RUI: High-resolution sediment records of late Holocene paleohydrology from the summer and winter rainfall regions of South Africa.

非洲的古气候研究在很大程度上依赖于湖泊沉积物岩心的分析，并提供了大量的证据表明，在第四纪晚期气候剧烈波动。然而，大部分工作都受到几个重要限制，包括（1）时间序列的时间分辨率粗糙，（2）由于不连续的沉积或在取芯过程中软上层沉积物的损失造成的空白，（3）沉积物定年的复杂性，（4）缺乏来自南半球的连续湖泊记录，（5）难以确定降水和温度对推断的环境变化的相对贡献。这些限制降低了气候重建的清晰度，阻碍了强有力的区域和全球尺度降雨动力学模型的发展，特别是对全新世晚期。PI和本科生分析硅藻（藻类与玻璃壳）和地球化学记录在湖泊沉积物核心代表了过去2000年，最近收集在南非与美国和非洲学生和同事。这些核心代表了大陆南部夏季和冬季降雨区的关键地点，它们包含了古水文波动的明确证据。的中心目标是澄清非洲降雨变率的性质和原因，在晚全新世。智力优点：这些分析，在每年到十年的增量和14 C，210铅，137铯，花粉指标进行了精细的时间分辨率异常高的非洲核心。这些详细的时间序列有助于改进与赤道和极地纬度记录有关的南部非洲关键古气候事件的性质和时间。他们还提供了持续的古水文记录，导致现代，并有助于澄清该地区的花粉和同位素为基础的研究的解释。这些研究结果被用来评估模型的雨季响应过去的全球变暖和变冷，非洲南极遥相关，太阳对非洲降雨的影响在过去的两千年。传递函数被用来将硅藻数据转换成在南非获得的全新世水化学参数的最长和最详细的重建。结果进行了比较，从赤道到极地纬度的其他记录，把南非的气候历史到全球context.Broader影响：降雨有更大的生态和社会影响，在非洲比温度本身没有。通过澄清南非最近的水文历史，这项研究支持的努力，模拟和预测降雨动态，以及南极和太阳的影响（和，间接地，温室效应）在过去和未来的非洲气候变化的作用。两名本科生正在帮助收集和分析他们的高级顶点项目在保罗史密斯的核心，一个小学院在一个服务不足的农村地区的纽约。与南非和英国的古生态学家的合作增强了PI和学生对研究设施，专业网络和专业知识的访问，数据存档在NOAA世界数据中心。国际联合的“自然选择”广播节目广泛广播这项工作的结果，并在北方国家公共广播电台网站上提供播客。

Paleoclimatic research in Africa has relied heavily upon analysis of lake sediment cores and has provided abundant evidence of dramatic climate fluctuations during the late Quaternary. However, much of that work has suffered from several important limitations, including (1) coarse temporal resolution of time series, (2) gaps due to discontinuous sedimentation or loss of soft upper sediments during coring, (3) complications in sediment dating, (4) a scarcity of continuous lake records from the southern hemisphere, and (5) difficulty in teasing out the relative contributions of rainfall and temperature to inferred environmental changes. These limitations have reduced the clarity of climate reconstructions and hindered the development of robust regional and global-scale models of rainfall dynamics, especially for the late Holocene.Under this RUI grant, the PI and undergraduate students analyze diatoms (algae with glassy shells) and geochemical records in lake sediment cores representing the last 2000 years that were recently collected in South Africa in collaboration with American and African students and colleagues. These cores represent key sites in the southern summer and winter rainfall regions of the continent and they contain clear evidence of paleohydrological fluctuations. The central goal is to clarify the nature and causes of African rainfall variability during the late Holocene.Intellectual merit: The fine temporal resolution of these analyses, conducted at annual to decadal increments and dated with 14C, 210Pb, 137Cs, and pollen indicators is unusually high for African cores. These detailed time series help to refine the nature and timing of key paleoclimate events in southern Africa in relation to records from equatorial and polar latitudes. They also provide continuous paleohydrological records leading into modern times, and help to clarify the interpretations of pollen- and isotope-based studies in the region. These findings are used to evaluate models of rainy season responses to past global warmings and coolings, of African-Antarctic teleconnections, and of solar influences on African rainfall during the last two millennia. Transfer functions are used to convert diatom data into the longest and most detailed reconstructions of Holocene water chemistry parameters that have ever been obtained in South Africa. Results are compared to other records ranging from equatorial to polar latitudes, putting the climatic history of South Africa into a global context.Broader impacts: Rainfall has much greater ecological and societal impacts in Africa than temperature alone does. By clarifying the recent hydrological history of South Africa, this study supports efforts to model and predict rainfall dynamics, as well as the roles of Antarctic and solar influences (and, indirectly, greenhouse warming) in relation to past and future African climate changes. Two undergraduate students are helping to collect and analyze cores for their senior capstone projects at Paul Smith's, a small college in an under-served rural region of upstate New York. Collaborations with paleoecologists in South Africa and Britain enhances PI and student access to research facilities, professional networks, and expertise, and the data is archived at the NOAA World Data Center. The internationally syndicated "Natural Selections" radio program broadcasts the results of this work widely and also makes podcasts available from the North Country Public Radio website.