Collaborative Research: High-Resolution, Low-Latitude Paleoclimatology from Newly Acquired Sediment Drill Cores from Lake Bosumtwi, Ghana"

博苏姆特维湖位于西非加纳热带森林低地的一个百万年前的陨石撞击坑内。该湖在水文上是封闭的，众所周知，它对降水/蒸发平衡和西非季风的强度非常敏感。博苏姆特维湖包含热带地区为数不多的、每年长时间的层状沉积记录之一，并且拥有迄今为止赤道西非最长、分辨率最高的古气候记录。这项工作洞察了热带地区在触发、加剧和传播气候变化以及应对全球和高纬度变化方面的作用。这项工作将产生关于西非气候和气溶胶在多个冰川周期中变化的第一个连续的准确的陆地记录，并对一个关键的甲烷来源区提供水文约束，并利用每年分层的沉积物来审查有关多个冰川终止的确切时间和变化模式的全球重大问题(例如，低纬地区对冰川消融事件的反应是什么，我们能否评估大冰盖融化和导致间冰期条件的速度？在以前的终止中，气候逆转的性质是什么？MIS11持续了多长时间，它是如何在热带地区表现出来的，它与轨道强迫，特别是最后的轨道强迫有什么真正的联系？温暖气候期间的各种干旱变化是什么？)该项目还研究了高纬度的突然变化如何与热带的同时代事件有关，并检验了一种假设，即~74KYR的博苏姆特维湖干旱事件与Toba火山喷发、北半球戏剧性的北半球降温和东非五大湖的严重低水位是同时代的，这表明泛非地区发生了严重的干旱危机，这可能是“早期现代人”人口瓶颈和当时有记录的非洲人迁出的原因。这项研究提供了一个重要的季风气候系统在温暖和寒冷气候期间的年度-年代际分辨率的快速气候变化的多代理记录。其次，这项研究通过提供沿IGBP PEP-III横断面的西非的新记录，研究了气候变化的区域模式和阶段性。广泛的影响：以前的研究表明，水文平衡的戏剧性突变可以在社会时间尺度上发生。暖气候全新世事件的原因(S)仍然知之甚少。这项对更长时间记录的研究，钻探了许多温暖的间冰期，包括一些可能比今天更温暖的间冰期，将进一步了解这些动力学。这项工作还将阐明与社会相关的关键争议，如冰盖融化的速度有多快，以及类似全新世的MIS11间冰期是如何结束的。对美国学生和博士后的培训将是跨学科和广泛的。

Lake Bosumtwi lies in a million-year-old meteorite impact crater located in the tropical forest lowlands of Ghana, in West Africa. The lake is hydrologically closed and known to be very sensitive to the precipitation/evaporation balance and the strength of the West African Monsoon. Lake Bosumtwi contains one of a very few, long annually laminated sediment records in the tropics, and has by far the longest, highest-resolution paleoclimate record in equatorial West Africa.Intellectual Merit: This grant studies interannual to millennial-scale West African monsoon dynamics over the last ~430 kyr (i.e., back through Marine Isotopic Stage [MIS] 11). This work provides insight into the role of the tropics in triggering, intensifying and propagating climate changes, as well as in responding to global and highlatitude changes. This work will produce the first continuous well-dated terrestrial record of West African climate & aerosol variability over multiple glacial cycles, and provide hydrologic constraints on a key methane source region, and use the annually-laminated sediments to examine globally significant questions regarding the exact timing and patterns of change over multiple glacial terminations (e.g., What is the low-latitude response to deglaciation events, and can we assess how fast large ice sheets melt and lead to interglacial conditions? What is the nature of climatic reversals on previous terminations? How long was MIS11, how was it manifested in the tropics, and how does it really relate to orbital forcing, particularly at the end? What is the full range of drought variability during warm climates?)The project also examines how the abrupt changes of the high-latitudes are related to coeval events in the tropics, and examines the hypothesis that a Lake Bosumtwi dessication event at ~74+ kyr is coeval with the Toba eruption, dramatic Northern Hemisphere cooling, and severe lowstands in the East African Great lakes, indicating a profound pan-African aridity crisis, that is perhaps responsible for the "early modern human" population bottleneck, and African exodus documented for that time. The study provides multiproxy records of rapid climate change at annual-decadal resolution of an important monsoonal climate system during both warm and cold climates. Second, this study addresses regional patterns and phasing of climate change by providing new records from West Africa, which is along the IGBP PEP-III transect.Broader Impacts:Previous studies indicate that dramatic abrupt shifts in hydrologic balance can occur on a spectrum of societal time scales. The cause(s) of the warm-climate Holocene events remain poorly understood. This study of the longer record, drilled through many warm interglacials, including some perhaps warmer than today, will further understanding of these dynamics. This work will also illuminate key societally-relevant controversies regarding how fast ice sheets can melt, and how the Holocene-like MIS11 interglacial ended. Training of US students and a post-doc will be interdisciplinary and extensive.