Shifting westerlies and precipitation patterns during the Late Pleistocene in southern Africa determined using glacier reconstruction and mass balance modelling
Shifting westerlies and precipitation patterns during the Late Pleistocene in southern Africa determined using glacier reconstruction and mass balance modelling
复制标题
使用冰川重建和质量平衡模型确定南部非洲晚更新世期间的西风带变化和降水模式
DOI：
10.1016/j.quascirev.2012.08.012
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发表时间：
2012
影响因子：
4
通讯作者：
Aidan Farrow
中科院分区：
文献类型：
--
作者：
S. Mills;S. Grab;B. Rea;S. Carr;Aidan Farrow
南非经历了一系列不同的气候制度，因此是研究晚更新世环境和气候变化的理想地区。然而，详细的、可量化的古气候数据在该地区很少。特别是，可靠的古气候数据对于解决关于次大陆冰期温度下降和水分可获得性的持续争议至关重要。接近冰川阈值的小型冰川对温度和降水的变化高度敏感，因此是过去气候条件的理想指标。本文根据莱索托高地的冰川重建和物质平衡模型，首次获得了南部非洲末次冰盛期(LGM)古降水的定量数据。通过重建以前的冰川及其动态，可以确定在特定气候条件下的冰川生存能力。在莱索托高地的五个地点进行的冰川重建产生了平衡线高度(ELA)从3095米到3298米的古冰川，重建的稳态质量平衡和流动动力学与现代类似物相当。研究了地形气候因素，温度-辐射指数模型表明，地形遮蔽是决定该地区小冰川存在的一个重要因素。末次盛冰期德拉肯斯堡冰川的出现表明降雨量可能会增加，季节性也会发生变化。这种趋势可能与西风波(冷锋)扰动频率增加有关，这是由于气压带北移，这也将增加高海拔地区的降雨量。应用高分辨率气候模式(HadAM3h)来测试这一点，显示了最后一个冰川周期期间降水的季节性时间变化，夏季降水明显减少。这可能对该地区小型冰川的物质平衡和生存产生重要影响，因为在春季-冬季-秋季期间会有更多的降雨量以雪的形式下降。
South Africa experiences a range of different climatic regimes and is thus an ideal region to investigate Late Pleistocene environmental and climate change. However, detailed quantifiable palaeoclimate data are sparse in the region. In particular, reliable palaeoclimatic data are essential to resolve ongoing controversies regarding temperature depression and moisture availability during glacial periods in the sub-continent. Small glaciers close to the glaciation threshold are highly sensitive to changes in temperature and precipitation and are therefore ideal indicators of past climatic conditions during their existence. This paper derives some of the first quantitative data on Last Glacial Maximum (LGM) palaeoprecipitation in southern Africa, based on glacier reconstruction and mass balance modelling for the Lesotho Highlands. The reconstruction of former glaciers and their dynamics enables the determination of glacier viability under specific climatic envelopes. Glacier reconstructions at five sites in the Lesotho Highlands yield palaeoglaciers with Equilibrium Line Altitudes (ELAs) ranging from 3095 to 3298 m a.s.l., and reconstructed steady-state mass balance and flow dynamics are comparable with modern analogues. Topoclimatic factors are investigated, with temperature-radiation-index modelling indicating that topographic shading was an important factor determining the existence of small glaciers in this region. The occurrence of glaciation in the Drakensberg during the LGM suggests a potential increase in precipitation and change in its seasonality. Such trends are likely associated with an increased frequency of westerly wave (cold front) disturbances due to the northward shift of pressure belts, which would also increase precipitation as snow at higher altitudes. The application of a high resolution climate model (HadAM3h) to test this, displays a change in the seasonal timing of precipitation during the Last Glacial cycle, with a decrease in precipitation evident during the summer months. This is likely to have had important implications for the mass balance and survival of small niche glaciers in the region, with more precipitation falling during the spring – winter – autumn months as snow.