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Half-precessional dynamics of monsoon rainfall near the East African Equator

机译：东非赤道附近季风降水的半演替动力学

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摘要

External climate forcings-such as long-term changes in solar insolation-generate different climate responses in tropical and high latitude regions. Documenting the spatial and temporal variability of past climates is therefore critical for understanding how such forcings are translated into regional climate variability. In contrast to the data-rich middle and high latitudes, high-quality climate-proxy records from equatorial regions are relatively few, especially from regions experiencing the bimodal seasonal rainfall distribution associated with twice-annual passage of the Intertropical Convergence Zone. Here we present a continuous and well-resolved climate-proxy record of hydrological variability during the past 25,000 years from equatorial East Africa. Our results, based on complementary evidence from seismic-reflection stratigraphy and organic biomarker molecules in the sediment record of Lake Challa near Mount Kilimanjaro, reveal that monsoon rainfall in this region varied at half-precessional (～11,500-year) intervals in phase with orbitally controlled insolation forcing. The southeasterly and northeasterly monsoons that advect moisture from the western Indian Ocean were strengthened in alternation when the inter-hemispheric insolation gradient was at a maximum; dry conditions prevailed when neither monsoon was intensified and modest local March or September insolation weakened the rain season that followed. On sub-millennial timescales, the temporal pattern of hydrological change on the East African Equator bears clear high-northern-latitude signatures, but on the orbital timescale it mainly responded to low-latitude insolation forcing. Predominance of low-latitude climate processes in this monsoon region can be attributed to the low-latitude position of its continental regions of surface air flow convergence, and its relative isolation from the Atlantic Ocean, where prominent meridional overturning circulation more tightly couples low-latitude climate regimes to high-latitude boundary conditions.
机译：外部气候强迫（例如日照的长期变化）在热带和高纬度地区产生不同的气候响应。因此，记录过去气候的时空变化对于了解如何将这种强迫转化为区域气候变化至关重要。与资料丰富的中高纬度相比，赤道地区的高质量气候代理记录相对较少，特别是来自经历了双峰季节性降雨分布且与热带辐合带每年两次通过有关的地区的记录。在这里，我们介绍了过去25,000年来自赤道东非的水文变异的连续性和良好解决的气候代理记录。我们的研究结果基于乞力马扎罗山附近查拉湖沉积记录中地震反射地层学和有机生物标志物分子的补充证据，揭示了该地区的季风降雨以与轨道周期同相的半进动（〜11500年）间隔变化受控的日照强迫。当半球间日照最大梯度最大时，从印度洋西部平流的东南风和东北风季风交替出现。当季风都没有加剧，局部的三月或九月的日照减弱削弱了随后的雨季时，干旱条件就盛行。在亚千年时间尺度上，东非赤道水文变化的时间模式具有明显的北高纬度特征，但是在轨道时间尺度上，它主要对低纬度日射强迫做出了响应。该季风区低纬度气候过程的优势可归因于其大陆表层气流汇聚区的低纬度位置，以及它与大西洋的相对隔离，那里的主要子午翻转环流更紧密地耦合了低纬度气候制度到高纬度边界条件。

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  • 来源
    《Nature》 |2009年第7273期|637-641|共5页
  • 作者

    Dirk Verschuren; Jaap S. Sinninghe Damste; Jasper Moernaut; Iris Kristen; Maarten Blaauw; Maureen Fagot; Gerald H. Haug;

  • 作者单位

    Limnology Unit, Department of Biology, Ghent University, Ledeganckstraat 35, 9000 Gent, Belgium;

    Faculty of Geosciences. Utrecht University, PO Box 80021, 3508 TA Utrecht, The Netherlands Department of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, PO Box 59,1790 AB Den Burg, The Netherlands;

    Renard Centre of Marine Geology, Department of Geology and Soil Science, Ghent University, Krijgs'aan 281 S8, 9000 Gent, Belgium;

    GeoForschungsZentrum Potsdam, Sektion 3.3 Klimadynamik und Sedimente, Telegrafenberg, D-14473 Potsdam, Germany;

    School of Geography, Archaeology and Palaeoecology, Queen's University Belfast, BT9 6AX Belfast, UK;

    Limnology Unit, Department of Biology, Ghent University, Ledeganckstraat 35, 9000 Gent, Belgium;

    Geological Institute, Department of Earth Sciences, ETH Zurich, CH-8092 Zurich, Switzerland DFG Leibniz Center for Earth Surface Process and Climate Studies, Potsdam University, D-14476 Potsdam, Germany;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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