Tracing Submarine Groundwater Discharge into the Ocean

海底泉水和渗漏水向海洋排放大量的水，但不是精确定义的量。最近的估计表明，这种由引力和对流力量驱动的放电的规模可能会在全球范围内产生重大影响。排出的流体可能包括淡水、伴生水、从蒸发岩沉积物中提取的卤水或循环海水。由于海底水文排泄物的组成可能与海水明显不同，这一过程能够对许多元素的海洋地球化学循环做出重大贡献。拟议的研究将确定利用示踪剂222Rn、226Ra和CH4的水柱常备作物的潜力，这些示踪剂相对于海水在地下水中含量极高，目的是定位和评估海底地下水向海洋的排放。在佛罗里达州西北部大陆架的一个相对较小的区域内，将为单一的最佳示踪剂222Rn建立详细的地球化学质量平衡，我们预计在该区域将发现可观的海底排放。将以离散泉水和弥散渗漏的形式测量地下水示踪剂浓度和通量。将评估底栖通量和其他过程，如平流和海-气交换，这些过程有助于改变现存量作物的水柱。将对这些测量进行模拟，以评估开发一种简单的示踪剂技术的前景，以确定适用于其他地区的排入海洋的地下水的数量。

Submarine springs and seeps discharge a substantial but not precisely defined quantity of water into the ocean. Recent estimates suggest that the magnitude of this discharge, driven by gravitational and convective forces, may be globally significant. Discharged fluids may consist of fresh water, connate waters, brines derived from evaporite deposits, or recirculated seawater. Because the composition of submarine hydrologic discharge may be markedly different than seawater, this process is capable of contributing significantly to the marine geochemical cycling of many elements. The proposed research will determine the potential of using water column standing crops of the tracers 222Rn, 226Ra and CH4, constituents greatly enriched in groundwater relative to seawater, for the purpose of locating and assessing submarine groundwater discharge to the ocean. A detailed geochemical mass balance will be constructed for the single best tracer, 222Rn, within a relatively small area on the continental shelf of northwest Florida, an area where we expect to find appreciable submarine discharge. Groundwater tracer concentrations and fluxes will be measured, both in the form of discrete springs and as disseminated seeps. Benthic fluxes and other processes, such as advection and air-sea exchange, which contribute to changes in the water column standing crop will be evaluated. These measurements will be modeled to evaluate the prospects of developing a simple tracer-based technique for determining the magnitude of groundwater discharge to the ocean applicable to other areas.