The efficacy of enhancing carbonate weathering for carbon dioxide sequestration
The efficacy of enhancing carbonate weathering for carbon dioxide sequestration
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DOI：
10.3389/fclim.2022.928215
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发表时间：
2022-08-11
影响因子：
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通讯作者：
Tipper, Edward T.
中科院分区：
文献类型：
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作者：
Knapp, William J.;Tipper, Edward T.
增强风化是一种地球工程战略，旨在提高大陆风化率，从而增加大气碳（HCO 3-）向海洋的输送。大多数增强风化研究都集中在硅酸盐岩石的能力上（例如，玄武岩）和矿物（例如，橄榄石、Mg 2SiO 4或硅灰石CaSiO 3）以除去大气中的CO2。然而，碳酸盐矿物（例如，方解石，CaCO 3）可以提供一个额外的，快速的方式来增加HCO 3-输出到海洋。最近的研究表明，如果碳酸是主要的溶解剂，通过增加土壤中方解石的溶解，可以从大气中去除0.84 GtC yr（-1）。目前尚不清楚的是，溶解在土壤中的大气CO2是否可以通过通常具有较低[pCO（2）]的河流输送到海洋。土壤（风化发生的地方）和河流（HCO 3-被运输的地方）之间方解石溶解度的这种差异可能导致在运输过程中形成大量的次生碳酸盐，释放通过溶解消耗的CO2。在这里，我们提出了一个模拟研究比较估计土壤溶解能力（SDC）在149个地球上最大的河流流域，在相应的河流中的碳（PTCC）的潜在运输能力。我们发现，如果河流与方解石处于不平衡状态（即，SIc = 1）。在这种情况下，0.92 Gt C yr（-1）可能被隔离在背景风化率之上，这类似于大气碳年增长的20%。如果河流与方解石处于平衡状态（即，SIc = 0），大约三分之二溶解在土壤沃茨中的碳由于河流中的方解石沉淀而损失，只有0.26 Gt的额外大气C yr（-1）可以被输送到海洋。总的来说，增强碳酸盐风化的功效是河流将碳酸盐风化产物输送到海洋的能力的函数，而不是土壤的溶解能力。这些研究结果的效率，提高硅酸盐风化海洋碱度增强的影响，作为二次碳酸盐沉淀在运输过程中并不总是考虑。
Enhanced weathering is a geoengineering strategy aiming to increase continental weathering rates, thereby increasing the delivery of atmospheric carbon (as HCO3-) to the oceans. Most enhanced weathering studies focus on the capacity of silicate rocks (e.g., basalt) and minerals (e.g., olivine, Mg2SiO4, or wollastonite CaSiO3) to remove atmospheric CO2. However, carbonate minerals (e.g., calcite, CaCO3) could provide an additional, rapid way to increase HCO3- export to the oceans. Recent studies suggest that 0.84 Gt C yr(-1) could be removed from the atmosphere through the enhanced dissolution of calcite in soils, provided carbonic acid is the main dissolution agent. What is not clear is whether atmospheric CO2 dissolved in soils can be transported by rivers, which typically have lower [pCO(2)], to the oceans. This difference in calcite solubility between soils (where weathering occurs) and rivers (where HCO3- is transported) may lead to large amounts of secondary carbonate formation during transport, releasing the CO2 consumed through dissolution. Here, we present a modeling study comparing the estimated soil dissolution capacity (SDC) in 149 of Earth's largest river basins, to the potential transport capacity of carbon (PTCC) in corresponding rivers. We find the SDC can only be exported to the oceans, without secondary carbonate precipitation, if rivers are in disequilibrium with respect to calcite (i.e., SIc = 1). In this instance, 0.92 Gt C yr(-1) may be sequestered above background weathering rates, which is similar to 20% of annual increases in atmospheric carbon. If rivers are at equilibrium with calcite (i.e., SIc = 0), approximately two-thirds of the carbon dissolved in soil waters are lost due to calcite precipitation in rivers, and just 0.26 Gt of additional atmospheric C yr(-1) can be transported to the oceans. Overall, the efficacy of enhanced carbonate weathering is a function of the capacity rivers have for transporting the products from carbonate weathering to the oceans, rather than the dissolution capacity of soils. These findings have implications for the efficiency of enhancing silicate weathering for ocean alkalinity enhancement, as secondary carbonate precipitation during transport is not always considered.