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

本项目旨在测试两个地中海型地区（东地中海-中东（EMME）和美国西南部（SW USA））以及美国东南部一个湿润亚热带地区（SE USA）是否存在与生长季节相关的碳14补偿，如果确定，则量化其规模和古气候相关性。碳-14与许多古气候和相关领域的时间依赖性研究有关，也是古气候研究中心的一些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，在一年中不同时间生长的植物可能反映了这个季节性碳-14循环的不同部分，这似乎是合理的。这项研究有可能推动古气候、古生态学和考古学领域的知识。精确的年龄深度建模对于确定过去事件的时间至关重要，该研究将尝试通过调查植物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半球校准曲线的校准，来改进放射性碳年龄校准。直到最近，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对碳相关的定年产生重大影响，特别是在碳-14校准曲线的反转和平台期。潜在的更广泛的影响包括让康奈尔大学和佐治亚大学的本科生参与树木年代学研究，同时支持佐治亚大学的一位早期职业科学家。该项目还将资助一名博士生，他将为公众开发宣传材料。研究结果将在国际考古日期间发布，并通过纽约州伊萨卡市的“拓展视野”项目向中学生推广。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.