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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >A 340,000 year continental climate record from tropical Africa - news from opal phytoliths from the equatorial Atlantic
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A 340,000 year continental climate record from tropical Africa - news from opal phytoliths from the equatorial Atlantic

机译：来自非洲热带地区的34万年大陆气候记录-来自赤道大西洋的蛋白石硅藻石新闻

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摘要

Information on the tropical African continental climate and vegetation during the last 340 kyr is derived from a detailed study of opal phytoliths at the eastern equatorial Atlantic site M16772 (1°21'S, 11°58'W). Total phytoliths as well as C_3 and C_4 grass phytoliths are compared to the distribution pattern of other continental climate proxies (freshwater and limnobiontic diatoms). Total phytolith accumulation rate is dominated by C_4 grasses and their variability confirms the cold stages and interstadials as times of arid conditions in the southern Sahara and Sahel regions, and indicates an increase in aridness from Termination II to Termination I. The good agreement between the total phytoliths and freshwater diatom records observed for most of the 340 kyr is interpreted as indicative of atmospheric dust as the main source of both sediment constituents to this core site. Exceptionally higher land rainfall and river input to the eastern equatorial Atlantic are suggested by the excess of freshwater diatoms over total phytoliths and the limnobiontic diatoms observed during ice growth phases of oxygen isotopic interglacial stages 9, 7 and the 5/4 transition. Major alterations in continental aridity and/or wind strength conditions over north Africa, as reflected by the total and arid phytolith frequency spectrum, appear clearly determined by global ice volume and the 100 kyr cycle characteristic for high-latitude climate change. Limnobiontic diatoms, which reflect lake desiccation, respond also to the 41 kyr obliquity cycle. Freshwater diatoms, on the other hand, contain significant variance at 23 kyr periodicities, reflecting the precessional forcing of the African monsoons which determine the precipitation level over the south Saharan and Sahelian source regions. rapid hydrological fluctuations, as depicted by the changes in the relative contribution of C_3 and C_4 grasses to the total phytoliths, appear to respond to higher than 19 kyr frequencies, which are observable in all but the aridity index spectra.
机译：有关过去340年来热带非洲大陆性气候和植被的信息来自对赤道东部大西洋站点M16772（南纬1°21'，西经11°58'）的蛋白石硅藻石的详细研究。将总植硅藻土以及C_3和C_4草的植硅藻土与其他大陆性气候代理（淡水和石灰石硅藻）的分布模式进行了比较。植硅体的总积累速率主要由C_4草决定，它们的变异性证实了南部撒哈拉和萨赫勒地区干旱时期和陆际间的干旱状况，并表明从第二终端到第一终端的干旱增加。 340年来大部分时间观测到的硅藻土和淡水硅藻记录被解释为指示大气尘埃是该核心地点两种沉积物成分的主要来源。氧同位素间冰期9、7和5/4过渡期的冰生长期中，淡水硅藻超过了总植硅体和线粒体硅藻，这表明赤道东大西洋的土地降雨量和河流输入量特别高。总的和干旱的植物硅酸盐频谱所反映的北非大陆干旱和/或风强度条件的重大变化，显然是由全球冰量和高纬度气候变化的100 kyr周期特征确定的。反映湖面干燥的小硅藻硅藻也对41年的倾角周期做出响应。另一方面，淡水硅藻在23年周期内具有明显的变化，反映了非洲季风的进动强迫，决定了南部撒哈拉和萨赫勒地区的降水水平。如C_3和C_4草对总植硅体的相对贡献的变化所描绘的那样，快速的水文波动似乎对高于19 kyr的频率作出响应，这在除干旱指数谱外的所有观测中都可以观察到。

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