Inner-shelf circulation and sediment dynamics on a series of shoreface-connected ridges offshore of Fire Island, NY
Inner-shelf circulation and sediment dynamics on a series of shoreface-connected ridges offshore of Fire Island, NY
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纽约州火岛近海一系列与岸面相连的海脊的内陆架环流和沉积物动力学
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发表时间：
2014
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通讯作者：
N. Marshall
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作者：
J. Warner;J. List;W. C. Schwab;G. Voulgaris;B. Armstrong;N. Marshall
沿着纽约州火岛近海的内大陆架的位置，以一系列与海岸相连的山脊（sfcr）为特征。这些沙脊的长度约为10公里，间距为3公里，脊槽起伏高达8米，从海岸线沿顺时针方向倾斜约30°。先前研究的稳定性分析解释了这样的砂脊是如何由风暴驱动的沿海岸流动形成和维持的，其中一个关键的维持机制是离岸偏转流动在山脊顶部和岸上的槽中。我们用一组有限的理想化数值模拟和观测数据分析来检验这些过程。模型结果证实，sfcr上的沿岸流动表现为脊顶上的离岸偏转流和槽内的陆上定向流，并显示出逆风的相反环流模式。为了进一步研究这些维持过程，2012年1月至4月，在火岛近海sfcr的七个站点部署了海洋仪器，测量了水位、洋流、波浪、悬浮沉积物浓度和底部应力。数据分析表明，在东北风的风暴中，海流在脊峰上的离岸偏转和在槽内的岸上偏转过程，在西南风的风暴中，海流在脊上的反向流动模式出现。悬沙通量的计算确定了与SFCR维持机制相一致的时期。从东北方向吹来的沿岸风将通量吹向离岸的脊顶，将通量吹向岸上的槽，这将促进脊的维持。然而，从西南方向吹来的沿岸风推动了相反的环流。风场与该地区发生的不同风暴类型（低压系统、冷锋和暖锋）有关。从有限的数据集中，我们发现低压系统驱动沉积物通量，倾向于促进稳定和维持sfcr，而冷锋型风暴似乎驱动环流，在相反的意义上，可能不是脊维持的支持机制。
Locations along the inner-continental shelf offshore of Fire Island, NY, are characterized by a series of shoreface-connected ridges (SFCRs). These sand ridges have approximate dimensions of 10 km in length, 3 km spacing, and up to ∼8 m ridge to trough relief and are oriented obliquely at approximately 30° clockwise from the coastline. Stability analysis from previous studies explains how sand ridges such as these could be formed and maintained by storm-driven flows directed alongshore with a key maintenance mechanism of offshore deflected flows over ridge crests and onshore in the troughs. We examine these processes both with a limited set of idealized numerical simulations and analysis of observational data. Model results confirm that alongshore flows over the SFCRs exhibit offshore veering of currents over the ridge crests and onshore-directed flows in the troughs, and demonstrate the opposite circulation pattern for a reverse wind. To further investigate these maintenance processes, oceanographic instruments were deployed at seven sites on the SFCRs offshore of Fire Island to measure water levels, ocean currents, waves, suspended sediment concentrations, and bottom stresses from January to April 2012. Data analysis reveals that during storms with winds from the northeast, the processes of offshore deflection of currents over ridge crests and onshore in the troughs were observed, and during storm events with winds from the southwest, a reverse flow pattern over the ridges occurred. Computations of suspended sediment fluxes identify periods that are consistent with SFCR maintenance mechanisms. Alongshore winds from the northeast drove fluxes offshore on the ridge crest and onshore in the trough that would tend to promote ridge maintenance. However, alongshore winds from the southwest drove opposite circulations. The wind fields are related to different storm types that occur in the region (low-pressure systems, cold fronts, and warm fronts). From the limited data set, we identify that low-pressure systems drive sediment fluxes that tend to promote stability and maintain the SFCRs while cold front type storms appear to drive circulations that are in the opposite sense and may not be a supporting mechanism for ridge maintenance.