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.

化学风化是指岩石在天然酸性的雨水中溶解的过程。这是因为大气中的二氧化碳溶解在雨中形成碳酸，雨水与岩石相互作用使岩石溶解。溶解的二氧化碳以碳酸氢盐的形式被困在河流和海水中（存在于所有自然水域，例如矿泉水中），在那里稳定地存在数千年或数万年，然后以碳酸钙（如水垢）的矿物形式永久储存起来，并以石灰石的形式沉积在海洋中。岩石溶蚀或化学风化是全球碳循环的一个主要过程，人们认为，这种陆地岩石的化学风化，以及随后以碳酸钙形式埋藏的碳，在地球历史上起着控制碳循环和气候的反馈作用。不同的岩石以不同的速度溶解，硅酸盐矿物的溶解导致大气中碳的永久减少，而石灰石的溶解虽然快得多，但只能吸收数千年的碳。这一点之所以重要，是因为河流运输了大量的碳（目前大气中由于人为活动增加的二氧化碳约占四分之一）。然而，科学家最近的研究对上述关于河流如何在碳循环中发挥重要作用的简化版本提出了质疑。锁在岩石（如富含有机质的页岩或石灰石）中的碳可以在化学风化过程中释放回大气，这相当于燃烧化石燃料。在亚马逊盆地，古代有机物在沉积运输过程中被氧化，向大气中释放二氧化碳。在长江（中国）和麦肯齐盆地（北美），少量硫酸（由含硫矿物如黄铁矿或“愚金”氧化释放）溶解石灰岩，将古老岩石中的二氧化碳释放到大气中。那么，河流究竟是大气中二氧化碳的净汇还是净源呢？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。我们现在已经开发出量化所有这些过程的方法，但这必须在全球范围内进行。要做到这一点，最好的办法是研究世界上最大的河流，因为这些河流代表了一些最大的碳通量，而我们不知道这些通量是来自大气还是来自大气，这表明我们对地球表面碳循环运作的认识存在严重缺陷。我们选择了世界上最大的三条河流——东南亚的伊洛瓦底江、萨尔温江和湄公河——作为碳运输的案例研究。加起来，这些河流输送的碳约占全球河流总碳通量的14%，约占英国碳排放量的一半，但对这些流域的研究太少，它们的影响在很大程度上是未知的。碳的转移最终是释放二氧化碳，还是这些河流流域充当了碳的汇？我们建议通过使用一系列同位素来限制这些盆地的现代碳收支，这将告诉我们是古代碳从岩石中释放出来，还是来自大气或生物圈的现代碳正在被消耗。我们将在两年的时间里对河流进行采样，但这里的一个关键问题是，两年的时间对更长的时间有多大的代表性。我们将解锁河流沉积物档案，以确定更长时间、千年时间尺度上的平均碳通量，从而全面了解这些流域的碳转移。

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

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

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