Vegetation response to glacial-interglacial climate variability near Lake Malawi in the southern African tropics
Vegetation response to glacial-interglacial climate variability near Lake Malawi in the southern African tropics
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DOI：
10.1016/j.palaeo.2010.01.025
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发表时间：
2011-04-01
影响因子：
3
通讯作者：
Cohen, Andrew S.
中科院分区：
文献类型：
--
作者：
Beuning, Kristina R. M.;Zimmerman, Kurt A.;Cohen, Andrew S.
从马拉维湖，非洲跨越过去的135 kyr花粉记录显示大量的和突然的植被响应之间的135和75 ka的多个极端干旱事件。峰在这两个相对丰度和总生产的罗汉果属花粉定义的前两个干旱事件。从135到127，再从117到105 kyr BP。罗汉果百分比保持在16%以上，峰值高达38%，表明一个时期的气候凉爽，导致山地森林类群向低海拔地区扩展。来自安哥拉边缘和刚果扇的海洋孢粉学记录显示，在这个时候（氧同位素阶段5d），整个非洲大陆在这个纬度上的气候相似的罗汉果属的百分比峰值相似。从105到90 ka，持续干旱导致马拉维湖的总花粉积累率下降到不到300粒/cm（2）/年，主要是草花粉。非洲历史上的这一事件严重到足以导致蕨类植物和森林分类群如Uapaca和Brachystegia以及山地分类群（Podocarpus，Olea spp.）和杜鹃花科）的花粉源区马拉维湖。在接下来的18,000年里，这些类群几乎都没有从周围的植被中出现。由此产生的半沙漠植被对于生活在马拉维湖地区或穿越马拉维湖地区的早期人类来说是不适宜居住的。在这些干旱的间隔之后增加的水分允许扩展，创建和维护马拉维湖周围更多样化的景观植被镶嵌，包括赞比西亚miombo林地，潮湿的万年青林地和非洲山地森林。每一个的相对丰度波动响应于冷却（即从60至56万年的非洲山地扩张）或水分平衡（即增加潮湿的万年青林地之间的75和65万年）。值得注意的是，与之前的20，000年相比，末次盛冰期（LGM）（30-15 ka）期间的植被组成没有显着变化。(C)2010爱思唯尔有限公司版权所有。
Pollen records from Lake Malawi, Africa spanning the last 135 kyr show substantial and abrupt vegetation response to multiple episodes of extreme aridity between 135 and 75 ka. Peaks in both the relative abundance and total production of Podocarpus pollen define the first two of these drought episodes. From 135 to 127 and again from 117 to 105 kyr BP. Podocarpus percentages remain above 16% with peak values as high as 38% indicating a period marked by a cool climate resulting in expansion of montane forest taxa to lower elevations. Marine palynological records from the Angola Margin and Congo Fan show similar peak Podocarpus percentages at this time (oxygen isotope stage 5d) indicating a similar climate across the African continent at this latitude. From 105 to 90 ka, continuing drought resulted in total pollen accumulation rates in Lake Malawi to fall to less than 300 grains/cm(2)/yr of predominately grass pollen. This episode in African history was severe enough to cause the disappearance of pteridophytes and forest taxa such as Uapaca and Brachystegia as well as montane taxa (Podocarpus, Olea spp. and Ericaceae) within the pollen source area of Lake Malawi. These taxa all remain nearly absent from the surrounding vegetation for the next 18,000 years. The resultant semi-desert vegetation would have been inhospitable for early humans living within or traveling through the Lake Malawi region. Increasing moisture following these arid intervals allowed expansion, creation and maintenance of a more diverse landscape vegetation mosaic around Lake Malawi including Zambezian miombo woodland, humid evergreen woodland and afromontane forests. The relative abundance of each fluctuated in response to either cooling (i.e. afromontane expansion from 60 to 56 ka) or moisture balance (i.e. increasing humid evergreen woodland between 75 and 65 ka). Notably there was no significant change in vegetation composition during the Last Glacial Maximum (LGM) (30-15 ka) as compared to the previous 20,000 years. (C) 2010 Elsevier B.V. All rights reserved.