Nearshore microfossil assemblages in a Caribbean reef environment show variable rates of recovery following Hurricane Irma
Nearshore microfossil assemblages in a Caribbean reef environment show variable rates of recovery following Hurricane Irma
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飓风艾尔玛后，加勒比珊瑚礁环境中的近岸微化石组合显示出不同的恢复率
作者：
Mitchell;Pilarczyk;Spiske
现代微化石分布反映了特定地点的栖息地，并为评估近岸环境中的沉积物运输路径提供了机会。当应用于地质记录中的过度冲刷沉积物时，它们可以深入了解沉积物的来源和运输，这些因素对于了解过去风暴和海啸的频率和强度模式非常重要。现代分布研究很少见，通常第一个确定的研究是在过度冲刷事件发生后立即进行的，作为事后现场调查的一部分。这是有问题的，因为目前尚不清楚过度冲刷事件对近岸微化石组合有何影响，以及它们恢复到事件前条件所需的时间间隔。本研究利用红色同体（Homotrema rubrum）的分布记录了飓风艾尔玛对英属维尔京群岛阿内加达海岸附近的近岸沉积物的影响，红色同体是一种在珊瑚礁中具有明确来源的结壳有孔虫。从飓风“艾尔玛”发生前六个月到飓风“艾尔玛”发生后十八个月，在两年内进行了四个采样间隔，从该岛南北海岸的三个横断面收集了表面沉积物。围绕 Medoids 的分区聚类分析显示，飓风艾尔玛将大量保存完好的碎片引入礁滩，使沉积物更加均匀，限制了有孔虫作为已知沉积物运输指标的效用。沿着两个北部横断面（近礁）的沉积物混合持续了七到十八个月，然后才恢复到接近飓风前的状况。然而，南部横断面（没有珊瑚礁）的红色同色藻浓度明显较低，未能在本研究评估的时间段内恢复，这表明面向大西洋和加勒比海的海岸线之间存在可变的恢复期。这项研究的结果表明，建议在大风暴发生后等待至少十八个月，然后再从珊瑚礁为主的海岸线的近岸环境中收集表面沉积物。
Modern microfossil distributions reflect site‐specific habitats and provide an opportunity to assess sediment transport pathways in the nearshore environment. When applied to overwash deposits in the geological record, they provide insight into sediment provenance and transport, factors important for understanding patterns of frequency and intensity of past storms and tsunamis. Modern distribution studies are rare and often the first established ones occur immediately after an overwash event as part of a post‐event field survey. This is problematic because it is unclear what effect overwash events have on nearshore microfossil assemblages and what time interval is necessary for them to return to pre‐event conditions. This study documents the impacts of Hurricane Irma on nearshore sediments off the coast of Anegada, British Virgin Islands, using distributions ofHomotrema rubrum, an encrusting foraminifer with a defined provenance in coral reefs. At four sampling intervals spanning two years, from six months pre‐Hurricane Irma to eighteen months after, surface sediment was collected from three transects on the northern and southern shores of the island. Partitioning Around Medoids cluster analysis revealed that Hurricane Irma introduced an influx of well‐preserved fragments into the reef flat and made the sediments more uniform, limiting the foraminifer’s utility as a known sediment transport indicator. The mixing of sediments along the two northern transects (reef proximal) persisted for seven to eighteen months before returning to near pre‐hurricane conditions. However, the southern transect (absence of reef), whereHomotrema rubrumconcentrations are significantly less, failed to recover within the time period assessed by this study, indicating a variable recovery period between Atlantic Ocean and Caribbean Sea facing shorelines. Results from this study suggest that a waiting period of at least eighteen months after a major storm is recommended before collecting surface sediment from the nearshore environments of reef‐dominated coastlines.
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