DeepEarthshape - Reaction fronts in deep regolith and their advance mechanism

地球上的大多数生态系统都存在于“深层生物圈”中--这些栖息地位于地球表面深处，处于永久的黑暗之中。风化带--地球“临界区”的地下部分，是这一栖息地的活跃部分。我们将使用创新的地球化学和同位素方法来探索塑造这一带的地球化学转换。我们在DeepEarthform包中做到这一点，该包将地球化学、微生物学、地球物理学、地质学和生物地球化学的项目联系起来。深度地球形态的概念源于地球形态第一阶段的发现。在所有四个主要研究地点，风化带都很深，以至于在深挖的土坑中从未遇到过风化锋面。同样引人注目的是，在腐泥岩中发现了相当数量的微生物生物量。在这里，我们将探索沿地球形状样带的降雨量和植被覆盖范围如何反映在风化锋面的推进中。具体地说，我们将评估以下假设：1)地球形状遗址的风化锋面是今天仍在演变的最近特征；2)侵蚀和元素溶解造成的质量迁移与风化锋面的推进速度大致平衡；以及3)风化带由一系列离散的嵌套锋面组成，反映了不同的化学风化驱动因素(例如，水渗透、铁氧化、矿物转化、微生物活动和有机碳的循环)。所有DeepEarth Shape项目的核心是钻探活动，其信息来自深层临界区的地球物理成像。在所有四个主要研究地点，我们将通过在未风化的基岩中钻穿土壤和腐泥岩来扩展先前的土壤挖掘。我们将通过铀衰变系列分析(以确定风化锋推进速率)和原位宇宙成因铍-10(10Be)分析(以确定地表剥蚀率)的创新组合，来评估深层风化物质的产生和地表损失之间的平衡。此外，我们还将利用陨石宇宙成因的10Be的深度分布作为水分入渗的替代，稳定的9Be的深度分布作为硅酸盐深部风化的替代。我们将对岩芯的矿物学和化学成分进行表征，并将测量元素耗竭、密度、孔隙率、表面积和铁氧化还原状态，以检测嵌套的风化前锋。我们将综合这些结果来评估嵌套风化锋的排列和推进速度如何取决于地球形状样带上的气候和植被。这两个因素的相对重要性将通过一个质量平衡模型进行评估，该模型将风化动力学与植物生物量生长的化学和营养需求联系起来。最终，这些结果将提供有关深层生物圈和临界区调节二氧化碳消耗从而影响地球气候的反馈信息。

The majority of Earth’s ecosystems exist in the “deep biosphere”—habitats located deep beneath the Earth’s surface in permanent darkness. The weathering zone - the subsurface part of the Earths “Critical Zone”, is an active part of this habitat. We will use innovative geochemical and isotope methods to explore the geochemical transformations shaping this zone. We do so within the DeepEarthshape package, that links projects in Geochemistry, Microbiology, Geophysics, Geology, and Biogeochemistry. The DeepEarthshape concept arose from findings in Earthshape phase 1. In all four primary study sites the weathering zone was so deep that the weathering front was never encountered in deeply excavated soil pits. Strikingly also, appreciable amounts of microbial biomass was found throughout the saprolite.Here we will explore how the range in rainfall and plant cover along the Earthshape transect is reflected in weathering front advance. Specifically we will evaluate the hypotheses that 1) weathering fronts at the Earthshape sites are recent features still evolving today; 2) mass removal by erosion and elemental dissolution is roughly balanced by the advance rate of the weathering front; and 3) the weathering zone comprises a series of discrete, nested fronts that reflect different drivers of chemical weathering (e.g. water infiltration, iron oxidation, mineralogical transformations, microbial activity, and cycling of organic carbon). At the heart of all DeepEarthshape projects is a drilling campaign, informed by geophysical imaging of the deep critical zone. At all four primary study sites we will extend previous soil excavations by drilling through soil and saprolite into the unweathered bedrock. We will assess the balance between production of weathered material at depth and loss at the surface through an innovative combination of Uranium-decay series analyses (to determine the rate of weathering front advance) and in situ cosmogenic Beryllium-10 (10Be) analyses (to determine surface denudation rates). In addition, we will use the depth distribution of meteoric cosmogenic 10Be as a proxy for water infiltration, and the depth distribution of stable 9Be as a proxy for silicate weathering at depth. We will characterise the cores for mineralogical and chemical composition, and will measure elemental depletion, density, porosity, surface area, and iron redox state to detect nested weathering fronts. We will synthesise these results to evaluate how the arrangement and advance rate of the nested weathering fronts depend on climate and vegetation along the Earthshape transect. The relative importance of these two factors will be evaluated through a mass balance model that links weathering kinetics with the chemical and nutrient demands of plant biomass growth. Ultimately, these results will inform as to the feedbacks through which the deep biosphere and critical zone modulate CO2 consumption and thus Earth’s climate.