Study of Seasonal Radiocarbon Variability in the Eastern Tropical Pacific During Periods of Decadal and Interannual Climate Shifts

在这个项目中，加州大学欧文分校（University of California at Irvine）的研究人员将确定过去400年不同气候时期热带太平洋东部表面放射性碳的详细变化。研究人员期望这些研究将有助于我们理解气候的自然变化如何影响海洋吸收化石燃料和生物质燃烧产生的过量二氧化碳的能力。将对位于厄尔尼诺“活动中心”的热带太平洋东部的季节性珊瑚带进行高精度AMS（加速器质谱）14C测量，以确定来自南太平洋的源水（可能是亚南极模态水）的低14C成分的变率。将测试三个假设：1)加拉帕戈斯群岛珊瑚的冬季14C值是PDO阶段的一个指标；(2)在17世纪初和19世纪初，热带东部太平洋冬季出现了长时间的上升流，这可能是由于亚南极模态水长时间被带入赤道下流造成的；3)加拉帕戈斯群岛冬季14C值揭示了气候的年际-年代际变化。为了验证这些假设，将进行以下研究：1)与斯坦福大学的同事合作，将在加拉帕戈斯群岛1900-1996年生长的珊瑚带中测量季节性14C，以确定在已知PDO处于负值阶段（1915-1925年和1945-1955年）的记录期间，冬季14C是否显着降低。将进行一项校正实验，以证明本研究中使用的珊瑚物种确实记录了整个季节信号。2)将对1598-1611年和1804-1825年生长的珊瑚带进行季节性14C和18O测量，以确定在这些不寻常的气候时期，冬季14C是否显著降低和/或持续时间更长。3)季节的14C测量将在显示明显的气候年际变化（ENSO）和以明显的年代际变化为主的时间段的珊瑚带进行。他计划与普林斯顿大学的同事合作，在他的海洋环流模拟实验中利用季节14C记录来计算赤道太平洋过去二氧化碳分压和二氧化碳排放通量的变异性。就更广泛的影响而言，该项目将支持一名研究生和两名本科生的工作，并提供实践经验，为他们成为科学家和教育工作者做好准备。PI参与与初中和高中青年一起开展外展活动。她也是佛罗里达海洋科学教育卓越中心（FCOSEE）的顾问委员会成员，协助开发大学水平的网络教育课程，并参与每年夏天的放射性碳和碳循环短期课程的教学。

In this project, investigators at the University of California at Irvine will determine the detailed changes of radiocarbon in the surface of the eastern tropical Pacific during distinctive climatic periods in the past 400 years. The researchers expect that these studies will aid in our understanding of how natural variability in climate can influence the ability of the ocean to absorb excess CO2 produced from fossil fuel and biomass burning. High-precision AMS (accelerator mass spectrometry) 14C measurements on seasonal coral bands from the eastern tropical Pacific, located in the "center of action" with respect to El Nino, will be made to determine the variability of the low 14C component of the source waters (presumably Sub-Antarctic Mode Water) from the South Pacific. Three hypotheses will be tested: 1) Wintertime 14C values in Galapagos corals are an indicator for the phase of the PDO; 2) Prolonged periods of winter-time upwelling were present at in the eastern tropical Pacific during the early 1600s and early 1800s, which were likely caused by prolonged entrainment of Sub-Antarctic Mode Water into the Equatorial Under Current; and 3) Wintertime 14C values at Galapagos reveal interannual-to-decadal variability in climate.To test these hypotheses, the following studies will be done: 1) Seasonal 14C and, in collaboration with colleagues at Stanford University, 18O will be measured in Galapagos coral bands that grew from 1900-1996 to determine if the winter-time 14C was significantly lower during recorded periods when the PDO was known to have been in a negative phase (1915-1925 and 1945-1955). A calibration experiment will be performed to demonstrate that the coral species used in this study is indeed recording the entire seasonal signal. 2) Seasonal 14C and 18O measurements of coral bands that grew from 1598-1611 and from 1804-1825 will be made to determine if the winter-time 14C was significantly lower and/or persisted for a longer period of time during these unusual climatic periods. 3) Seasonal 14C measurements will be made of coral bands from time periods that display clear interannual variability in climate (ENSO) and those that are dominated by distinct decadal variability. Collaboration with colleagues at Princeton University is planned to utilize the seasonal 14C records in his ocean circulation modeling experiments designed to calculate variability of past pCO2 and CO2 out-gassing fluxes in the equatorial Pacific.In terms of broader impacts, the project will support the work of one graduate student and two undergraduate students and provide hands-on experience that will prepare them for careers as scientists and educators. The PI is involved with developing outreach activities in conjunction with middle and high school youths. She is also on the advisory board for FCOSEE (Florida Center for Ocean Science Education Excellence COSEE) to assist in developing web-based educational classes at the college level, and participates in teaching a short course on Radiocarbon and the Carbon Cycle every summer.