Climate Change Science Institute and Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831.
Environmental Science Division, Argonne National Laboratory, Lemont IL 60439.
Proc Natl Acad Sci U S A. 2023 Feb 21;120(8):e2212171120. doi: 10.1073/pnas.2212171120. Epub 2023 Feb 13.
We used a model for permafrost hydrology informed by detailed measurements of soil ice content to better understand the potential risk of abrupt permafrost thaw triggered by melting ground ice, a key open question associated with permafrost response to a warming Arctic. Our spatially resolved simulations of a well-characterized site in polygonal tundra near Utqiaġvik, Alaska, agree well with multiple types of observations in the current climate. Projections indicate 63 cm of bulk subsidence from 2006 to 2100 in the strong-warming Representative Concentration Pathway 8.5 climate. Permafrost thaw as measured by the increase in active layer thickness (ALT)-the thickness of the soil layer that thaws each summer-is accelerated by subsidence, but the effect is relatively small. The ALT increases from the current-day value of approximately 50 cm to approximately 180 cm by 2100 when subsidence is included compared to about 160 cm when it is neglected. In these simulations, previously identified positive feedbacks between subsidence and thaw are self-limiting on decadal time frames because landscape runoff and increasing evapotranspiration result in drier tundra with weaker surface/atmosphere coupling. These results for a tundra site that is representative of large swathes of the Alaska North Slope suggest that subsidence is unlikely to lead to abrupt thaw over large areas. However, subsidence does have significant effects on the hydrology of polygonal tundra. Specifically, subsidence increases landscape runoff, which helps maintain streamflow in the face of increased evapotranspiration but also causes drier tundra conditions that could have deleterious effects on sensitive Arctic wetland ecosystems.
我们使用了一个冻土水文模型，该模型基于土壤冰含量的详细测量，以更好地了解因融土冰而引发的冻土突然融化的潜在风险，这是与北极地区冻土对变暖的反应相关的一个关键未解决的问题。我们对阿拉斯加乌特恰维克附近多边形冻原的一个特征明显的地点进行了空间分辨率模拟，这些模拟与当前气候下的多种观测结果吻合良好。预测表明，在强升温的代表性浓度路径 8.5 气候下，从 2006 年到 2100 年，整体下沉将达到 63 厘米。活跃层厚度（ALT）的增加——即每年夏季融化的土壤层的厚度——作为冻土融化的衡量标准，由于下沉而加速，但这种影响相对较小。与忽略下沉时相比，包括下沉因素后，到 2100 年，ALT 将从目前的约 50 厘米增加到约 180 厘米，而忽略下沉时约为 160 厘米。在这些模拟中，下沉和融化之间先前确定的正反馈在数十年的时间框架内是自我限制的，因为景观径流和不断增加的蒸散作用导致冻原更加干燥，地表/大气耦合作用减弱。这些对于一个代表阿拉斯加北坡大片地区的冻原地点的模拟结果表明，下沉不太可能导致大面积的突然融化。然而，下沉确实对多边形冻原的水文学产生了重大影响。具体而言，下沉会增加景观径流，这有助于在蒸散增加的情况下保持溪流流量，但也会导致冻原更加干燥，这可能对敏感的北极湿地生态系统产生有害影响。
