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摘要 : 人们对更新世海洋环境和南极洲的气候变异已有相当充分的认识,但对大部分陆地表面,尤其是非洲的古气候变异仍不清楚。

 人们对更新世海洋环境和南极洲的气候变异已有相当充分的认识,但对大部分陆地表面,尤其是非洲的古气候变异仍不清楚。Thomas Johnson及同事呈现了非洲东南部马拉维湖过去130万年间的干旱记录,表明自约90万年前的中更新世气候转型开始,当地气候在气温和降雨的10万年强偏心率周期外,逐渐变得更为湿润。过去50万年来,影响马拉维湖气候变异的似乎是二氧化碳和尘埃,而非全球冰储量。


A progressively wetter climate in southern East Africa over the past 1.3 million years


African climate is generally considered to have evolved towards progressively drier conditions over the past few million years, with increased variability as glacial–interglacial change intensified worldwide1, 2, 3. Palaeoclimate records derived mainly from northern Africa exhibit a 100,000-year (eccentricity) cycle overprinted on a pronounced 20,000-year (precession) beat, driven by orbital forcing of summer insolation, global ice volume and long-lived atmospheric greenhouse gases4. Here we present a 1.3-million-year-long climate history from the Lake Malawi basin (10°–14° S in eastern Africa), which displays strong 100,000-year (eccentricity) cycles of temperature and rainfall following the Mid-Pleistocene Transition around 900,000 years ago. Interglacial periods were relatively warm and moist, while ice ages were cool and dry. The Malawi record shows limited evidence for precessional variability, which we attribute to the opposing effects of austral summer insolation and the temporal/spatial pattern of sea surface temperature in the Indian Ocean. The temperature history of the Malawi basin, at least for the past 500,000 years, strongly resembles past changes in atmospheric carbon dioxide and terrigenous dust flux in the tropical Pacific Ocean, but not in global ice volume. Climate in this sector of eastern Africa (unlike northern Africa) evolved from a predominantly arid environment with high-frequency variability to generally wetter conditions with more prolonged wet and dry intervals.

来源: Nature 浏览次数:1


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