ESH: Response of Extreme Hydrologic Events to Climate Change: Upper Mississippi River

9807715 Knox本研究的总体目标是系统地汇编和分析高质量的冲积地层数据，以确定密西西比河上游主干河谷对全新世（冰后期）气候变化的陆地水文响应。 具体目标包括：1. 定量记录与区域全新世气候事件相关的密西西比河上游岛屿堤坝和沼泽环境中记录的大洪水和极端洪水的重现频率;2. 定量记录与区域全新世气候事件相关的密西西比河上游支流河口滞水环境中记录的大洪水和极端洪水的重现频率; 定量记录现代记录的大洪水和极端洪水的复发频率，（历史）岛屿堤坝和后沼泽以及密西西比河上游支流河口滞水环境的冲积沉积物。独特的地层档案是可用的，因为密西西比河上游经历了整个全新世的持续逐渐加积，在末次冰期和之后不久，冰川湖排水在该地区的进步造成了晚更新世（晚冰期）冲积层的深深的战壕。 从那时起，支流沉积物的重新流动逐渐填满了密西西比河上游的主要河谷。 这里提出的研究是一个长期的研究计划的主要研究人员调查水文地貌对气候变化的反应在密西西比河流域上游的一个关键组成部分。 然而，我以前的研究主要集中在密西西比河上游的小型支流系统上。 早期的研究表明，洪水水文和沉积物的流动性和存储在5-200平方公里的流域面积的小支流强烈响应，即使是很小的气候变化。 这些变化通常涉及空气质量和风暴路径边界调整，这些调整与年平均温度1-2 ℃的变化和年平均降水量不超过10- 20%的变化有关。 因为造成小流域洪水的物理过程（5-200 km 2）不一定与非常大的密西西比河上游流域相同（100，000 - 300，000平方公里），本研究还将研究流域尺度转移如何影响降雨，融雪，研究方法包括野外、实验室和定量分析三个阶段。 野外工作的主要组成部分包括从河漫滩冲积地点和支流河口的静水沉积地点提取连续岩心。 在大多数情况下，将对沉积物芯样进行详细的沉积学和地球化学分析，取样间隔为1厘米或更短。 将进行统计分析，以研究历史记录的洪水和气候数据之间的关系，与地质记录的气候/洪水的关系进行比较的UMR.The拟议的研究直接有助于提高陆地地球系统科学的理解，强调水文系统，以及它是如何受到古气候变化的影响。 这项研究将提供一个高质量的物理古记录，重点是气候和极端水文事件之间的联系，特别是涉及大型河流系统的大洪水系统的系统汇编。 从拟议的研究结果，预计将提供一个系统的评估，如何在过去的全新世古气候和古气候事件之间的突然过渡的幅度和重现频率的极端洪水在密西西比河上游的行为。 这一信息在考虑海洋和大气环流系统“突然翻转”的后果时应该是非常有用的。

9807715KnoxThe general objective of this research involves the systematic compilation and analysis of high quality alluvial stratigraphic data to determine the terrestrial hydrologic responses to Holocene (post-glacial) climatic changes in the mainstem upper Mississippi River valley. Specific objectives include:1. to quantitatively document recurrence frequencies of large and extreme floods recorded in upper Mississippi River island levee and backswamp environments in association with regional Holocene climatic episodes;2. to quantitatively document recurrence frequencies of large and extreme floods recorded in upper Mississippi River tributary mouth slackwater environments in association with regional Holocene climatic episodes; and,3. to quantitatively document recurrence frequencies of large and extreme floods recorded in modern (historical) alluvial sediments for island levees and backswamps and for tributary mouth slackwater environments of the upper Mississippi River.The unique stratigraphic archive is available because the upper Mississippi River has experienced ongoing gradual aggradation throughout the Holocene following an episode when drainage of glacial lakes at and soon after the last glacial advance in the region caused deep entrenchment of late Pleistocene (late glacial age) alluvium. Since then, remobilization of sediment from tributaries has been gradually refilling the main valley of the upper Mississippi River. The research proposed here is a key component of a long-term research program by the principal investigator to investigate hydrogeomorphic responses to climatic change in the upper Mississippi River valley. My previous research, however, has focused on small tributary systems of the upper Mississippi River. The earlier research showed that flood hydrology and sediment mobility and storage in small tributaries of 5-200 km2 drainage area were strongly responsive to even small climate changes. Those changes typically involved air mass and storm track boundary adjustments that were associated with changes of mean annual temperature of 1-2 C and changes of mean annual precipitation of not greater than 10-20%. Because the physical processes responsible for floods on small watersheds (5-200 km2) are not necessarily the same as for the very large upper Mississippi River watershed (100,000 - 300,000 km2), the present research will also examine how watershed scale transfer affects the sensitivity of rain, snowmelt, and combined rain and snowmelt floods to climate change.The methodology for the research involves field, laboratory, and quantitative analyses phases. The major component of fieldwork involves the extraction of continuous cores from floodplain alluvial sites and from slackwater sedimentary sites in tributary mouths. Detailed sedimentological and geochemical analyses will be applied to sediment cores at sampling intervals of 1 cm or less in most situations. Statistical analyses will be undertaken to study relationships between historically recorded flood and climatic data for comparison with the geologic record of climate/flood relationships on the UMR.The proposed research contributes directly to improved understanding of terrestrial Earth system science emphasizing the hydrologic system and how it has been influenced by paleoclimate variability. The research will provide a systematic compilation of a high quality physical paleorecord that focuses on the linkage between climate and extreme hydrologic events, especially involving large floods on a large river system. Results from the proposed research are expected to provide a systematic evaluation of how magnitudes and recurrence frequencies of extreme floods on the upper Mississippi River behaved within past Holocene paleoclimates and during what appear to be abrupt transitions between paleoclimate episodes. This information should prove quite useful in contemplating the consequences of "abrupt flips" in circulation systems of the ocean and atmosphere.