Carbon Thaw Rate Doubles When Accounting for Subsidence in a Permafrost Warming Experiment
Carbon Thaw Rate Doubles When Accounting for Subsidence in a Permafrost Warming Experiment
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DOI：
10.1029/2019jg005528
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发表时间：
2020-06
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通讯作者：
H. Rodenhizer;J. Ledman;M. Mauritz;S. Natali;E. Pegoraro;C. Plaza;E. Romano;C. Schädel;Meghan Taylor;E. Schuur
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作者：
H. Rodenhizer;J. Ledman;M. Mauritz;S. Natali;E. Pegoraro;C. Plaza;E. Romano;C. Schädel;Meghan Taylor;E. Schuur
永久冻土融化通常通过活动层厚度或从地表测量的最大季节性融化来测量。然而，之前的工作表明，这种测量本身无法解释地面沉降，因此低估了永久冻土融化。为了确定沉降对观测到的永久冻土融化和解冻土壤碳储量的影响，我们使用高精度 GPS 量化了沉降，并在阿拉斯加永久冻土南界附近的永久冻土变暖实验中确定了其环境驱动因素。在永久冻土温度接近 0°C 的情况下，9 年来在对照地块中观察到了 10.8 厘米的下沉。实验性的空气和土壤变暖使沉降增加了五倍，并产生了被淹没的微型场地。在所有处理中，冰和土壤流失分别导致了 85-91% 和 9-15% 的沉降。考虑到沉降，永久冻土融化的深度比活性层厚度深 19%（对照）到 49%（变暖），活性层内新解冻的碳量比活性层深 37%（对照）到 113%（变暖）。随着活性层加深，额外的碳融化，进入大气的碳通量和地下水中碳的横向传输可能会增加。然而，由于沉降测量有限，这种影响的程度在景观尺度上是不确定的。因此，为了确定环极地地区永久冻土融化的全部范围及其对碳循环的反馈，有必要更广泛地量化环极地地区的沉降。
Permafrost thaw is typically measured with active layer thickness, or the maximum seasonal thaw measured from the ground surface. However, previous work has shown that this measurement alone fails to account for ground subsidence and therefore underestimates permafrost thaw. To determine the impact of subsidence on observed permafrost thaw and thawed soil carbon stocks, we quantified subsidence using high‐accuracy GPS and identified its environmental drivers in a permafrost warming experiment near the southern limit of permafrost in Alaska. With permafrost temperatures near 0°C, 10.8 cm of subsidence was observed in control plots over 9 years. Experimental air and soil warming increased subsidence by five times and created inundated microsites. Across treatments, ice and soil loss drove 85–91% and 9–15% of subsidence, respectively. Accounting for subsidence, permafrost thawed between 19% (control) and 49% (warming) deeper than active layer thickness indicated, and the amount of newly thawed carbon within the active layer was between 37% (control) and 113% (warming) greater. As additional carbon thaws as the active layer deepens, carbon fluxes to the atmosphere and lateral transport of carbon in groundwater could increase. The magnitude of this impact is uncertain at the landscape scale, though, due to limited subsidence measurements. Therefore, to determine the full extent of permafrost thaw across the circumpolar region and its feedback on the carbon cycle, it is necessary to quantify subsidence more broadly across the circumpolar region.