Geophysical site survey for drilling into a sedimented shallow-water hydrothermal system

海洋浅水热液系统（MSWHS）与深海热液系统相反，发生在近岸浅水环境中，它们可以通过排放还原的热热液对沿海海洋产生相当大的影响。其中一个被研究得最好的MSWHS位于Milos岛南侧的palechori湾，这里一直是众多科学研究的焦点。然而，尽管经过了超过25年的研究，在古chori湾产生具有不同化学成分的热液流体的地下过程和机制尚不清楚。与大多数其他地点相比，古chori湾的MSWHS被沉积物（厚度未知）覆盖。因此，热液流体以较低的速率渗透过沉积物盖层，然后进入古藻里湾海水。这将允许沉积物-热液流体相互作用，这将导致化学叠印，掩盖真正的热液信号。因此，沉积厚度是古深里湾热液最终化学成分的控制因素，这是一个可行的假设。考虑到这一点，我们建议进行沉积物覆盖的地球物理调查，并为古chori湾生成其厚度图。该图可与已有的古chori湾孔隙流体温度和元素分布图相结合，评价沉积厚度对热液流体物理化学组成的影响。这些新信息将为收集沉积物岩心提供基础，这对于解决古chori湾更大的问题和后续研究是必要的，例如：(1)MSWHS是否是典型的弧型表生热液系统？这些过程以重要的方式调节元素的释放通量，需要理解以破译更深层次反应的特征。(2)沉积物厚度和流体通量速率是否决定了浅层海底沉积物承载反应对热液流体组成的影响程度？(3)断平面从基底向上的地方流体通量是否最高？

Marine shallow-water hydrothermal systems (MSWHS), as opposed to deep-sea hydrothermal systems, occur in shallow-water nearshore settings where they can have a considerable impact on the coastal ocean through discharge of reduced, hot hydrothermal fluids. One of the best-studied MSWHS is located in Paleochori Bay on the south side of Milos Island, which has been the focus of numerous scientific studies. However, despite more than 25 years of research, the subsurface processes and mechanisms that generate hydrothermal fluids with contrasting chemical compositions in Paleochori Bay are unclear. In contrast to most other locations, the MSWHS in Paleochori Bay is covered by sediments (of unknown thickness). Thus, the hydrothermal fluids percolate through the sediment cover before venting into Paleochori Bay seawater at low rates. This would allow for sediment-hydrothermal fluid interaction, which should cause a chemical overprint that obscures the true hydrothermal signal. Hence, it is a viable hypothesis that sediment thickness should be a controlling factor for the final chemical composition of hydrothermal fluids in Paleochori Bay. With this in mind, we propose to conduct a geophysical survey of the sediment cover and to generate a map of its thickness for Paleochori Bay. This map can be combined with existing maps of temperature and element distribution in Paleochori Bay pore fluids to evaluate the impact of sediment thickness on the physicochemical composition of the hydrothermal fluids. This new information will be the basis for collecting sediment cores, which are necessary for addressing the bigger questions and subsequent research for Paleochori Bay, such as, (1) Is the MSWHS a typical arc-hosted epigenetic hydrothermal system. These processes modulate the release fluxes of elements in significant ways and need to be understood to decipher the signatures of deeper-seated reactions. (2) Do sediment thickness and fluid flux rates determine the magnitude that sediment-hosted reactions in the shallow subseafloor play in modifying hydrothermal fluid composition? (3) Are fluid flux rates highest where fault planes come up through the basement?