SGER - Carbon cycle processes affected by ENSO and transitional SOI conditions: Development of a new geologic tool for using speleothems as a proxy for carbon cycle dynamics

碳循环过程受ENSO和过渡性SOI条件的影响：开发一种新的地质工具，利用洞穴沉积物作为碳循环动力学的替代物，利用高分辨率微取样技术对伯利兹的洞穴沉积物进行稳定同位素分析，我们发现石笋d13 C值在年际到亚季节时间尺度上存在较大波动。这些结果揭示了d13 C值与最近的厄尔尼诺事件之间存在非常强的相关性。由于该地区在厄尔尼诺和拉尼娜期间没有出现重大的天气异常，因此发现这种关系令人困惑。d13 C值的石笋可能反映了覆盖森林生态系统碳收支的变化，这些变化对ENSO相关的当地天气的微妙变化很敏感。初步研究表明，石笋d13 C的变化反映了重要的生态系统过程，如土壤pCO 2和/或土壤-大气CO2通量的变化。因此，洞穴沉积物可以被用作探索碳循环动力学及其对环境条件的响应的工具。我们发现SOI与C同位素地质记录的相关性提出了许多问题。这一记录是否揭示了ENSO通过其对陆地生态地球化学系统的影响而引起的全球碳循环年际变化的一个新来源？厄尔尼诺现象是否对生态系统产生了压力，这反映在同位素分馏上？分馏差异的来源是在植被中，在土壤中，还是在地下水中？生态系统中的哪些过程放大了与ENSO有关的环境变化的幅度，并导致这些变化通过地下水传播并记录在石笋中？因此，该SGER项目的具体目标是在SOI的中性阶段捕获植被，凋落物，土壤气体/水分，地下水和洞穴滴水的碳同位素组成，以补充在最近的厄尔尼诺期间已经收集的样本。比较厄尔尼诺现象和过渡时期样本的碳同位素分析，以确定同位素分馏差异的位置（例如植被、土壤呼吸等）。这个SGER项目将用于捕捉预计在2003年夏季发生的厄尔尼诺和拉尼娜现象之间的短暂过渡。因此，它具有时间敏感性，因为下一次通过中立条件的过渡要几年时间才能实现。我们将从环境空气、植被、落叶、土壤、土壤气体和水、地下水、雨水、洞穴空气和滴水中收集样本。土壤和植被样本已获得必要的美国进口许可证。该项目的结果将提供一个中性基线，使我们能够探索洞穴碳地球化学系统如何响应ENSO事件，并确定地质记录中保存的ENSO信号的地球化学机制。最终，这个拟议的项目将为陆地生态系统、天气、碳循环和地质记录之间的关系提供新的见解。

ABSTRACTSGER - Carbon cycle processes affected by ENSO and transitional SOI conditions:Development of a new geologic tool for using speleothems as a proxy for carbon cycledynamics.Using high-resolution microsampling techniques for stable isotope analysis of speleothems from Belize, we found large fluctuations in stalagmite d13C values at inter-annual to sub-seasonal time scales. These results reveal a remarkably strong correlation between d13C values and recent El NiNo events. Discovery of this relation is puzzling in light of the absence of significant weather anomalies during El NiNo and La NiNa intervals for this area. d13C values of this stalagmite likely reflect changes in the overlying forest ecosystem carbon budget that are sensitive to subtle modifications of local weather related to ENSO. Preliminary work suggests that the stalagmite d13C variations reflect changes in important ecosystem processes such as soil pCO2 and/or soil-atmospheric CO2 flux. As such, speleothems may be used as a tool for exploring carbon cycle dynamics and their response to environmental conditions.Our discovery of the correlation of SOI and the geologic record of C isotopes raises anumber of questions. Does this record reveal a new source of interannual variability in the global carbon cycle due to ENSO through its effects on terrestrial biogeochemical systems? Does El NiNo produce a stress on the ecosystem that is reflected in isotopic fractionation? Is the source of the fractionation difference in the vegetation, in the soil, or in the groundwater? What process(es) within the ecosystem serve to amplify the magnitude of ENSO-related environmental changes and leads to their being transmitted by groundwater and recorded in stalagmites? Consequently, the specific objectives of this SGER project are to capture carbon isotopic composition of vegetation, litter, soil gas/moisture, ground water, and cave drip water during a neutral phase of SOI, to complement the samples already collected during the recent El NiNo. Compare the carbon isotopic analyses of El NiNo and transitional samples to constrain location of differences in isotopic fractionation (e.g. vegetation, soil respiration, etc.). This SGER project will serve to capture the brief transition between El NiNo and La NiNa conditions that is expected to occur during the summer of 2003. As such it is time-sensitive, as the next transition through neutral conditions will not occur for several years. We will collect samples from ambient air, vegetation, leaf litter, soil, soil gas and water, groundwater, rainwater, cave air, and drip water. U.S. import permits have been obtained as necessary for soil and vegetation samples. Results from this project will provide a neutral baseline that will enable us to explore how the cave carbon biogeochemical system responds to ENSO events and identify the biogeochemical mechanisms responsible for the ENSO signal preserved in the geologic record. Ultimately this proposed project will provide the basis for new insights into the relationships between terrestrial ecosystems, weather, the carbon cycle, and the geological record.