Collaborative Research: A multiple-technique approach for deconvolving tropical cyclone effects on Late Quaternary geomorphic change in arid southwestern North America

北半球的东太平洋是地球上产生强烈热带气旋最多的地区之一，这些热带气旋在干旱的北美西南部海岸登陆，极大地增强了径流、洪水以及相关的侵蚀和沉积。 最近的研究表明，这些大规模事件改变了历史和地质时间尺度（几十年到数千年）的水文和生态系统平衡。该项目将评估这些风暴在地质过去发生在北美西南部海岸向北多远的地方，以及它们通过降雨和侵蚀控制内陆多远的地貌变化事件。具体目标是确定以前记录的热带气旋主导下加利福尼亚半岛南部大型冲积扇系统径流和沉积物沉积的时期是否可以在下加利福尼亚州中部、加利福尼亚州南部沙漠，甚至远至亚利桑那州南部索诺兰沙漠以北检测到。数据将测试消散的气旋是否是数千年来冲积扇沉积的驱动因素，以及是否可以建立温和潮湿的古气候到当前干旱气候之间的过渡期的时间相关性。将首次为北美西南部的太平洋海岸制定涵盖过去几千年的热带气旋登陆年表。这项研究有可能为加利福尼亚州南部和墨西哥西北部的大风暴预测情景提供信息，这与需要对罕见和极端事件进行风险评估的社区的危害管理相关。该项目将通过博士后、研究生和本科生的实地合作，采用分层方法，为下一代地球科学家的培训做出贡献。事实证明，这种方法对于纳入代表性不足的少数群体来说是成功的，并且通过与墨西哥合作者和学生一起计划的研究也得到了加强。该项目将通过使用技术连接实地考察和课堂，为印第安纳州和亚利桑那州的小学生提供独特的、更广泛的教育体验。该项目将把最近建立的南下加利福尼亚州冲积扇年代学与新获得的冲积扇和古风暴学记录进行比较。将首次开发太平洋沿岸比斯开诺沙漠过度冲刷沉积物的全新世古风暴记录。推断的热带风暴活动将与该地区和索诺兰沙漠北部的内陆冲积扇沉积进行比较，从而根据观测到的沿海和冲积沉积学、地层学和具体代理记录来区分来自不同水分源的信号。将通过探测不同时间段来评估驱动沉积的不同水分来源的影响，并与独立的古气候指标进行比较。发光、宇宙成因和放射性碳地质年代学的贝叶斯分析将提高年龄控制精度。轨道时间尺度上的耦合冲积和海岸记录将有助于了解该地区第四纪冲积沉积与水文气候变化之间的联系，并将增加我们对冲积扇加速响应干旱水文气候变化的基本原理的理解。该项目将测试热带环流的千禧年和轨道尺度变化对该地区景观演变的影响，这反过来对于测试水文极端事件和相关景观变化事件的发生和影响模型至关重要。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Eastern Pacific Ocean in the Northern Hemisphere is one of the most prolific regions on Earth in terms of generation of intense tropical cyclones that make landfall on the coasts of arid southwestern North America and dramatically enhance runoff, flooding, and associated erosion and sedimentation. Recent research indicates that these large-scale events have altered the hydrological and ecosystem balances over historical and geological timescales (decades to thousands of years). This project will assess how far north along the coast of southwestern North America these storms have occurred in the geologic past, and how far inland they controlled geomorphic change events through rain and erosion. The specific goal is to determine if previously documented periods when tropical cyclones dominated runoff and sediment deposition across large alluvial fan systems of the southern Baja California peninsula can be detected in central Baja California, the southern California deserts, and even as far north as the southern Arizona Sonoran Desert. Data will test whether dissipating cyclones were drivers of alluvial fan sedimentation over thousands of years, and if a temporal correlation can be established to a period of transition between a milder, humid paleoclimate to the current arid climate. For the first time, a tropical cyclone landfall chronology covering the last few millennia will be developed for the Pacific coast of southwestern North America. This research has the potential to inform large-storm prediction scenarios for southern California and northwestern Mexico, which is relevant to hazards management for communities in need of risk assessment of rare and extreme events. The project will contribute to the training of the next generation of earth scientists using a tiered approach, with field-based collaboration of postdoctoral fellows, graduate and undergraduate students. This approach has been proven successful for inclusion of underrepresented minorities, enhanced also with planned research alongside Mexican collaborators and students. The project will provide unique broader educational experiences for grade-school students in Indiana and Arizona, through the use of technology to connect fieldwork and classrooms.This project will compare a recently established alluvial fan chronology in southern Baja California, with newly-obtained alluvial fan and paleotempestological records. A Holocene paleotempestological record of overwash deposits in the Pacific coastal Vizcaino Desert will be developed for the first time. The inferred tropical storm activity will be compared with inland alluvial fan deposition in this area and in the northern Sonoran Desert, enabling discrimination of signals from different moisture sources, based on observed coastal and alluvial sedimentology, stratigraphy, and specific proxy records. Effects of different sources of moisture that drive sedimentation will be assessed by probing different time periods, and compared to independent paleoclimatic proxies. Bayesian analysis of luminescence, cosmogenic, and radiocarbon geochronology will improve age control precision. The coupled alluvial and coastal record at orbital timescales will help to understand linkages between Quaternary alluvial sedimentation and hydroclimatic variability in the region, and will increase our understanding of basic principles of alluvial fan aggradation in response to change in arid hydroclimates. The project will test effects of millennial- and orbital-scale shifts in tropical circulation on landscape evolution of the region, which are, in turn, critical to test models of occurrence and effects of hydrological extremes and associated landscape changing events.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.