CARBON DIOXIDE EMISSIONS BY ROCK ORGANIC CARBON OXIDATION AND THE NET GEOCHEMICAL CARBON BUDGET OF THE MACKENZIE RIVER BASIN
CARBON DIOXIDE EMISSIONS BY ROCK ORGANIC CARBON OXIDATION AND THE NET GEOCHEMICAL CARBON BUDGET OF THE MACKENZIE RIVER BASIN
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DOI：
10.2475/06.2019.02
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发表时间：
2019-06-01
影响因子：
2.9
通讯作者：
Burton, Kevin W.
中科院分区：
文献类型：
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作者：
Horan, Kate;Hilton, Robert G.;Burton, Kevin W.
岩石中的有机碳暴露于氧化风化可向大气释放二氧化碳（CO2）并消耗大气中的氧气。除了火山作用、变质作用和硫酸对碳酸盐矿物的风化作用外，这也是数百万年时间尺度上大气中二氧化碳的主要来源。硅酸盐风化和有机碳埋藏导致的CO2释放和CO2下降之间的平衡决定了风化和侵蚀过程中的净地球化学碳收支。然而，岩石衍生的有机碳（成岩有机碳，OCpetro）的氧化率仍然受到很大的限制。在这里，我们使用CO2作为代理跟踪和量化的OCpetro氧化在加拿大的麦肯齐河流域，其他碳通量已得到很好的约束之前的CO2释放。2009年至2013年期间，在麦肯齐河及其主要支流（哈德河、皮尔河和北极红河）的测量站沿着收集了河水和沉积物样本。为了评估硅酸盐、硫化物和OCpetro矿物相的CO2输入，我们将溶解的CO2浓度[Re]（diss）归一化为钠离子和硫酸根离子浓度。这种方法表明，> 85%的[Re]（diss）来自主要河道中的OCpetro。[Re]（diss）和排水测量用于量化溶解Re产率。河流沉积物提供了盆地中经历风化的物质的Re与OCpetro比率的测量值，并且与已发表的岩石样本非常一致。溶解Re产量与河流沉积物[Re]/[OCpetro]比率相结合，以估计OCpetro风化的CO2排放量。这是0.45（+0.19）/齐盖奇克的麦肯齐河的碳排放量为（-0.11）公吨，tC km（-2）yr（-1）（3.8（+1.5）/X-0.9 10（4）摩尔km（-2）yr（-1）），Peel、Arctic Red和硬集水区的年径流量分别为0.94（+0.41）/（-0.26）tC km（-2）Yr（-1）、0.78（+0.35）/（-0.21）tC km（-2）Yr（-1）和1.01（+0.42）/（-0.25）tC km（-2）Yr（-1）。当与已发表的硅酸盐和碳酸盐风化速率以及生物圈有机碳的沉积埋藏一起考虑时，这些数据表明，由于风化和侵蚀的碳转移，麦肯齐河流域的上部目前作为大气CO2汇，其容量约为1 tC km（-2）yr（-1）（约为8 x 10（4）moles km（-2）yr（-1））。在末次盛冰期期间，地球化学碳平衡可能会有很大的不同：OCpetro和碳酸盐矿物氧化风化产生的CO2排放量可能会增加，再加上生物圈碳埋藏减少，可能会使平衡向CO2的净来源倾斜。
The exposure of organic carbon in rocks to oxidative weathering can release carbon dioxide (CO2) to the atmosphere and consume atmospheric oxygen. Alongside volcanism, metamorphism, and the weathering of carbonate minerals by sulfuric acid, this is a major source of atmospheric CO2 over million year timescales. The balance between CO2 release and CO2 drawdown by silicate weathering and organic carbon burial sets the net geochemical carbon budget during weathering and erosion. However, the rates of rock-derived organic carbon (petrogenic organic carbon, OCpetro) oxidation remain poorly constrained. Here, we use rhenium as a proxy to trace and quantify CO2 release by OCpetro oxidation in the Mackenzie River Basin, Canada, where the other carbon fluxes have been well constrained previously. River water and sediment samples were collected between 2009 and 2013 at gauging stations along the Mackenzie River and its main tributaries (hard, Peel and Arctic Red). To assess rhenium inputs from silicate, sulfide and OCpetro mineral phases we normalize dissolved rhenium concentrations, [Re](diss), to sodium and sulfate ion concentrations. This approach suggests that >85 percent of [Re](diss), is derived from OCpetro in the main river channels. [Re](diss) and water discharge measurements are use to quantify dissolved Re yields. River sediments provide a measure of the Re to OCpetro ratio of materials undergoing weathering in the basin, and agree well with published rock samples. Dissolved Re yields are combined with river sediment [Re]/[OCpetro] ratios to estimate the CO2 emissions by OCpetro weathering. These are 0.45 (+0.19)/(-0.11) metric tonnes of carbon, tC km(-2) yr(-1) for the Mackenzie River at Tsiigehtchic (3.8 (+1.5)/X-0.9 10(4) moles km(-2) yr(-1)), and 0.94 (+0.41)/(-0.26) tC km(-2) Yr(-1) 0.78 (+0.35)/(-0.21) tC km(-2) yr(-1) and 1.01 (+0.42)/(-0.25) tC km(-2)Yr(-1) for the Peel, Arctic Red and hard catchments, respectively. When considered alongside published silicate and carbonate weathering rates and the sedimentary burial of biospheric organic carbon, these data suggest that the upper part of the Mackenzie River Basin presently acts as an atmospheric CO2 sink of similar to 1 tC km(-2)yr(-1) (similar to 8 x 10(4) moles km(-2) yr(-1)) as a result of the carbon transfers by weathering and erosion. During the Last Glacial Maximum, it is possible that the net geochemical carbon balance may have been very different: potential increases in CO2 emissions from oxidative weathering of OCpetro and carbonate minerals, coupled with reduced biospheric carbon burial, may have tipped the balance to a net source of CO2.