Direct evidence for thinning and retreat of the southernmost Greenland ice sheet during the Younger Dryas
Direct evidence for thinning and retreat of the southernmost Greenland ice sheet during the Younger Dryas
复制标题
DOI：
10.1016/j.quascirev.2021.107105
复制
发表时间：
2021-09
影响因子：
4
通讯作者：
A. Carlson;A. Reyes;Emily Gusterson;Y. Axford;K. Wilcken;D. Rood
中科院分区：
文献类型：
--
作者：
A. Carlson;A. Reyes;Emily Gusterson;Y. Axford;K. Wilcken;D. Rood
在末次冰消期期间，北大西洋气候在伯林期（∼14.7ka）突然变暖，进入新仙女木期（∼12.9ka）冷却，并在全新世（∼11.7ka）再次突然变暖。虽然这些事件是由格陵兰冰芯定义的，但格陵兰冰盖边缘对气候突变的反应仍然存在相当大的不确定性。为了完善冰盖的冰消历史，我们在位于海岸和内陆冰缘中间的格陵兰峡湾最南端的五个地点的基岩上的巨石中提出了新的宇宙成因核素表面暴露年龄。我们发现冰盖在三个局部地形高点以下变薄，分别为 12.7 ± 0.3 ka (n = 3)、13.1 ± 0.4 ka (n = 1, 2 个异常值) 和 12.3 ± 0.2 ka (n = 3)，峡湾向上退缩在 12.5 ± 0.3 ka (n = 3) 和12.7 ± 0.2 ka (n = 4) 基于峡湾中部海洋界限上方的两个地点。因此，这些峡湾中部的 10Be 年龄表明，格陵兰岛最南端的冰盖在新仙女木期期间变薄和退缩。我们假设这种变薄和退缩是对全新世之前海洋变暖和/或新仙女木期间由于北方夏季日照高峰造成的夏季短波辐射强迫的反应。我们的结果也支持了先前假设的新仙女木大气变冷代理记录中的冬季偏差，因为新仙女木期间的夏季大幅变冷可能抵消了海洋变暖和直接辐射强迫的影响，从而抑制了冰盖后退。
During the last deglaciation, North Atlantic climate abruptly warmed at the Bølling (∼14.7 ka), cooled into the Younger Dryas (∼12.9 ka) and abruptly warmed again into the Holocene (∼11.7 ka). While these events are defined by Greenland ice cores, there is still considerable uncertainty on Greenland ice-sheet margin responses to abrupt climate change. To refine the ice sheet's deglacial history, we present new cosmogenic nuclide surface exposure ages from boulders on bedrock at five sites in southernmost Greenland fjords located midway between the coast and inland ice margin. We find ice-sheet thinning below three local topographic highs at 12.7 ± 0.3 ka (n = 3), 13.1 ± 0.4 ka (n = 1, 2 outliers), and 12.3 ± 0.2 ka (n = 3), with up-fjord retreat at 12.5 ± 0.3 ka (n = 3) and 12.7 ± 0.2 ka (n = 4) based on two sites just above the mid-fjord marine limit. These mid-fjord10Be ages therefore show southernmost Greenland ice-sheet thinning and retreat during the Younger Dryas. We hypothesize that this thinning and retreat was a response to ocean warming prior to the Holocene and/or summer shortwave radiative forcing during the Younger Dryas due to peak boreal summer insolation. Our results also support a previously hypothesized winter bias in proxy records of Younger Dryas atmospheric cooling, since a large summer cooling during the Younger Dryas could have counteracted the effects of ocean warming and direct radiative forcing, inhibiting ice-sheet retreat.