Department of Geological and Environmental Sciences, Appalachian State University, Box 32067, Boone, NC, 28608, USA.
School of Geoscience, Physics, and Safety, University of Central Missouri, Warrensburg, MO, 64093, USA.
Nat Commun. 2020 Apr 14;11(1):1826. doi: 10.1038/s41467-020-15579-0.
The uncertain response of marine terminating outlet glaciers to climate change at time scales beyond short-term observation limits models of future sea level rise. At temperate tidewater margins, abundant subglacial meltwater forms morainal banks (marine shoals) or ice-contact deltas that reduce water depth, stabilizing grounding lines and slowing or reversing glacial retreat. Here we present a radiocarbon-dated record from Integrated Ocean Drilling Program (IODP) Site U1421 that tracks the terminus of the largest Alaskan Cordilleran Ice Sheet outlet glacier during Last Glacial Maximum climate transitions. Sedimentation rates, ice-rafted debris, and microfossil and biogeochemical proxies, show repeated abrupt collapses and slow advances typical of the tidewater glacier cycle observed in modern systems. When global sea level rise exceeded the local rate of bank building, the cycle of readvances stopped leading to irreversible retreat. These results support theory that suggests sediment dynamics can control tidewater terminus position on an open shelf under temperate conditions delaying climate-driven retreat.
海洋终端出口冰川对气候变化的反应在短期观测范围之外的时间尺度上是不确定的，这使得未来海平面上升的模型变得不确定。在温带潮汐边缘，大量的冰川下融水形成了冰碛垄（海洋浅滩）或冰接触三角洲，这些地貌减少了水深，稳定了基岩线，并减缓或逆转了冰川后退。在这里，我们展示了一个来自综合大洋钻探计划（IODP）站点 U1421 的放射性碳定年记录，该记录跟踪了阿拉斯加科迪勒拉冰原最大的出口冰川在末次冰盛期气候转变期间的末端位置。沉积速率、冰漂碎屑以及微化石和生物地球化学示踪剂表明，冰川反复发生典型的潮汐冰川循环的突然崩塌和缓慢前进，这在现代系统中也有观察到。当全球海平面上升超过了银行建设的局部速度时，冰川的前进循环就停止了，导致了不可逆转的后退。这些结果支持了这样一种理论，即认为在温带条件下，沉积物动力学可以控制开阔陆架上海水终端的位置，从而延迟气候驱动的后退。
