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岩心的分析，并提供了第四纪晚期气候剧烈波动的大量证据。然而，这项工作的许多工作都受到几个重要限制，包括：(1)时间序列的时间分辨率不高，(2)取心过程中不连续沉积或上层软沉积物损失造成的空白，(3)沉积物测年的复杂性，(4)缺乏南半球的连续湖泊记录，以及(5)难以梳理出降雨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，并阻碍了强大的区域和全球尺度降雨动力学模型的发展，特别是在全新世晚期。在这项研究资助下，PI和本科生分析硅藻(具有玻璃壳的藻类)和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地球化学记录。这些岩心代表了非洲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全新世晚期降雨量变化的性质和原因。智力优势：这些分析以每年到十年为增量进行，用14C、210Pb、137Cs和花粉指示器测定日期，在时间上的精细分辨率对非洲岩心来说是异常高的。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。它们还提供了通向现代的连续古水文记录，并有助于澄清该地区基于花粉和同位素的研究的解释。这些发现被用于评估雨季对过去全球变暖和降温的反应模型、非洲-南极遥相关模型以及过去两千年来太阳对非洲降雨的影响模型。传递函数用于将硅藻数据转换为南非有史以来获得的最长和最详细的全新世水化学参数重建。结果与从赤道到极地纬度的其他记录进行了比较，将南非的气候历史置于全球范围内。广泛的影响：与温度本身相比，降雨对非洲的生态和社会影响要大得多。通过澄清南非最近的水文历史，这项研究有助于对降雨动态以及南极和太阳影响(以及间接的温室效应)在过去和未来非洲气候变化中的作用进行建模和预测。两名本科生正在帮助收集和分析他们在Paul Smith‘s的高级Capstone项目的核心内容。Paul Smith’s是一所小型学院，位于纽约州北部一个服务不足的农村地区。与南非和英国的古生态学家的合作加强了PI和学生对研究设施、专业网络和专业知识的接触，数据存档在NOAA世界数据中心。国际辛迪加的“自然选择”广播节目广泛广播这项工作的结果，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.