Glacier flow instabilities can rapidly increase sea level through enhanced ice discharge. Surge-type glacier accelerations often occur with a decadal to centennial cyclicity suggesting internal mechanisms responsible. Recently, many surging tidewater glaciers around the Arctic Barents Sea region question whether external forces such as climate can trigger dynamic instabilities. Here, we identify a mechanism in which climate change can instigate surges of Arctic tidewater glaciers. Using satellite and seismic remote sensing observations combined with three-dimensional thermo-mechanical modeling of the January 2009 collapse of the Nathorst Glacier System (NGS) in Svalbard, we show that an underlying condition for instability was basal freezing and associated friction increase under the glacier tongue. In contrast, continued basal sliding further upstream increased driving stresses until eventual and sudden till failure under the tongue. The instability propagated rapidly up-glacier, mobilizing the entire 450 km2 glacier basin over a few days as the till entered an unstable friction regime. Enhanced mass loss during and after the collapse (5–7 fold compared to pre-collapse mass losses) combined with regionally rising equilibrium line altitudes strongly limit mass replenishment of the glacier, suggesting irreversible consequences. Climate plays a paradoxical role as cold glacier thinning and retreat promote basal freezing which increases friction at the tongue by stabilizing an efficient basal drainage system. However, with some of the most intense atmospheric warming on Earth occurring in the Arctic, increased melt water can reduce till strength under tidewater glacier tongues to orchestrate a temporal clustering of surges at decadal timescales, such as those observed in Svalbard at the end of the Little Ice Age. Consequently, basal terminus freezing promotes a dynamic vulnerability to climate change that may be present in many Arctic tidewater glaciers.
展开▼
机译：冰川流动的不稳定性会通过增加冰的排出而迅速增加海平面。喘振型冰川加速常常以十年到一百年的周期性出现，表明内部机制负责。最近，北极巴伦支海地区周围的许多潮水冰川质疑诸如气候等外力是否会引发动态不稳定。在这里，我们确定了一种机制，在这种机制下，气候变化会引发北极潮水冰川激增。利用卫星和地震遥感观测资料以及2009年1月在斯瓦尔巴特群岛纳霍斯特冰川系统（NGS）坍塌的三维热力学模型，我们证明了不稳定性的潜在条件是冰川下的基底冻结和相关摩擦的增加舌。相反，持续的基底滑动进一步向上游滑动会增加驱动压力，直到最终和突然的直至舌头衰竭为止。这种不稳定性迅速蔓延到冰川上，随着耕作进入不稳定的摩擦状态，几天内动员了整个450 km 2 冰川盆地。坍塌过程中和坍塌之后质量损失的增加（与坍塌前的质量损失相比，降低了5到7倍），再加上区域上升的平衡线高度，极大地限制了冰川的质量补充，表明了不可逆转的后果。气候起反常作用，因为冷冰川变薄和后退会促进基础冰冻，通过稳定有效的基础排水系统增加舌头的摩擦。但是，随着北极发生一些地球上最强烈的大气变暖，增加的融化水会降低，直到潮水冰川舌下的强度来协调年代际尺度上的潮汐的时间聚集，例如在斯瓦尔巴群岛末期观测到的那些。小冰河世纪。因此，基础终点冻结促进了许多北极潮水冰川中可能存在的气候变化的动态脆弱性。
展开▼
