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Stable isotopes in precipitation recording South American summer monsoon and ENSO variability: observations and model results

机译：记录南美夏季风和ENSO变化的降水中的稳定同位素：观测值和模型结果

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摘要

The South American Summer Monsoon (SASM) is a prominent feature of summertime climate over South America and has been identified in a number of paleoclimatic records from across the continent, including records based on stable isotopes. The relationship between the stable isotopic composition of precipitation and interannual variations in monsoon strength, however, has received little attention so far. Here we investigate how variations in the intensity of the SASM influence δ~(18)O in precipitation based on both observational data and Atmospheric General Circulation Model (AGCM) simulations. An index of vertical wind shear over the SASM entrance (low level) and exit (upper level) region over the western equatorial Atlantic is used to define interannual variations in summer monsoon strength. This index is closely correlated with variations in deep convection over tropical and subtropical South America during the mature stage of the SASM. Observational data from the International Atomic Energy Agency-Global Network of Isotopes in Precipitation (IAEA-GNIP) and from tropical ice cores show a significant negative association between δ~(18)O and SASM strength over the Amazon basin, SE South America and the central Andes. The more depleted stable isotopic values during intense monsoon seasons are consistent with the so-called "amount effect", often observed in tropical regions. In many locations, however, our results indicate that the moisture transport history and the degree of rainout upstream may be more important factors explaining interannual variations in δ~(18)O. In many locations the stable isotopic composition is closely related to El Nino-Southern Oscillation (ENSO), even though the moisture source is located over the tropical Atlantic and precipitation is the result of the southward expansion and intensification of the SASM during austral summer. ENSO induces significant atmospheric circulation anomalies over tropical South America, which affect both SASM precipitation and δ~(18)O variability. Therefore many regions show a weakened relationship between SASM and δ~(18)O, once the SASM signal is decomposed into its ENSO-, and non-ENSO-related variance.
机译：南美夏季风（SASM）是南美夏季气候的显着特征，并且已在整个非洲大陆的许多古气候记录中得到确认，包括基于稳定同位素的记录。迄今为止，稳定的降水同位素组成与季风强度的年际变化之间的关系鲜为人知。在这里，我们基于观测数据和大气环流模型（AGCM）的模拟，研究了SASM强度的变化如何影响降水中的δ〜（18）O。赤道西大西洋上空SASM入口（低层）和出口（上层）区域上的垂直风切变指数用于定义夏季风强度的年际变化。该指数与SASM成熟阶段热带和亚热带南美深对流变化密切相关。来自国际原子能机构全球降水同位素网络（IAEA-GNIP）和热带冰芯的观测数据表明，亚马逊盆地，南美东南部和南美洲的δ〜（18）O与SASM强度之间存在显着的负相关。安第斯山脉中部。在强烈的季风季节中，更稳定的同位素值会耗尽，这与通常在热带地区观察到的所谓的“量效应”相一致。然而，在许多地方，我们的结果表明，水分的迁移历史和上游降雨的程度可能是解释δ〜（18）O年际变化的更重要因素。在许多地区，稳定的同位素组成与厄尔尼诺-南方涛动（ENSO）密切相关，即使水分源位于热带大西洋上空，而降水也是南半球夏季南半球南极扩张和集约化的结果。 ENSO引起南美洲热带地区明显的大气环流异常，这影响了SASM降水和δ〜（18）O的变化。因此，一旦SASM信号分解为ENSO相关的和非ENSO相关的方差，许多区域在SASM与δ〜（18）O之间的关系就会减弱。

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  • 来源
    《Climate dynamics》 |2005年第4期|p.401-413|共13页
  • 作者

    M. Vuille; M. Werner;

  • 作者单位

    Climate System Research Center, Department of Geosciences, Morrill Science Center, University of Massachusetts, 611 North Pleasant Street, Amherst, MA, 01003-9297 USA;

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  • 正文语种 eng
  • 中图分类 大气科学（气象学）;
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