The dynamics of warming during the last deglaciation in high-elevation regions of Eastern Equatorial Africa
The dynamics of warming during the last deglaciation in high-elevation regions of Eastern Equatorial Africa
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DOI：
10.1016/j.quascirev.2022.107416
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发表时间：
2022-02-23
影响因子：
4
通讯作者：
Marshall, Charlie
中科院分区：
文献类型：
--
作者：
Garelick, Sloane;Russell, James;Marshall, Charlie
热带山区环境，例如非洲赤道鲁文佐里山脉，被认为对气候变化特别敏感。鲁文佐里地区持续变暖正在通过冰川退缩、火灾和洪水影响当地环境和社区。非洲其他地区的古气候重建表明，在最后一次冰川终止期间，从大约21000年前（ka）到全新世早期到中期，伴随着冰川退缩，出现了相当大的变暖。量化这些变化很困难，但有助于评估鲁文佐里未来的影响。在这里，我们基于乌干达鲁文佐里山脉马霍马湖（海拔 2,990 米；masl）的支链甘油二烷基甘油四醚 (brGDGT) 的相对丰度，提出了类似于 21000 年 (kyr) 温度的重建。我们的记录与现有的鲁文佐里冰川冰碛 Be-10 暴露年龄相结合表明，冰消变暖和冰川退缩开始于大约 20 ka，并在大约 18-18.5 ka 加速。快速变暖开始的时间与南极冰芯大气温室气体（GHG）辐射强迫的冰期后上升时间相匹配（Brook等，1996；Marcott等，2014；Monnin等，2004；Schilt等，2010）。我们的温度重建结果显示，从末次盛冰期 (LGM) 到全新世晚期，气温升高了 4.9 摄氏度。这一增幅高于热带东非低海拔地区记录中观察到的平均气温升高 2-4 摄氏度，但与该地区其他高海拔地区观察到的情况相似。因此，较高海拔地区变暖的加剧证实了该地区末次盛冰期期间温度下降率急剧上升。我们的结果还表明，全新世中期相对于全新世晚期，气温升高了 3 摄氏度。这表明当时冰冻高度高于鲁文佐里山顶海拔，可能导致鲁文佐里山脉在大约 5 至 7 ka 期间完全消融。因此，全新世中期可能是这些山脉在未来几十年可能经历的冰川和环境变化的潜在模拟。总体而言，我们记录中观察到的温度变化的时间和幅度对于热带非洲未来变暖的气候模型预测具有重要意义。 (C) 2022 Elsevier Ltd. 保留所有权利。
Tropical mountain environments, such as the Rwenzori Mountains in equatorial Africa, are thought to be particularly sensitive to climate change. Ongoing warming in the Rwenzori is impacting local environments and communities through glacial retreat, fires, and flooding. Paleoclimate reconstructions from elsewhere in Africa suggest considerable warming accompanied glacier retreat during the last glacial termination, from similar to 21 thousand years before present (ka) through the early to mid-Holocene. Quantifying these changes has been difficult but could help to assess future impacts in the Rwenzori. Here, we present a similar to 21 thousand-year (kyr) temperature reconstruction based on the relative abundance of branched glycerol dialkyl glycerol tetraethers (brGDGTs) from Lake Mahoma (2,990 m above sea level; m asl) in the Rwenzori Mountains, Uganda. Our record, paired with existing Rwenzori glacial moraine Be-10 exposure ages, suggests that deglacial warming and glacial retreat began by similar to 20 ka and accelerated at similar to 18-18.5 ka. The timing of the onset of rapid warming matches the timing of the post-glacial rise in radiative forcing from atmospheric greenhouse gases (GHGs) from Antarctic ice cores (Brook et al., 1996; Marcott et al., 2014; Monnin et al., 2004; Schilt et al., 2010). Our temperature reconstruction registers similar to 4.9 degrees C warming from the Last Glacial Maximum (LGM) to the late Holocene. This increase is larger than the average similar to 2-4 degrees C warming observed in records from lower elevation sites in tropical East Africa, but similar to that observed at other high-elevation sites in this region. The increased warming at higher elevations thus confirms that the temperature lapse rate steepened during the LGM over this region. Our results also indicate similar to 3 degrees C of warming during the mid-Holocene relative to the late Holocene. This suggests that the freezing-level height rose above Rwenzori summit elevations at that time, likely causing complete deglaciation of the Rwenzori Mountains from similar to 5 to 7 ka. The mid-Holocene is thus a potential analog for the glacial and environmental changes that these mountains are likely to experience in the coming decades. Overall, the timing and magnitude of temperature change observed in our record has important implications for climate model projections of future warming in tropical Africa. (C) 2022 Elsevier Ltd. All rights reserved.