Characterisation of water masses and phytoplankton nutrient limitation in the East Australian Current separation zone during spring 2008     

C.S. Hassler  J.R. DjajadikartaM.A. Doblin  J.D. EverettP.A. Thompson 《Deep Sea Research Part II: Topical Studies in Oceanography》2011,58(5):664-677

This study focuses on the comparison of oceanic and coastal cold-core eddies with inner-shelf and East Australian Current (EAC) waters at the time of the spring bloom (October 2008). The surface water was biologically characterised by the phytoplankton biomass, composition, photo-physiology, carbon fixation and by nutrient-enrichment experiments. Marked differences in phytoplankton biomass and composition were observed. Contrasted biomarker composition suggests that biomarkers could be used to track water masses in this area. Divinyl chlorophyll a, a biomarker for tropical Prochlorophytes, was found only in the EAC. Zeaxanthin a biomarker for Cyanophytes, was found only within the oceanic eddy and in the EAC, whereas chlorophyll b (Chlorophytes) was only present in the coastal eddy and at the front between the inner-shelf and EAC waters.This study showed that cold-core eddies can affect phytoplankton, biomass, biodiversity and productivity. Inside the oceanic eddy, greater phytoplankton biomass and a more complex phytoplankton community were observed relative to adjacent water masses (including the EAC). In fact, phytoplankton communities inside the oceanic eddy more closely resembled the community observed in the inner-shelf waters. At a light level close to half-saturation, phytoplankton carbon fixation (gC d⁻¹) in the oceanic eddy was 13-times greater than at the frontal zone between the eddy and the EAC and 3-times greater than in the inner-shelf water. Nutrient-enrichment experiments demonstrated that nitrogen was the major macronutrient limiting phytoplankton growth in water masses associated with the oceanic eddy. Although the effective quantum yield values demonstrate healthy phytoplankton communities, the phytoplankton community bloomed and shifted in response to nitrogen enrichments inside the oceanic eddy and in the frontal zone between this eddy and the EAC. An effect of Si enrichment was only observed at the frontal zone between the eddy and the EAC. No response to nutrient enrichment was observed in the inner-shelf water where ambient NO_x, Si and PO₄ concentrations were up to 14, 4 and 3-times greater than in the EAC and oceanic eddy. Although results from the nutrient-enrichment experiments suggest that nutrients can affect biomass and the composition of the phytoplankton community, the comparison of all sites sampled showed no direct relationship between phytoplankton biomass, nutrients and the depth of the mixed layer. This is probably due to the different timeframe between the rapidly changing physical and chemical oceanography in the separation zone of the EAC.  相似文献   

Airborne imagery of a disintegrating Sargassum drift line     

George O. Marmorino  W.D. MillerGeoffrey B. Smith  Jeffrey H. Bowles 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(3):316-321

Airborne hyperspectral and thermal infrared imagery collected over the Florida Current provide a view of the disintegration of a Sargassum drift line in 5 m s⁻¹ winds. The drift line consists mostly of rafts 20-80 m² in size, though aggregations larger than 1000 m² also occur. Rafts tend to be elongated, curved in the upwind direction, and 0.1-0.5 °C warmer than the surrounding ocean surface. Long weed ‘trails’ extending upwind from the rafts are evidence of plants dropping out and being left behind more rapidly drifting rafts. The raft line may be a remnant of an earlier Sargassum frontal band, which is detectible as an upwind thermal front and areas of submerged weed. Issues are identified that require future field measurements.  相似文献   

A western boundary current east of New Caledonia: Observed characteristics     

Florent Gasparin  Alexandre Ganachaud  Christophe Maes 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(9):956-969

Waters from the South Equatorial Current (SEC), the northern branch of the South Pacific subtropical gyre, are a major supply of heat to the equatorial warm pool, and have an important contribution to climate variability and ENSO which motivated the Southwest Pacific Ocean and Climate Experiment (SPICE, CLIVAR/WCRP). Initially a broad westward current extending from the equator to 30°S, the SEC splits upon arriving at the major islands and archipelagoes of Fiji (18°S, 180°E), Vanuatu (16°S, 168°E), and New Caledonia (22°S, 165°E), resulting in a complex system of western boundary currents and zonal jets that feed the Coral and Solomon Seas. We focus here on the formation of one specific jet feeding the Coral Sea, the North Caledonian Jet (NCJ). Using a combination of recent oceanographic cruises, we describe the ocean circulation to the northeast of New Caledonia, where the SEC forms a western boundary current that ultimately becomes the NCJ. This current, which we document for the first time and propose to refer to as the East Caledonian Current (ECC), has its core located 10-100 km off the east coast of New Caledonia, and extends vertically to at least 1000 m depth. Water mass properties show continuous westward transports through the ECC, from the SEC to the NCJ in both the South Pacific Tropical Waters in the thermocline and Antarctic Intermediate Waters near 700 m depth. The ECC extends about 100 km horizontally; its average 0-1000 m transport was estimated at 14.5±3 Sv off the north tip of the New Caledonian reef, with a maximum of 20 Sv in May 2010. South of that the upstream branch of the ECC east of the Loyalty is close to 8 Sv suggesting an important additional contribution from central Pacific waters carried by the SEC at 16°S and diverted to our region through the western boundary current system east of Vanuatu.  相似文献   

秋季长江口北支表层海水pCO2变化特征     

郑旻辉  张海生  潘建明  于培松  刘小涯  张海娜  刘俊峰 《海洋学研究》2011,(3):57-62

根据2009年9月首次获得的长江口北支海水pCO2实测数据,结合温度、盐度等参数,对长江口北支海水pCO2时空分布、变化特征及其影响因素进行了研究.研究结果表明,长江口北支海水pCO2总体呈现出淡水端高,咸水端低的特点;在同等盐度条件下,长江口北支海水pCO2明显高于长江口南支;长江口北支南段海水pCO2与盐度之间有着...  相似文献   

Numerical study on the bifurcation of the North Equatorial Current     

Yulong Liu  Qi Wang  Jun Song  Xiande Zhu  Xiaoqing Gong  Fang Wu 《中国海洋大学学报(英文版)》2011,10(4):305-313

A 1.5-layer reduced-gravity model forced by wind stress is used to study the bifurcations of the North Equatorial Current(NEC).The authors found that after removing the Ekman drift,the modelled circulations can serve well as a proxy of the SODA circulations on the σθ=25.0 kg m～-3 potential density surface based on available long-term reanalysis wind stress data.The modelled results show that the location of the western boundary bifurcation of the NEC depends on both zonal averaged and local zero wind stress curl latitude.The effects of the anomalous wind stress curl added in different areas are also investigated and it is found that they can change the strength of the Mindanao Eddy(ME),and then influence the interior pathway.  相似文献   

地幔橄榄岩中橄榄石的指示意义   总被引：3，自引：0，他引：3  

汤艳杰  张宏福  英基丰  杨蔚  赵新苗  苏本勋  肖燕 《地球科学与环境学报》2011,33(1):24-33

橄榄石是地幔橄榄岩和辉石岩的主要组成矿物,但也经常以斑晶和捕虏晶的形式出现在玄武质岩石中。结合近年来在地幔橄榄岩的主要元素(如Mg和Fe)组成特征以及Li、Mg和Fe稳定同位素地球化学方面的研究成果,重点对橄榄石的地球化学特征与华北克拉通岩石圈地幔演化过程之间的联系进行了讨论,旨在加深对华北克拉通岩石圈地幔演化过程的理解。现有研究表明:地幔橄榄岩中橄榄石的矿物学特征、元素和同位素地球化学组成能够很好地指示岩石圈地幔的特征及其演化过程,因而具有重要的意义。对于克拉通地区的地幔橄榄岩来说,橄榄石的Mg#通常可以指示岩石圈地幔的属性,古老、难熔的地幔橄榄岩中的橄榄石一般具有较高的Mg#(>92),而新生的岩石圈地幔橄榄岩中的橄榄石则具有较低的Mg#(<91)。因此,地幔橄榄岩中橄榄石的Mg#在一定程度上具有年龄意义。橄榄岩中橄榄石的Li、Mg和Fe同位素组成也可以明确指示岩石圈地幔的属性及其所经历的演化过程,正常地幔的δ7Li、δ26Mg和δ57Fe组成相对均一,如果上述同位素组成偏离正常地幔值,则说明岩石圈地幔经历了熔体/流体的交代作用。华北克拉通地区地幔橄榄岩捕虏体中橄榄石的Li、Mg和Fe同位素组成研究表明:该区的岩石圈地幔经历了多个阶段、不同来源的熔体/流体的改造过程。  相似文献   

南极绕极流区中尺度涡动动能年际变化和转换机制   总被引：1，自引：0，他引：1       下载免费PDF全文

张文霞  孟祥凤 《极地研究》2011,23(1):42-48

采用多种资料研究南大洋南极绕极流(Antarctic Circumpolar Current,ACC)区中尺度涡的年际变化规律及机制.通过分析网格化融合卫星海洋资料AVISO(Archiving,Validation and Interpretation of Satellites Oceanographic DATA...  相似文献   

华北克拉通五台群LA-ICP-MS锆石U-Pb年龄和Hf同位素特征   总被引：2，自引：0，他引：2  

陈雪  陈岳龙  李大鹏  刘烊  魏娟娟  闫家盼 《地质通报》2015,34(5):861-876

通过对五台群石咀亚群金刚库组4个典型样品的LA-ICP-MS锆石U-Pb年龄和Hf同位素研究,对五台群的形成时代及华北克拉通新太古代—古元古代期间的地壳演化进行了探讨。锆石U-Pb同位素测定结果表明,侵入金刚库组中的片麻状花岗岩锆石的U-Pb年龄为2548Ma,因此五台群的上限年龄约为2.5Ga;金刚库组黑云母石英片岩和片麻状石英闪长岩的原岩锆石U-Pb年龄分别为2663Ma和2636Ma,因此五台群的下限年龄约为2.7Ga。五台群的地质年龄为2.5~2.7Ga,属于新太古代。锆石Hf同位素研究结果表明,黑云母石英片岩和片麻状石英闪长岩的二阶段Hf模式年龄(tDM2)均为2.8Ga左右,指示2.8Ga左右是五台山区乃至整个华北克拉通地壳生长的重要时期;片麻状花岗岩tDM2平均为2.57Ga,与锆石结晶年龄非常接近,表明2.5Ga左右也是华北克拉通地壳的主要增生期。地壳的增长是幕式的,2.8Ga和2.5Ga都是华北克拉通地壳生长时期。  相似文献   

华北地块南缘花山、五丈山岩体LA-ICP-MS锆石U-Pb年龄、地球化学特征及成因   总被引：4，自引：0，他引：4  

聂政融  王晓霞  柯昌辉  杨阳  吕星球 《地质通报》2015,34(8):1502-1516

花山复式岩体位于华北地块南缘,采用LA-ICP-MS技术测得复式岩体中的中细粒似斑状黑云二长花岗岩的锆石U-Pb年龄为128±1Ma,此年龄被解释为成岩年龄。该岩体及邻近的五丈山岩体中花岗岩具有高硅、富碱特征,为准铝-弱过铝质高钾钙碱性系列;在稀土和微量元素上,富集LREE、Rb、Ba、K、Sr等大离子亲石元素,亏损HREE、Zr、Hf、Ta、Nb、P、Ti等高场强元素,总体上Eu异常不明显,显示出I-A过渡型花岗岩的特征。锆石Lu-Hf同位素组成表明,花山花岗岩的ε_Hf(t)主要变化于-25.8~-19.6之间,t_DM2为2.81~2.43Ga,显示源区物质以古老的壳源物质为主,有年轻组分的参与。与岩体外围多金属成矿年龄的对比分析发现,外围金、钼矿床与花山复式岩体的年龄一致,比五丈山岩体晚20~25Ma,表明金、钼矿的形成与花山岩体在时空上联系密切,该岩体可能为成矿提供了热源。  相似文献   

华北克拉通辽东半岛新元古代早期基性岩浆活动:辉绿岩墙年代学和岩石地球化学证据     

韩吉龙  王清海 《世界地质》2015,34(4):886-902

华北克拉通辽东半岛地区广泛发育侵位于青白口系不同层位中的辉绿岩(脉)岩墙,对其锆石CL图像、U--Pb定年和岩石地球化学特征研究得出以下结论。锆石类型有三组:前两组锆石具有早期岩浆作用的锆石属性或结晶基底的变质锆石属性,反映该区辉绿岩岩浆上升过程受到了陆壳的混染;第三组锆石多呈自形--半自形短柱状,发育岩浆振荡生长环带结构或条带结构,具原生岩浆成因锆石属性,锆石SHRIMP U--Pb定年显示其加权平均年龄为832.3±8.1 Ma(n=14,MSWD=1.3),可以代表辉绿岩的结晶年龄。岩石地球化学组成,其具有低Si O_2、Al_2O_3,高TFe_2O_3、MgO、Ti O_2的特征,这与拉斑玄武岩特征相似;其稀土元素总量相对较低(ΣREE=71.88×10~-6~129.64×10~-6),且具弱的正Eu异常和铌亏损;略富集轻稀土元素(LREE)、富集大离子亲石元素(LILE:Rb、Pb、Ba)和高场强元素(HFSE:Th、U、Zr、Ti、Hf),而亏损高场强元素(HFSE:Nb、Sm、Gd、P)等;以上特征指示岩浆源区为富集型地幔,且上侵位就位过程中受陆壳不同程度的同化混染。本文对辉绿岩的研究显示华北克拉通辽东半岛地区在新元古代早期存在基性岩浆活动,结合前人对华北克拉通中元古代晚期—新元古代早期构造--岩浆事件的研究成果,进一步证明了华北克拉通东北部在新元古代早期经历了挤压汇聚后的伸展裂解演化过程,这与Rodinia超大陆聚合和裂解事件一致。  相似文献