中国南海环礁潮下礁盘的沉积动力学

IF 2.6 3区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Marine Geology Pub Date : 2024-05-21 DOI:10.1016/j.margeo.2024.107310
Jin Li , Andrew D. Ashton , Ya Ping Wang , Xiaomei Xu , Shu Gao
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引用次数: 0

摘要

中国南海的环礁面积占世界总面积的 15%。印度洋-太平洋地区的大多数礁滩通常发育到当代海平面,与此不同的是,中国南海的礁滩有相当一部分淹没在 5-20 米深处。为了深入了解现代过程,确定这些潮下礁滩是否由水动力积极塑造,我们对一个 12 米深的西南向礁滩进行了为期 8 个月的现场观测。测量结果表明,海浪的季节性变化和稳定的潮汐流十分普遍。东北季风(1 月至 5 月)对礁石平地的影响不大,而西南季风(6 月至 9 月)则使礁石长期暴露在大浪中(平均显著波高 1.3 米,平均轨道速度 0.22 米/秒)。这种暴露导致形成移动的海床波纹和粗粒珊瑚沙的夹带。对潜在床面负载迁移率的估算表明,海浪和海流的共同作用导致礁石平地的物质流失,进入环礁湖或沿着环礁的前礁斜坡向下移动。在观测期间,这种沉积物损失相当于礁床被侵蚀 28 毫米。由于这些潜在的损失可能会被珊瑚礁的生长所补偿,我们的测量结果表明,就礁床海拔而言,现代沉积物预算在潮下礁坪的维护方面发挥了重要作用。因此,深礁平地并不一定属于先前确定的放弃模式;珊瑚沉积物的供应和运输引起的流失之间的平衡可能会导致一种平衡形态,或一种 "锁定 "模式。
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Sediment dynamics on a subtidal reef flat of an atoll in the South China Sea

Atolls in the South China Sea comprise 15% of the world's total in area. In contrast to most reef flats in the Indo-Pacific region, which typically develop up to contemporary sea level, a significant portion of their reef flats in the South China Sea are inundated at depths of 5–20 m. To gain insights into modern processes and determine whether these subtidal reef flats are actively shaped by hydrodynamics, we carried out an in situ observation on a 12 m-deep southwest-facing reef flat over a period of 8 months. The measurements revealed a prevalence of seasonally varying waves and stable tidal currents. While the reef flat remained sheltered from the northeast monsoon (January–May), the southwest monsoon (June–September) led to prolonged reef exposure to substantial waves (mean significant wave height of 1.3 m, with an orbital velocity of 0.22 m/s on average). Such an exposure resulted in the formation of mobile bed ripples and entrainment of coarse-grained coral sands. Estimates of potential bedload transport rate indicated that the combined action of waves and currents caused material loss from the reef flat, with movement into the lagoon or down the fore-reef slope of the atoll. This sediment loss was equivalent to reef bed erosion of up to 28 mm during the observation period. As these potential losses may be compensated by coral reef growth, our measurements implied that modern sediment budgeting has played a significant role in the maintenance of subtidal reef flats, in terms of bed elevation. Hence, the deep reef flat does not necessarily belong to the previously identified give-up pattern; a balance of coral sediment supply and transport-induced loss may result in an equilibrium morphology, or a “lock-up” pattern.

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来源期刊
Marine Geology
Marine Geology 地学-地球科学综合
CiteScore
6.10
自引率
6.90%
发文量
175
审稿时长
21.9 weeks
期刊介绍: Marine Geology is the premier international journal on marine geological processes in the broadest sense. We seek papers that are comprehensive, interdisciplinary and synthetic that will be lasting contributions to the field. Although most papers are based on regional studies, they must demonstrate new findings of international significance. We accept papers on subjects as diverse as seafloor hydrothermal systems, beach dynamics, early diagenesis, microbiological studies in sediments, palaeoclimate studies and geophysical studies of the seabed. We encourage papers that address emerging new fields, for example the influence of anthropogenic processes on coastal/marine geology and coastal/marine geoarchaeology. We insist that the papers are concerned with the marine realm and that they deal with geology: with rocks, sediments, and physical and chemical processes affecting them. Papers should address scientific hypotheses: highly descriptive data compilations or papers that deal only with marine management and risk assessment should be submitted to other journals. Papers on laboratory or modelling studies must demonstrate direct relevance to marine processes or deposits. The primary criteria for acceptance of papers is that the science is of high quality, novel, significant, and of broad international interest.
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