The Biophysical Role of Water and Ice Within Permafrost Nearing Collapse: Insights From Novel Geophysical Observations
The Biophysical Role of Water and Ice Within Permafrost Nearing Collapse: Insights From Novel Geophysical Observations
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DOI：
10.1029/2021jf006104
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发表时间：
2021-06-01
影响因子：
3.9
通讯作者：
Waldrop, M. P.
中科院分区：
文献类型：
--
作者：
James, S. R.;Minsley, B. J.;Waldrop, M. P.
多年冻土融化对水文、热力和生物过程的影响仍不确定，部分原因是地下测量能力有限。为了更好地理解热喀斯特环境中的地下过程，我们在阿拉斯加费尔班克斯附近的阿拉斯加泥炭地实验场，沿着森林多年冻土和塌陷疤痕沼泽之间的融化梯度，将地球物理和生物地球化学仪器并置。环境地震噪声监测提供了对水和冰饱和度变化的连续高时间分辨率测量。地震波速变化图确定了最靠近最年轻沼泽的夏季波速大幅降低的区域，表明沼泽边缘可能存在融化和扩张。这些结果与对未冻水含量随深度的钻孔核磁共振补充测量结果非常吻合，该测量显示，沿研究样带，最靠近沼泽边缘的多年冻土含有最多的未冻水，体积含量高达25%。对多年冻土内甲烷的原位测量显示，在这些沼泽边缘位置甲烷浓度较高，高达土壤气体的30%。在沼泽边缘观察到了多年冻土上的融区，这表明融区的形成和常年液态水可能推动沼泽横向扩张，并在融化之前加剧多年冻土碳损失。将地震监测与冬季地表二氧化碳通量进行比较，发现根据时间和与沼泽的距离不同而有不同的响应，这体现了地下水和冰对微生物活动和地表排放的控制作用。这项研究展示了一种多学科方法，用于对地下物理性质如何影响温室气体产生、排放和热喀斯特发育有新的认识。
The impact of permafrost thaw on hydrologic, thermal, and biotic processes remains uncertain, in part due to limitations in subsurface measurement capabilities. To better understand subsurface processes in thermokarst environments, we collocated geophysical and biogeochemical instruments along a thaw gradient between forested permafrost and collapse-scar bogs at the Alaska Peatland Experiment site near Fairbanks, Alaska. Ambient seismic noise monitoring provided continuous high-temporal resolution measurements of water and ice saturation changes. Maps of seismic velocity change identified areas of large summertime velocity reductions nearest the youngest bog, indicating potential thaw and expansion at the bog margin. These results corresponded well with complementary borehole nuclear magnetic resonance measurements of unfrozen water content with depth, which showed permafrost soils nearest the bog edges contained the largest amount of unfrozen water along the study transect, up to 25% by volume. In situ measurements of methane within permafrost soils revealed high concentrations at these bog-edge locations, up to 30% soil gas. Supra-permafrost talik zones were observed at the bog margins, indicating talik formation and perennial liquid water may drive lateral bog expansion and enhanced permafrost carbon losses preceding thaw. Comparison of seismic monitoring with wintertime surface carbon dioxide fluxes revealed differential responses depending on time and proximity to the bogs, capturing the controlling influence of subsurface water and ice on microbial activity and surficial emissions. This study demonstrates a multidisciplinary approach for gaining new understanding of how subsurface physical properties influence greenhouse gas production, emissions, and thermokarst development.