SGER: Mobilization and Deposition of Organic Matter along the Louisiana Coast following Hurricane Katrina

飓风和大风暴在沿海海洋沉积物和有机质的运输和再分配中起着至关重要但往往不可预测的作用。之前对飓风Lili影响的研究，比卡特里娜飓风小得多，揭示了风暴路径以西的大陆架区域有大量的向海运输和细沉积物沉积。此外，在整个地区观测到与这些细沉积物相关的大量有机碳和氮的沉积，大大超过了该地区这些物质的长期积累。根据飓风莉莉之后的早期发现，考虑到其更大的震级和强度，卡特里娜飓风（约4米的风暴潮，135-160英里/小时的风速）可能在更大的区域内动员和重新分配了大量的沉积物和相关有机物。大部分离岸输送可能发生在风暴路径的西部地区，那里的风主要是离岸方向的。受影响的区域范围从较远的阿查法拉亚河水下三角洲到较近的密西西比河三角洲和相关峡谷。俄勒冈州立大学（Oregon State University）的研究人员将利用这项探索性研究小额赠款的资金收集样本，并对受卡特里娜飓风影响地区的海底沉积物进行分析，以评估其对路易斯安那州大陆架沿岸沉积物和有机物的动员和沉积的影响。提议的工作的直接目的是在风暴沉积物被侵蚀和混合之前，在它们保留其独特的化学特征（如短寿命同位素，有机碳含量）时对它们进行取样。在东卡罗莱纳大学和杜兰大学的同事的合作下，他的研究小组将在路易斯安那大陆架沿线的几个地点进行海底采样，这些地点之前已经进行了采样，并对沉积物积累速率和沉积有机质进行了表征。这些观测结果将提供基线信息，与卡特里娜飓风事件后收集的样本结果进行比较。俄勒冈州立大学的研究小组将分析在这些地点收集的沉积物，以确定风暴层中有机物的浓度和组成。有机物的化学分析（例如稳定同位素、放射性碳浓度、陆源和海洋生物标记物）将有助于确定有机物来源的特征，从而获得有关被动员物质最终来源的信息。这些结果将对如此大的风暴对该地区沉积学和生物地球化学的影响产生新的见解。具体来说，它将提供关于大风暴的作用的详细信息，作为一种机制，从陆架的近海地区向更近海地区输出陆源物质，如密西西比峡谷和推进的Atchafalaya水下三角洲斜地形。拟议工作的更广泛影响包括收集和分析在沿海系统中受到大飓风影响的海底样本，该系统具有完善的信息基线。与其他研究小组的合作将加强对此类随机事件期间沿海系统中沉积物和有机物循环的理解。该提案还将包括本科生参与工作的实地和实验室方面。

ABSTRACTOCE-0553090Hurricanes and large storms play a critical but often unpredictable role in the transport and redistribution of sediments and organic matter in the coastal ocean. Previous work on the effects of Hurricane Lili, a much smaller storm than Hurricane Katrina, revealed large seaward transport and deposition of fine sediments onto the shelf region west of the storm track. Furthermore, massive deposition of organic carbon and nitrogen associated with these fine sediments was observed throughout the region, vastly exceeding the long-term accumulation of these materials in this area. Based on earlier findings following Hurricane Lili and given its much larger magnitude and intensity, Hurricane Katrina (~ 4m storm surge, 135-160 mph winds) may have potentially mobilized and redistributed much larger amounts of sediment and associated organic matter over a much wider area. The majority of the offshore transport likely occurred in the western region of the storm track, where winds were predominantly in the offshore direction. The impacted area ranges from the more distal Atchafalaya River subaqueous delta to the more proximal Mississippi River delta and associated canyon. With funding from this Small Grant for Exploratory Research, investigators at the Oregon State University will collect samples and carry out analyses of seabed sediments from the region affected by Hurricane Katrina to evaluate its effects on the mobilization and deposition of sediment and organic matter along the Louisiana Shelf. The immediacy of the proposed work is to sample the storm deposits before they are eroded and mixed and while they retain their unique chemical (e.g. short-lived isotopes, organic carbon contents) characteristics. In cooperation with colleagues at East Carolina University and Tulane University, he research team will sample the seabed at several locations along the Louisiana Shelf that have been previously sampled and for which the sediment accumulation rates and sedimentary organic matter have been characterized. These observations will provide baseline information that will be compared to the findings from samples collected after the Katrina event. The Oregon State group will analyze the sediments collected at these sites to determine the concentration and composition of organic matter in the storm layer. The chemical analyses of the organic matter (e.g. stable isotopes, radiocarbon concentrations, terrigenous and marine biomarkers) will help characterize the sources of the organic matter, which will yield information on the ultimate source of the mobilized materials. These results will yield novel insights into the effects of such large storms on the sedimentology and biogeochemistry of this region. Specifically, it will provide detailed information on the role of large storms as a mechanism for the export of terrigenous materials from the inshore regions of the shelf to the more offshore regions, such as the Mississippi Canyon and the prograding Atchafalaya subaqueous-delta clinoform.The broader impacts of the proposed work include the collection and analyses of seabed samples impacted by a major hurricane in a coastal system that has a well-developed baseline of information. Collaboration with other research groups will enhance the understanding of sediment and organic matter cycling in coastal systems during such stochastic events. The proposal will also include involvement by undergraduate students in the field and laboratory aspects of the work.