Response of tropical African and East Atlantic climates to orbital forcing over the last 1.7 Ma
Response of tropical African and East Atlantic climates to orbital forcing over the last 1.7 Ma
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过去 1.7 Ma 热带非洲和东大西洋气候对轨道强迫的响应
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
U. Röhl
中科院分区：
文献类型：
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作者：
B. Jahn;R. Schneider;P. Müller;B. Donner;U. Röhl
摘要介绍了刚果扇大洋钻探计划（ODP）1075站1.7Ma以来的有机质积累、有机碳同位素组成和铁含量记录，并与赤道上升流区ODP 663站的相应记录进行了比较。他们讨论非洲降水和刚果河流量的变化，并在贸易风驱动的海洋生产力的变化的背景下，在典型的米兰科维奇强迫周期的热带大西洋。在刚果扇，升高的总有机碳质量积累率（TOC MAR）和铁的强度主要发生在间冰期时，非洲季风最强烈。应用于TOC MAR的带通滤波显示出明显的岁差变化，表明非洲气候主要受低纬度日射变化的控制。只有在过去的0.6 Ma，一个增强的冰川间冰期气候变化的间隔，是岁差TOC MAR信号叠加了一个强大的100 ka的振荡。相比之下，陆地铁输入刚果扇的变化表明明显的100万年的变化已经很好的全球冰川-间冰期循环增加幅度之间的0.9和0.6马。倾斜周期的Fe信号强烈表示为最后0.9马。河流Fe输入的岁差方差的最高振幅发生时，振幅在100 ka振荡处于中间水平，揭示了800 ka周期的相移相对于岁差强迫。连同一个明显的800 ka的信号，在100 ka的振幅变化在过去的1.7 Ma，刚果风扇铁记录，因此表明，偏心调制的低纬太阳能直接影响赤道非洲季风系统，并可能在陆地上的风化条件。这进一步表明，低纬岁差强迫和季风响应在热带地区可能发挥了重要作用，在全球气候的100 ka周期之前，巨大的大陆冰盖存在。
Abstract Records of organic matter accumulation, organic carbon isotopic composition and iron content covering the last 1.7 Ma are presented for the Congo Fan Ocean Drilling Program (ODP) Site 1075, and are compared with their counterparts from ODP Site 663 in the equatorial upwelling region. They are discussed with regard to variations in African precipitation and Congo River discharge and in the context of changes in trade-wind-driven marine productivity for the tropical Atlantic at periodicities typical of Milankovitch forcing. On the Congo Fan, elevated total organic carbon mass accumulation rates (TOC MAR) and Fe intensities occur predominantly during interglacial periods when the African monsoon was most intense. Band-pass filtering applied to TOC MAR shows distinct precessional variations, indicating that the African climate was largely controlled by low-latitude insolation changes. Only for the last 0.6 Ma, an interval of enhanced glacial-interglacial climate changes, is the precessional TOC MAR signal superimposed by a strong 100 ka oscillation. In contrast, variations in terrestrial iron input to the Congo Fan indicate pronounced 100 ka variance already well before global glacial-interglacial cycles increased in amplitude between 0.9 and 0.6 Ma. Obliquity cycles in the Fe signal are strongly expressed for the last 0.9 Ma. The highest amplitudes in the precessional variance of fluvial Fe input occur when amplitudes in the 100 ka oscillation were at intermediate levels and reveal a 800 ka cycle in phase shift with respect to precessional forcing. Together with a pronounced 800 ka signal in the 100 ka amplitude variations during the last 1.7 Ma, the Congo Fan iron record therefore suggests that eccentricity modulation of the low-latitude insolation directly influenced the equatorial African monsoon system and probably the weathering conditions on land. It further suggests that low-latitude precessional forcing and monsoonal response in the tropics might have played an important role for 100 ka cycles in global climate well before huge continental ice sheets existed.