Hydrological constraints of paleo-Lake Suguta in the Northern Kenya Rift during the African Humid Period (15-5 ka BP)
Hydrological constraints of paleo-Lake Suguta in the Northern Kenya Rift during the African Humid Period (15-5 ka BP)
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DOI：
10.1016/j.gloplacha.2013.09.005
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发表时间：
2013-12
影响因子：
3.9
通讯作者：
A. Junginger;M. Trauth
中科院分区：
文献类型：
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作者：
A. Junginger;M. Trauth
在非洲湿润时期(AHP，15-5 Ka BP)，肯尼亚北部裂谷的Suguta山谷发育了一个近300米深、覆盖2200 Km2的古湖泊。来自湖泊沉积和古海岸线的数据表明，13.9亿年前已经存在一个大型古湖泊，并在100年或更短的时间内记录到高达100亿米的快速水位波动，在AHP末期(500万年)达到最后的低谷。我们使用水平衡模型来评估这些水位波动的突发性，并确定其原因。我们观察到，AHP中的波动是由降水量的突然变化引起的，降水量为26%-40%。尽管没有连续的湖泊数据记录苏古塔河谷AHP的开始，但我们从水平衡模型得出结论，只有在14.8ka BP之前AHP的突然开始才可能导致有记录的高水位。模拟结果表明，降雨量的突然增加是刚果空中边界(CAB)向东迁移的直接结果，这是由于北半球夏季最大日照期间东非和南亚之间的大气压力梯度增强所致。相比之下，AHP的结束肯定是渐进的，尽管当亚洲和非洲之间的气压梯度下降使CAB无法到达研究区域时，降水来源发生了突然变化。这种突然性可能是由于岁差的同期变化而缓冲的，在9-10月期间赤道出现了日照最大值。这一变化将意味着唯一的雨源是热带辐合带(ITCZ)，在短暂的雨季，热带辐合带将携带更多的水分，从而在大约1000年的时间里减缓水位的下降，同时伴随着日照的减少。这项研究的结果表明，非洲东北部的人类有多少时间可以适应不断变化的气候，从狩猎和采集到耕种和放牧。
During the African Humid Period (AHP, 15–5 ka BP) an almost 300 m deep paleo-lake covering 2200 km2developed in the Suguta Valley, in the Northern Kenya Rift. Data from lacustrine sediments and paleo-shorelines indicate that a large paleo-lake already existed by 13.9 ka BP, and record rapid water level fluctuations of up to 100 m within periods of 100 years or less, and a final lowstand at the end of the AHP (5 ka BP). We used a hydro-balance model to assess the abruptness of these water level fluctuations and identify their causes. We observed that fluctuations within the AHP were caused by abrupt changes in precipitation of 26–40%. Despite the absence of continuous lacustrine data documenting the onset of the AHP in the Suguta Valley, we conclude from the hydro-balance model that only an abrupt onset to the AHP, prior to 14.8 ka BP, could have led to high water levels recorded. The modeling results suggest that the sudden increase in rainfall was the direct consequence of an eastward migration of the Congo Air Boundary (CAB), caused by an enhanced atmospheric pressure gradient between East Africa and southern Asia during a northern hemisphere (NH) summer insolation maximum. In contrast, the end of the AHP must have been gradual despite an abrupt change in the source of precipitation when a decreasing pressure gradient between Asia and Africa prevented the CAB from reaching the study area. This abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during September–October. This change would have meant that the only rain source was the Intertropical Convergence Zone (ITCZ), which would have carried a greater amount of moisture during the short rainy season thus slowing the fall in water level over a period of about 1000 years in association with the reduction in insolation. The results of this study provide an indication of the amount of time available for humans in north-eastern Africa to adapt in response to a changing climate, from hunting and gathering to farming and herding.