Collaborative Research: Factors Controlling Chemical Weathering in Regions of Very High Physical Weathering Rates

[03:9755 . carey]在过去的十年里，关于地球表面化学风化的最终控制展开了一场辩论。有些人认为，物理风化的速度，而不是气候，是化学风化的主要控制因素。物理风化作用在快速构造隆升地区最为显著。快速抬升的构造机制与高频率降雨事件是西南太平洋/澳大拉西亚地区许多高海拔海洋岛屿的主要特征。那里的高海拔岛屿（hsi）每年产生至少33%的进入海洋环境的沉积物。正因为如此，hsi具有地球上已知的最高物理风化率。我们之前的研究项目（EAR 0096285）确定了新西兰一些流域的化学风化速率。将新测定的化学风化速率与先前测定的物理风化速率进行比较表明，尽管化学风化速率与物理风化速率之比较低，但化学风化的绝对速率却是有史以来最高的。台湾的初步观测表明，那里的化学风化速率也很高。目前的项目是返回新西兰和台湾收集水、悬浮泥沙和土壤泥沙样本，以便进行以下工作：使用一套放射性核素（7Be, 137Cs, 210Pb）来确定新西兰两个先前调查过的流域的土壤和洪泛平原沉积物的停留时间；2. 采用主要、次要和微量元素分析方法，评价了以火山岩为主要岩性的新西兰和台湾流域的物理和化学风化速率；3. 利用活动1和2的数据以及我们之前的研究结果，开发一个定量框架来评估物理和化学风化速率之间的关系，特别是在这些高度物理风化的地区。在我们收集7Be、137Cs和210Pb的土壤和河床沉积物剖面的地点，我们将收集更多的样品，以供将来分析铀和钍系列核素。这些样品将被存档，直到时间和资金允许，我们将使用ICP-MS在俄勒冈州立大学的MARC分析中心分析这些样品。这些数据将用于计算流域停留时间。我们计划这些额外的活动是为了回应审稿人的评论，即最初选择的核素的半衰期太短，无法用于计算可能的分水岭停留时间。利用铀和钍的数据，我们可以使用Plater等人（1994）、Vigier等人（2001）、Moreira-Nordemann（1980）和Marques等人（2003）的方法来计算侵蚀速率和时间尺度，以及流域停留时间。这项工作的更广泛影响将包括为研究生提供培训，以及与新西兰和台湾科学家建立国际伙伴关系。pi计划建立一个网站，其中将放置来自拟议研究和EAR 0096285的所有数据，以便广泛的科学界可以访问。这项研究在促进对大气中二氧化碳浓度的全面了解方面具有重要的社会意义。由于地球表面硅酸盐矿物的化学风化作用被认为是大气CO2浓度的主要控制因素，因此本研究对理解温室气体调节机制具有重要意义。这是两位博士的合作提案。俄亥俄州立大学的Carey和Lyons，新罕布什尔大学的Dibb博士，台湾中央研究院的Kao博士，以及新西兰国家水与大气研究所的Hicks博士。

0309755CareyOver the past decade, a debate has taken place concerning the ultimate controls on chemical weathering at Earth's surface. Some have argued that the rate of physical weathering, not climate, is the major control on chemical weathering. Physical weathering is highest in areas of rapid tectonic uplift. Rapidly uplifting tectonic regimes with high frequency rainfall events are the dominant feature of many high-standing oceanic islands in the SW Pacific/Australasian region. High-standing islands (HSIs) there produce at least 33% of the sediment entering the marine environment annually. Because of this, HSIs have some of the highest physical weathering rates known on Earth. Research in our previous grant (EAR 0096285) determined chemical weathering rates in some New Zealand watersheds. Comparison of newly determined chemical weathering rates to the previously determined physical weathering rates showed that, although the ratio of chemical to physical weathering is low, the absolute rates of chemical weathering are some of the highest ever observed. Preliminary observations from Taiwan indicate that chemical weathering rates there are also very high. The current project is a return to New Zealand and Taiwan to collect water, suspended sediment and soil and sediment samples in order to conduct the following work: 1. Use a suite of radionuclides (7Be, 137Cs, 210Pb) to determine residence times of sediments in the soils and floodplains of two previously investigated watersheds in New Zealand; 2. Use a full suite of major, minor and trace element analyses to evaluate the physical and chemical weathering rates in New Zealand and Taiwan watersheds whose primary lithology is volcanic rocks; 3. Use data from activities 1 and 2 and the results of our previous research to develop a quantitative framework to evaluate the relationship between physical and chemical weathering rates, especially in these regions of very high physical weathering. At the locations where we collect soil and streambed sediment profiles for 7Be, 137Cs and 210Pb, we shall collect additional samples for future analysis of uranium and thorium series nuclides. These samples will be archived until time and funds permit, we shall analyze these samples using the ICP-MS at OSU's MARC analytical center. The data will be used for calculation of watershed residence times. We plan these additional activities in response to the reviewer comment that the original choice of nuclides had half-lives too short to be useful in calculating the likely watershed residence times. Using the uranium and thorium data, we can use the approaches of Plater et al. (1994), Vigier et al. (2001), Moreira-Nordemann (1980) and Marques et al. (2003) to calculate erosion rates and timescales, and watershed residence times.Broader impacts of the work will include training provided to graduate students and the building of international partnerships with New Zealand and Taiwanese scientists. The PIs plan to establish a website where all the data from the proposed research and from EAR 0096285 will be placed so that it will be accessible by the broad scientific community. This research has important societal relevance in contributing to the overall understanding of CO2 concentration in the atmosphere. Because the chemical weathering of silicate minerals on the surface of Earth is thought to be the major control on the atmospheric CO2 concentration, this research has important implications for understanding the mechanisms of greenhouse gas regulation.This is a collaborative proposal among Drs. Carey and Lyons at The Ohio State University, Dr. Dibb at the University of New Hampshire, Dr. Kao of Academia Sinica, Taiwan, and Dr. Hicks of the National Institute of Water and Atmospheric Research, New Zealand.