A New Mechanism for Submarine Groundwater Discharge From Continental Shelves
A New Mechanism for Submarine Groundwater Discharge From Continental Shelves
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DOI：
10.1029/2019wr026866
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发表时间：
2020-10
影响因子：
5.4
通讯作者：
C. George;W. Moore;S. White;E. Smoak;S. Joye;A. Leier;Alicia M. Wilson
中科院分区：
文献类型：
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作者：
C. George;W. Moore;S. White;E. Smoak;S. Joye;A. Leier;Alicia M. Wilson
海洋示踪剂研究表明，在被动边缘环境中，大量含盐地下水排入海洋。这些结果尚未得到广泛认可，因为海底地下水排放（SGD）的位置和原因尚不清楚。在这里，我们报告了来自南大西洋湾一个新的长期海底监测网络的观测结果，该网络支持远离海岸的大规模SGD。在南卡罗来纳州的查尔斯顿附近的研究区域，我们通过振动钻孔和啁啾地震勘探确定了水文地层学，从海底威尔斯井中采集水样，并使用热作为示踪剂监测SGD。我们探测到从距离海岸10-15 km的海底发出的盐水SGD的显著脉冲。这些脉冲与海平面突然下降30厘米相吻合。基于对当时海洋条件的分析，我们提出，上升流有利的风降低了该地区的海平面，导致咸水从连接陆地和海洋的封闭沿海含水层中排出。在被动海岸边缘，叠置承压含水层和海平面变化的组合几乎无处不在。这种以前被忽视的组合可以解释广泛的其他已发表的观测结果，并促进比简单的潮汐波动更动态的流动。这种新的机制可以解释Ra示踪信号在沿海大西洋，并支持显着的营养物质输入到海洋。这些大的天然地球化学通量可能对陆地上的地下水使用敏感。
Marine tracer studies indicate that large volumes of saline groundwater discharge to the ocean in passive margin settings. These results have not found widespread recognition because the location and cause(s) of this submarine groundwater discharge (SGD) are unclear. Here we report observations from a new long‐term seafloor monitoring network in the South Atlantic Bight that support large‐scale SGD far from shore. In the study area near Charleston, South Carolina, we determined hydrostratigraphy via vibracoring and chirp seismic surveys, collected water samples from seafloor wells, and used heat as a tracer to monitor SGD. We detected significant pulses of saline SGD issuing from the seafloor 10–15 km from shore. These pulses coincided with abrupt sea level declines of up to 30 cm. Based on an analysis of marine conditions at the time, we propose that upwelling‐favorable winds depressed sea level in the region, causing saline groundwater to discharge from confined coastal aquifers that connect land and ocean. The combination of stacked confined aquifers and variations in sea level are nearly ubiquitous in passive coastal margins. This previously overlooked combination can explain a wide range of other published observations and promotes more dynamic flows than simple tidal fluctuations. This new mechanism may explain Ra tracer signals in the coastal Atlantic Ocean and supports significant nutrient inputs to the ocean. These large natural geochemical fluxes may be sensitive to groundwater usage on land.