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The effect of coastal landform development on decadal-to millennial-scale longshore sediment fluxes: Evidence from the Holocene evolution of the central mid-Atlantic coast, USA
Quaternary Science Reviews ( IF 4 ) Pub Date : 2021-07-30 , DOI: 10.1016/j.quascirev.2021.107096
Justin L. Shawler 1 , Christopher J. Hein 1 , Chloe A. Obara 2 , Mahina G. Robbins 2 , Sebastien Huot 3 , Michael S. Fenster 4
Affiliation  

The behavior of siliciclastic coastal systems is largely controlled by the interplay between accommodation creation and infilling. Factors responsible for altering sediment fluxes to and along open-ocean coasts include cross-shore mobilization of sediment primarily from tidal currents and storms as well as changes in alongshore transport rates moderated by changing wave conditions, river sediment inputs, artificial shoreline hardening and modification, and natural sediment trapping in updrift coastal landforms. This paper focuses on the latter relationships. To address understudied interactions between updrift coastal landforms and downdrift coastal behavior, we quantify the volume and fluxes of sediment trapped in the Assateague-Chincoteague-Wallops barrier-island complex along the Virginia, USA coast and relate these volumes to downdrift coastal-system behavior. During the last ca. 2250 years, these barriers trapped 216 million m3 of sand through the growth of complex beach- and foredune-ridge systems. A period (ca. 400 to 190 years ago) of reduced/no progradation on Chincoteague and Assateague islands corresponds with sediment sequestration in updrift flood-tidal deltas. This finding emphasizes the important control of tidal inlets on alongshore sediment fluxes on barrier-island coasts. Rapid historical spit elongation during the last 190 years has trapped an average of 681,000 m3 yr−1 of sand; this occurred coincident with downdrift barrier-island erosion/migration at long-term rates of >3 m yr−1. Historical sand fluxes to the elongating spit on southern Assateague Island and progradational beach ridges on northernmost Wallops Islands are equivalent to at least 60% of estimated regional longshore transport rates. We therefore propose that sediment trapping and associated wave refraction are the primary drivers of downdrift barrier erosion, while storminess and sea-level rise are secondary forcings of change affecting equally the entire barrier-island chain. Global context is provided by a compilation of sediment trapping through growth of similar longshore sand sinks, which indicates the volume of sediment incorporated into the elongating spit end of Assateague Island is similar to sandy beach- and foredune-ridge plains (108 m3), but average annual trapping at the spit is at least six times greater than those at most mainland-attached, progradational systems. However, Chincoteague and Wallops, two progradational barrier islands, incorporate sand at rates broadly similar to large strandplains. Our findings emphasize the need to account for natural longshore sediment trapping in multi-decadal coastal management efforts on sandy, siliciclastic coasts.



中文翻译:

海岸地貌发展对十年至千年尺度沿岸沉积物通量的影响:来自美国中大西洋沿岸全新世演化的证据

硅质碎屑海岸系统的行为在很大程度上受住宿创造和填充之间的相互作用控制。影响公海沿岸和沿公海沿岸沉积物通量的因素包括主要来自潮汐流和风暴的沉积物跨岸流动,以及由变化的波浪条件、河流沉积物输入、人工海岸线硬化和修改引起的沿岸运输速率的变化,和自然沉积物捕获在上升的沿海地貌中。本文重点讨论后者的关系。为了解决上浮海岸地貌和下流海岸行为之间研究不足的相互作用,我们量化了沿弗吉尼亚州的 Assateague-Chincoteague-Wallops 屏障岛复合体中捕获的沉积物的体积和通量,美国海岸并将这些体积与下流海岸系统行为联系起来。在最后2250年,这些障碍被困2.16亿米3砂通过复杂滩上─和前沙丘脊系统的发展。Chincoteague 和 Assateague 岛上的一段时期(大约400 至 190 年前)减少/没有进积与上流洪水-潮汐三角洲中的沉积物封存相对应。这一发现强调了潮汐入口对屏障岛海岸沿岸沉积物通量的重要控制。在过去的 190 年里,历史上的快速吐痰伸长率平均捕获了 681,000 m 3  yr -1的沙子;这与下流屏障岛侵蚀/迁移同时发生,长期速率> 3 m yr -1. 阿萨蒂格岛南部的细长沙嘴和瓦洛普斯群岛最北端的进积海滩山脊的历史沙流量至少相当于估计的区域沿海运输率的 60%。因此,我们提出沉积物捕获和相关的波浪折射是下流屏障侵蚀的主要驱动因素,而暴风雨和海平面上升是对整个屏障岛链产生同等影响的次要变化强迫。全球背景由通过类似沿岸沙汇的生长捕获的沉积物汇编提供,这表明纳入阿萨蒂格岛拉长的沙嘴端的沉积物体积类似于沙滩和前海脊平原(10 8  m 3),但在唾液中的年平均捕获量至少是大多数与大陆相连的进积系统的六倍。然而,Chincoteague 和 Wallops 这两个进积障碍岛以与大型滨海平原大致相似的速度掺入沙子。我们的研究结果强调需要考虑在沙质、硅质碎屑海岸的数十年海岸管理工作中捕获天然沿岸沉积物。

更新日期:2021-07-30
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