DeepEarthshape - Reaction fronts in deep regolith and their advance mechanism

地球上的大部分生态系统存在于“深层生物圈”——位于地球表面深处的永久黑暗的栖息地。风化带-地球“临界带”的地下部分，是这个栖息地的活跃部分。我们将采用创新的地球化学和同位素方法来探索形成该带的地球化学转变。我们在DeepEarthshape软件包中这样做，该软件包将地球化学、微生物学、地球物理学、地质学和生物地球化学项目联系起来。deep pearthshape概念源于Earthshape阶段1的发现。4个主要研究点的风化带均较深，深基坑未见风化锋。同样引人注目的是，在整个腐岩中发现了数量可观的微生物生物量。在这里，我们将探讨沿地形样带的降雨量和植被覆盖范围是如何反映在风化锋推进中的。具体来说，我们将评估以下假设：1)地球形状遗址的风化前沿是最近的特征，今天仍在演变；2)侵蚀和元素溶蚀造成的物质流失与风化锋的推进速率大致平衡；3)风化带由一系列离散的嵌套锋面组成，这些锋面反映了不同的化学风化驱动因素（如水渗透、铁氧化、矿物转化、微生物活动和有机碳循环）。所有DeepEarthshape项目的核心都是钻探活动，由深部临界带的地球物理成像提供信息。在所有四个主要的研究地点，我们将通过钻探土壤和腐岩进入未风化的基岩来扩展之前的土壤挖掘。我们将通过铀衰变系列分析（以确定风化锋推进的速度）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度风化物质的产生和地表损失之间的平衡。此外，我们将使用大气宇宙成因10Be的深度分布作为水入渗的代表，稳定9Be的深度分布作为硅酸盐在深度风化的代表。我们将描述岩心的矿物学和化学成分，并将测量元素枯竭、密度、孔隙度、表面积和铁氧化还原状态，以检测嵌套的风化锋。我们将综合这些结果来评估巢状风化锋的排列和推进速度如何取决于气候和地球形状样带沿线的植被。这两个因素的相对重要性将通过一个质量平衡模型来评估，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，这些结果将为深层生物圈和临界带调节二氧化碳消耗从而调节地球气候的反馈提供信息。

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.