Atmospheric controls on precipitation isotopes and hydroclimate in high-elevation regions in Eastern Africa since the Last Glacial Maximum
Atmospheric controls on precipitation isotopes and hydroclimate in high-elevation regions in Eastern Africa since the Last Glacial Maximum
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DOI：
10.1016/j.epsl.2021.116984
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发表时间：
2021-05-25
影响因子：
5.3
通讯作者：
Olago, Daniel O.
中科院分区：
文献类型：
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作者：
Garelick, Sloane;Russell, James M.;Olago, Daniel O.
自末次盛冰期 (LGM) 以来，热带非洲经历了水文气候条件的巨大变化，类似于 826.5 至 19000 年（ka 或 kyr）前。化石叶蜡的氢同位素组成（δ D-蜡）被认为记录了过去降水氢同位素组成的变化（δ D-降水），越来越多地用于研究非洲过去的水文气候变化，并且通常被解释为反映降水量随时间的变化（即量效应）。尽管现在有许多来自热带非洲的此类三角洲 D 降水记录，但来自赤道非洲最东部的可靠的三角洲 D 降水记录却很少有足够的长度和分辨率来评估末次盛冰期期间和之后控制水文气候变化的机制。我们根据从位于肯尼亚山海拔 3,078 米 (masl) 的鲁通杜湖 (Lake Rutundu) 收集的沉积物岩芯中的三角洲 D-蜡分析，生成了新的三角洲 D-降水记录。该记录显示了与过去 25 kyr 已知气候事件相对应的三角洲 D 降水的巨大变化，包括 Heinrich 1 stadial (H1) 和新仙女木 (YD) 期间的 D 富集，以及非洲湿润期 (AHP) 全新世部分期间的 D 消耗。我们还观察到末次盛冰期相对于全新世晚期的 D 消耗，考虑到数量效应，这可以解释为末次盛冰期的气候条件比今天更加湿润。然而，由于该地点的其他水文气候代理表明鲁通杜湖的末次盛冰期气候较为干燥，并且由于该高海拔地点的降水同位素可能受到与低海拔地区不同的过程的影响，因此我们使用单柱瑞利蒸馏模型来评估与温度和海拔相关的对高海拔 dDprecip 的影响。这表明，在这种高海拔环境中，温度递减率的变化对δ D-降水有很强的控制作用，并且更陡的递减率可以解释我们所在地末次盛冰期期间观察到的D-消耗。鲁通杜湖三角洲 D 降水记录与东非其他基于叶蜡的三角洲 D 降水记录的比较表明，与热带雨带年平均位置和强度相关的经向降水梯度的变化，反过来又受到岁差日照强迫的驱动，可能是过去 25 kyr 东非水文气候的主要控制因素，从而导致末次盛冰期期间的整体区域干燥。 (C) 2021 Elsevier B.V. 保留所有权利。
Tropical Africa experienced large changes in hydroclimatic conditions since the Last Glacial Maximum (LGM), similar to 826.5 to 19 thousand years (ka or kyr) ago. The hydrogen isotopic composition of fossil leaf waxes (delta D-wax), assumed to record past variations in the hydrogen isotopic composition of precipitation (delta D-precip), is increasingly being used to study past hydroclimatic change in Africa, and are commonly interpreted to reflect variation in the amount of precipitation through time (i.e., the amount effect). Although there are now many such delta D-precip records from tropical Africa, there are few robust delta D-precip records from easternmost equatorial Africa of sufficient length and resolution to evaluate the mechanisms governing hydroclimate variation during and since the LGM. We produced a new delta D-precip record based on analyses of delta D-wax in sediment cores collected from Lake Rutundu, situated at an elevation of 3,078 meters above sea level (m asl) on Mt. Kenya. This record displays large variations in delta D-precip corresponding with known climate events over the past 25 kyr, including D-enrichment during the Heinrich 1 stadial (H1) and the Younger Dryas (YD), and D-depletion during the Holocene portion of the African Humid Period (AHP). We also observe D-depletion during the LGM relative to the late Holocene, which, considering the amount effect, could be interpreted to imply that LGM climate conditions were wetter than today. However, because other hydroclimate proxies at this site indicate a drier LGM climate at Lake Rutundu, and since precipitation isotopes at this high-elevation site are likely influenced by different processes than at low elevations, we used a single-column Rayleigh distillation model to evaluate temperature and altitude-related effects on high-elevation dDprecip. This revealed that a change in the temperature lapse rate exerts strong control on delta D-precip in this high-elevation setting, and that a steeper lapse rate could explain the observed D-depletion during the LGM at our site. Comparison of the Lake Rutundu delta D-precip record with other leaf-wax based delta D-precip records from East Africa indicates that changes in the meridional precipitation gradient associated with the mean annual position and intensity of the tropical rain belt, in turn driven by precessional insolation forcing, were likely a primary control on East African hydroclimate over the past 25 kyr, thereby contributing to overall regional drying during the LGM. (C) 2021 Elsevier B.V. All rights reserved.