和地表反照率的改变,进而对气候系统产生影响。该文采用历史文献分析、原始潜在植被恢复等方法,结合驱动力分析,重建了过去300年东北地区林地和草地自然覆盖变化状况。可提供空间分辨率至县、时间分辨率约为100年的东北地区林地和草地覆盖数据,为气候模拟、碳排放估计等相关研究提供真实的历史数据;得到对过去300年,东北地区林地和草地覆盖变化特征的认识:过去300年,东北地区林地、草地所占比例分别减少了约15％、10％;18—19世纪,东北的天然植被覆盖几乎处于原始状态,林地、草地减少的地区主要集中在辽东、辽西等农垦区;1900—1950年为林地、草地减少最为迅速的时期,辽东、辽西的天然植被几乎均被破坏殆尽,鸭绿江流域、长白山地区森林减少十分显著,草地界线已明显向西退缩;20世纪后半期,林地覆盖在空间上呈扩张趋势,局部地区仍在减少,而草地覆盖在空间上则一直呈缩小趋势。      

安徽省近33年农业气象灾害年景评估

利用安徽省1978-2010年农作物播种面积、受灾类型及其受灾面积资料,分析农业气象灾害时空分布特征;采用灰色关联度及农业气象综合灾损模型,开展农业气象灾害年景评估.结果表明:安徽省气象灾害造成的农作物受灾面积年际波动大;农业气象灾害空间分布特点为淮北地区最重,江淮之间南部和沿江地区次之,大别山区、皖南山区以及部分城市周边相对较轻.各类气象灾害对农业受灾的影响大小依次为:暴雨洪涝＞旱灾＞风雹灾＞低温雨雪冰冻灾,其中暴雨洪涝和旱灾影响大,受灾程度重;安徽省农业气象灾害较轻年景出现频率为55％,其中灾害最轻年份为1981年,而较重年景占12％.灾害最重的年份为1991年.上述年景评估结果与安徽省农业受灾历史记录较吻合.     

50 million years of genomic stasis in endosymbiotic bacteria

Comparison of two fully sequenced genomes of Buchnera aphidicola, the obligate endosymbionts of aphids, reveals the most extreme genome stability to date: no chromosome rearrangements or gene acquisitions have occurred in the past 50 to 70 million years, despite substantial sequence evolution and the inactivation and loss of individual genes. In contrast, the genomes of their closest free-living relatives, Escherichia coli and Salmonella spp., are more than 2000-fold more labile in content and gene order. The genomic stasis of B. aphidicola, likely attributable to the loss of phages, repeated sequences, and recA, indicates that B. aphidicola is no longer a source of ecological innovation for its hosts.     

近50年夏季气候变化及对嘉定农业生产的影响

应用上海嘉定站夏季平均气温、最高气温、最低气温资料,对当地近50年夏季气温变化进行了统计分析,发现近50年气温上升明显,降水变化趋势不明显,并针对这一现象提出调整种植季节、调整农业产业结构等建议。