Three million years of monsoon variability over the northern Sahara
Three million years of monsoon variability over the northern Sahara
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DOI：
10.1007/s00382-003-0355-z
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发表时间：
2003-12-01
期刊：
影响因子：
4.6
通讯作者：
Wehausen, R
中科院分区：
文献类型：
--
作者：
Larrasoaña, JC;Roberts, AP;Wehausen, R
我们提出了一个300万年的记录，风成尘埃供应到地中海东部，根据来自海洋钻探计划网站967沉积物的磁性赤铁矿含量。我们的记录具有近似400年的平均时间分辨率。地球化学数据证实了这一记录的赤铁矿含量作为一个代理供应的风成尘从撒哈拉。我们推断，地中海东部沉积物中的风成赤铁矿来自位于撒哈拉中部分水岭以北的阿尔及利亚东部、利比亚和埃及西部低地（类似于北纬21度）。在佐证早期的工作，我们涉及到沙尘通量最小的非洲夏季季风锋的撒哈拉中部分水岭以北的渗透。这将增加源区的土壤湿度和植被覆盖，与“绿色撒哈拉”气候模型的结果一致。我们的研究结果表明，这种向北的季风渗透在整个过去300万年的日照最大期间复发。正如预期的那样，这种轨道岁差尺度机制在短（类似于100-kyr）和长（类似于400-kyr）离心率时间尺度上都是可调节的。我们还观察到一个强有力的表达类似的41-kyr周期，我们讨论的高纬度和低纬度的机制，涉及南半球纬向温度的对比和变化的纬度的热带地区，分别。我们还观察到中更新世过渡期（类似于0.95 Ma）的次米兰科维奇变率显著增加，这表明千年尺度气候变率（包括季风动力学）与北方冰盖大小之间存在联系。
We present a 3 million year record of aeolian dust supply into the eastern Mediterranean Sea, based on hematite contents derived from magnetic properties of sediments from Ocean Drilling Program Site 967. Our record has an average temporal resolution of similar to400 years. Geochemical data validate this record of hematite content as a proxy for the supply of aeolian dust from the Sahara. We deduce that the aeolian hematite in eastern Mediterranean sediments derives from the eastern Algerian, Libyan, and western Egyptian lowlands located north of the central Saharan watershed (similar to21degreesN). In corroboration of earlier work, we relate dust flux minima to penetration of the African summer monsoon front to the north of the central Saharan watershed. This would have enhanced soil humidity and vegetation cover in the source regions, in agreement with results from "green Sahara" climate models. Our results indicate that this northward monsoon penetration recurred during insolation maxima throughout the last 3 million years. As would be expected, this orbital precession-scale mechanism is modulated on both short (similar to100-kyr) and long (similar to400-kyr) eccentricity time scales. We also observe a strong expression of the similar to41-kyr (obliquity) cycle, which we discuss in terms of high- and low-latitude mechanisms that involve Southern Hemisphere meridional temperature contrasts and shifts in the latitudes of the tropics, respectively. We also observe a marked increase in sub-Milankovitch variability around the mid-Pleistocene transition (similar to0.95 Ma), which suggests a link between millennial-scale climate variability, including monsoon dynamics, and the size of northern hemisphere ice sheets.