Thermal and hydrological investigations of degrading permafrost

我们研究计划的长期目标是了解永久冻土地形对控制地面温度的因素变化的反应，特别是地表条件和气候的变化。永久冻土是指在两年或更长时间内保持在0摄氏度或以下的地面。控制永久冻土存在的主要因素是气候，而最近的气候变暖导致整个北方的永久冻土温度上升。当季节性融化的活动层穿透到永久冻土层顶部的冰层时，这种变暖的实际后果最大。 我们建议研究加拿大西部北极地区气候与多年冻土的关系，以及活动层的加深。我们将强调四个主题。 (1)在怀特霍斯附近，那里的永久冻土接近0摄氏度，由于融化冰所需的能量，地面温度对气候的反应不敏感。我们打算比较有和没有永久冻土的邻近地点，以确定尽管季节性冻结和融化，但没有永久冻土的地点在多大程度上更有效地呈现气候变暖信号。我们有25年的地面温度记录可供参考。 (2)在北极西部海岸附近，我们将研究坡角对活动层增厚的影响。我们预计，在平坦的地形上，从永久冻土中释放出来的水可能会留在原地并冻结回来，但可能会从山坡上流失。因此，我们预计山坡上的下沉比平地上的更大。我们预计，如果多年冻土的顶部每年都随着融化而变化，那么年气候与活动层厚度之间的关系将随着坡度的变化而变化。 (3)在北极西部，我们观察到束缚冻土带多边形的冰楔普遍融化。这些楔形物几乎是纯冰，它们的融化导致了最大可能的下沉。楔形物位于积雪槽的下方，因此，随着积雪深度及其隔热效果的增加，下沉可能会导致进一步变暖。在低地，水通常积聚在水槽中。我们希望确定低谷加深的速度，它对水和雪深度的依赖，以及它是否在楔形区加速。我们将研究海槽的冻结，因为只有当活跃层重新冻结后，下面的永久冻土才可能冷却。我们或许能够预测关键的水和雪深度，在这个深度时，谷底的成分不会冻结，而冰楔则完全融化。 (4)最后，我们将研究从北极西部海岸通过不列颠山脉到老乌鸦平原的多年冻土和气候梯度，以确定由于山脉的影响，多年冻土与气候的关系如何变化。我们怀疑最冷的地面是在山谷底部形成冬季逆温层的地方。我们希望确定山脉对永久冻土温度的影响，因为它们阻碍了沿海天气向内陆移动。

The long-term objective of our research program is to understand the response of permafrost terrain to changes in factors that control ground temperatures, particularly changes in surface conditions and climate. Permafrost is ground that remains at or below 0C for two or more years. The principal factor governing the presence of permafrost is climate, and recent climate warming has led to increases in permafrost temperature throughout the North. The practical consequences of such warming are greatest when the seasonally thawed active layer penetrates into icy ground at the top of permafrost. We propose to study the relations between climate and permafrost in western Arctic Canada, and deepening of the active layer. We will emphasize four topics. (1) Near Whitehorse, where permafrost is close to 0 C, ground temperatures do not respond sensitively to climate because of energy needed for thawing ice. We intend to compare adjacent sites with and without permafrost, to determine how much more efficiently sites without permafrost present the climate warming signal, despite seasonal freezing and thawing. We have a 25 year record of ground temperatures to draw upon. (2) Near the western Arctic coast, we will examine the effect of slope angle on active-layer thickening. We expect that in flat terrain water liberated from permafrost may remain in place and freeze back, but it may run off from hill slopes. Therefore we expect greater subsidence on hill sides than in flat ground. We expect the association between annual climate and active-layer thickness to vary with slope angle if the top of permafrost changes each year with thawing. (3) In the western Arctic, we observe widespread thawing of the ice wedges that bound tundra polygons. These wedges are almost pure ice, and their melting leads to the greatest possible subsidence. The wedges lie below troughs in which snow accumulates, so subsidence may lead to further warming, as the depth of snow and its insulation effect increase. In lowlands water commonly accumulates in the troughs. We wish to determine the rate of trough deepening, its dependence on water and snow depth, and whether it accelerates in the wedges. We will study freeze-back of the troughs, for only once the active layer has refrozen may underlying permafrost cool. We may be able to forecast critical water and snow depths at which trough constituents do not freeze back and ice wedges melt completely. (4) Finally, we will study the gradient in permafrost and climate from the western Arctic coast through British Mountains to Old Crow Flats to determine how permafrost-climate relations change due to the influence of the mountains. We suspect that the coldest ground is found where winter inversions develop in mountain valley floors. We wish to determine the effects on permafrost temperatures of the mountains as they block coastal weather from moving inland.