Intra-Annual Radiocarbon (14C) Offsets, Chronology and Paleoclimate

该项目的具体目标是测试两个地中海型地区（包括东地中海-中东（EMME）和美国西南部（SW USA））以及美国东南部（SE USA）的一个潮湿亚热带地区是否存在与生长季节相关的小碳-14抵消，如果确定，量化它们的规模和古气候相关性。碳-14与古气候和相关领域的许多时间依赖性研究有关，也是古气候研究中许多碳循环模型的关键示踪剂。最近的研究揭示了大气中碳-14的明显季节性循环。通过高精度的测量，植物在一年中不同的时间生长可能反映了季节性碳14循环的不同部分。这项研究有可能在古气候学、古生态学和考古学领域推进知识。精确的年龄-深度模型对于确定过去事件的时间至关重要，该研究将试图通过调查植物每年放射性碳吸收的季节性物候差异的潜在影响以及这些偏差如何影响基于广泛使用但空间偏差的北方半球校准曲线的校准来改善放射性碳年龄校准。分析精度排除了探索这种差异，因为它们低于测量检测，但分析测量的进步现在使这种调查成为可能。虽然很小，但这些分析差异可能会对碳相关测年产生重大影响，特别是在碳-14校准曲线的逆转和平台期。潜在的更广泛的影响包括在康奈尔大学和格鲁吉亚大学的树木年代学研究涉及本科生，同时也支持在格鲁吉亚的早期职业科学家。该项目还将支持一名博士生，他将为公众编写宣传材料。研究成果将在国际考古日期间分发，并通过纽约伊萨卡的“拓展你的视野”（EYH）计划向中学生推广。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

This project specifically aims to test whether small growing-season-related Carbon-14 offsets exist for two Mediterranean-type areas comprised of the East Mediterranean-Middle East (EMME) and the Southwest United States (SW USA), as well as one humid sub-tropical area Southeast United States (SE USA), and, if identified, quantify their scale and paleoclimate relevance.Carbon-14 is relevant to many temporally-dependent investigations in paleoclimate and related fields, as well as a key tracer for a number of carbon-cycle models central to paleoclimate research. Recent studies have revealed a distinct seasonal cycle in atmospheric Carbon-14. With high-precision measurement it seems plausible that plants growing at substantially different times of the year may reflect different portions of this seasonal Carbon-14 cycle. This research has the potential to advance knowledge in the fields of paleoclimate, paleoecology, and archaeology. Precise age-depth modelling is critical to establishing the timing of past events, and the research will attempt to improve radiocarbon age calibration by investigating the potential impacts of seasonal phenological differences in annual radiocarbon uptake by plants and how those biases may impact calibration based on widely used but spatially-biased northern hemisphere calibration curve.Until recently, analytical precision precluded exploring such differences since they were below measurement detection but advances in analytical measurements now make this inquiry possible. Although small, these analytical differences could have significant effects on carbon-related dating, especially at times of reversals and plateaus in the Carbon-14 calibration curve. The potential Broader Impacts include involving undergraduates in dendrochronology research at both Cornell University and the University of Georgia while also supporting an early career scientist at Georgia. The project would also support a PhD student who will develop outreach materials for the public. Research results will be distributed during International Archaeology Day and outreach to middle school students through the Expanding Your Horizons (EYH) program in Ithaca, New York.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.