RUI: SG: Field and Laboratory Tests of Pyrogenic Organic Compounds in Australian Stalagmites as a Novel, High-Resolution Paleofire Proxy

2019-2020年澳大利亚许多地区发生的大火是全球趋势的一部分。气温上升，在某些情况下，加上长期的干旱和灭火努力，创造了有利于异常强烈和广泛的火灾的条件，包括美国西部的许多地区。虽然在本世纪是罕见的，但目前还不清楚这种火灾活动在地球长期历史上有多不寻常。为了更好地将现代火灾活动置于更长期的背景下，有必要对卫星时代(1979年至今)之前发生的燃烧进行重建。古代火灾的记录来自树木年轮上的烧伤伤疤，来自湖泊沉积物中的木炭，以及沉积在冰川冰上和储存在冰川中的火灾衍生化合物。在热带的澳大利亚西北部，无法恢复这样的数据。该项目的目标是开发从该地区洞穴中的石笋中回收火灾衍生化合物的方法。这些结果有望使人们更清楚地了解石笋作为过去燃烧的一种新记录的效用，并允许将其应用于其他容易起火的地区，包括美国西部。该项目还将为本科生提供培训机会。火在热带生态中起着至关重要的作用，但现在的燃料负荷、点火来源和背景气候条件往往与一个世纪前或更多年前有明显不同。由于高分辨率、长期记录的火灾频率和强度远远超出仪器时代，处理火灾制度正在变化的程度变得复杂。在欧洲牧民到来之前以及在与现代不同的气候时期(如小冰期：1450-1850)，了解火灾活动的频率和强度，对于管理当前的火灾、估计火灾对动植物多样性的级联影响以及维持生态系统的复原力至关重要。这项研究旨在提炼一种能够解决这些限制的新型古火替代品：石笋中的热解有机化合物(包括多环芳烃，PAHs)。PI及其合作者之前的研究表明，来自澳大利亚热带洞穴的石笋保存了随着时间的推移，热源化合物的类型和丰度的变化，这些变化与最近洞穴附近的火灾活动一致。燃烧生物质产生多环芳烃，然后通过季风雨将其输送到下面的洞穴中，并在滴水结晶时并入石笋中。虽然这些结果非常有希望，但在这种方法能够更广泛地应用之前，还需要进一步仔细研究洞穴系统的生化和水文机制。为此，PI和合作者将进行实地和实验室实验：(I)在规定的洞穴遗址燃烧之前、之后和一年后测量土壤和洞穴滴水中的有机化合物，如多环芳烃，(Ii)在同时代的石笋样本中复制热源有机化合物的分布，以及(Iii)将20世纪石笋中的古火灾信号与遥感数据和来自历史文献的火灾记录进行比较。这项工作还将为康奈尔学院的几名本科生提供野外和实验室方法方面的培训，这是推进他们作为科学家职业生涯的关键一步。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The massive fires that burned across many parts of Australia in 2019-2020 are part of a global trend. Rising temperatures, coupled in some cases with prolonged droughts and fire suppression efforts, have created conditions conducive to unusually intense and widespread fires, including across many parts of the western United States. While exceptional for the century, it is unclear how unusual this fire activity is over long-term Earth history. In order to better place modern fire activity into a longer-term context, it is necessary to develop reconstructions of burning that occurred prior to the satellite era (1979-present). Records of ancient fire have been developed from burn scars on tree rings, from charcoal in lake sediments, and from fire-derived compounds deposited on and stored in glacial ice. In tropical Northwest Australia, it is not possible to recover such data. The goal of this project is to develop methods to recover fire-derived compounds from stalagmites in caves in that region. Results are expected to provide a clearer understanding of the utility of stalagmites as a novel record of past burning, and allow its application to other fire-prone regions, including the western United States. The project will also provide opportunities for undergraduate student training.Fire plays a critical role in the ecology of the tropics, but fuel loads, sources of ignition, and background climate conditions are often markedly different now than they were a century or more ago. Addressing the extent to which fire regimes are changing is complicated by the sparsity of high-resolution, long-term records of fire frequency and intensity spanning far beyond the instrumental era. Understanding the frequency and intensity of fire activity prior to the arrival of European pastoralists and during intervals of climate distinct from the modern era (e.g, the Little Ice Age: CE 1450- 1850) is critically important for managing current fires, estimating cascading effects of fires on plant and animal diversity, and maintaining ecosystem resiliency. This study aims to refine a novel paleofire proxy capable of addressing these limitations: pyrogenic organic compounds (including polycyclic aromatic hydrocarbons, PAHs) in stalagmites. Previous research by the PI and collaborators has revealed that stalagmites from a tropical Australian cave preserve changes in the type and abundance of pyrogenic compounds over time, with these shifts consistent with recent fire activity proximal to the cave. Burning of biomass produces PAHs, which are then transported into the underlying cave by monsoon rains, and incorporated into stalagmites as they crystallize from dripwater. While these results are extremely promising, the biochemical and hydrological mechanics of the cave system need to be further scrutinized before this method can be applied more widely. Toward that end, the PI and collaborators will perform field and laboratory experiments: (i) measurements of organic compounds such as PAHs in soil and cave dripwater prior to, immediately following, and a year after a prescribed burn over the cave site, (ii) replication of pyrogenic organic compound distributions in a coeval stalagmite sample, and (iii) comparison of the paleofire signals in a 20th century stalagmite to remote sensing data and records of fire derived from historical documents. This work will also provide training to several undergraduates at Cornell College in field and laboratory methods, a critical step in advancing their careers as scientists.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.