GRGC: Weathering, Plants and the Long-Term Carbon Cycle

小行星9417325 大陆上钙和镁硅酸盐矿物的风化，随后在海洋中以碳酸盐形式沉淀释放的钙和镁，对地质时期的大气CO2水平产生了重大控制。 这一过程的一个重要方面是植物在风化过程中改变矿物溶解速率所起的作用。 古生代陆地维管植物的兴起和演化是否影响了硅酸盐风化的速率， 大气中二氧化碳的含量 从岩相学研究，使用电子探针，我们已经发现，在夏威夷岛上的年轻的玄武岩流的维管植物的生长结果在强烈的蚀刻和去除的Ca和Mg硅酸盐在附近的植物根。 结果发现，在高等植物下的初始风化的相对速率比在地衣下或在没有任何植物生命的情况下大得多。 同样在Mt。我们在圣海伦斯发现了一个十年前的火山灰存款，它显示了紧邻植物细根的化学变化的证据，但没有远离细根的证据。 虽然这种岩相学研究在定性到半定量的意义上是有用的，但需要一种更好的方法来量化植物对硅酸盐风化的影响。 这可以通过研究排出岩石的溶液的化学性质来完成。 在新罕布什尔州的哈伯德布鲁克实验森林站，在自然室外条件下进行的一项多年持续控制实验的初步水化学结果表明，树木对硅酸盐风化的影响最小为1.5-3.5倍。 我们建议通过检查排出冰岛玄武岩的沃茨的化学成分来检验这一结果。 冰岛是我们拟议研究的理想之地，因为岩石富含火山玻璃和钙镁硅酸盐，不含碳酸钙，足够年轻，植被覆盖度存在变化，不存在人为酸雨，泉水和溪流沃茨可以很容易地取样。 （在夏威夷岛上进行水样采集是不可能的，因为那些年轻的玄武岩流渗透性很强，植物覆盖率也有变化。） 对冰岛的考察表明，有几个地方可以从植被和非植被地区收集沃茨，这些地区彼此足够接近，共享相同的基岩岩性、小气候和外观。这使得有可能进行实验的定量作用，当地的植物生活对硅酸盐风化。 此外，在冰岛，Sigurdur Gislason博士在风化解决方案的化学方面已经拥有相当多的专业知识，他将在该领域为我们提供帮助。 Gislason博士对冰岛泉水沃茨的初步化学数据表明，植物对风化速率的影响应该是巨大的。

9417325 Berner The weathering of Ca and Mg silicate minerals on the continents, followed by the precipitation of the liberated Ca and Mg in the oceans as carbonates, has exerted a major control on the level of atmospheric CO2 over geologic time. An important aspect of this process is the role played by plants as they modify the rate of mineral dissolution during weathering. Did the rise and evolution of vascular land plants over the Phanerozoic affect the rate of silicate weathering, and in turn the level of atmospheric CO2? From petrographic studies using the electron microprobe we have discovered that on the island of Hawaii the growth of vascular plants on young basalt flows results in intense etching and removal of Ca and Mg silicates in the vicinity of plant rootlets. As a result relative rates of initial weathering under higher plants were found to be much greater than under lichens or in the absence of any plant life. Similarly at Mt. St. Helens we found that a ten year old volcanic ash deposit shows evidence of chemical alteration immediately adjacent to plant rootlets but no evidence away from the rootlets. Although this petrographic study has been useful in a qualitative to semi-quantitative sense, there is a need for a better way to quantify the effects of plants on silicate weathering. This can be done through the study of the chemistry of solutions draining the rocks. Our preliminary water chemical results of a multiyear ongoing controlled experiment on the effects of young growing trees and grass on silicate weathering, conducted under natural outdoor conditions at the Hubbard Brook Experimental Forest Station in New Hampshire, indicate a minimum silicate weathering rate enhancement by the trees of a factor of 1.5-3.5. We propose to check this result by examining the chemistry of waters draining the basaltic rocks of Iceland. Iceland is ideal for our proposed study in that the rocks are rich in volcanic glass and Ca and Mg silicates , contain no CaCO3, are young enough that variations in the degree of vegetational coverage is present, anthropogenic acid rain is absent and spring and stream waters can be easily sampled. (Water sampling on the island of Hawaii was impossible due to the great permeability of those young basalt flows that exhibit variations in plant coverage.) A reconnaissance visit to Iceland shows that there are several localities where waters can be collected from vegetated and unvegetated areas that are sufficiently nearly to one another that they share the same bedrock lithology, microclimate, aspect. etc. This makes it possible to conduct an experiment on the quantitative role of the local plant life on silicate weathering. Also, there is considerable expertise already available on the chemistry of weathering solutions in Iceland, in the person of Dr. Sigurdur Gislason, and we will be assisted by him in the field. Dr. Gislason's preliminary chemical data on Icelandic spring waters suggest that the effect of plants on weathering rate should be substantial.