Collaborative Research: Late Quaternary Paleoenvironments of Cuatro Cienegas, Mexico, a Hotspot of Endemism in North America

湖泊和湿地的沉积物保存了过去2万年来地球气候、植被和生态动态变化的重要证据。在这个项目中，研究人员将研究沉积档案，以记录墨西哥北部奇瓦瓦沙漠Cuatro ci<s:1>内加斯山谷的生态和环境历史。Cuatro cisamnegas拥有独特的沙漠泉水系统，是北美特有物种最集中的地方，可以与加拉帕戈斯群岛相提并论。Cuatro ci<s:1>内加斯生物群的高度地方性被解释为该山谷长期与世隔绝和环境稳定的结果。20世纪70年代分析的沉积物芯的花粉记录最初被解释为支持这一假设，但最近对原始记录的重新评估，以及来自附近背包鼠中心的新花粉数据，挑战了山谷内长期环境稳定的假设。旧记录的一个复杂之处在于大块沉积物的早期放射性碳年代的不确定性。该研究项目将利用两个新的沉积物岩心，其中包含适合AMS测年的大型化石，以及丰富的花粉和木炭，这将提供植被和火灾历史的信息。研究人员将通过记录Cuatro ci<s:1>内加斯山谷过去的环境条件，用可靠的年代测定和更高的分辨率来测试Cuatro ci<s:1>内加斯山谷长期稳定的假设。这些岩心是2008年从Privada Pozas Azules保护区的湿地中恢复的，该保护区包含大量处于不同演替阶段的天坑池塘（Pozas）。从Poza Cortador的12.3米剖面跨越了14000多年，显示了从深水Poza到具有新兴湿地植被的沼泽的演替证据。附近Poza Tule的剖面覆盖了近5000年。适合花粉保存的连续沉积环境在北美干旱地区极为罕见。所分析的沉积物记录将为奇瓦瓦沙漠的晚冰期和全新世条件提供重要证据，并为了解北美冰川地区以外的环境变化提供见解。Cuatro ciacimnegas山谷已成为研究生物地理学、生态学和进化等基础问题的天然实验室，而这项长期历史研究将增加这个天然实验室的价值。该研究项目的结果将为古气候学和生物地理学提供信息，并将为许多物种形成、共同进化、微生物进化和天体生物学的研究提供关键的背景，这些研究集中在Cuatro cisamugas山谷的独特物种和物种组合上。项目成果还将为管理、保护和恢复瓜阿特罗·奇萨内加斯自然资源和地方性生物多样性的持续努力提供信息。该研究项目将为一些研究生和本科生提供教育机会，并为K-12学生和项目外展服务的其他人提供教育机会。本项目由地理与空间科学项目和人口与社区生态项目共同支持。

Sediments in lakes and wetlands preserve important evidence of changes in Earth's climate, vegetation, and ecological dynamics over the past 20,000 years. In this project, researchers will study sedimentary archives to document the ecological and environmental history of the Cuatro Ciénegas valley in the Chihuahuan desert of northern Mexico. Cuatro Ciénegas is home to a unique desert spring system that supports North America's highest concentration of endemic species, garnering comparisons to the Galapagos Islands. The high endemism of the Cuatro Ciénegas biota has been explained as a consequence of long-term isolation and environmental stability in the valley. A pollen record from a sediment core analyzed in the 1970s was originally interpreted as supporting this hypothesis, but recent reevaluation of the original record, along with new pollen data from a nearby packrat midden, challenged the assumption of long-term environmental stability within the valley. A complication with the old record is uncertainty over early radiocarbon dates on bulk sediment. This research project will make use of two new sediment cores that contain macrofossils suitable for AMS dating along with abundant pollen and charcoal that will provide information on both vegetation and fire history. The researchers will test the hypothesis of long-term stability in the Cuatro Ciénegas valley by documenting, with secure dating and at higher resolution, past environmental conditions in Cuatro Ciénegas. The cores were recovered in 2008 from wetlands in the Reserva Privada Pozas Azules, which contains a large assemblage of sinkhole ponds, or pozas, in various stages of succession. The 12.3 m profile from Poza Cortador spans over 14,000 years and shows evidence of succession from a deep-water poza to a marsh with emergent wetland vegetation. A profile from nearby Poza Tule covers the last c. 5000 years. Continuous depositional environments suitable for pollen preservation are exceptionally rare in the arid regions of North America. The sediment records to be analyzed will provide important evidence of Late Glacial and Holocene conditions in the Chihuahuan Desert and provide insight into the environmental changes that occurred outside of glaciated regions of North America. The Cuatro Ciénegas valley has become a natural laboratory for studying fundamental issues in biogeography, ecology, and evolution, and this research on long-term history will increase the value of this natural laboratory. The results of the research project will inform paleoclimatology and biogeography, and will provide crucial context for the many studies of speciation, coevolution, microbial evolution and astrobiology that focus on the unique species and species assemblages of the Cuatro Ciénegas valley. Project results will also inform ongoing efforts to manage, conserve, and restore the natural resources and endemic biodiversity of Cuatro Ciénegas. The research project will provide educational opportunities for several graduate and undergraduate students, and for K-12 students and others served by project outreach. This project is jointly supported by the Geography and Spatial Sciences Program and the Population and Community Ecology Program.