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

这项应用是为了探索活动边缘高地的海底地下水排放，并加深对其在将硅酸盐风化产物转移到海洋中的重要性的认识。它将利用台湾命运计划资助的邮轮，对台湾近海海域进行采样。像台湾这样的快速侵蚀山地具有很高的化学风化速率。这些制度提供了对气候敏感的反馈，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鲜为人知。适当的硅酸盐化学风化通量的定量知识对于理解对地球表面环境的基本控制和对该环境稳定性的限制是必不可少的。这种了解对于估计大陆向海洋的地球化学和营养通量、对海洋组成的主要控制以及生物生产力的模式也很重要。长期以来，河流一直被视为向海洋排放淡水的主要渠道，但海底地下水排放(SGD)在体积上可能是重要的。SGD的成分可能与河水不同，一些深层循环地下水的溶质浓度已被发现高于地表水。SGD来自活动边缘高地，其化学成分基本上是未知的。根据台湾山带东侧潜水典型地段的海水化学和同位素组成，以及附近陆上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，并对其在该山带硅酸盐风化通量中的重要性有进一步的认识。之所以选择台湾进行这项研究，是因为它是少数几个风化速率较高的地区之一，其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。在过去的五年中，我们对台湾山区12条河流的风化通量进行了系统的测量。我们发现，陆地上出现的地下水可能对河流硅酸盐风化通量的贡献高达40%。台湾超过一半的基岩起伏低于海平面，我们的假设是SGD中的溶质是台湾总风化通量的重要组成部分。为了实现我们计算这一山脉带长期碳收支的总体目标，必须限制与SGD有关的通量。该项目的样本将在2010年11月12日至14日的短途巡航期间以及之前几天的陆上沿台湾东北海域的三个样带采集。利用一系列具有不同半衰期的Ra同位素，以及Rn、Sr和O同位素，以及主要的阳离子和阴离子，我们将计算台湾山脉两侧的一段SGD的大小，并估计相关的风化通量。所有样品采集都是通过现有的赠款和协议提供资金的，我们的一个研究伙伴将免费完成对短期Ra同位素的研究工作。这项申请是为了支持将于2011年3月1日在剑桥举行的进一步的分析和建模工作。这将包括采样区域的化学物质平衡计算，以及利用公共领域的降水量、蒸散量和河流流量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.