Doctoral Dissertation Research: Multiproxy Analysis of Tropical Cyclones and Climate Variability at Big Thicket National Preserve, Texas

因为树木是固定的有机体，它们依赖于周围的环境。树木将大气二氧化碳中的碳和土壤水分中的氧吸收到每年的木材(纤维素)层中。当使用已建立的树枝年代学技术准确地确定年轮的年代时，高分辨率的稳定同位素年表可以记录环境变化。这项博士论文研究项目将研究树木年轮稳定同位素(碳和氧)和树木年轮宽度与各种气候特性的关系，如干旱、温度、降水、热带气旋事件以及德克萨斯州大锡克特国家保护区的大规模海洋/大气振荡模式。树轮气候记录将使用取自活的长叶松树的小直径增量核心来编制。每个年轮的宽度和化学成分将被分析，以提供德克萨斯州墨西哥湾沿岸的气候变异性和热带气旋频率和变异性的记录。热带气旋(飓风)系统可以产生降雨，其化学信号与正常降雨不同。来自热带气旋事件的降雨应与现有土壤水取代或混合，并可能在土壤中停留长达六周。由于飓风对居住在美国东南部墨西哥湾和大西洋沿岸的许多人构成了威胁，从生物和化学记录中建立数百年的飓风记录的能力对于加强对这些事件在最近一段时间发生了怎样的变化以及了解未来可能发生的变化至关重要。一项用于描述美国东南部热带气旋事件和气候变异性的氧同位素研究，在同位素年表的任何部分只使用了一棵树，但由于几个原因，这种单木年表在解释区域气候方面可能存在问题。这项研究项目将试图通过解决几个可能的限制来克服这些问题。首先，树木用于光合作用的土壤水的化学(同位素)成分在整个林分中可能不是均匀的。其次，热带气旋事件特有的化学特征雨水的量可能不会均匀地取代林分上现有的土壤水分。最后，一棵树可能不能捕捉到足够多的共同气候信号来表征区域气候的影响。这个项目将通过分析单树同位素年表和多树年表来测试这些可能的限制。这些结果应该有助于描述林分土壤水分同位素组成中存在的变异性。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

Because trees are stationary organisms, they are dependent on their surrounding environment. Trees incorporate carbon from atmospheric carbon dioxide and oxygen from soil moisture into annual layers of wood (cellulose). When the annual rings are accurately dated using established dendrochronological techniques, high-resolution stable isotope chronologies can document environmental change. This doctoral dissertation research project will examine the relationships between tree-ring stable isotopes (carbon and oxygen) and tree-ring width with various climate properties, such as drought, temperature, precipitation, tropical cyclone events, and large-scale ocean/atmospheric oscillation patterns at Big Thicket National Preserve in Texas. Tree-ring climate records will be developed using small-diameter increment cores taken from living longleaf pine trees. The width and chemistry of each annual tree ring will be analyzed to provide a record of climate variability and tropical cyclone frequency and variability along the Texas Gulf Coast. Tropical cyclone (hurricane) systems can produce rainfall with a chemical signal distinct from that of normal rainfall. Rainfall from tropical cyclone events should replace or mix with existing soil waters and may remain in the soil for up to six weeks. Tree-ring cellulose therefore can be used to identify both modern and past hurricane events.Because hurricanes pose a threat to many people living along the Gulf and Atlantic coasts of the southeastern United States, the capability to build centuries-long hurricane records from biological and chemical records is crucial to enhance understanding about how these events have changed through recent times, as well as for understanding the possible changes that could occur in the future. One oxygen isotope study used to characterize tropical cyclone events and climate variability in the southeastern U.S. used only one tree for any portion of the isotope chronology, but such single-tree chronologies may be problematic for interpreting regional climate for several reasons. This research project will attempt to overcome these problems by addressing several possible limitations. First, the chemical (isotopic) composition of soil water being used by trees for photosynthesis may not be homogeneous across an entire stand. Second, the amount of chemically distinctive rainwater characteristic of tropical cyclone events may not uniformly replace the existing soil moisture evenly across a stand. Finally, a single tree may not be capable of capturing enough of the common climate signal to characterize the effects of regional climate. This project will test these possible limitations by analyzing single-tree isotope chronologies versus multiple-tree chronologies. The results should help characterizing the variability that exists in the isotopic composition of soil moisture in a stand. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.