Global CO2-consumption by chemical weathering: What is the contribution of highly active weathering regions?
Global CO2-consumption by chemical weathering: What is the contribution of highly active weathering regions?
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DOI：
10.1016/j.gloplacha.2009.07.007
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发表时间：
2009-12-01
影响因子：
3.9
通讯作者：
Koehler, Peter
中科院分区：
文献类型：
--
作者：
Hartmann, Jens;Jansen, Nils;Koehler, Peter
硅酸盐化学风化所消耗的二氧化碳以及由此产生的硅酸盐/碳酸盐风化比影响长期气候变化。然而，人们对高活性风化区的空间扩展及其在全球二氧化碳消耗中的比例知之甚少。由于这些地区可能对全球气候变化具有重要意义，因此这里以高分辨率计算全球二氧化碳消耗量，以充分代表它们。在以前的研究中，使用两种不同的方法估计全球二氧化碳消费量：i)基于大河水化学通量的反向方法和ii)应用空间显式二氧化碳消费量函数的正向方法。第一种方法的估算结果没有提供高活跃区的空间分辨率，第二种方法基于1度或2度网格分辨率，应用了6种岩性类别，同时包括3种沉积物类别（页岩、砂岩和碳酸盐岩）。应用的岩性分类方案是否能充分代表全球范围内沉积物中二氧化碳的消耗，目前仍不确定。这是由于沉积物性质、成岩历史以及在硅酸盐为主的岩性分类中明显的碳酸盐的贡献具有很大的可变性。为了解决这些问题，我们将高分辨率数据训练后的二氧化碳消耗模型应用于包含15个岩性类别的全球矢量岩性图。校准数据来自代表各种风化速率的地区。由此产生的全球化学风化所消耗的二氧化碳与之前的估计相似（2.37 Mt C a(-1)），但硅酸盐风化所占的比例为63%。因此比以前的估计（49%到60%）要大。强化岩性分类方案的应用表明，区分不同类型的沉积岩及其成岩历史对评价岩石风化的空间分布具有重要意义。研究结果强调了热点（10倍于全球平均风化速率）和过度活跃区（5 ~ 10倍于全球平均风化速率）的作用。仅全球9%的地表面积就承担了化学风化所消耗的约50%的二氧化碳（或者如果考虑热点和过度活跃区域：3.4%的地表面积对应全球28%的二氧化碳消耗）。内啡肽区对全球二氧化碳消耗量的贡献仅为370万摄氏度（-1）。如果确定的高度活跃地区受到持续的全球气候变化导致的水文循环总体空间格局变化的影响，预计将对全球二氧化碳消耗率产生重大影响。具体来说，如果将末次盛冰期与目前的条件进行比较，全球碳循环很可能也受到了这些变化的影响。预计这些结果将有助于改进全球碳和全球循环模式。(C) 2009 Elsevier B.V.版权所有
CO2-consumption by chemical weathering of silicates and resulting silicate/carbonate weathering ratios influences long-term climate changes. However, little is known of the spatial extension of highly active weathering regions and their proportion of global CO2-consumption. As those regions may be of significant importance for global climate change, global CO2-consumption is calculated here at high resolution, to adequately represent them. In previous studies global CO2-consumption is estimated using two different approaches: i) a reverse approach based on hydrochemical fluxes from large rivers and ii) a forward approach applying spatially explicit a function for CO2-consumption. The first approach results in an estimate without providing a spatial resolution for highly active regions and the second approach applied six lithological classes while including three sediment classes (shale, sandstone and carbonate rock) based at a 1 degrees or 2 degrees grid resolution. It remained uncertain, if the applied lithological classification schemes represent adequately CO2-consumption from sediments on a global scale. This is due to the large variability of sediment properties, their diagenetic history and the contribution from carbonates apparent in silicate dominated lithological classes. To address these issues, a CO2-consumption model, trained at high-resolution data, is applied here to a global vector based lithological map with 15 lithological classes. The calibration data were obtained from areas representing a wide range of weathering rates. Resulting global CO2-consumption by chemical weathering is similar to earlier estimates (237 Mt C a(-1)) but the proportion of silicate weathering is 63%. and thus larger than previous estimates (49 to 60%). The application of the enhanced lithological classification scheme reveals that it is important to distinguish among the various types of sedimentary rocks and their diagenetic history to evaluate the spatial distribution of rock weathering. Results highlight the role of hotspots (> 10 times global average weathering rates) and hyperactive areas (5 to 10 times global average rates). Only 9% of the global exorheic area is responsible for about 50% of CO2-consumption by chemical weathering (or if hotspots and hyperactive areas are considered: 3.4% of exorheic surface area corresponds to 28% of global CO2-consumption). The contribution of endorheic areas to the global CO2-consumption is with 3.7 Mt C a(-1) only minor. A significant impact on the global CO2-consumption rate can be expected if identified highly active areas are affected by changes in the overall spatial patterns of the hydrological cycle due to ongoing global climate change. Specifically if comparing the Last Glacial Maximum with present conditions it is probable that also the global carbon cycle has been affected by those changes. It is expected that results will contribute to improve global carbon and global circulation models. (C) 2009 Elsevier B.V. All rights reserved.