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1.
古海洋缺氧事件与地球历史中水圈的节律颜佳新（中国地质大学，武汉，４３００７４）在现代大洋中，缺氧层往往位于水体中部。从浅水向深水，随水深增大，水体中溶氧量一般逐步下降。而底层水体由于受两极下沉水体充氧的影响缺氧并不明显。深海钻探对中、新生代沉积地层的... 相似文献
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寒武纪晚期到奥陶纪早期的海洋动物多样性整体水平较低,生物地球化学研究认为可能与海洋氧化还原状态波动有关,但仍证据较少。保存良好的海相碳酸盐岩沉积被认为能够记录古代海水的地球化学信息,其铀同位素组成 (δ238U) 可用来反映全球海洋的氧化还原状态。文章测定了华南瓦儿岗剖面寒武系第十阶底部海相碳酸盐岩的δ238U值,结果显示在寒武纪第十期早期U同位素组成可能存在三次负漂移,对应的δ238U值分别为-0.8‰、-0.55‰和-0.60‰,指示三个海洋缺氧时段。通过U同位素质量平衡模型计算得出,三个缺氧时段全球海洋底层水体分别约有22％、3.5%和5%的缺氧面积。初步推断第一次缺氧可能与风化输入营养元素增强致初级生物生产力提高有关,而其后的两次缺氧可能与原先的海底缺氧水体在海侵阶段上涌扩散有关。 相似文献
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为研究磨刀门盐水混合层化特征,基于SCHISM模型,建立了三维盐度数值模型,根据实测资料对其进行验证。结合水体势能异常理论,对枯季磨刀门河口混合层化的时空变化特征及深槽与浅滩的层化机制差异进行分析。结果表明:磨刀门河口小潮时水体层化最强,中潮时水体层化最弱,且拦门沙至挂定角段水体层化始终较强。磨刀门深槽水体层化主要受纵向平流、纵向水深平均应变和垂向混合影响,而浅滩水体层化则受横向平流、横向水深平均应变和垂向混合影响;磨刀门河口表、底层水体湍动能耗散率较高,而中间水层存在低耗散区,且涨潮时湍动能耗散率比落潮时大。 相似文献
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松辽盆地白垩纪缺氧地质事件的地质地球化学特征 总被引：15，自引：2，他引：13
松辽盆地白垩纪出现多期缺氧地质事件,它与全球白垩纪的地质事件相对应。青山口组一段及嫩江组一段出现较明显的缺氧地质事件,表现为有机质丰度高的源岩沉积。可溶有机质具有较低的姥植比,生物标志物出现了28,30 双降藿烷及保存了相对较为完整的C34或C35藿烷、重排甾烷的含量很低、有伽马蜡烷的存在等特征。松辽盆地在白垩纪时存在缺氧事件和海侵事件,与此同时,缺氧事件造成了这些地层中富含并具有高度分散性区域特征的生物化石的组合,形成了层序地层学上的密集段;缺氧事件又反作用于底栖生物,导致了松辽盆地古生物演化史上的生物绝灭事件。松辽盆地以持续沉降为主,湖盆水域迅速扩大,水体加深,近岸湖水表层生物生产率提高,底层水循环不畅导致了湖水底层水体缺氧,引发了古湖泊缺氧事件。在松辽盆地的缺氧事件中形成了青山口组一段及嫩江组一段的黑色泥岩(部分地区发育页岩),成为松辽盆地的主力油源层,为大庆油田的形成奠定了良好的物质基础。 相似文献
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桑沟湾水体中有机磷农药残留组成与分布 总被引：2，自引：1，他引：1
采用气相色谱-质谱法定量测定桑沟湾海域水体中有机磷农药残留,分析了其组成与分布特征。2009年4月(春季)和10月(秋季)桑沟湾海域水体中8种有机磷农药的含量测定结果表明:桑沟湾有机磷农药的总浓度水平是春季小于秋季,有机磷农药的总浓度范围为0.001～0.265μg/L,均值为0.061μg/L。该海域水体中共检出6种有机磷农药,马拉硫磷和对硫磷是桑沟湾水体中主要的有机磷农药污染物。有机磷农药分布特征大致呈现春季表层水体中近岸高,离岸低,由湾口向湾内递减,底层水体中在湾口处浓度最高;秋季表层水体中由西北岸、东北湾口向湾中央渐增,底层水体中呈现由湾内向湾口递增的趋势。本研究提供的数据可为了解该海域的有机磷农药污染分布情况提供参考。 相似文献
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磨刀门水道盐度混合层化机制 总被引：3，自引：0，他引：3
基于Simpson方法和磨刀门水道2009年枯季水文实测资料,选取上、下游两个站位的径流层化、潮汐混合、风致扰动3个影响河口水体分层的主要因素进行盐度混合的层化机制分析。研究表明:由于M1站位处上游,径流作用相对占优,分层不明显,只在涨潮急流时出现微弱的盐度分层;M2站则水体分层明显,小潮期间径流作用占主导,水体呈持续性分层,当由小潮转为中潮后,潮流作用增强,出现周期性分层现象,大潮以后,由于上游径流增加,潮流与径流作用相当,仍为周期性分层,但分层有所加强。层化的发育程度依赖径流致层化作用与潮汐、风致混合作用的博弈。 相似文献
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为监测珠江口河网区水体的盐度变化,基于同步测量的水体黄色物质、盐度和水体表面光谱数据,利用MATLAB分析了水体光谱反射率和黄色物质浓度之间的关系。结果表明:在磨刀门水道,反射率与黄色物质在400nm处的吸收系数g400有较好关系,在R704/R513处,R2=0.70;在虎门水道,g400与反射率比值R703/R488之间也有较强的负相关,R2=0.58。同样,又分析了磨刀门和虎门水道黄色物质吸收系数与表面盐度的关系,都发现了较好的相关性,R2>0.67。根据以上分析,得到了一种珠江口河网区水体表面盐度监测的新方法,并采用中等分辨率成像光谱仪(MERIS)的模拟数据来进行模型验证,结果表明利用MERIS数据对珠江口河网区咸潮进行监测是可行的(均方根误差小于0.308%)。 相似文献
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沉积物颜色是其物质组成和形成环境的重要标志,对古海洋古环境重建有特殊指示意义。国际大洋发现计划(IODP)368航次在南海北部钻取的U1502站沉积岩心中发现了上百米红褐色-绿灰色韵律沉积层,但其成因不明。为探究其物源和红绿韵律沉积层的成因,我们对该站位岩心样品开展了矿物学和地球化学分析,包括粒度、黏土矿物、常微量元素和Sr-Nd同位素组成、有机碳含量及碳酸盐碳氧同位素组成分析。物源分析表明,U1502站沉积物陆源输入以珠江为主而吕宋次之,红层相对绿层有稍多的吕宋物质贡献。地球化学指标指示红绿沉积层的形成没有遭受热液、冷泉流体的影响,其形成是南海晚中新世构造演化和冰期-间冰期旋回中水体通风、底层水氧化还原环境改变及早期成岩作用共同影响的结果。结合以前南海北部沉积物源研究及沉积物颜色频谱分析,推测红绿层可能分别对应了间冰期-冰期时间尺度。指标重建指示了红绿层分别形成于偏氧化和偏还原的底层水氧化还原环境。自中中新世以来随着吕宋岛弧与欧亚板块碰撞,南海海盆从开放的环境变得相对封闭,其深部通风和氧化还原条件开始呈现典型的冰期-间冰期旋回模式。红层对应了间冰期高海平面时期南海深层水通风良好、水体偏氧化的沉积环境,而绿层则指示了冰期低海平面时期南海层化加强、水体偏还原的环境。不同的氧化还原条件控制了早期成岩作用中致色含铁自生矿物如赤铁矿的形成与转化,最终引起沉积层颜色韵律变化。 相似文献
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珠江河口沉积物粒度特征及其对底层水动力环境的指示 总被引：17，自引：3，他引：14
珠江口伶仃洋及邻近海域沉积物粒级变化大。频率分布曲线形态的变化揭示了珠江河口不同区域泥沙来源的差异。在平面分布上,粗粒级含量从西北部和北部向东南部迅速降低,而细粒级含量高值往往出现在河口中部。表层沉积物平均粒径梯度变化方向与珠江口悬浮物的运移方向大致吻合。反演获得的底层海流不同区域的优势速度与实测资料相符。两者较好地指示了沉积物多年平均优势海流速度和方向,表明利用沉积物粒度数据比较成功地反演出了珠江口沉积物推积前的搬运水动力环境。 相似文献
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采用物理模型实验方法对不同潮差驱动下咸水入侵距离进行实验研究,结果表明存在潮差临界值使得咸水入侵距离最短,当潮差小于该临界值,咸水入侵距离随潮差增大呈快速减小趋势,而大于该临界值则呈缓慢增大趋势。基于实验数据对盐淡水混合进行理论分析,揭示了实验现象的产生机制:①潮差增大过程中盐淡水混合由高度分层变为均匀混合,导致驱动咸潮入侵的动力发生了改变;②当盐淡水为弱混合类型,盐淡水高度分层,重力环流输运是盐进入河口的主要方式,潮汐强度增大减小了盐淡水分层,减弱了重力环流的输运作用,因此入侵距离变小;③当盐淡水为强混合类型,盐淡水混合均匀,重力环流输运作用大大减弱,潮汐扩散成为主要的输运方式,潮汐增强使得扩散能力增大,因此潮汐强度越大,咸潮入侵距离越大。 相似文献
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Relationships among bottom-water dissolved oxygen (DO), vertical stratification, and the factors responsible for stratification-destratification in this shallow, low tidal-energy estuary were studied using a 15-yr set of biweekly measurements, along with some recent continuous-monitoring data. Hypoxia develops only when there is both vertical water-column stratification and warm water temperature (>15°C). In July, 75% of the DO readings were <5 mg 1?1, and one-third were <1 mg 1?1. Severe hypoxia occurs more frequently in the upper half of the estuary than near the mouth. Both the time series data and correlation analysis results indicate that stratification events and DO levels are tightly coupled with variations in freshwater discharge and wind stress. Stratification can form or disappear in a matter of hours, and episodes lasting from one to several days seem to be common. Estimated summertime respiration rates in the water and sediments are sufficient to produce hypoxia if the water is mixed only every 6–12 d. There has been no trend toward lower bottom water DO in the Pamlico River Estuary over the past 15 yr. *** DIRECT SUPPORT *** A01BY059 00002 相似文献
13.
根据Deleersnijder定义的一个平均年龄概念,运用耦合了物质输运模式的一个三维水动力-富营养化数值模型(HEM-3D),研究了位于美国北卡罗莱纳州Pamlico河口(PRE)的污染物输运时间在不同淡水流量影响下的分布情况。模型结果表明,在正常期,污染物被输运出PRE需要大约65d的时间。而在枯水期和洪水期,污染物分别需要230d和20d时间被输运出PRE。这表明物质输运过程明显受淡水流量的影响。污染物输运时间的空间变化显著受河口中盐度入侵的影响,咸水入侵在其可以达到的最大区域形成了一个盐度锋面,而这个锋面阻碍了污染物向外的输运。盐度层化对输运时间的垂向分布影响显著,输运时间垂向梯度随着盐度层化的增强而增大。 相似文献
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为研究磨刀门水道咸潮上溯的动力特性,基于非结构网格海洋模型（Finite Volume Coastal Ocean Model,FVCOM）,构建了覆盖珠江河口及其上游网河区的高分辨率三维斜压数值模型,采用实测资料对其进行率定和验证,并开展了咸潮上溯的数值模拟计算。根据计算结果和实测资料,对磨刀门水道大、中、小潮期间的盐淡水分层与混合特征、盐分物质的分层输移机制进行分析,探讨其咸潮上溯强度时空分布差异的原因。结果表明:小潮期,底层累积盐通量明显大于表层,净输移方向为陆向;大潮期,表层累积盐通量明显大于底层,净输移方向为海向;而平衡点一般出现于中潮期,这就是磨刀门水道咸潮上溯最强和最弱时刻分别出现于小潮和大潮后的中潮期的原因所在。 相似文献
15.
We describe the tidal circulation and salinity regime of a coastal plain estuary that connects to the ocean through a flood
tide delta. The delta acts as a sill, and we examine the mechanisms through which the sill affects exchange of estuarine water
with the ocean. Given enough buoyancy, the dynamics of tidal intrusion fronts across the sill and selective withdrawal (aspiration)
in the deeper channel landward appear to control the exchange of seawater with estuarine water. Comparison of currents on
the sill and stratification in the channel reveals aspiration depths smaller than channel depth during neap tide. During neap
tide and strong vertical stratification, seawater plunges beneath the less dense estuarine water somewhere on the sill. Turbulence
in the intruding bottom layer on the sill promotes entrainment of fluid from the surface layer, and the seawater along the
sill bottom is diluted with estuarine water. During ebb flow, salt is effectively trapped landward of the sill in a stagnant
zone between the aspiration depth and the bottom where it can be advected farther upstream by flood currents. During spring
tide, the plunge point moves landward and off the sill, stratification is weakened in the deep channel, and aspiration during
ebb extends to the bottom. This prevents the formation of stagnant water near the bottom, and the estuary is flooded with
high salinity water far inland. The neapspring cycle of tidal intrusion fronts on flood coupled with aspiration during ebb
interacts with the sill to play an important role in the transport and retention of salt within the estuary. 相似文献
16.
Development of seasonal hypoxia was studied weekly in the western narrows of Long Island Sound (WLIS) during the summers of 1992 and 1993 by measuring hydrographic properties, biological oxygen demand (BOD), biomass, production, and mortality of phytoplankton and bacterioplankton in the water column. Dissolved oxygen in bottom waters was low and variable during stratified periods (19–51% saturation), oscillating in and out of hypoxic conditions (defined as <3 mg O2 l−1 or 94 μM O2). Hypoxia was more prevalent in 1993 than in 1992, corresponding to greater water column stratification in 1993. Microbial BOD in bottom waters appeared to be fueled by delivery of autochthonous carbon from phytoplankton blooms rather than allochthonous carbon input. Phytoplankton production responded to elevated NH4 + concentrations, especially when the mixed layer was shallow. NH4 + concentrations generally varied as a function of the preceding week's rainfall (r2=0.765). Bacterial production did not covary with phytoplankton production, yet was closely correlated with particulate organic carbon, which was chlorophyll-rich. Results indicate that the timing and severity of hypoxia development are strongly coupled to allochthonous input of NH4 + after heavy precipitation. Observations illustrate for the first time that bottom waters in this system oscillate in and out of hypoxia on an almost weekly basis rather than sustain them over the entire stratified period. The frequency of these oscillations depends upon variations in nutrients, planktonic production and export, and bottom water ventilation. 相似文献
17.
Periodic frontogenesis in a region of freshwater influence 总被引：1，自引：0，他引：1
Observations are presented from a series of three conductivity-temperature-depth (CTD) surveys of the salinity and temperature structure of Liverpool Bay, a region that is strongly influenced by the input of fresh water from the rivers of northwest England. The surveys demonstrate the development, seaward movement, and eventual decay of a haline front. The frontogenesis is driven by the relaxation of a freshwater-induced horizontal density gradient following the decrease in tidal range at neap tides. It results in the area of Liverpool Bay being stratified for a period of 8 d before the increase in tidal mixing as the spring tide approaches returns the region to its initial vertically mixed state. In Liverpool Bay this process usually repeats on the spring-neap cycle, though strong wind-mixing may prevent the frontogenesis and subsequent stratification. Analysis with a 1-dimensional numerical model suggests that relaxation of an initially nonlinear horizontal density field, creating the front, is triggered by the stability produced by tidal straining of the water column during the ebb half-cycle. The reduction in tidal mixing energy approaching neap tide does not lead to frontogenesis without this initial stability. Such a regular stratification signal will have a marked effect on the local environment. The periodic frontogenesis will act as a tidal pump, moving buoyant substances in the water column offshore, while the onshore residual currents lower in the water column will more deeper dissolved substances inshore. The cycling of stability on the springneap time scale is considerably faster than the seasonal cycle of thermal stratification in the shelf seas, but is similar in creating the conditions required for phytoplankton blooms. Conditions favorable for enhanced primary production may therefore occur frequently in such regions of freshwater influence. 相似文献
18.
Hypoxia/anoxia in bottom waters of the Rappahannock River, a tributary estuary of Chesapeake Bay, was observed to persist throughout the summer in the deep basin near the river mouth; periodic reoxygenation of bottom water occurred on the shallower sill at the river mouth. The reoxygenation events were closely related to spring tide mixing. The dissolved oxygen (DO) in surface waters was always near or at the saturation level, while that of bottom waters exhibited a characteristic spatial pattern. The bottom DO decreased upriver from river mouth, reaching a minimum upriver of the deepest point of the river and increasing as the water becaume shallower further upriver. A model was formulated to describe the longitudinal distribution of DO in bottom waters. The model is based on Lagrangian concept—following a water parcel as it travels upriver along the estuarine bottom. The model successfully describes the characteristic distribution of DO and also explains the shifting of the minimum DO location in response to spring-neap cycling. A diagnostic study with the model provided insight into relationships between the bottom DO and the competing factors that contribute to the DO budget of bottom waters. The study reveals that both oxygen demand, either benthic or water column demand, and vertical mixing have a promounced effect on the severity of hypoxia in bottom waters of an estary. However, it is the vertical mixing which controls the longitudinal location of the minimum DO. The strength of gravitational circulation is also shown to affect the occurrence of hypoxia. An estuary with stronger circulation tends to have less chance for hypoxia to occur. The initial DO deficit of bottom water entering an estuary has a strong effect on DO concentration near the river mouth, but its effect diminishes in the upriver direction. 相似文献
19.
Data are presented from several experiments in the freshwater-saltwater interface (FSI) region of the Tamar Estuary. Longitudinal surveys of salinity and suspended particulate matter (SPM) at high water showed that the location of the FSI could be predicted in terms of a power-law regression with freshwater runoff. Longitudinal transects also were surveyed over periods of several hours. The FSI was observed to advect into the region on the flood with strong vertical mixing. After high water, stratification became intense as fresher water ebbed in the surface layers. The near-bed water in the stratified region began to ebb between 2 h and 3 h before low water. A model of the vertical structure of longitudinal currents showed that the enhanced stratification on the ebb, coupled with the longitudinal density gradient, partly produced this long period of slack, near-bed currents following high water. A strong turbidity maximum (TM) occurred during spring tides and was located slightly up-estuary of the FSI at high water. Longitudinal transects during a period of low freshwater runoff and large neap tide showed that at the start of the flood the TM was associated with the FSI region. As the FSI advected up-estuary on the flood there was considerable resuspension of sediment at the FSI. Some of this SPM moved with the FSI and reached the limit of saline intrusion, where it formed a slowly-eroding TM as particles settled during the long, high-water slack period. As the near-bed currents increased on the ebb and the FSI moved down-estuary, strong vertical mixing and resuspension of recently deposited sediment occurred in the unstratified water behind the FSI and the associated TM advected down-estuary. Additional effects were present with stronger tides and increased runoff. 相似文献