SILICATE WEATHERING FLUXES IN SUBMARINE GROUNDWATER DISCHARGE FROM AN ACTIVE MARGIN HIGHLAND: TAIWAN

本申请旨在探索活动边缘高地的海底地下水排放，并了解其在将硅酸盐风化产物转移到海洋中的重要性。它将利用台湾FATES计划资助的一次巡航，对台湾近海沃茨进行采样。像台湾这样快速侵蚀的山区，化学风化率非常高。这些制度提供了气候敏感的反馈，缓和了长期的全球碳循环，但风化过程的性质和位置，以及化学通量的大小仍然知之甚少。硅酸盐化学风化通量的定量知识是必不可少的，以了解对地球表面环境的基本控制和环境稳定性的限制。这种了解对于估计大陆的地球化学和流入海洋的营养物质、对海洋组成的主要控制和生物生产力模式也很重要。长期以来，河流一直被认为是淡水排入海洋的主要渠道，但海底地下水排放（SGD）可能具有重要的体积。SGD的成分可能与河水不同，并且已经发现一些深层循环地下水的溶质浓度高于地表水。来自活动边缘高地的SGD，其化学性质基本上是未知的。根据台湾山带东翼淹没区代表性剖面上方海水的化学和同位素组成，以及附近陆地集水区的地表水和地下水，我们将确定台湾海底地下水排放的强度和模式，并了解其在该山带硅酸盐风化通量中的重要性。选择台湾进行这项研究，是因为台湾是少数几个在高风化率地区的地点之一，在这些地区，风化过程的主要控制参数（主要是温度、降水、侵蚀、植被、岩性和水文）是众所周知的。在过去五年中，我们系统地测量了台湾山区12条河流的风化通量。我们已经发现，地下水出现在陆地上可能会贡献高达40%的河流硅酸盐风化通量。超过一半的台湾的基岩浮雕低于海平面，我们的假设是，在SGD的溶质是一个显着的一部分，从台湾的总风化通量。为了实现我们的总体目标，计算长期的碳预算的山区带，SGD绑定的通量必须加以限制。本项目的样本将于2010年11月12日至14日在台湾东北部沿海的沿着三个样带采集，并在前几天在陆地上采集。使用一系列的Ra-同位素具有不同的半衰期，以及Rn-，Sr-，和O-ixotopes，和主要的阳离子和阴离子，我们将计算SGD的大小在台湾山脉侧翼的一部分，并估计相关的风化通量。所有样品收集都是通过现有的赠款和协议资助的，关于短寿命Ra同位素的工作将由我们的一个研究合作伙伴免费完成。此应用程序是为了支持进一步的分析和建模工作，从2011年3月1日起在剑桥进行。这将包括采样区的化学物质平衡计算，以及在公共领域使用降水、蒸散和河流排放数据进行更广泛的水平衡计算，以评估更广泛的SGD模式。

This application is to explore submarine groundwater discharge from an active margin highland, and to develop an understanding of its importance in transferring products of silicate weathering to the ocean. It will take advantage of a funded cruise in the Taiwan FATES programme to sample inshore ocean waters off Taiwan. Rapidly eroding mountain belts like Taiwan have very high chemical weathering rates. These regimes provide the climate-sensitive feedbacks that moderate the long-term global carbon cycle, but the nature and location of weathering processes, and the magnitude of the chemical fluxes remain poorly known. A proper quantitative knowledge of silicate chemical weathering fluxes is essential to understand a fundamental control on Earth's surficial environment and the limits to the stability of that environment. Such an understanding is also important for estimating continental geochemical and nutrient fluxes to the oceans, major controls on ocean composition and patterns of biological productivity. Rivers have long been seen as the principal conduits for freshwater discharge to the oceans, but submarine groundwater discharge (SGD) may be volumetrically significant. SGD can have a composition that is different from river water, and some deep circulating groundwater has been found to have higher solute concentrations than surface water. SGD from active margin highlands, and its chemistry are essentially unknown. From the chemical and isotopic composition of seawater above a representative section of the submerged east flank of the Taiwan mountain belt, and surface and groundwater from nearby catchments on land, we will determine the intensity and pattern of submarine groundwater discharge from Taiwan, and develop an understanding of its importance in the silicate weathering flux from this mountain belt. Taiwan has been chosen for this study because it is one of very few locations in a high weathering rate regime where the major controlling parameters on weathering processes (principally temperature, precipitation, erosion, vegetation, lithology and hydrology) are well known. In the past five years we have systematically measured weathering fluxes in 12 rivers draining the Taiwan mountains. We have found that groundwater emerging on land may contribute as much as 40% of the riverine silicate weathering flux. More than half of Taiwan's bedrock relief is below sealevel, and our hypothesis is that solutes in SGD are a significant part of the total weathering flux from Taiwan. In order to achieve our overall aim of calculating the long-term carbon budget of this mountain belt, the SGD-bound flux must be constrained. Samples for this project will be collected along three transects off NE Taiwan during a short cruise from 12 to 14 November 2010, and in preceding days on land. Using a range of Ra-isotopes with different half-lives, as well as Rn-, Sr-, and O-ixotopes, and major cations and anions, we will calculate the magnitude of SGD on a section of the Taiwan range flank, and estimate the associated weathering flux. All sample collection is funded through existing grants and agreements, and work on short-lived Ra-isotopes will be done by one of our research partners free of charge. This application is for support of further analytical and modelling work, to take place in Cambridge from 1 March 2011. This will include chemical mass balance calculations for the sampling area, and a broader water balance calculation with precipitation, evapotranspiration and river discharge data in the public domain to assess broader patterns of SGD.