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

热带非洲的古气候研究在很大程度上依赖于对湖泊沉积岩心中微化石的分析，利用这些工具，它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，这项工作中的许多工作都受到了几个重要限制，其中包括：(1)微化石系列的时间分辨率相对较低，(2)由于侵蚀和/或不连续沉积而造成的记录不完整，(3)难以梳理出过去的降雨、风和其他气候因素对化石记录中观察到的变化的相对贡献，以及(4)岩芯的放射性碳测年困难，包括古代碳库效应和日期数量不足。这些限制不仅降低了许多古气候重建的清晰度，而且往往阻碍了不同地点之间的比较。对于这个瑞的建议，PI以2厘米的间隔从东非维多利亚湖对9.9米长的沉积物岩芯进行了亚采样，并提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重大贡献。在这种长度的热带记录中，时间细节将是史无前例的，在大约9000 14C年的跨度内产生16-18年的分辨率。维多利亚湖的全新世沉积体系是非常均匀的，因此这一记录的数据内插应该是相当可靠的。由于这个岩心来自近海，它包含了过去湖泊水位波动的证据(由于气候变化)，表现为沿海硅藻相对丰度的变化。此外，指示水柱混合制度的其他硅藻化石分类群将记录过去季风风活动的波动。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极详细的记录，深入了解热带短期周期性气候振荡的作用，寻找太阳强迫非洲气候周期性变化的证据，并确认大约7200年前向更多热带降雨季节性的突然气候过渡的时间和性质，以及在东非仍未得到充分记录的“中世纪暖期”和“小冰期”。这项研究的结果也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范围内。

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.