Millennial-scale variations in dustiness recorded in Mid-Atlantic sediments from 0 to 70 ka
Millennial-scale variations in dustiness recorded in Mid-Atlantic sediments from 0 to 70 ka
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DOI：
10.1016/j.epsl.2017.10.034
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发表时间：
2018-01-15
影响因子：
5.3
通讯作者：
Huybers, Peter J.
中科院分区：
文献类型：
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作者：
Middleton, Jennifer L.;Mukhopadhyay, Sujoy;Huybers, Peter J.
副热带大西洋尘埃沉积的沉积记录对大气环流和北非干旱的千年和轨道尺度变化提供了重要的限制。恒定通量代理，例如地外氦 3，产生的尘埃通量记录独立于横向沉积物运输和可能与年龄模型导出的质量积累率相关的有限分辨率引起的偏差。然而，使用恒定通量代理约束的大西洋沙尘记录分布稀疏，并且通常仅限于过去 20 ka。在这里，我们使用地外氦 3 和在大西洋中脊北纬 26 度和北纬 29 度收集的两个沉积物岩芯中对钛、钍和陆源氦 4 的测量，将北非尘埃沉积的大西洋记录扩展到 70 ka，并将结果与亚热带北大西洋尘埃沉积的模型估计值进行比较。尽管横向沉积物输送存在差异，但北纬 26 度和北纬 29 度之间的尘埃代理通量具有良好的相关性，并强调了地外氦 3 在限制尘埃沉积的千禧年尺度变化方面的效用。大西洋中部沙尘通量趋势与沿西北非边缘观察到的沙尘通量趋势之间的相似性证实了先前对过去 20 ka 沙尘通量变化的解释，并表明长距离传输和沉积过程并没有过度掩盖北非沙尘排放的信号。 70 ka 中大西洋记录显示，从海洋同位素第 4 阶段到末次盛冰期，北非的尘埃量略有增加，而与非洲湿润期相关的尘埃量急剧减少。在千禧年尺度上，新记录显示短暂的尘埃极大期与北大西洋寒冷时期（例如新仙女木期和多个海因里希体育场）一致。大西洋中部沙尘通量与之前对北非干旱的限制之间的相关性很高。然而，在非洲湿润期之前，降水对尘埃通量变化的控制作用较小，此时风的变化控制着持续干燥尘源地区的尘埃排放。因此，大西洋中部的沙尘记录支持这样的假设：干旱和风力都会导致气候条件变化时沙尘通量的变化。 (C) 2017 Elsevier B.V. 保留所有权利。
Sedimentary records of dust deposition in the subtropical Atlantic provide important constraints on millennial- and orbital-scale variability in atmospheric circulation and North African aridity. Constant flux proxies, such as extraterrestrial helium-3, yield dust flux records that are independent of the biases caused by lateral sediment transport and limited resolution that may be associated with age-model derived mass accumulation rates. However, Atlantic dust records constrained using constant flux proxies are sparsely distributed and generally limited to the past 20 ka. Here we extend the Atlantic record of North African dust deposition to 70 ka using extraterrestrial helium-3 and measurements of titanium, thorium, and terrigenous helium-4 in two sediment cores collected at 26 degrees N and 29 degrees N on the Mid-Atlantic Ridge and compare results to model estimates for dust deposition in the subtropical North Atlantic. Dust proxy fluxes between 26 degrees N and 29 degrees N are well correlated, despite variability in lateral sediment transport, and underscore the utility of extraterrestrial helium-3 for constraining millennial scale variability in dust deposition. Similarities between Mid-Atlantic dust flux trends and those observed along the Northwest African margin corroborate previous interpretations of dust flux variability over the past 20 ka and suggest that long distance transport and depositional processes do not overly obscure the signal of North African dust emissions. The 70 ka Mid-Atlantic record reveals a slight increase in North African dustiness from Marine Isotope Stage 4 through the Last Glacial Maximum and a dramatic decrease in dustiness associated with the African Humid Period. On the millennial-scale, the new records exhibit brief dust maxima coincident with North Atlantic cold periods such as the Younger Dryas, and multiple Heinrich Stadials. The correlation between Mid-Atlantic dust fluxes and previous constraints on North African aridity is high. However, precipitation exerts less control on dust flux variability prior to the African Humid Period, when wind variability governs dust emissions from consistently dry dust source regions. Thus, the Mid-Atlantic dust record supports the hypothesis that both aridity and wind strength drive dust flux variability across changing climatic conditions. (C) 2017 Elsevier B.V. All rights reserved.