Grazing suppression of dimethylsulphoniopropionate (DMSP) accumulation in iron-fertilised, sub-Antarctic waters     

S.D. Archer  K. SafiA. Hall  D.G. CummingsM. Harvey 《Deep Sea Research Part II: Topical Studies in Oceanography》2011,58(6):839-850

The impact of in situ iron fertilisation on the production of particulate dimethylsulphoniopropionate (DMSPp) and its breakdown product dimethyl sulphide (DMS) was monitored during the SOLAS air-sea gas exchange experiment (SAGE). The experiment was conducted in the high nitrate, low chlorophyll (HNLC) waters of the sub-Antarctic Southern Ocean (46.7°S 172.5°E) to the south-east of New Zealand, during March-April, 2004. In addition to monitoring net changes in the standing stocks of DMSPp and DMS, a series of dilution experiments were used to determine the DMSPp production and consumption rates in relation to increased iron availability. In contrast to previous experiments in the Southern Ocean, DMS concentrations decreased over the course of the 15-d iron-fertilisation experiment, from an integrated volume-specific concentration in the mixed layer on day 0 of 0.78 nM (measured values 0.65-0.91 nM) to 0.46 nM (measured values 0.42-0.47 nM) by day 15, in parallel with the surrounding waters. DMSPp, chlorophyll a and the abundance of photosynthetic picoeukaryotes exhibited indiscernible or only moderate increases in response to the raised iron availability, despite an obvious physiological response by the phytoplankton. High specific growth rates of DMSPp, equivalent to 0.8-1.2 doublings d⁻¹, occurred at the simulated 60% light level of the dilution experiments. Despite the high production rates, DMSPp accumulation was suppressed in part by microzooplankton grazers who consumed between 61% d⁻¹ and 126% d⁻¹ of the DMSPp production. Temporal trends in the rates of production and consumption illustrated a close coupling between the DMSP-producing phytoplankton and their microzooplankton grazers. Similar grazing and production rates were observed for the eukaryotic picophytoplankton that dominated the phytoplankton biomass, partial evidence that picoeukaryotes contributed a substantial proportion of the DMSP synthesis. These rates for DMSPp and picoeukaryotes were considerably higher than for chlorophyll a, indicating higher cycling rates of the DMSP-producing taxa than for the bulk phytoplankton community. When compared to the total phytoplankton community, there was no evidence of selection against the DMSP-containing phytoplankton by the microzooplankton grazers; the opposite appeared to be the case. SAGE demonstrated that increased iron availability in the HNLC waters of the Southern Ocean does not invariably lead to enhanced DMS sea-air flux. The potential suppression of DMSPp accumulation by grazers needs to be taken into account in future attempts to elevate DMS emission through in situ iron fertilisation and in understanding the hypothesised link between levels of Aeolian iron deposition in the Southern Ocean, DMS emission and global albedo.  相似文献   

Push moraines in the upper valley of Santa Cruz river,southwest Argentina. Structural analysis and relationship with Late Pleistocene paleoclimate     

《Journal of South American Earth Sciences》2015

The upper cliff of the Santa Cruz River was used to assess the proglacial environments of the Argentino Glacier outlet of Late Pleistocene age. These cliffs show glaciolacustrine, fluvioglacial and till deposits, where only the first one are deformed. Glacial landforms in the area and these structures suggest that the ice mass advanced, topographically controlled, towards the east from the Patagonian Ice Sheet pushing up the proglacial sediments.The spatial arrangement of thrusts and overturned folds, the drumlins-flutes moraine directions and the end moraines shape, allow inferring the dynamic and the Argentino glacier profile. Detailed analyses of the glaciotectonic structures indicate that these have two origins: load in the north with stress transfer to the southeast, and push from the west. Through the analysis of deformed sediments, their thickness and their sedimentary and structural features, three zones of deformations were recognized. Each of these zones was associated to glacial advances because of changes of the regional climate conditions.  相似文献   

南冲绳海槽沉积物中淡水硅藻的发现及1000年以来台风降雨的重建     

李冬玲  蒋辉  徐晓群  沙龙滨  李铁刚 《第四纪研究》2015,35(3)

利用主成分分析法对冲绳海槽南部MD05-2908孔近1000年来沉积物硅藻数据进行研究发现,MD05-2908孔各样品在主成分一上的得分情况与该于孔淡水硅藻含量、夏季海水表层盐度变化以及台湾近1000年来的降水异常有良好的相关性,因此,各样品在主成分一上的得分可作为台湾东北部台风降雨指标,用来指示台风强降雨事件对南冲绳海槽海洋环境的影响情况.近1000年来台湾东北部台风强降雨事件波动增加,在1500～1800A.D.期间达到峰值;此外,5次典型的强台风降雨记录,分别发生于1040A.D.、1310A.D.、1530A.D.、1690A.D.和1900A.D.,其平均重现周期为215年(160～270年).利用MD05-2908孔各样品在主成分一上的得分重建的台风记录与广东、台湾等地已有的台风记录有较好的对应关系,进一步验证了硅藻作为研究工具重建古台风记录的可行性.  相似文献   

Secondary Calcification of Planktic Foraminifera from the Indian Sector of Southern Ocean     

Rahul MOHAN  Suhas S. SHETYE  Manish TIWARI  Narayanpillai ANILKUMAR 《《地质学报》英文版》2015,89(1):27-37

This study focused on planktic foraminifera in plankton tows and surface sediments from the western Indian sector of Southern Ocean in order to evaluate the potential foraminiferal secondary calcification and/or dissolution in the sediment. It is found that the symbiotic foraminiferal species are abundant in the subtropical region, whereas non-symbiotic species dominate in the sub-Antarctic and polar frontal regions. The distribution of the symbiotic and non-symbiotic foraminiferal species is controlled by temperature, salinity, light, nutrients and phytoplankton biomass. There is also a lateral southern extent in abundance of planktic foraminifera from surface sediments to plankton tows. The shell weights of the planktic foraminifera N. pachyderma, G. bulloides and G. ruber within the surface sediments are on an average heavier by 27%, 34% and 40% respectively than shells of the same size within the plankton tows, indicative of secondary calcification. The planktic foraminiferal isotopes show the presence of heavier isotopes in the surface sediment foraminifera as compared to plankton tows, thus confirming secondary calcification. Secondary calcification in G. ruber occurs in the euphotic zone, whereas in case of N. pachyderma and G. bulloides it is at deeper depths. We also observed a decrease in the shell spines in surface sediment foraminifera as compared to plankton tows, indicative of the morphological changes that foraminifera underwent during gametogenesis.  相似文献   

辽南上达子堡金矿化区黄铁矿标型特征及意义     

李勇 《吉林地质》2015,(2)

上达子堡金矿化区主要出露古元古界辽河群盖县岩组二岩段,是金成矿物质的矿源层。黄铁矿标型特征指示目前区内的剥蚀水平相当于中上部,按黄铁矿垂直分带规律,{210}+{100}、{210}习性晶体向深部有可能逐渐增加,因此,本金矿化区深部含金量可能高于浅部。  相似文献   

巢湖地区二叠系栖霞组和三叠系南陵湖组石灰岩生物标志物特征与生烃潜力——以平顶山和马家山剖面为例     

宋换新  志刚  包建平 《海相油气地质》2015,(2)

对安徽巢湖地区平顶山和马家山剖面下二叠统栖霞组和下三叠统南陵湖组进行了地层沉积特征及暗色石灰岩生烃潜力的综合分析,并对这两个层位的样品进行了饱和烃生物标志物特征研究。结果表明,两个层位的石灰岩都属于有效烃源岩,均具有一定的生烃潜力。南陵湖组石灰岩饱和烃以高丰度的长链三环萜烷、重排藿烷、重排甾烷为特征,表明其形成于偏弱氧化的沉积环境。栖霞组沉积期水体能量相对较低,受陆源物质影响明显,栖霞组石灰岩萜烷系列为常规的分布模式,但其甾烷成熟度参数明显低于平衡值,认为高的热演化程度是造成栖霞组石灰岩20S/(20S+20R)-ααα-C29甾烷值和ββ/(ββ+αα)-C29甾烷值"倒转"的主要原因。  相似文献   

羌塘南缘多龙矿集区荣那斑岩-高硫型浅成低温热液Cu-(Au)套合成矿:综合地质、热液蚀变及金属矿物组合证据   总被引：16，自引：12，他引：4  

李光明  张夏楠  秦克章  孙兴国  赵俊兴  印贤波  李金祥  袁华山 《岩石学报》2015,31(8):2307-2324

位于羌塘南缘多龙矿集区内的荣那斑岩-高硫型浅成低温热液Cu-(Au)矿床系近年来中铝西藏与西藏地质五队合作勘查取得重大找矿突破的铜矿床,控制资源量已达超大型规模,但对该矿床的成因类型仍存在争议。本文根据详细的钻孔岩芯、结合光学显微镜、扫描电镜观察、硫化物的电子探针分析,认为该矿床成矿与早白垩世花岗闪长斑岩有关。矿体主要产于下中侏罗统色哇组长石石英砂岩和成矿斑岩体中,矿体呈东西走向、南倾的隐伏状,延深巨大,金属矿化以铜为主,伴有金、银矿化,偶见钼矿化。热液蚀变具有两阶段蚀变:与斑岩型矿化有关的黑云母化、角岩化、硅化-绢云母化及硅化-伊利石-绿泥石化以上部叠加的高级泥化,蚀变分带明显。相应的该矿床具有斑岩型细脉浸染状矿化和以硫砷铜矿为特征的高硫型矿化,含铜矿物主要分为4个带,大致与蚀变分带相对应,下部主要为斑铜矿-黄铜矿;过渡带以斑铜矿-铜蓝组合为特征;中上部为蓝辉铜矿-砷黝铜矿-硫砷铜矿组合;顶部主要由为辉铜矿-蓝辉铜矿组成。总体上,矿床中上部为Cu-S体系、向下转变Cu-Fe-S体系。与其它类似矿床相比,该矿床硫化物中以富Zn、贫金为特征。综上认为该矿床为斑岩-高硫型浅成低温热液Cu-(Au)套合成矿的典型实例,其勘查突破为羌塘南缘火山岩区及覆盖区的找矿打开了一扇窗口。  相似文献   

西藏冈底斯南缘雄村铜金矿床成矿斑岩厘定及其锆石U-Pb和黑云母Ar-Ar年龄分析   总被引：1，自引：0，他引：1  

邹银桥  黄文婷  梁华英  伍静  林书平  王秀璋 《岩石学报》2015,31(7):2053-2062

雄村特大型斑岩铜金矿床主要以细脉浸染状产于强烈蚀变岩石中,赋矿岩石原岩成因类型存在争议。本文对多个赋矿蚀变岩石作了系统光薄片显微鉴定,在多个蚀变较弱的矿化样品中发现赋矿岩石具斑状结构,其基质主要为钾长石,斑晶主要为斜长石、钾长石及少量石英,显示石英正长斑岩及二长斑岩(少量)矿物组成特征。结合前人工作,可以认为雄村铜金矿床赋矿岩石为正长斑岩、火山岩及少量二长斑岩。正长斑岩发育斑岩铜金矿床成矿早期常见的钾硅化蚀变及磁铁矿化蚀变,锆石具高的Ce4+/Ce3+比值(334~3084,平均值为1169),显示高氧逸度岩浆特征,和世界斑岩铜金矿床成矿岩体一致;这表明石英正长斑岩为雄村铜金矿床成矿岩体。石英正长斑岩锆石LA-ICP-MS U-Pb年龄为173.7±2.1Ma(MSWD=0.23),石英正长斑岩钾化阶段形成的黑云母40Ar/39Ar坪年龄为48.3±0.9Ma(MSWD=1.58),远小于锆石U-Pb年龄却与矿区东北部始新世花岗岩基的年龄一致,显示Ar-Ar年龄受后期地质事件影响而发生重置。通过上述研究,可以认为雄村铜金矿床为与石英正长斑岩有关的斑岩型矿床,形成时代约173Ma,和新特提斯洋洋壳向北俯冲诱发的岩浆事件有关,矿区内云母受后期地质事件影响重置,不能记录其形成时代。  相似文献   

Physical analog (centrifuge) model investigation of contrasting structural styles in the Salt Range and Potwar Plateau,northern Pakistan     

《Journal of Structural Geology》2015

We use scaled physical analog (centrifuge) modeling to investigate along- and across-strike structural variations in the Salt Range and Potwar Plateau of the Himalayan foreland fold-thrust belt of Pakistan. The models, composed of interlayered plasticine and silicone putty laminae, comprise four mechanical units representing the Neoproterozoic Salt Range Formation (basal detachment), Cambrian–Eocene carapace sequence, and Rawalpindi and Siwalik Groups (Neogene molasse), on a rigid base representing the Indian craton. Pre-cut ramps simulate basement faults with various structural geometries.A pre-existing north-dipping basement normal fault under the model foreland induces a frontal ramp and a prominent fault-bend-fold culmination, simulating the Salt Range. The ramp localizes displacement on a frontal thrust that occurs out-of-sequence with respect to other foreland folds and thrusts. With a frontal basement fault terminating to the east against a right-stepping, east-dipping lateral ramp, deformation propagates further south in the east; strata to the east of the lateral ramp are telescoped in ENE-trending detachment folds, fault-propagation folds and pop-up structures above a thick basal detachment (Salt Range Formation), in contrast to translated but less-deformed strata with E–W-trending Salt-Range structures to the west. The models are consistent with Salt Range–Potwar Plateau structural style contrasts being due to basement fault geometry and variation in detachment thickness.  相似文献   

Displacement transfer from fault-bend to fault-propagation fold geometry: An example from the Himalayan thrust front     

《Journal of Structural Geology》2015

The leading edge of the ENE-trending Himalayan thrust front in Pakistan exhibits along-strike changes in deformational style, ranging from fault-bend to fault-propagation folds. Although the structural geometry is very gently deformed throughout the Salt Range, it becomes progressively more complex to the east as the leading edge of the emergent Salt Range Thrust becomes blind. Surface geology, seismic reflection, petroleum well, and chronostratigraphic data are synthesized to produce a 3-D kinematic model that reconciles the contrasting structural geometries along this part of the Himalayan thrust front. We propose a model whereby displacement was transferred, across a newly-identified lateral ramp, from a fault-bend fold in the west to fault-propagation folds in the east and comparable shortening was synchronously accommodated by two fundamentally different mechanisms: translation vs. telescoping. However, substantially different shortening distribution patterns within these structurally contrasting segments require a tear fault, which later is reactivated as a thrust fault. The present geometry of this S-shaped displacement transfer zone is a combined result of the NW–SE compression of the lateral culmination wall and associated tear fault, and their subsequent modification due to mobilization of underlying ductile salt.  相似文献