No support for carbon storage of >1,000 GtC in northern peatlands
No support for carbon storage of >1,000 GtC in northern peatlands
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DOI：
10.1038/s41561-021-00769-2
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发表时间：
2021-06
影响因子：
18.3
通讯作者：
Zicheng Yu;F. Joos;T. Bauska;B. Stocker;H. Fischer;J. Loisel;V. Brovkin;G. Hugelius;Christoph Nehrba
中科院分区：
文献类型：
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作者：
Zicheng Yu;F. Joos;T. Bauska;B. Stocker;H. Fischer;J. Loisel;V. Brovkin;G. Hugelius;Christoph Nehrba
超大的泥炭碳储量7没有得到来自全球碳预算重建的自上而下限制的支持。我们的模型模拟结果表明，在全新世期间，泥炭碳储量增加1000GTC将导致大气二氧化碳减少到220ppm以下，大气δ13CO2增加到高于观测值0.8‰以上，深海溶解无机碳的δ13C(δ13C-DIC)在整个全新世稳步上升(图1)。首先，我们的盒子模型计算表明，如图2F所示，将泥炭碳吸收简化为600ppm的大气信号是错误的，这是因为海洋的补偿作用忽略了海洋的补偿作用，海洋的补偿作用在与此相关的千年时间尺度上减少了高达80%的大气扰动。我们假设Nichols和Peteet相反地将他们估计的陆地碳储量增加2.12GTC/ppm，得出了声称的泥炭碳吸收相关的大气二氧化碳在全新世减少300ppm。用我们的模型将相同的泥炭碳吸收转化为大气二氧化碳信号，产生了大约60ppm的下降(图1B)。第二，我们的模拟表明，超大的泥炭碳储量很难与大气和海洋的碳收支相协调。以前，观测到的大气二氧化碳浓度和冰芯δ13C的变化被用来划分陆地生物圈和海洋的贡献，对全新世期间的陆地碳收支提供了全球约束。测量到的二氧化碳浓度从265ppm 11KYR AGO(Ka)增加到1750Ce的278ppm和δ13C的微小变化(图1B，c)被用来重建全新世时期前工业前陆地净碳吸收约250GTC(参考文献。11)。这种全新世陆地碳平衡反映了在全新世早期，通过北方森林的生长和早期泥炭的积累-与观察到的早期全新世大气和海洋δ13C值12的增加-以及在全新世晚期的碳释放50GTC相一致。过去5KYR陆地碳储量的小幅减少与图2e所示同期泥炭碳储量约400GTC的估计增加形成了对比。必须调用具有生物来源δ13C签名的400-500GTC的补偿碳源来完成预算。对这份预算的详细分析得出的结论是，早期农学家因土地利用变化而产生的二氧化碳排放量不足以弥补这一差距13。尼科尔斯和皮特7对泥炭碳储量的估计比使用的高出一倍，这使得协调预算变得更加困难。Nichols和Peteet 7没有讨论这一冲突。Nichols和Peteet没有讨论碳收支与陆地碳源之间的平衡，而是认为“平衡泥炭地碳汇的最重要机制”是在全新世期间由风力驱动的上升流持续从深海释放碳。这种机制需要从深海中损失比泥炭地碳汇本身所暗示的更大的碳，并且没有得到海洋δ13C和碳酸盐离子变化的观察和模拟的支持。例如，南大洋上升流的增加将进一步增加深海14中的δ13C-DIC，而泥炭地再生长的δ13C-DIC的增加已经站不住脚(图1D)，但δ13C值在7ka之后保持不变，正如从δ的海底13C数据堆…观察到的那样
The exceptionally large peat carbon storage 7 is not supported by top-down constraints from the global carbon budget reconstructions. Our model simulation results show that an increase in peat carbon storage of> 1,000 GtC during the Holocene would induce a decrease in atmospheric CO2 to below 220 ppm, an increase in atmospheric δ13CO2 to a value more than 0.8‰ higher than the observed and a steady rise in deep ocean δ13C of dissolved inorganic carbon (δ13C-DIC) throughout the Holocene (Fig. 1). First, our box-model calculations demonstrate that the simplified conversion of peat carbon uptake into an atmospheric signal of> 600 ppm, as shown in their Fig. 2f, was erroneous due to the neglection of the compensating effect by the ocean that acts to reduce any atmospheric perturbation by up to 80% on the millennial time scale relevant here 10. We assume that Nichols and Peteet instead converted their estimated terrestrial carbon stock increase by a division factor of 2.12 GtC per ppm to arrive at the claimed peat carbon uptake-related decrease in atmospheric CO2 of> 300 ppm during the Holocene. Translating the same peat carbon uptake into an atmospheric CO2 signal with our model yielded a decrease of about 60 ppm (Fig. 1b).Second, our simulations suggest that exceptionally large peat carbon storage is difficult to reconcile with the atmospheric and oceanic carbon budgets. Previously, the observed changes in atmospheric CO2 concentration and in δ13C from ice cores have been used to partition the contributions from the land biosphere and ocean, providing a global constraint on land carbon budget during the Holocene. The measured increase in CO2 concentration from 265 ppm 11 kyr ago (ka) to 278 ppm in 1750 ce and the small change in δ13C (Fig. 1b, c) were used to reconstruct the preindustrial terrestrial net carbon uptake over the Holocene epoch to be about 250 GtC (ref. 11). This total Holocene land carbon balance reflects a strong uptake in the early Holocene through the growth of boreal forests and early peat buildup—consistent with the observed early Holocene increase in atmospheric and oceanic δ13C values 12—and a carbon release of 50 GtC during the late Holocene 11. The small decrease in land carbon storage in the past 5 kyr contrasts with the large estimated increase in peat carbon storage of~ 400 GtC during the same time period as in their Fig. 2e. A compensating carbon source of 400–500 GtC with a biogenic δ13C signature would have to be invoked to close the budget. A detailed analysis of this budget concluded that CO2 emissions from land use change by early agriculturalists were not sufficient to close the gap 13. The twofold higher estimates of peat carbon storage by Nichols and Peteet 7—compared with the one used 13—make it even harder to reconcile the budget. This conflict is not discussed in Nichols and Peteet 7. Rather than balancing the carbon budget with terrestrial carbon sources, Nichols and Peteet suggest that the “most important mechanism for balancing the peatland sink” is a continued carbon release from the deep ocean by the wind-driven upwelling during the Holocene. This mechanism requires an even greater loss of carbon from the deep ocean than implied by the peatland carbon sink alone, and is not supported by observation and simulation of marine δ13C and carbonate ion changes. For example, an increase in Southern Ocean upwelling would further increase δ13C-DIC in the deep ocean 14 from the already untenable increase in δ13C-DIC from peatland regrowth (Fig. 1d), yet δ13C values remained constant after 7 ka, as observed from a stack of benthic δ13C data …