Net ecosystem CO_2 exchange and controlling factors in a steppe——Kobresia meadow on the Tibetan Plateau

Knowledge of seasonal variation of net ecosystem CO2 exchange (NEE) and its biotic and abiotic controllers will further our understanding of carbon cycling process, mechanism and large-scale modelling. Eddy covariance technique was used to measure NEE, biotic and abiotic factors for nearly 3 years in the hinterland alpine steppe--Korbresia meadow grassland on the Tibetan Plateau, the present highest fluxnet station in the world. The main objectives are to investigate dynamics of NEE and its components and to determine the major controlling factors. Maximum carbon assimilation took place in August and maximum carbon loss occurred in November. In June, rainfall amount due to monsoon climate played a great role in grass greening and consequently influenced interannual variation of ecosystem carbon gain. From July through September, monthly NEE presented net carbon assimilation. In other months, ecosystem exhibited carbon loss. In growing season, daytime NEE was mainly controlled by photosynthetically active radiation (PAR). In addition, leaf area index (LAI) interacted with PAR and together modulated NEE rates. Ecosystem respiration was controlled mainly by soil temperature and simultaneously by soil moisture. Q10 was negatively correlated with soil temperature but positively correlated with soil moisture. Large daily range of air temperature is not necessary to enhance carbon gain. Standard respiration rate at referenced 10℃(R10) was positively correlated with soil moisture, soil temperature, LAI and aboveground biomass. Rainfall patterns in growing season markedly influenced soil moisture and therefore soil moisture controlled seasonal change of ecosystem respiration. Pulse rainfall in the beginning and at the end of growing season induced great ecosystem respiration and consequently a great amount of carbon was lost. Short growing season and relative low temperature restrained alpine grass vegetation development. The results suggested that LAI be usually in a low level and carbon uptake be relatively low. Rainfall patterns in the growing season and pulse rainfall in the beginning and at end of growing season control ecosystem respiration and consequently influence carbon balance of ecosystem.     

Response of canopy quantum yield of alpine meadow to temperature under low atmospheric pressure on Tibetan Plateau

An open-path eddy covariance system was set up in Damxung rangeland station to measure the carbon flux from July to October, 2003. The canopy quantum yield (α) of alpine meadow was calculated by the linear function between the net ecosystem carbon dioxide exchange (NEE) and the photosynthetic active radiation (PAR) under low light, and how it was influenced by the temperature was also discussed. Results showed that the canopy or decreased almost linearly with temperature, with the decrease in every 1℃increase of temperature similar to those measured on leaf level of C3 plant. At the beginning, the decrease of canopyαwith temperature was 0.0005 umol CO2·μmol-1 PAR; while it increased to 0.0008μmol CO2·μmol-1 PAR in September, showing a rising trend with plant growing stages. Compared with the canopy a calculated with rectangular hyperbola function, the value in the paper was lower. However, the method advanced here has the advantages in examining the relationship betweenαand the key environmental factors, such as temperature.     

Geomorphic characteristics of the Minjiang drainage basin (eastern Tibetan Plateau) and its tectonic implications: New insights from a digital elevation model study

Abstract   The Minshan Mountain and adjacent region are the major continental escarpments along the eastern Tibetan Plateau. The Minjiang drainage basin is located within the plateau margin adjacent to the Sichuan Basin. Based on the analysis of the digital elevation model (DEM) acquired by the Shuttle Radar Topography Mission (SRTM), we know that the Minjiang drainage basin has distinct geomorphic characteristics. The regular increasing of local topographic relief from north to south is a result of the Quaternary sediment deposition within the plateau and the holistic uplift of the eastern margin of the Tibetan Plateau versus the Sichuan Basin. Results from DEM-determined Minjiang drainage sub-basins and channel profiles show that the tributaries on the opposite sides are asymmetric. Lower perimeter and area of drainage sub-basins, total channel length and bifurcation ratio within eastern flank along the Minjiang mainstream are the result of the Quaternary differential uplift of the Minshan Mountain region. Shorter stream lengths and lower bifurcation ratio might be the indications of the undergrowth and newborn features of these eastern streams, which are also representative for the eastern uplift of the Minshan Mountain.     

南羌塘盆地扎仁古油藏白云岩储层特征及成因研究

根据薄片、铸体薄片、压汞、阴极发光等研究,详细描述了南羌塘盆地扎仁古油藏白云岩的储层特征,并对白云岩成因作了初步研究。认为该白云岩在沉积期后变化中经历了多种成岩作用改造,其中影响白云岩储集性的作用主要有白云石化作用、溶蚀作用、重结晶作用和构造应力作用,对白云岩孔渗改善起了积极作用。白云岩主要储集空间为晶间孔、晶间溶孔,储集物性良好。广泛发育的白云石环边结构等淡水成因标志表明,该区白云岩是通过大气水-海水孔隙混合流体交代灰岩所形成的。     

青藏高原的金属矿产

青藏高原地处印度板块与亚欧板块的衔接部位,长期处于岗瓦纳大陆边缘,大约在65 Ma时印度板块与亚欧板块发生碰撞,对过去构造格局和金属矿产等改造,同时产生新的构造格局和金属矿产,因此青藏高原的金属矿产别具一格。本文讨论青藏高原的铬、铁、铜钼、铅锌、锡、金、锑、铯等优势矿产。     

藏北长江源地区河流地貌特征及其对新构造运动的响应

对藏北长江源地区河谷地貌和新构造变形调查发现,该区具有平行式水系格局,河谷地貌以形态不同的窄谷和宽谷为特点,新近纪以来该区主要经历了早期挤压和晚期伸展构造演化过程,产生了褶皱-逆冲、走滑剪切、正断层和地堑构造3种构造变形样式。长江源区河谷地貌的形成演化明显受新构造运动的影响,新构造运动不仅控制了河谷地貌形态与水系格局,而且影响了河流阶地分布以及洪(冲)积扇的形态、结构。长江源地区主要水系至少自全新世以来是沿新构造运动产生的不同性质断裂构造溯源侵蚀发育而成。     

青藏高原区域重磁异常的东西向分区及其构造地质特征

自从大陆整合以来作为一个整体的青藏高原继续受着印度板块向北俯冲的影响,也必定不断地改造着原各地体的结构构造,形成了高原整体意义上东西向的差异。这种差异与原本各地体的组成、结构和东西向延伸不一致。这不仅表现在南北向断裂构造跨各单个地体范围的出现,而且,逐步形成了东西的分区。这种分区突出地表现在区域重力与磁场的特征上,这不仅是局部的岩石磁性与密度变化的结果,而且是由于印度板块向北俯冲过程中,在其前缘的不同部位上经受的压力不同,以及地块的隆升与扩张作用的差异造成了高原东西各区段的地壳组分与厚度的变化。青藏高原的南北向断裂构造并非地壳上层的局部断裂,它具有深层的原因。由于印度板块向北推进的过程中不是均匀地齐头并进,而是在帕米尔高原以东的青藏高原范围内存在着推进速度和俯冲深度的差异,随着高原隆升的加剧高原本身出现断裂,自中新生代以来就存在着一定差异,所以南北向的断裂构造比目前地表见到的多些,而且具有较大的深度,Moho面的深度和地壳厚度都受南北向断裂的控制,并形成了区域重磁场的变化。同时,高原的东西向拉张作用也使南北断裂带发育加剧。     

青藏高原北羌塘新生代火山岩中的麻粒岩捕虏体

北羌塘枕头崖地区新生代火山岩主要岩石类型为安山岩和英安岩类。其中,安山岩在一定程度上显示了埃达克质火山岩的特征,如高Sr(>1000×10-6)、Sr/Y>50以及低Yb(<2×10-6),表明其应源于榴辉岩相的青藏高原加厚陆壳中下部(>45km深度)。而英安岩类富集LILE,如Rb、Ba、Th、U和K等,亏损HFSE,如Ti、Nb、Ta和Sr等,尤其是Sr显著亏损,表明其应源于斜长石稳定的麻粒岩相源区。该区新生代安山岩和英安岩中麻粒岩捕虏体可分为两种类型,即二辉石麻粒岩和单斜辉石麻粒岩。二辉石麻粒岩平衡温度为783~818℃,单斜辉石麻粒岩形成压力在0·845~0·858GPa之间,来源深度约为27·9~28·3km,表明它们是来自青藏高原加厚陆壳中部的岩石样品,代表了本区英安岩类火山岩的源区物质组成。     

小波分析在重力界面反演中的应用

基于Parker-Oldenburg反演方法，分析了低通滤波器B（K）的不同阈值对位场分离的影响。分别采用小波变换和低通滤波对青藏高原地区布格重力异常进行了位场分解和莫霍面反演，并将反演结果与地震资料作比较。结果表明，在重力位场分解中小波多尺度分解可以代替低通滤波器B（K），避免了闻值的选取。     

高原低涡移出高原的观测事实分析

应用天气学、统计学原理,结合TRMM资料,分析了1998—2004年5—9月移出高原的低涡的活动特征。结果指出:6—8月是高原低涡移出高原影响中国东部天气的主要时段,它与高原低涡在高原上的活动特征及西南低涡移出高原特征均不同;移出高原的高原低涡的涡源主要在曲麻莱附近、德格附近,这与高原上产生低涡的涡源不同;移出高原的高原低涡的移动路径多数是随低槽的活动而向东、向东南移动,这与高原低涡在高原上多数是沿切变线移向东北不同,高原低涡移出高原后,不仅影响中国的范围广,还可能影响到朝鲜半岛、日本;高原低涡移出高原后涡的强度、性质会有变化,在高原以东活动时间长(≥36 h)的高原低涡,移出高原前多数为暖性低涡,移出高原后多数为斜压性低涡,低涡加强、多数可产生暴雨、大暴雨;高原低涡移出高原后移到海洋上,往往因下垫面不同而变化,出海后都有降水加强、多数位势高度下降的现象;移出高原后的高原低涡因东面海上热带气旋活动而少动,与其南面热带气旋活动相向而行,因季风低压少动而少动的现象。