Earth's weathering reactor: carbon source or sink over short and long time-scales?

地球的风化反应堆：短期和长期的碳源或碳汇？

• 批准号: NE/P011659/1
• 负责人: Edward Tipper
• 金额: $ 70.65万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FP011659%2F1
• 关键词: Earth; weathering; reactor; carbon; source

Chemical weathering is the process by which rocks dissolve in rainwater, which is naturally acidic. This is because atmospheric carbon dioxide dissolves in rain to form carbonic acid, and the rainwater interacts with rocks making them dissolve. The dissolved carbon dioxide becomes trapped in river and seawater, as bicarbonate (present in all natural waters such as mineral water for example), where it resides stably for thousands, or tens of thousands of years, and is then stored permanently in a mineral form as calcium carbonate (like limescale) and deposited as limestone in the oceans. Rock dissolution or chemical weathering is a major process in the global carbon cycle and it is thought that this terrestrial chemical weathering of rocks, and subsequent burial of carbon as calcium carbonate, acts as the feedback which has controlled the carbon cycle and thus climate over Earth history. Different rocks dissolve at different rates and the dissolution of silicate minerals results in a permanent drawdown of atmospheric carbon, whereas the dissolution of limestones, although much faster, only draws down carbon for 1000s of years. The reason this matters is that rivers transport a significant amount of carbon (about a quarter of the present increase in atmospheric carbon dioxide due to anthropogenic activities). However, recent research by scientists has called into question the above, simplified version of how rivers play an important role in the carbon cycle. Carbon locked up in rocks (such as shales rich in organic matter or limestones) can be released back to the atmosphere during chemical weathering, which represents the natural equivalent of fossil fuel burning. In the Amazon basin, ancient organic matter becomes oxidised during sedimentary transport, releasing carbon dioxide to the atmosphere. In the Yangtze (China) and Mackenzie Basins (North America), small amounts of sulphuric acid (released by the oxidation of sulphur-bearing minerals such as pyrite, or 'fools gold') dissolves limestone, releasing carbon dioxide from ancient rocks to the atmosphere. So are rivers a net sink for carbon dioxide from the atmosphere or a net source? In the context of environmental change there is a clear need to better understand carbon fluxes associated with weathering. We have now developed methods to quantify all these processes, but this must be done at a global scale. The best way to do this is to work on the largest rivers in the world, as these represent some of the largest fluxes of carbon and the fact that we don't know if these fluxes are TO or FROM the atmosphere represents a serious deficit in our knowledge of the operation of the carbon cycle at Earth's surface. We have selected three of the largest rivers in the world as case studies for carbon transport, the Irrawaddy, Salween and Mekong from SE Asia. Combined, these rivers transport about 14% of the global total riverine flux of carbon, or about half the UK's carbon emissions, but there is so little work on these basins that their impact is largely unknown. Does the transfer of carbon end up releasing carbon dioxide, or do these river basins act as a sink for carbon? We propose to constrain the modern carbon budgets in these basins by using a series of isotopes, that will tell us if ancient carbon is being released from rocks, or whether modern carbon derived from the atmosphere or biosphere is being consumed. We will conduct our sampling of the rivers over a 2-year period, but a key question here is how representative is a two-year period of the longer term. We will unlock the archive of river sediments to determine carbon fluxes averaged over longer, millennial time-scales to comprehensively understand carbon transfer in these basins.

化学风化是岩石溶解在雨水中的过程，这种雨水是天然酸性的。这是因为大气二氧化碳溶于雨中以形成碳酸，雨水与岩石相互作用，使其溶解。溶解的二氧化碳被困在河流和海水中，作为碳酸氢盐（例如，存在于所有天然水域，例如矿物水），在那里它稳定稳定成千上万，或数万年，然后以矿物质形式永久存储为碳酸盐（如limescale），并沉积在海洋中的碳酸盐（如limescale）。岩石溶解或化学风化是全球碳循环中的一个主要过程，人们认为岩石的这种陆地化学风化，随后将碳作为碳酸钙埋葬，是控制碳循环的反馈，从而控制了地球历史上的气候。不同的岩石以不同的速率溶解，硅酸盐矿物质的溶解导致大气碳的永久缩减，而石灰岩的溶解虽然快得多，但仅将碳降低了1000年。这很重要的是，河流运输了大量碳（由于人为活性而导致的大气二氧化碳的目前增加了四分之一）。但是，科学家的最新研究使上述河流如何在碳循环中发挥重要作用的简化版本。在化学风化期间，可以将碳锁在岩石（例如富含有机物或石灰石的页岩）中的碳（例如富含有机物或石灰岩的页岩），这代表了化石燃料燃烧的天然等效物。在亚马逊盆地中，古代有机物在沉积运输过程中被氧化，将二氧化碳释放到大气中。在长江（中国）和麦肯齐盆地（北美）中，少量的硫酸（由黄铁矿等含硫矿物质的氧化或“傻瓜金”释放）使石灰石溶解，将二氧化碳从古代岩石中释放到大气中。那么，河流是大气或净源的二氧化碳的净水槽吗？在环境变化的背景下，显然需要更好地了解与风化有关的碳通量。现在，我们开发了量化所有这些过程的方法，但这必须在全球范围内完成。做到这一点的最好方法是在世界上最大的河流上工作，因为这些河流代表了一些最大的碳磁通量，而且我们不知道这些通量是否往返或来自大气的事实代表了我们对碳循环在地面表面运行的了解的严重赤字。我们已经选择了世界上最大的三条河流作为碳运输的案例研究，来自东南亚亚洲的Irrawaddy，Salween和Mekong。这些河流结合在一起，大约是全球总河流通量碳的14％，约占英国碳排放的一半，但这些盆地的工作很少，以至于它们的影响在很大程度上是未知的。碳的转移最终会释放二氧化碳，还是这些河流盆地作为碳的水槽？我们建议通过使用一系列同位素来限制这些盆地中的现代碳预算，这将告诉我们是否从岩石中释放出古代碳，或者是否正在消耗大气或生物圈中衍生出的现代碳。我们将在2年的时间内对河流进行抽样，但是这里的一个关键问题是代表长期的两年时间。我们将解锁河流沉积物的档案，以确定较长的千禧一代时间表的平均碳通量，以全面了解这些盆地的碳转移。

项目成果

The reactive transport of Li as a monitor of weathering processes in kinetically limited weathering regimes

• DOI: 10.1016/j.epsl.2019.01.034
• 发表时间: 2019-04-01
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Bohlin, Madeleine S.;Bickle, Mike J.
• 通讯作者: Bickle, Mike J.

CARBON DIOXIDE EMISSIONS BY ROCK ORGANIC CARBON OXIDATION AND THE NET GEOCHEMICAL CARBON BUDGET OF THE MACKENZIE RIVER BASIN

• DOI: 10.2475/06.2019.02
• 发表时间: 2019-06-01
• 期刊: AMERICAN JOURNAL OF SCIENCE
• 影响因子: 2.9
• 作者: Horan, Kate;Hilton, Robert G.;Burton, Kevin W.
• 通讯作者: Burton, Kevin W.

Temperature dependent lithium isotope fractionation during glass dissolution

• DOI: 10.1016/j.gca.2021.09.005
• 发表时间: 2021-11
• 期刊: Geochimica et Cosmochimica Acta
• 影响因子: 5
• 作者: Thomas L. Goût;Madeleine Bohlin;E. Tipper;G. Lampronti;I. Farnan

Clay mineralogy, strontium and neodymium isotope ratios in the sediments of two High Arctic catchments (Svalbard)

• DOI: 10.5194/esurf-6-141-2018
• 发表时间: 2017-09
• 作者: R. Hindshaw;N. Tosca;A. Piotrowski;E. Tipper

High-precision determination of lithium and magnesium isotopes utilising single column separation and multi-collector inductively coupled plasma mass spectrometry.

• DOI: 10.1002/rcm.8020
• 发表时间: 2018-01-30
• 期刊: Rapid communications in mass spectrometry : RCM
• 作者: Bohlin MS;Misra S;Lloyd N;Elderfield H;Bickle MJ
• 通讯作者: Bickle MJ