The Arctic is getting warmer and wetter. Here, we document two independent examples of how associated extreme precipitation patterns have severe implications for high Arctic ecosystems. The events stand out in a 23-year record of continuous observations of a wide range of ecosystem parameters and act as an early indication of conditions projected to increase in the future. In NE Greenland, August 2015, one-quarter of the average annual precipitation fell during a 9-day intensive rain event. This ranked number one for daily sums during the 1996–2018 period and caused a strong and prolonged reduction in solar radiation decreasing CO₂ uptake in the order of 18–23 g C m⁻², a reduction comparable to typical annual C budgets in Arctic tundra. In a different type of event, but also due to changed weather patterns, an extreme snow melt season in 2018 triggered a dramatic gully thermokarst causing rapid transformation in ecosystem functioning from consistent annual ecosystem CO₂ uptake and low methane exchange to highly elevated methane release, net source of CO₂, and substantial export of organic carbon downstream as riverine and coastal input. In addition to climate warming alone, more frequent occurrence of extreme weather patterns will have large implications for otherwise undisturbed tundra ecosystems including their element transport and carbon interactions with the atmosphere and ocean.

北极越来越暖和。在这里，我们记录了两个独立的例子，说明相关的极端降水模式如何对北极高海拔生态系统产生严重影响。这些事件在对各种生态系统参数的连续观测的23年记录中脱颖而出，并且可以作为未来预计将增加的状况的早期指示。在为期9天的强降雨天气中，2015年8月在格陵兰东北部，年平均降水量下降了四分之一。这在1996-2018年期间的每日总收入排名第一，并导致强烈且长时间的太阳辐射减少，从而减少了18-23 g C m ^-2的CO ₂吸收，其减少量可与北极苔原的典型年度C预算相比。在不同类型的事件中，而且由于天气模式的变化，2018年的极端融雪季节触发了一个剧烈的沟壑型喀斯特地貌，导致生态系统功能迅速转变，从稳定的年度生态系统CO ₂吸收和低甲烷交换到甲烷高度释放， CO _2的净来源，以及下游作为河流和沿海投入的大量有机碳出口。除了气候变暖以外，极端天气模式的更频繁发生将对原本不受干扰的冻原生态系统产生重大影响，包括其元素迁移以及与大气和海洋的碳相互作用。