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   

The strengthening East Australian Current, its eddies and biological effects — an introduction and overview     

Iain M. Suthers  Jock W. YoungMark E. Baird  Moninya RoughanJason D. Everett  Gary B. BrassingtonMaria Byrne  Scott A. CondieJason R. Hartog  Christel S. HasslerAlistair J. Hobday  Neil J. HolbrookHamish A. Malcolm  Peter R. OkePeter A. Thompson  Ken Ridgway 《Deep Sea Research Part II: Topical Studies in Oceanography》2011,58(5):538-546

The poleward flowing East Australian Current (EAC) is characterised by its separation from the coast, 100-200 nautical miles north of Sydney, to form the eastward flowing Tasman Front and a southward flowing eddy field. The separation zone greatly influences coastal ecosystems for the relatively narrow continental shelf (only 15-50 km wide), particularly between 32-34°S. In this region the continental shelf has a marked shift in the seasonal temperature-salinity relationship and elevated surface nitrate concentrations. This current parallels the portion of the coast where Australia’s population is concentrated and has a long history of scientific research. However, understanding of physical and biological processes driven by the EAC, particularly in linking circulation to ecosystems, is limited. In this special issue of 16 papers on the EAC, we examine the effects of climatic wind-stress forced ocean dynamics on EAC transport variability and coastal sea level, from ENSO to multi-decadal time scales; eddy formation and structure; fine scale connectivity and larval retention. Comparisons with the poleward-flowing Leeuwin Current on Australia’s west coast show differences in ecosystem productivity that can be attributed to the underlying physics in each region. On average there is double the chlorophyll a concentration on the east coast than the west. In comparison to the Leeuwin, the EAC may have less local retention of larvae and act as a partial barrier to onshore transport, which may also be related to the local spawning and early life history of small pelagic fish on each coast. Inter-annual variations in the EAC transport produce a detectable sea-level signal in Sydney Harbour, which could provide a useful fisheries index as does the Fremantle sea level and Leeuwin Current relationship. The EAC’s eddy structure and formation by the EAC are examined. A particular cold-core eddy is shown to have a “tilt” towards the coast, and that during a rotation the flow of particles may rise up to the euphotic zone and then down beneath. In a warm-core eddy, surface flooding is shown to produce a new shallower surface mixed layer and promote algal growth. An assessment of plankton data from 1938-1942 showed that the local, synoptic conditions had to be incorporated before any comparison with the present. There are useful relationships of water mass characteristics in the Tasman Sea and separation zone with larval fish diversity and abundance, as well as with long-line fisheries. These fisheries-pelagic habitat relationships are invaluable for fisheries management, as well as for climate change assessments.There is further need to examine the EAC influence on rainfall, storm activity, dust deposition, and on the movements by fish, sharks and whales. The Australian Integrated Marine Observing System (IMOS) has provided new infrastructure to determine the changing behaviour of the EAC and its bio-physical interaction with the coasts and estuaries. The forecasting and hindcasting capability developed under the Bluelink project has provided a new tool for data synthesis and dynamical analysis. The impact of a strengthening EAC and how it influences the livelihoods of over half the Australian population, from Brisbane to Sydney, Hobart and Melbourne, is just being realised.  相似文献   

Defining dynamic pelagic habitats in oceanic waters off eastern Australia     

A.J. Hobday  J.W. YoungC. Moeseneder  J.M. Dambacher 《Deep Sea Research Part II: Topical Studies in Oceanography》2011,58(5):734-745

Although many species in the pelagic ocean are widespread, they are not randomly distributed. These species may have associations with particular water masses or habitats, but to best understand patterns in the ocean, these habitats must be identified. Previous efforts have produced static or seasonal climatologies, which still represent smearing over habitats. The Eastern Tuna and Billfish Longline Fishery (ETBF) targets a range of high trophic level species in oceanic waters off eastern Australia. In this study, dynamic ocean habitats in the region were identified for each month based on cluster analysis of five oceanographic variables averaged at a monthly time scale and a spatial scale of 0.5° for the period 1995-2006. A total of seven persistent habitats were identified off eastern Australia with intra and interannual variation in size and location, indicating the importance of spatial and temporal variation in the dynamics of the region. The degree to which these dynamic habitats were distinguished was tested using (i) stable isotope analysis of top fish predators caught in the region and (ii) estimates of variation in estimated abundance generated from catch data from the fishery. More precise estimates (measured as lower total CV) of isotopic values from swordfish (Xiphias gladius), yellowfin tuna (Thunnus albacares) and albacore (Thunnus alalunga) were obtained for 4 of 6 isotope comparisons using the dynamic habitat groupings, which indicate that stratifying by pelagic habitat improved precision. Dynamic habitats produced more precise abundance estimates for 7 of 8 large pelagic species examined, with an average reduction in total CV of 19% compared to when abundance was estimated based on static habitat stratification. These findings could be used to guide development of effective monitoring strategies that can distinguish patterns due to environmental variation, and in the longer term, climate change.  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   

黄海暖流的路径及机制研究   总被引：9，自引：1，他引：8  

赵胜  于非  刁新源  司广成 《海洋科学》2011,35(11):73-80

利用NASA/AVHRR 反演的每日海表面温度资料, 法国航天局AVISO 发布的海表面高度资料,中国气象科学数据共享服务网成山头台站的日均风场资料, 首先对黄海海表面温度分布进行了分析,揭示了表征黄海暖流的暖水舌存在两个分支。然后对1981 年10 月～2010 年5 月这两个分支发生情况进行了统计, 得出两个分支并...  相似文献   

日本海主要海峡体积输运的季节变化特征     

董津生  徐佳佳 《海洋湖沼通报》2011,(1):13-20

利用变分资料同化技术对P矢量方法进行优化处理,并采用此优化后的P矢量方法优化计算了日本海环流和日本海主要海峡的体积输运.日本海的主要环流系统,比如对马暖流(TWC)及其分支,东朝鲜暖流(EKWC)和日本近岸分支(JNB),极地锋海流(PFC),和日本海中的反气旋式涡,都能够被很好地一一反映出来.另外,优化后的P矢量方法...  相似文献   

上海淤泥质潮滩潮锋作用及其形成机制初步探讨^*   总被引：7，自引：1，他引：7  

徐元  王宝灿 《地理研究》1994,13(3):60-68

本文具体讨论了上海淤泥质潮滩的潮锋作用过程,定性给出了潮锋的形成机制,认为潮锋作用及其水体高含沙量现象的本质在于“潮锋带水体水流加速效应”,即,由于潮滩坡面变化平缓的特殊性,涨潮水体前锋沿程存在着一持续时间可达数十分钟的水流加速过程.最后,本文初步探讨了潮锋作用在滩面塑造过程中的地位,并重新定义了潮锋作用的内容.  相似文献   

关于人工源极低频电磁波发射源的讨论——均匀空间交流点电流源的解   总被引：6，自引：4，他引：2       下载免费PDF全文

陈小斌  赵国泽 《地球物理学报》2009,52(8):2158-2164

大功率人工源极低频电磁波（Control Source of Extremely Low Frequency method, CSELF）技术中,辐射天线由布设在高大地电阻率区的接地长导线源构成,通过接地点向大地注入数百安培的强电流.目前有关强电流在大地中的流动特性和分布规律,尚未完全弄清楚.本文提出一个新思路,将CSELF发射天线分解为两部分:交变的接地长导线源和接地处的交流点电流源,二者响应的叠加构成总场.本文重点讨论了均匀空间下交流点电流源的求解,对比研究了交流点电流源响应、直流点电流源响应之间的差异.结果表明,在小范围内（场源距几十、几百米以内）,均匀空间下交流点电流源场和直流源场差别较小,可相互近似,但在大范围内,交流点电流场比直流场的衰减要快得多.由于CSELF辐射天线跨度上百公里,场源距很大,其电流分布规律遵循交变场规则,不能近似为直流场.  相似文献   

Delayed baroclinic response of the Antarctic circumpolar current to surface wind stress   总被引：2，自引：0，他引：2  

XiaoYi Yang  RuiXin Huang  Jia Wang  DongXiao Wang 《中国科学D辑(英文版)》2008,51(7):1036-1043

The Antarctic Circumpolar Current (ACC) responds to the surface windstress via two processes, i.e., the instant barotropic process and the delayed baroclinic process. This study focuses on the baroclinic instability mechanism in ACC, which was less reported in the literatures. Results show that the strengthening of surface zonal windstress causes the enhanced tilting of the isopycnal surface, leading to more intense baroclinic instability. Simultaneously, the mesoscale eddies resulting from the baro- clinic instability facilitate the transformation of mean potential energy to eddy energy, which causes the remarkable decrease of the ACC volume transport with the 2-year lag time. This delayed negative cor- relation between the ACC transport and the zonal windstress may account for the steadiness of the ACC transport during last two decades.  相似文献   

现代地壳运动与地震监测预报研究的现状和发展趋势   总被引：7，自引：1，他引：6  

王静瑶  吴云 《地球科学进展》2000,15(1):84-89

综述了近年来美国、日本的GPS连续观测系统和INSAR空间测地技术在现代地壳运动和地震监测预报研究中的应用现状和发展趋势。  相似文献