Toledo Mauro B de, Bush Mark B
Departamento de Geologia, Universidade Federal Fluminense, Niterói, RJ, Brazil.
An Acad Bras Cienc. 2008 Mar;80(1):191-203. doi: 10.1590/s0001-37652008000100014.
Pollen, charcoal, and C14 analyses were performed on a sediment core obtained from Lake Tapera (Amapá) to provide the palaeoenvironmental history of this part of Amazonia. A multivariate analysis technique, Detrended Correspondence Analysis, was applied to the pollen data to improve visualization of sample distribution and similarity. A sedimentary hiatus lasting 5,500 years was identified in the Lake Tapera. Because the timing of the hiatus overlapped with the highest Holocene sea-level, which would have increased the local water table preventing the lake from drying out, it is clear that sea-level was not important in maintaining the lake level. Lake Tapera probably depended on riverine flood waters, and the sedimentary gap was caused by reduced Amazon River discharge, due to an extremely dry period in the Andes (8,000-5,000 years BP), when precipitation levels markedly decreased. The lack of Andean pollen (river transported) in the record after this event supports this interpretation. The pollen analysis shows that when sedimentation resumed in 1,620 cal. years BP, the vegetation around the lake was changed from forest into savanna. This record demonstrates the need to improve our understanding of climate changes and their associated impacts on vegetation dynamics.
对取自塔佩拉湖（阿马帕州）的一个沉积岩芯进行了花粉、木炭和碳-14分析，以呈现亚马逊地区这一部分的古环境历史。一种多元分析技术——去趋势对应分析，被应用于花粉数据，以改善样本分布和相似性的可视化。在塔佩拉湖发现了一个持续5500年的沉积间断。由于该间断的时间与全新世最高海平面重叠，这会使当地地下水位上升，防止湖泊干涸，所以很明显海平面在维持湖泊水位方面并不重要。塔佩拉湖可能依赖于河流洪水，而沉积间断是由于安第斯山脉极端干旱时期（公元前8000 - 5000年）降水显著减少，导致亚马逊河流量减少造成的。该事件之后记录中缺乏安第斯花粉（由河流输送）支持了这一解释。花粉分析表明，当沉积在公元前1620年重新开始时，湖泊周围的植被从森林转变为稀树草原。这一记录表明有必要加深我们对气候变化及其对植被动态相关影响的理解。
