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首页> 外文学位 >Exploring seasonal climate variability in East African trees: High-resolution oxygen and carbon isotope records of cellulose of vitex payos from Chyulu Hills, Kenya.
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Exploring seasonal climate variability in East African trees: High-resolution oxygen and carbon isotope records of cellulose of vitex payos from Chyulu Hills, Kenya.

机译：探索东非树木的季节性气候变化：肯尼亚丘尤鲁希尔斯（Cyulu Hills）的高产荆豆纤维素的高分辨率氧和碳同位素记录。

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摘要

A nearly continuous, annually resolved record of cellulosic delta 18O and delta13C is presented for the East African tree Vitex payos for the recent through the late 19th century. The isotope data of individual rings is cross-calibrated against atmospheric variables during the late 20th century to ascertain how and when during the year cellulose obtains its delta18O and delta13 C value in response to environmental conditions at the tree site. During the late 20th century the delta18O and delta 13C obtained from alpha cellulose from annual rings of Vitex payos correlates strongly with precipitation amount and with relative humidity, with depleted (enriched) delta18O and depleted (enriched) delta13C values associated with increased (reduced) precipitation and relative humidity. The strongest correlations are found between cellulose delta18O and the amount of precipitation and the relative humidity during December-February, although temperature contributes to the observed isotopic variance as well. Relative humidity in December-February appears to have the strongest correlation to annual cellulosic delta 13C. The results of this cross-correlation study are used to develop a preliminary seasonal growth model for Vitex payos that reflects variations in precipitation amount and relative humidity during the December-February growing season. During the late 20th century the East Africa continent and the western Indian Ocean basin experienced anomalously wet conditions in summer (December-February) when sea surface temperatures (SSTs) were anomalously warm in the western Indian Ocean and zonal winds were anomalously strong in association with positive phases of the Indian Ocean Dipole (IOD) and/or El Nino Southern Oscillation (ENSO). Using the correlation between cellulosic isotopic values and hydroclimate variability over East Africa and Indian Ocean SSTs during the late 20th century a preliminary climate reconstruction is proposed for the pre-20th century fromVitex payos delta 18O and delta13C. The isotopic record of Vitex payos indicates the late 19th century was anomalously wet over East Africa when compared to the late 20th century, consistent with lake level changes and ice core isotopic data. Climate model simulations indicate the wetter pre-20th century climate was a response to enhanced warming in the western Indian Ocean basin, generating a low pressure center and easterly surface winds that brought moisture to East Africa. The annually resolved isotopic data from Vitex payos suggest much of the observed and modeled hydroclimate variability at multidecadal to century scales is a response to SST anomalies in the western Indian Ocean. The results of the present study should help guide future phenological studies of Vitex payos and other Vitex species in equatorial East Africa. Importantly, stable isotope data obtained from individual growth rings suggests that the annual production of cellulose in Vitex payos occurs during a short seasonal period from January to February, information that could not be inferred directly from tree ring width data alone. Further improvements in sampling tree rings at intra-annual resolution and in-situ monitoring of weather/climate variables, including isotopic variability of moisture would be necessary in order to fully utilize cellulosic delta 18O as a climate proxy, with the potential for becoming a continent-wide hydrologic monitoring network, the first of its kind from Africa. The isotopic database for Vitex payos is among the few available terrestrial climate records provides estimates of how hydrologic budgets varied over East Africa during the past several centuries.
机译：对于近至19世纪后期的东非Vitex payos树，提供了几乎连续的，每年解析的纤维素delta 18O和delta13C记录。在20世纪后期，针对大气变量对各个环的同位素数据进行了交叉校准，以确定在一年中纤维素如何以及何时获得响应树木现场环境条件的delta18O和delta13 C值。在20世纪末，从Vitex payos年轮的α纤维素中获得的delta18O和delta13C与降水量和相对湿度密切相关，与（增加的）delta18O耗尽（耗尽）的delta13C值升高（减少）相关。和相对湿度。在12月至2月期间，发现纤维素delta18O与降水量和相对湿度之间存在最强的相关性，尽管温度也对观察到的同位素变化有所贡献。十二月至二月的相对湿度似乎与年度纤维素三角洲13C的相关性最强。这项互相关研究的结果用于为Vitex payos建立初步的季节性增长模型，该模型反映了12月至2月生长期的降水量和相对湿度的变化。在20世纪后期，东非大陆和西印度洋盆地在夏季（12月至2月）经历了异常潮湿的条件，当时西印度洋的海表温度（SSTs）异常温暖，而纬向风异常强烈。印度洋偶极子（IOD）和/或厄尔尼诺南方涛动（ENSO）的正相。利用20世纪末东非和印度洋海表温度的纤维素同位素值与水气候变化之间的相关性，提出了20世纪前的Vitex payos delta 18O和delta13C初步气候重建。 Vitex payos的同位素记录表明，与20世纪后期相比，东非的19世纪末异常潮湿，这与湖泊水位变化和冰芯同位素数据一致。气候模型模拟表明，二十世纪前的湿润气候是对印度洋西部盆地变暖的一种反应，产生了低压中心和东风，将湿气带到东非。来自Vitex payos的每年解析的同位素数据表明，在数十个世纪至一个世纪尺度上，许多观察到的和模拟的水气候变化是对印度洋西部海温异常的响应。本研究的结果应有助于指导赤道东非Vitex payos和其他Vitex物种的未来物候研究。重要的是，从单个年轮获得的稳定同位素数据表明，Vitex payos中纤维素的年产量在1月至2月的短季节内发生，这不能仅从树环宽度数据中直接推断出信息。为了充分利用纤维素三角洲18O作为气候代用品，有必要进一步改进以年内分辨率采样的年轮并对天气/气候变量进行现场监测，包括湿度的同位素变化，以便充分利用纤维素三角洲18O作为气候代用品。范围广泛的水文监测网络，这是非洲首创。 Vitex payos的同位素数据库是少数可利用的陆地气候记录之一，它提供了过去几个世纪中东非水文预算如何变化的估计。

著录项

  • 作者

    Horan, Patrick Devin.;

  • 作者单位

    University of Southern California.;

  • 授予单位 University of Southern California.;
  • 学科 Climate Change.;Biology Plant Physiology.
  • 学位 M.S.
  • 年度 2011
  • 页码 114 p.
  • 总页数 114
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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