Coral reef boulders as recorders of cyclone activity over the last 3500 years (Fakarava Atoll, Tuamotu, French Polynesia)

IF 2.6 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology Pub Date : 2025-06-11 DOI:10.1016/j.margeo.2025.107605

Lucien F. Montaggioni , Bernard Salvat , Éric Brunaud , Edwige Pons-Branchu , Gilbert Poli , Bertrand Martin-Garin

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引用次数: 0

Abstract

Extreme marine hazard events are expected to increase in the next future as a response to global warming. Estimating their frequency and magnitude in the recent past is of prime concern to better project their future impacts. In tropical reef provinces, coral boulders deposited on reef top surfaces can be used as key proxies for defining the occurrence – recurrence time and effects of paleo-storms. The present study defines origin, morphometry, location, orientation, timing and mode of deposition of a number of coral reef boulders present on reef-flats surfaces, along the south-eastern rim areas of Fakarava Atoll, north-west Tuamotu, central South Pacific. These boulders, extracted from the upper forereef spurs, were projected onto the reef-flat zone, at distances of 51 to 235 m from the outer reef edge. Among the 44 described boulders >20 m³, only 19 were revealed to be covered by well-preserved coral colonies in growth position and as such, were submitted to physical analysis and U/Th dating. Upper reef spurs have been built from about 5000 to 3000 cal. yr BP. Dominantly platy in shape, with sharp broken, lateral faces, the 19 investigated boulders range between 3 and 8.5 m long, 4 and 82 m³ in volume, 6.8 to 139.4 tons in weight. The minimum flow velocities to initially move and uplifted these blocks were estimated between about 4 to >13 m/s. Morphometric comparison of the boulder set investigated at Fakarava with those from nearby atolls recognized as cyclone-moved strongly suggests that boulder detachment and deposition at Fakarava have resulted from cyclogenesis than tsunamigenic impacts. Contrary to cyclone-related boulder deposition that appears to have occurred mainly during the last centuries in the nearby atolls, U/Th dating of boulders at Fakarava reveals that cyclogenesis has increased between 3400 and 2300 cal. yr BP (15th–4th centuries BC) and between 2,000 and 1,700 cal. yr BP (1st–4th centuries AD) in the considered region, with an expected mean reccurrence time of around 30 to 50 years. This intensification of cyclone activity is interpreted as related to amplified enso phases in the south Pacific.

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珊瑚礁巨石作为过去3500年气旋活动的记录者（法属波利尼西亚土阿莫土法卡拉瓦环礁）

由于全球变暖，预计未来极端海洋灾害事件将会增加。在最近的过去估计它们的频率和大小是更好地预测它们未来影响的首要问题。在热带珊瑚礁省，沉积在礁顶表面的珊瑚巨石可以作为确定古风暴发生-复发时间和影响的关键指标。本研究确定了沿南太平洋中部土阿莫土西北法卡拉瓦环礁东南边缘地区的礁滩表面上出现的一些珊瑚礁巨石的起源、形态、位置、方向、时间和沉积模式。这些巨石是从上部的前礁刺中提取出来的，被投射到离外礁边缘51到235米的礁滩地带。在描述的44块20立方米的巨石中，只有19块被保存完好的珊瑚群落所覆盖，因此需要进行物理分析和U/Th定年。上礁刺形成于约5000至3000 cal. yr BP。被调查的19块巨石主要呈板状，具有锋利的破碎侧面，长度在3至8.5米之间，体积在4至82立方米之间，重量在6.8至139.4吨之间。最初移动和抬升这些区块的最小流速估计在4到13米/秒之间。法卡拉瓦研究的巨石组与附近被认为是气旋移动的环礁的巨石组的形态计量学比较强烈地表明，法卡拉瓦的巨石分离和沉积是由气旋形成而不是海啸形成的影响造成的。与旋风相关的巨石沉积似乎主要发生在最近几个世纪附近的环礁相反，Fakarava巨石的U/Th定年显示，在考虑的地区，旋风形成在3400至2300 cal. yr BP（公元前15 - 4世纪）和2000至1700 cal. yr BP（公元1 - 4世纪）之间增加，预计平均复发时间约为30至50年。这种气旋活动的增强被解释为与南太平洋enso阶段的放大有关。

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来源期刊

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.