Jin Li , Andrew D. Ashton , Ya Ping Wang , Xiaomei Xu , Shu Gao
{"title":"中国南海环礁潮下礁盘的沉积动力学","authors":"Jin Li , Andrew D. Ashton , Ya Ping Wang , Xiaomei Xu , Shu Gao","doi":"10.1016/j.margeo.2024.107310","DOIUrl":null,"url":null,"abstract":"<div><p>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.</p></div>","PeriodicalId":18229,"journal":{"name":"Marine Geology","volume":null,"pages":null},"PeriodicalIF":2.6000,"publicationDate":"2024-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Sediment dynamics on a subtidal reef flat of an atoll in the South China Sea\",\"authors\":\"Jin Li , Andrew D. Ashton , Ya Ping Wang , Xiaomei Xu , Shu Gao\",\"doi\":\"10.1016/j.margeo.2024.107310\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>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.</p></div>\",\"PeriodicalId\":18229,\"journal\":{\"name\":\"Marine Geology\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":2.6000,\"publicationDate\":\"2024-05-21\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Marine Geology\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S002532272400094X\",\"RegionNum\":3,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"GEOSCIENCES, MULTIDISCIPLINARY\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Marine Geology","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S002532272400094X","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOSCIENCES, MULTIDISCIPLINARY","Score":null,"Total":0}
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.
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.