The effects of solar irradiation changes on the migration of the Congo Air Boundary and water levels of paleo-Lake Suguta, Northern Kenya Rift, during the African Humid Period (15–5 ka BP)
The effects of solar irradiation changes on the migration of the Congo Air Boundary and water levels of paleo-Lake Suguta, Northern Kenya Rift, during the African Humid Period (15–5 ka BP)
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非洲湿润期（15-5 ka BP）期间太阳辐射变化对刚果空气边界迁移和肯尼亚北部裂谷古苏古塔湖水位的影响
DOI：
10.1016/j.palaeo.2013.12.007
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Trauth
中科院分区：
文献类型：
--
作者：
Junginger;Roller;Trauth
非洲湿润期（AHP，15-5 ka BP）300 m深的古苏加塔湖（北方肯尼亚裂谷）的水位记录有助于解释西非季风（WAM）和印度夏季风（ISM）的年代际至百年强度变化。该水位记录来自三个不同的来源：（1）放射性碳年代测定和水库校正的湖相沉积物中的粒度变化，（2）盆地内古海岸线的海拔和年龄，以及（3）水平衡模拟的结果，为了解放大器古苏加塔湖水位变化（突变或渐进）的特征提供了重要的见解。这些综合分析的结果表明，在苏加塔谷的AHP高位是在刚果空气边界（CAB），这反过来又造成了一个增强的东非和印度之间的大气压力梯度在北方半球的日照最大的东北移动的直接后果。在不到100年的时间里，水位迅速下降到90米，最好的解释是太阳辐射的变化，要么降低东非-印度的大气压力梯度，阻止CAB到达研究区域，要么降低大气中的整体湿度，或者两者兼而有之。相比之下，虽然没有很好地记录在我们的记录中，我们假设一个逐步结束的AHP，尽管突然变化的降水来源时，亚洲和非洲之间的压力梯度下降，防止CAB到达苏加塔谷。这种不稳定性可能是由于岁差的同时变化而得到缓冲的，岁差的变化在10月期间在赤道产生了最大日射量。无论情况是否如此，来自Suguta山谷的水位记录都证明了轨道控制的日射变化和太阳辐射的短期变化作为影响东非裂谷湖显著水位变化的因素的重要性。
The water-level record from the 300 m deep paleo-lake Suguta (Northern Kenya Rift) during the African Humid Period (AHP, 15–5 ka BP) helps to explain decadal to centennial intensity variations in the West African Monsoon (WAM) and the Indian Summer Monsoon (ISM). This water-level record was derived from three different sources: (1) grain size variations in radiocarbon dated and reservoir corrected lacustrine sediments, (2) the altitudes and ages of paleo-shorelines within the basin, and (3) the results of hydro-balance modeling, providing important insights into the character of water level variations (abrupt or gradual) in the amplifier paleo-Lake Suguta. The results of these comprehensive analyses suggest that the AHP highstand in the Suguta Valley was the direct consequence of a northeastwards shift in the Congo Air Boundary (CAB), which was in turn caused by an enhanced atmospheric pressure gradient between East Africa and India during a northern hemisphere insolation maximum. Rapidly decreasing water levels of up to 90 m over less than a hundred years are best explained by changes in solar irradiation either reducing the East African–Indian atmospheric pressure gradient and preventing the CAB from reaching the study area, or reducing the overall humidity in the atmosphere, or a combination of both these effects. In contrast, although not well documented in our record we hypothesize a gradual end of the AHP despite an abrupt change in the source of precipitation when a decreasing pressure gradient between Asia and Africa prevented the CAB from reaching the Suguta Valley. The abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during October. Whether or not this is the case, the water-level record from the Suguta Valley demonstrates the importance of both orbitally-controlled insolation variations and short-term changes in solar irradiation as factors affecting the significant water level variations in East African rift lakes.
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