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161.
Lead (Pb) isotope ratios were measured in the marine macroalga Iridaea cordata collected from four locations in the Windmill Islands, East Antarctica. Based on the masses of thalli collected, samples analysed in this study were likely to be a mixture of one and two year old thalli. For a sample of thalli of various ages (<12 months to 2 years old) from the same site there was no apparent variation in Pb concentration or Pb isotope ratio with thallus mass/age, indicating that contaminant sources had been constant over the lifetime of the thalli sampled. I.cordata samples close to the Thala Valley waste disposal site (Brown Bay Inner) near the Australian Station, Casey, displayed isotopic signatures (208Pb/204Pb 35.99; 206Pb/207Pb 1.066; n = 3; average values shown) trending towards that possessed by major Australian Pb sources (Broken Hill and Mt Isa, 208Pb/204Pb 35.60; 206Pb/207Pb 1.041) suggesting that these samples had been exposed to anthropogenic Pb originating from the Thala Valley waste disposal site. Material collected hundreds of metres from the tip location at Brown Bay Outer had isotopic values (208Pb/204Pb 36.32; 206Pb/207Pb 1.088; n = 10) intermediate between Brown Bay Inner and sites further from the contaminant source at Sparkes Bay and Wilkes (208Pb/204Pb 36.46; 206Pb/207Pb 1.094; n = 4) showing that contaminant transport was predominantly restricted to Brown Bay Inner. This study demonstrates that the isotope ratios of Pb in marine macroalgae can provide valuable information as to the origin and extent of heavy metal flux in a marine environment. 相似文献
162.
In this paper, we document the evolution of the emergent Panarea dome in the Aeolian islands (Southern Italy), placing particular emphasis on the reconstruction of the explosive events that occurred during the final stage of its evolution. Two main pyroclastic successions exposing fall deposits with different compositions have been studied into detail: the andesitic Palisi succession and the basaltic Punta Falcone succession. The close-in-time deposition of the two successions, the dispersal area and grain-size distribution of the deposits account for their attribution to vents located in the western sector of the present island and erupting almost contemporaneously. Vents could have been aligned along NNE-trending regional fracture systems controlling the western flank of the dome and possibly its collapse. Laboratory analyses have been devoted to the characterization of the products of the two successions that have been ascribed to vulcanian- and to strombolian-type eruptions respectively. The vulcanian eruption started with a vent-clearing phase that occurred by sudden decompression of a pressurized magma producing ballistic bombs and a surge blast and the development of a vulcanian plume. Vulcanian activity was almost contemporaneous to strombolian-type fall-out eruptions. The coeval occurrence of basaltic and andesitic eruptions from close vents and the presence of magmatic basaltic enclaves in the final dacitic lava lobe of the dome allow us to speculate that the intrusion of a basaltic dyke played a major role in triggering explosive eruptions. The final explosive episodes may have been caused by extensional tectonics fracturing the roof of a zoned shallow magma chamber or by the intrusion of a new basaltic magma into a more acidic and shallow reservoir. Intrusion most likely occurred through the injection of dykes along the western cliff of the present Panarea Island inducing the collapse of the western sector of the dome. 相似文献
163.
A structural field study was made of 578 sheet intrusions (mostly dykes) and 153 (mostly normal) faults dissecting the Anaga and Teno massifs, where a complex volcanic succession of Tertiary age (the ‘Old Basaltic Series’) representing the shield-building stage of Tenerife (Canary Islands) crops out. Many of the intrusions, mostly sub-vertical mafic dykes, are emplaced by multiple magma injections, with cumulative thicknesses mostly less than 2 m. Dyke tips are exposed and preserved for 12% of the dykes. Three differently oriented sets of dykes exist in the Anaga massif (NNW–SSE, NNE–SSW, E–W), whereas there is only one main set in Teno, trending NNW–SSE. Dyke swarms and other structural features having similar orientations also exist in other Canary Islands. A minimum value of the horizontal component of extension induced by dykes is computed using a step of 5° of azimuth, accounting also for the dip of dykes. The cumulative crustal dilation is at least 300 m (4%) in Anaga and 270 m (6%) in Teno; the maximum extension peaks at N75° in Anaga and N60° in Teno, indicating a general prevailing extension in direction ENE–WSW. Most of the measured faults are normal and strike NNW–SSE. Computation of palaeostresses from inversion of fault-slip data sets suggests the existence of a polyphase brittle deformation due to an extensional stress field with the minimum compressive principal axes trending NE–SW and WNW–ESE. 相似文献
164.
165.
Strontium, neodymium isotopic compositions and trace elements of the detrital sediments of Core NS90-103 from South China
Sea were analyzed. The results show that the87Sr/86Sr ratios of the detritus during the last glacial range from 0.722 4 to 0.723 0. They are significantly higher than those
during the Holocene and the maximum of the last interglacial, which range from 0.721 0 to 0.721 7. This indicates stronger
continental weathering during the last glacial. On the other hand, the143Nd/144Nd ratios of these detritus are higher during the last glacial too, similar to the variation of the87Sr/86Sr ratios. The trace element geochemistry of these detritus indicates that more authigenic sediments, such as ferromanganese,
during the last glacial may partly contribute to the increase of143Nd/144Nd ratios. Furthermore, much more detritus from continent of South China to the north of the South China Sea may probably
contribute to143Nd/144Nd ratios increase during the last glacial, which was the result of the enhancement of northeast monsoon. 相似文献
166.
珠海万山群岛海上生态公园建设规划构想 总被引:2,自引:0,他引:2
万册群岛位于珠江口门,拥有优越的区位条件,理想的旅游气候,众多的岛屿,广阔的海域,丰富的生物和旅游资源,发展海上生态旅游大有可为。根据珠海市旅游发展战略定位-国际旅游度假会议会展城,认为万山群岛是实施这一战略的重要组成部分,提出建设“万山群岛海上生态公园”的规划构想和若干建议。 相似文献
167.
168.
双壳类食悬浮物类与食沉积物类的发育变化是反映水动力环境的一种指标。对南海南部NS93- 1 2 - 58柱样 1 4ka来微型双壳类营养结构分析表明 ,晚更新世末次冰期向冰后期全新世转化阶段 ,食沉积物类一度较为发育 ,表明南海南部表层环流很不活跃 ,从这一转化阶段到全新世早期 ,双壳类食悬浮物类与食沉积物类的比例有规律地变大 ,表明随着气候转暖 ,海水温度增高 ,海平面上升 ,海流作用显著增强。该柱样整样分析表明 ,双壳类食悬浮物类占据着明显的优势 ,显示了 1 4ka来南海海流作用一直比较强烈。在全新世中晚期 ,双壳类主要栖息在次表层水团的海底 ,仍以食悬浮物类为主 ,可能与南海南部陆坡上升流发育有关 相似文献
169.
Wavenumber and depth properties of temperature finestructure in the region around the Ryukyu Islands
INTRODUCTIONTheoceanicfinestructureintheEastChinaSea (ECS)Kuroshioregionhadbeenstudiedbyvariousresearchers.Fangetal.(1 988)studiedthefeaturesofthefinestructureinthesouthernshelfareaandtheKuroshioareaintheECSbyusingCTDdata .Baoetal.(1 996)analyzedsomefeaturesofthermohalinefinestructureandrevealeditsrelationwiththewatermassesandcurrentssysteminthenorthernECS .ButoceanicfinestructureintheeasternregionoftheKuroshiohassel dombeenstudied .Inthispaper,basedon 4 2CTDprofilesgatheredinsum… 相似文献
170.
Yii Siang Hii Siti Aisyah Alias Monica Riofrio Nadia Ordoniez Hernain Moreano 《极地研究(英文版)》2013,(4):273-280
This study aims to report baseline soil nutrients, specifically the organic carbon, nitrogen and phosphorus profile, in soil samples collected from Puntta Fort William on Greenwich Island in maritime Antarctic. Samples were collected along two transect lines during the early summer of 2008. Ward's method of hierarchical agglomerative clustering was employed to group the sampling points based on their physico-chemical properties. In this context, the soil samples can be grouped into three major clus- ters: (1) Samples with intensive biological activities, (2) samples from the area recently exposed by glacial retreat and (3) samples from barren and dried areas. Nutrient contents in Punta Fort William are driven by the intensity of biological activities as well as melt water from the Qnito glacier. 相似文献