ESH: RUI: A 9,000 Year Diatom Record of Climate Fluctuations From Lake Victoria, East Africa, With Decade-Scale Resolution

9808972 stager热带非洲的古气候研究在很大程度上依赖于对湖泊沉积物岩心中的微化石的分析，并利用这些工具提供了自更新世以来赤道温度、水文和气候季节性剧烈波动的大量证据。然而，这项工作的大部分都受到了一些重要的限制，其中包括：(1)微化石系列的时间分辨率相对较粗；(2)由于侵蚀和/或不连续沉积的原因，记录不完整；(3)难以梳理出过去降雨、风和其他气候因素对化石记录中观测到的变化的相对贡献；(4)岩心的放射性碳定年困难。包括古碳库效应和日期不足。这些限制不仅降低了许多古气候重建的清晰度；它们经常阻碍网站之间的比较。在这个RUI提案中，PI以2厘米的间隔对东非维多利亚湖9.9米长的沉积物岩心进行了亚采样，并建议对保存在这些亚样本中的硅藻（带有玻璃壳的单细胞藻类）进行高分辨率分析，以避免上述限制。这个项目的结果很可能对我们理解全新世赤道气候的历史和背后的强迫机制做出了重大贡献。在这段时间的热带记录中，时间细节将是前所未有的，在大约9000 - 14C年的时间跨度中产生16-18年的分辨率。维多利亚湖的全新世沉积制度非常一致，因此对这一记录的日期插值应该是相当可靠的。由于这个岩心来自近海地点，它包含了过去湖泊水位波动（由于气候变化）的证据，这种波动以沿海硅藻相对丰度的变化为代表。此外，其他指示水柱混合制度的硅藻化石分类将产生过去季风风活动波动的记录。从这些异常详细的硅藻记录中，应该有可能重建东非干旱的长期和异常详细的记录，深入了解热带地区短期周期性气候振荡的作用，寻找非洲气候周期性太阳强迫的证据，并确认大约7200年前气候突然转变为更大的热带降雨季节性的时间和性质。以及东非的“中世纪温暖期”和“小冰期”间隔，这两个时期的记录仍然很少。本研究结果还将与其他古气候数据集进行比较，包括赤道多代理记录和高分辨率极地冰芯记录，将维多利亚湖的气候历史置于全球背景下。

9808972StagerPaleoclimatic research in tropical Africa relies heavily upon analysis of microfossils in lake sediment cores, and with these tools it has provided abundant evidence of dramatic fluctuations in equatorial temperatures, hydrology, and climatic seasonality since the Pleistocene. However, much of this work has suffered from several important limitations, among them (1) relatively coarse temporal resolution of microfossil series, (2) incomplete records due to erosion and/or discontinuous sedimentation, (3) difficulty in teasing out the relative contributions of past rainfall, winds, and other climatic factors to observed changes in the fossil record, and (4) difficulties in radiocarbon dating of cores, including ancient carbon reservoir effects and insufficient number of dates. These limitations have not only reduced the clarity of many paleoclimatic reconstructions; they often hinder comparisons between sites.For this RUI proposal, the PI has subsampled a 9.9 m long sediment core from Lake Victoria, East Africa, at 2 cm intervals, and proposes to conduct a high-resolution analysis of the diatoms (single-celled algae with glass shells) preserved in those subsamples that will avoid the aforementioned limitations. The results of this project are likely to represent a significant contribution to our understanding of the history of, and forcing mechanisms behind, equatorial climates of the Holocene. The temporal detail will be unprecedented among tropical records of this length, yielding 16-18 year resolution over a span of roughly 9,000 14C years. Holocene sedimentation regimes in Lake Victoria have been remarkably uniform, so date interpolation for this record should be quite reliable. Because this core comes from an inshore site, it contains evidence of past lake level fluctuations (due to climatic changes) as represented by changes in the relative abundances of littoral diatoms. In addition, other fossil diatom taxa indicative of water column mixing regimes will yield a record of past fluctuations in monsoonal wind activity. From these unusually detailed diatom records, it should be possible to reconstruct a long and exceptionally detailed record of East African droughts, to gain insights into the role of short-term periodic climate oscillations in the tropics, to seek evidence of cyclic solar forcing of African climates, and to confirm the timing and nature of the abrupt climatic transition to greater tropical rainfall seasonality ca. 7200 years ago, as well as of the "Medieval Warm Period" and "Little Ice Age" interval which are still poorly documented in East Africa. The results of this study will be compared to other paleoclimatic datasets as well, including equatorial multi-proxy records and high-resolution polar ice core records, putting the climatic history of Lake Victoria into a global context.