NOAA/WDS Paleoclimatology - North European Alps Termination-II Stalagmite Stable Isotope Data

Understanding the sequence of events that take place during glacial-interglacial climate transitions is important for improving our knowledge of abrupt climate change. Here, we present a new stacked, high-resolution, precisely-dated speleothem stable isotope record from the northern Alps, which provides an important record of temperature and moisture-source changes between 134 and 111 ka for Europe and the wider North Atlantic realm. The record encompasses the penultimate deglaciation (Termination II (TII)), which lies beyond the limit of radiocarbon dating, thus providing an important new archive for a crucial period of rapid paleoclimate change. Warmer and wetter ice-free conditions were achieved by 134.1 ± 0.7 ka (modelled ages) as indicated by the presence of liquid water at the site. Temperatures warmed further at 133.7 ± 0.5 ka and led into an interstadial, synchronous with slightly elevated monsoon strength during the week monsoon interval. The interstadial experienced an unstable climate with a trough in temperature associated with a slowdown in Atlantic Meridional Overturning Circulation (AMOC) and a reduction in North Atlantic Deep Water (NADW) formation. The interstadial ended with a more extreme cold reversal lasting 500 years in which NADW formation remained active but the subpolar gyre weakened allowing cool polar waters to penetrate southwards. The main warming associated with TII was very rapid, taking place between 130.9 ± 0.9 and 130.7 ± 0.9 ka coeval with initial monsoon strengthening. Temperatures then plateaued before being interrupted by a 600-year cold event at 129.1 ± 0.6 ka, associated once again with penetration of polar waters southwards into the North Atlantic and a slowdown in monsoon strengthening. Sub-orbital climate oscillations were thus a feature of TII in the north Atlantic realm, which broadly resemble the Bølling/Allerød-Younger Dryas-8.2 ka event pattern of change observed in Termination I despite monsoon records indicating strong differences between the last and penultimate deglaciation.

理解冰期-间冰期气候转换过程中的事件序列，对于深化我们对突发性气候变迁的认知至关重要。本文报道一套采自北阿尔卑斯山的全新堆叠式高分辨率精确定年洞穴石笋（speleothem）稳定同位素记录，该记录为欧洲乃至更广域北大西洋区域134至111千年间的温度与水汽源变化提供了关键载体。该记录涵盖了倒数第二次冰消期（终结期II，简称TII），其年代超出放射性碳定年法的测限范围，因此为这一快速古气候变迁的关键时段提供了全新的重要档案。研究点位存在液态水的迹象表明，134.1±0.7千年（模拟年代）时区域已进入温暖湿润的无冰环境。133.7±0.5千年时温度进一步升高，区域进入一间冰阶阶段，此时恰好对应弱季风时段内季风强度略有增强的时期。该间冰阶时期气候并不稳定，出现温度谷值，这与大西洋经向翻转环流（Atlantic Meridional Overturning Circulation，AMOC）减缓及北大西洋深层水（North Atlantic Deep Water，NADW）生成减弱密切相关。该间冰阶以一场持续500年的极端冷反转事件告终，此阶段北大西洋深层水生成仍在持续，但副极地环流减弱，致使寒冷极地水团向南侵浸。与终结期II相关的主升温过程极为迅速，发生于130.9±0.9千年至130.7±0.9千年之间，与季风初始增强同步发生。此后温度趋于平稳，直至129.1±0.6千年时被一场持续600年的冷事件打断，该事件同样与极地水团向南侵入北大西洋及季风增强进程放缓相关。由此可见，亚轨道尺度气候振荡是北大西洋区域终结期II的典型特征；尽管季风记录显示末次与倒数第二次冰消期的终结过程存在显著差异，但该振荡模式与终结期I所观测到的博令-阿勒罗德-新仙女木-8.2千年事件（Bølling/Allerød-Younger Dryas-8.2 ka event）的变化格局大体相似。