OSCAR - Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge

年轻洋壳的冷却是负责将热量从固体地球转移到水圈的主要物理过程。在大洋中脊附近，快速冷却主要是海水通过多孔性和裂隙的玄武岩地壳的热液循环。然后，这些热液主要沿着海脊排入海洋。在这个跨学科的项目中，我们将研究固体地球和海洋中这种热损失和热液循环的影响。我们将首次建立一个受地球物理、地质和物理海洋学数据约束的综合模型，其中包括固体地球和海洋中的路径，包括通过海底的通量。最快速的热交换发生在快速扩张的海脊附近，那里几乎没有沉积物，受到热液流动的驱动。寒冷的海水进入山脊两侧断裂的玄武岩，流经可渗透的地壳，在轴向岩浆室附近变得过热。这种高度浮力的水迅速上升，并沿着山脊轴线逃逸到海洋中，众所周知，它形成了独特的喷口，称为黑色烟囱。一旦进入海洋，热水通过夹带与周围的冷水混合，形成一股羽流，上升到其中性密度点。卷吸过程可能会使羽流中的水体积增加几个数量级，从而提供一种机制来加热并将最稠密的水从底部边界层中抬起。然后，作为全球温盐循环系统的一部分，这些水可以更容易地进行进一步混合和加热。地壳中热液流动的强度随着距离海脊轴线的距离而衰减，这是由于地球化学蚀变产物堵塞了通道，从而改变了地壳的地球物理性质，随着年龄的增长，远洋沉积物将破裂的玄武岩上地壳与上覆水隔离，阻止了直接的水交换。在这里，传导热损失是由这层沉积物的厚度和结构决定的。该项目将获得一个跨学科的数据集，该数据集将物理海洋学和地球物理学整合到一个单一的数据采集巡航中。利用这些数据，我们将建立新的综合模型并将其参数化，这些模型将为包括可渗透海床在内的洋脊附近的热过程提供有价值的见解和新的限制条件。这些数据和所产生的模型将为综合多物理实验设定一个新的基准，并将导致对海洋脊处的流体和热通量的新的理解，而且同样重要的是，将更好地理解地球物理和海洋数据在大洋轴脊背景下的实际解析情况，以及一个可适用于世界各地类似海洋脊系的预测模型。

The cooling of young oceanic crust is the main physical process responsible for removing heat from the solid Earth to the hydrosphere. Close to the mid-ocean ridge rapid cooling is dominated by hydrothermal circulation of seawater through the porous and fractured basalt crust. This hydrothermal fluid is then discharged into the ocean mainly along the ridge. In this interdisciplinary project we will investigate the effects of this heat loss and hydrothermal circulation in both the solid Earth and the ocean. We will, for the first time, derive an integrated model which will be constrained by geophysical, geological and physical oceanography data that includes pathways in both the solid Earth and the ocean including fluxes through seabed.The most rapid heat exchange occurs close to the fast-spreading ridges, where there are little or no sediments, driven by hydrothermal flow. Cold ocean water enters the fractured basalt in areas on the ridge flanks and flows through the permeable crust becoming super-heated in the proximity of the axial magma chamber. This highly buoyant water ascends rapidly and escapes into the oceans along the ridge axis and is known to form distinct vents called black smokers. Once in the ocean the hot water mixes with the ambient cold water through entrainment and forms a plume that rises to its point of neutral density. The entrainment process may increase the volume of the water in the plume by several orders of magnitude thereby providing a mechanism to heat and lift the densest waters away from the bottom boundary layer. These waters are then more readily available for further mixing and heating as part of the global thermohaline circulation system. The intensity of the hydrothermal fluid flow in the crust decays with distance from the ridge axis because of clogging of the pathways by geochemical alteration products which changes the geophysical properties of the crust and with age, pelagic sediments isolate the fractured basaltic upper crust from the overlaying water preventing direct water exchange. Here conductive heat loss is determined by the thickness and structure of this layer of sediment.The project will acquire an interdisciplinary dataset which integrates physical oceanography and geophysics into a single data acquisition cruise. Using these data we will build and parameterise new integrated models that will provide valuable insight and new constraints of the thermal processes close to ocean ridges that includes a permeable seabed. These data and resultant models will set a new benchmark for integrated multi-physics experiments and will result in a new understanding of the fluid and heat fluxes at ocean ridges and, as importantly a better understanding of what geophysical and oceanographic data actually resolve in the context in an oceanic axial ridge setting, and a predictive model that can be applied to similar ocean ridge systems world-wide.