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对湖泊沉积物岩心的分析，并提供了大量的证据证明晚第四纪期间气候的剧烈波动。然而，大部分工作都受到几个重要的限制，包括：(1)时间序列的粗时间分辨率；(2)在取芯过程中由于不连续沉积或软上部沉积物的损失而产生的间隙；(3)沉积物定年的复杂性；(4)南半球连续湖泊记录的缺乏；(5)难以梳理出降雨和温度对推断环境变化的相对贡献。这些限制降低了气候重建的清晰度，并阻碍了强大的区域和全球尺度降雨动力学模式的发展，特别是对于全新世晚期。在RUI的资助下，PI和本科生分析了最近在南非与美国和非洲的学生和同事合作收集的代表过去2000年的湖泊沉积物岩心中的硅藻（具有玻璃壳的藻类）和地球化学记录。这些岩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。中心目标是澄清非洲在全新世晚期降雨变化的性质和原因。知识价值：这些分析的精细时间分辨率，以年至年代际增量进行，并以14C， 210Pb， 137Cs和花粉指标为年代，对非洲岩心来说异常高。这些详细的时间序列有助于根据赤道和极地纬度的记录，完善南部非洲关键古气候事件的性质和时间。它们还提供了持续到现代的古水文记录，并有助于澄清该地区基于花粉和同位素的研究的解释。这些发现被用来评估雨季对过去全球变暖和变冷的响应模式、非洲-南极遥相关模式以及过去两千年中太阳对非洲降雨的影响模式。传递函数用于将硅藻数据转换为迄今为止在南非获得的最长和最详细的全新世水化学参数重建。将结果与从赤道到极地纬度的其他记录进行比较，将南非的气候历史置于全球背景下。更广泛的影响：在非洲，降雨对生态和社会的影响比温度本身大得多。通过澄清南非最近的水文历史，本研究支持了模拟和预测降雨动态的努力，以及南极和太阳影响（以及间接的温室变暖）在过去和未来非洲气候变化中的作用。在保罗史密斯学院（Paul Smith's），两名本科生正在帮助收集和分析他们高年级毕业项目的核心，这是一所位于纽约州北部一个服务不足的农村地区的小型学院。与南非和英国的古生态学家合作，提高了PI和学生对研究设施、专业网络和专业知识的使用，数据存档在NOAA世界数据中心。国际联合的“自然选择”广播节目广泛传播这项工作的结果，并在北部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.