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南永2井珊瑚礁“红色与黑色沉积夹层”的成因及环境意义初探 总被引:3,自引:1,他引:2
南沙群岛南永2井珊瑚礁古地磁学和地球化学研究发现:“黑色沉积夹层”的底界(99.69m)与布容正极性/松山反极性(B/M)转换、δ^18O曲线冷/暖(19/20)气候变换界限相对应,距今年龄约0.78Ma;“红色沉积夹层”与留尼汪事件I(Reunion I)地球磁场极性漂移(反转)相对应,距今年龄约2.04~2.01Ma.相对于正常的浅色礁岩沉积,黑色沉积层的磁化率(χ)、剩余磁化强度(Mr)以及MnO和Fe2O3含量均呈明显正异常;红色沉积层的磁化率(χ)、剩余磁化强度(Mr)和Fe2O3含量也出现正异常,结合古生物的分析结果,认为这一对特殊而典型的“沉积夹层”与古气候的突变有关,即全球气候变化以及所伴随的地球磁场极性反应,直接影响到古生物的生境状况,同时也影响到某些化学元素,特别是Fe和Mn等氧化还原敏感性元素的分散与富集,如当气候突然变暖时,冰期时浓缩的Fe和Mn等金属会大量氧化稀释;而当气候突然变冷时,原来被氧化的高价铁等又高度浓缩,这可能是珊瑚礁与“红与黑”沉积事件产生和消失的重要原因之一。 相似文献
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YIN Jianqiang CHEN Qingchao ZHANG Guxian HUANG Liangmin LI Kaizhi 《科学通报(英文版)》2006,51(B12):154-164
This study aims to examine spatial and temporal variations of zooplankton species composition, density and biomass distribution and community structure, based on the data obtained from three separate cruises carded out in November 1997, April and July 1999. Results show that 244 species of zooplankton and 8 groups of planktonic larvae were identified, which were dominated by copepods, followed by amphipods, ostracods and medusae. The total species were 201 and 198 for the cruises of November 1997 and July 1999, respectively, and no obvious seasonal variation of species richness was observed. The distribution of zooplankton species richness decreased from pelagic to coastal waters. Average richness of species in each station was higher in the cruises of November 1997(62) and April 1999(61) than in the cruise in July 1999 (56), which was mainly a result from the pelagic or coastal water mass movement made by the monsoon. Zooplankton in the upper waters (0--100 m) around Nansha Islands belonged to the typical tropic pelagic fauna, most of them were pelagic warm-water species, followed by coastal warm-water species and euryhaline warm-water species. The number of dominant species ranged from 5 to 7 in each cruise. No obvious seasonal succession of dominant species was ob- served. Sagitta enflata, Cypridina narni, Cosmocalanus darwinii, Pleuromamma gracilis and Echino-pluteus larva were the main dominant species. The average of zooplankton biomass and density in three cruises were 31, 32, 28 mg·m^-3 and 31, 39, 35 ind·m^-3, respectively. Copepods were the most abundant, followed by chaetognaths. Zooplankton high biomass distributed mainly in the northwestern waters around Nansha Islands, and generally occurred in the areas of oceanic front and upweUing. The main reason for zooplankton quantity without obvious seasonal variation was the relative steady temperature dynamics in the waters around Nansha Islands. 相似文献
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正一个属于中国的永久性南海据点是如何建成的。在1994年12月底,为配合南海渔政部门建设渔港需要,国家海洋局组织有关部门专家派"向阳红14号"考察船,对南海的美济礁进行了为期半个月的多学科珊瑚礁环境调查和勘测。 相似文献
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南海领土争议的由来与现状 总被引:1,自引:0,他引:1
当前所谓的"南海领土争议",主要是指南沙群岛的争议。南沙群岛在南海的东南角,分布区域南北长约1000公里。中国最早发现和命名了南沙群岛,最早并持续对南沙群岛行使主权管辖,国际社会也长期予以承认。 相似文献
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珊瑚共生虫黄藻密度结合卫星遥感分析2007 年南沙群岛珊瑚热白化 总被引:4,自引:0,他引:4
以珊瑚大量损失共生虫黄藻为特征的珊瑚白化, 是当今全球变暖背景下珊瑚礁大面积死 亡和退化的主要因素, 但白化的特征、过程和白化后的恢复等则因海域环境不同而有所差异. 依托2007 年6 月的南沙群岛航次, 在美济礁和渚碧礁进行了实地生态调查和采样, 室内分析了珊瑚共生虫黄藻密度、近10 年来南沙海域实测海表温度(SST)和调查期间的NOAA 卫星遥感资料, 探讨了2007 年发生在南沙群岛的珊瑚白化事件. 研究结果显示: (1) 白化的珊瑚主要分布在水深5 m以内, 最大可至20 m, 至少有35 种石珊瑚白化; (2) 珊瑚总白化率(单位面积内白化珊瑚个数占总珊瑚个数的比例) 为15.6%, 发生白化最严重的为枝状杯形珊瑚 (白化率为23%) 和鹿角珊瑚 (白化率为21%), 块状滨珊瑚和蜂巢珊瑚的白化率低, 没有发现菌珊瑚白化, 显示了菌珊瑚对高温有较高的耐受性; (3) 白化了的珊瑚损失了共生虫黄藻72%~90%, 而肉眼观察未白化的珊瑚也损失了31%~53%的虫黄藻, 指示当时南沙群岛的珊瑚正处于白化的初始阶段; (4) 调查期间实测月平均SST 为30.8℃, 为1998 年以来最高, 结合NOAA卫星的热点(Hotspot)和周热度指数(DHW), 认为2007 年6 月南沙群岛异常高SST 是导致美济礁和渚碧礁珊瑚白化的主要原因. 本研究还发现, 单纯用卫星遥感预警珊瑚白化事件可能会存在低估的现象. 相似文献
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