黄岩岛环礁地貌近40年变化的遥感分析

重建珊瑚礁的地貌变化历史将有助于理解珊瑚礁对气候变化的响应规律。因此,本文选择以南海中部相对孤立、低潮时部分露出的黄岩岛环礁（15°09'N,117°45'E）为对象,基于1977年至2019年间的Landsat和Sentinel-2共22景遥感影像来探讨南海珊瑚礁地貌的变化历史与规律。首先结合实测水深数据探讨遥感影像灰度的变化与珊瑚礁地貌带分界线位置的对应关系;然后通过基于梯度矢量流的主动轮廓线模型（GVF-Snake）和手动边缘提取相结合的方式,提取出黄岩岛环礁主要的地貌带分界线;进而利用数字化海岸线分析系统（DSAS）定量分析这些地貌带分界线位置的变化,并利用线性拟合来探讨这些地貌面积的变化趋势。结果表明：1）黄岩岛外海与礁前斜坡分界线、礁前斜坡与礁坪分界线、潟湖坡与潟湖底分界线均具有向外海移动的趋势,它们的平均移动速率分别是0.36 m/a、0.06 m/a和0.23 m/a,而礁坪与潟湖坡分界线则具有向潟湖移动趋势,平均移动速率为0.16 m/a;2）潟湖底的面积和礁体总面积都呈现增加的趋势,潟湖坡的面积有减少趋势,礁坪的面积则在1977年至1997年间以114523 m²/a的速率增加,其后在1997年至2019年间则以11289 m²/a的速率减少。进一步分析认为,近40年来,黄岩岛珊瑚礁生态系统退化致使其造礁能力的减弱,加之海平面上升、风暴潮侵蚀、海水溶解等因素的综合影响,导致黄岩岛珊瑚礁面积减少。

     

川东北地区长兴组生物礁成礁类型及分布

目前在川东北地区发现了龙岗、普光、黄龙、五百梯等多个生物礁气藏,它们具有储层较厚、面积较大、储量丰度高等特点,展示出了广阔的滚动勘探开发前景。本文根据野外露头与钻井资料,结合前人研究成果,通过对生物礁的造礁生物古生态特征研究,按照生物礁所处的古地理位置、礁体的形态和礁岩的特征,归纳总结出川东北地区长兴组生物礁主要分为台地边缘礁和台内点礁,其特征差异明显。台地边缘礁主要表现为规模较大,礁组合相带完整,礁体旋回较少,水体能量强,其分布受古地理位置、古地貌环境控制,主要沿海槽两侧呈串珠状分布;台内点礁主要表现为规模较小,水体能量较弱,造礁生物个体较小,无礁前礁后沉积,礁体旋回较多,发育有凝块石,主要发育在长兴组中下部,分布规律性不强,主要受古地貌影响,沿台内局部高地随机分布。     

Facies distribution of the Lower Cambrian cryptic microbial and epibenthic archaeocyathan-microbial communities, western Anti-Atlas, Morocco

Marine microbial communities recorded in the Moroccan Anti‐Atlas were unaffected across the Neoproterozoic–Cambrian transition. A stromatolite‐dominated consortium was replaced at the beginning of the Atdabanian (ca 20 Myr after the Neoproterozoic–Cambrian boundary) by shelly metazoan and thromboid consortia, which contain the oldest biostratigraphically significant fossils of the Moroccan Cambrian. The associated collapse of microbial mat (stromatolitic) growth appears to coincide with a change from pre‐Atdabanian shallow‐water restricted conditions into Atdabanian deeper, open‐sea conditions. It is postulated that this environmental change led to an episode of improved water circulation over carbonate platform interiors, promoting shelly metazoan immigration into the region. The Tiout/Amouslek lithostratigraphic contact in the early Atdabanian marks the end of an episodically unstable seafloor as suggested by the abundance of slumping and sliding structures, and synsedimentary microfaults and cracks recorded in the underlying Tiout Member. Concurrent with the transition is the occurrence of a network of cryptic fissures and cavities that provided habitats for a coelobiontic chemosynthetic–heterotrophic microbial community composed of stromatolitic crusts, Renalcis–Epiphyton–Girvanella intergrowths, and Kundatia thalli. In the overlying Amouslek Formation, archaeocyathan–thromboid reefs were constrained by substrate stability, water depth and subsidence rate. Four reef geometries are distinguished: (i) patch reefs surrounded by shales, (ii) bioherms in which flank beds intercalate laterally with carbonate and shale inter‐reef sediments, (iii) biostromes or low‐relief structures formed as a result of lateral accretion of patch reefs, and (iv) kalyptrate complexes that nucleated because of a marked tendency for aggregation, and in which patch reefs and bioherms occur stacked together bounded by clay–marl–silt seams.     

Storm‐dominated sedimentation in a protected basin fringed by coral reefs,Nara Inlet,Whitsunday Islands,Great Barrier Reef,Australia

Hydrodynamic data and samples of bed sediment were collected from Nara Inlet, a small incised embayment in the Whitsunday Islands, central Great Barrier Reef. Measured tidal currents in the inlet do not exceed 0.2 ms^–1 even at spring tides. Swell waves dominate much of the inner shelf of the Great Barrier Reef but are absent from in the inlet due to the presence of a fringing reef at the inlet mouth. On the silty sand floor of the inlet, particle size decreases towards the inlet head. Most of the bed is too coarse to be remobilised by fair‐weather wave and tides, and we predict that bedload sediment transport thresholds are only exceeded in the inlet during cyclones. The observed distribution of bed sediments is consistent with landward dispersal of sediment under storm conditions. Over 20 m of (presumably Holocene) sediments occurs in the inlet and the seismic character of the infill is consistent with the observed textural variation of the modern sediments. We infer that sediment accumulation on the floor of the inlet has been storm dominated throughout much of the Holocene.     

Celestite formation, bacterial sulphate reduction and carbonate cementation of Eocene reefs and basinal sediments (Igualada, NE Spain)

Petrographic and geochemical studies of an Upper Eocene reef and associated basinal sediments from the mixed carbonate–siliciclastic fill of the south‐eastern Pyrenean foreland basin near Igualada (NE Spain) provide new insights into the evolution of subsurface hydrology during the restriction of a marine basin. The reef deposits are located on delta‐lobe sandstones and prodelta marls, which are overlain by hypersaline carbonates and Upper Eocene evaporites. Authigenic celestite (SrSO₄) is an important component in the observed diagenetic sequences. Celestite is a significant palaeohydrological indicator because its low solubility constrains transportation of Sr²⁺ and SO₄^2? in the same diagenetic fluid. Stable isotopic analyses of carbonates in the reef indicate that meteoric recharge was responsible for aragonite stabilization and calcite cementation. Sulphur and oxygen isotope geochemistry of the celestite demonstrates that it formed from residual sulphate after bacterial sulphate reduction, but also requires that there was a prior episode of sulphate recycling. Meteoric water reaching the reef and basinal areas was most probably charged with SO₄^2? from the dissolution of younger Upper Eocene marine evaporites. This sulphate, combined with organic matter present in the sediments, fuelled bacterial sulphate reduction in the meteoric palaeoaquifer. Strontium for celestite precipitation was partly derived in situ from dissolution of aragonite corals in the reef and basinal counterparts. However, ⁸⁷Sr/⁸⁶Sr data also suggest that Sr²⁺ was partly derived from dissolution of overlying evaporites. Mixing of these two fluids promoted celestite formation. The carbonate stable isotopic data suggest that the local meteoric water was enriched in ¹⁸O compared with that responsible for stabilization of other reefs along the basin margin. Furthermore, meteoric recharge at Igualada post‐dated evaporite deposition in the basin, whereas other parts of the same reef complex were stabilized before evaporite formation. This discrepancy resulted from the spatial distribution of continental siliciclastic units that acted as groundwater conduits.     

Emergence of co-management governance for Hawai‘i coral reef fisheries

Governance failures associated with top-down management have spawned a myriad of institutional arrangements to engage resource users in decision-making through co-management. Although co-management can take many forms and may not always lead to positive outcomes, it has emerged as a promising governance option available to meet social and ecological goals. Recent research on co-management of small-scale fisheries has used comparative approaches to test factors associated with social and ecological success. Less is known however, about how co-management institutional arrangements emerge and persist in the face of socioeconomic and environmental change. Here, we examine the emergence of co-management governance using a case study from coral reef fisheries in the Hawaiian Islands. We used a mixed methods approach, combining a robust policy analysis and a set of key respondent interviews to trace the evolution of this co-management arrangement. Our research uncovers a set of linked drivers and social responses, which together comprise the emergence phase for the evolution of co-management in this case study. Drivers include resource depletion and conflict, and social responses comprise self-organization, consensus building, and collective action. We share insights on key factors that affect these phases of emergence, drawing on empirical findings from our policy review and key respondent interviews. We conclude by describing ways that our findings can directly inform policy and planning in practice, including the importance of documenting the ‘creation story’ that spawned the new institutional arrangement, ensuring that enabling conditions are present, the complexity of defining community, the connection between process legitimacy and outcomes, and understanding the costs and timelines associated with co-management governance transitions.     

The main issues affecting coasts of the Indian and western Pacific Oceans: a meta-analysis from Seas at the Millennium

A review of the world oceans in three volumes by 365 scientists, provides scope for several ‘meta-analyses' of the main problems affecting over 100 areas in the year 2000. This article summarises the main issues affecting a sub-set of the reviewed areas, covering Asian, African and Arabian countries dealt with in Volume 2, which included over 50 articles. From all issues raised, assessment is made of the nature of the major ones, including evaluation of reasons why so many of them remain important issues after so much attention to them. These include long standing problems, several problems more newly flagged as becoming particularly important, the issue of global warming and no less than three related issues connected with fishing and over exploitation. One or two issues such as industrial pollution and sewage, previously considered of almost universal concern, almost traditional pollution issues even, continue to feature strongly for some countries, but while these were almost always referred to in Seas chapters, by and large these categories appear not to be the most pressing of issues today, except in localized areas (albeit areas where huge numbers of people live). Perhaps other issues have simply taken over. They are excluded from this article.     

南沙群岛岛礁地形地貌TM影像特征分析

根据南沙海区的地形地貌特征，利用TM图像，对不同的珊瑚礁、珊瑚沙发育状况和岛礁的地质特征与生态特征进行了分析，研究了水下礁、滩的物质组份、发育程度及TM影像特征，提出了30m以浅岛礁分类方法，查清了南沙海域岛、礁、滩、沙的形态和分布，细化并完善了南沙群岛岛礁分类。     

Middle and Late Devonian microbial carbonates,reefs and mounds in Guilin,South China and their sequence stratigraphic,paleoenvironmental and paleoclimatic significance

The importance of calcimicrobes and microbialite in carbonate platform and reefal environments has been stressed in recent literature. Burne and Moore[1] introduced the term microbialite to describe the clotted, laminated and undifferentiated fabrics formed by mi-crobial communities. Microbialites are organosedi-mentary deposits that have accreted as a result of ben-thic (prokaryotic or eukaryotic) communities, trapping and binding detrital sediment[1]. Microbial organisms and microbialite are…     

基于底质类型变化监测的2005—2018年西沙永乐群岛珊瑚礁白化分析

在海洋环境变化和人类活动的双重影响下,我国珊瑚礁白化现象日趋严重,珊瑚礁健康状况、珊瑚种群数量和丰富度呈逐年下降的趋势。本文基于2005-2007年QuickBird卫星影像、2011-2012年QuickBird/WorldView-2卫星影像和2016-2018年GF-1/2卫星影像等3期高分辨率遥感数据,以西沙永乐群岛羚羊礁、中建岛等14个岛礁为研究区（以下统称永乐群岛）,利用支持向量机（support vector machine,SVM）分类方法结合人机交互信息提取方法完成了3期永乐群岛的珊瑚礁底质类型分类,并通过珊瑚礁底质类型变化分析了永乐群岛珊瑚礁白化特征。主要结论包括：（1）提出了一种珊瑚礁白化程度分级的方法,将永乐群岛白化状况分为轻度、中度、重度和严重白化4个等级,通过分析发现在监测时段内14个岛礁中有13个发生了不同程度的白化,其中10个发生了重度白化（白化率20%以上）,1个严重白化（羚羊礁,白化率为33.36%）;（2）根据监测数据统计,上述珊瑚岛礁的白化主要是由珊瑚丛生区白化引起的,2005-2018年永乐群岛珊瑚丛生区白化面积占总的发生白化区域面积的70.55%;（3）14个岛礁中只有甘泉岛的活珊瑚覆盖在逐渐增加,活珊瑚覆盖面积由2006年5月10日的87.13 hm²增加到2018年3月7日的107.80 hm²。