Collaborative Research: RAPID--Characterizing the Water Isotope Signature of an El Nino Event for Paleoclimate and Hydroclimate Studies

该项目在快速响应研究（Rapid）计划的支持下获得资金，利用厄尔尼诺Niño/南方涛动（ENSO）对2023-2024水年的强到非常强的预测，建立降水和溪流采样站的纵向阵列，以约束强ENSO事件的大气水δ氧18、氘过量和δ氧17信号。研究人员将在一年的时间里每月采集降水和溪水样本，并分析这些样本中的氧和氢同位素。他们还将在2023年秋季和2024年春季收集同一纵向样带上的小溪流水的现场样本，并使用混合单粒子拉格朗日综合轨迹（HYSPLIT）模型模拟降水的来源和途径，同时使用空间统计数据生成我们在美国西南部的稳定同位素结果的等高线。这项研究的前提是，考虑到ENSO在改变美国西南部冬季水文气候方面发挥着巨大的作用，关于美国西南部干旱和半干旱地区的水文气候（包括降水、蒸散和径流）将如何对二氧化碳上升和气温升高做出反应，仍然存在很大的不确定性。利用全球气候模式（GCM）对未来气候的预测和古气候记录，研究ENSO将如何随着变暖而变化，这些研究提供了大量数据，但这些数据缺乏约束。美国西南部水文气候的许多古气候证据及其与ENSO的联系来自过去的大气水氧同位素的代用记录，典型的假设是，较低的代用δ氧-18对应于较大的冬季湿度和向ENSO条件的转变。因此，测试美国西部水文气候对变暖的敏感性及其与ENSO之间联系的能力依赖于限制ENSO与整个美国西部的大气水三角洲氧-18之间的关系。然而，这种因果关系对于未来可能主导气候的强ENSO事件尚未得到证实。此外，目前还没有关于ENSO如何改变δ氧-17值的数据，而δ氧-17值正在成为一种有前景的分析同位素工具，用于限制古气候中碳酸盐和粘土同位素档案中湿源动力学和蒸发效应的作用。潜在的更广泛的影响包括支持两名研究生，并提供一个长期监测数据集，以改进过去ENSO事件的强度和频率的重建，这将有助于限制在该地区观测到的未来预测所需的变率范围。这项研究很好地适应了RAPID项目潜在的变革性、高风险和快速反应的研究要求。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 secures funds under the auspices of the Rapid Response Research (RAPID) program to take advantage of the strong-to-very strong El Niño/Southern Oscillation (ENSO) forecast for the water year 2023-2024 to establish a longitudinal array of precipitation and stream sampling stations to constrain the meteoric water delta oxygen-18, deuterium-excess, and delta oxygen-17 signal of a strong ENSO event. The researchers will sample precipitation and stream water monthly over the course of a year and analyze these samples for oxygen and hydrogen isotopes. They will also collect spot samples of small-stream waters across this same longitudinal transect during Fall 2023 and Spring 2024 and simulate the source and pathways of precipitation using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model while using spatial statistics to produce isoscapes of our stable isotope result across the southwestern United States (U.S.).This research is premised on the idea that substantial uncertainty remains regarding how hydroclimate (including precipitation, evapotranspiration and runoff) in the arid and semi-arid southwestern U.S. will respond to rising carbon dioxide and warmer temperatures considering that ENSO plays an outsize role in modifying wintertime southwestern U.S. hydroclimate. There is a large body of data from research that examines how ENSO will change in response to warming, utilizing both Global Climate Model (GCM) projections of future climate and paleoclimate records but these data are poorly constrained. Much of the paleoclimate evidence of southwestern U.S. hydroclimate and its links to the ENSO comes from proxy records of past meteoric water oxygen isotopes, with the typical assumption that lower proxy delta oxygen-18 corresponds with greater wintertime moisture and a shift towards ENSO conditions. Consequently, the ability to test the sensitivity of western U.S. hydroclimate to warming and its links with ENSO relies upon constraining the relationship between the ENSO and meteoric water delta oxygen-18 across the western U.S. This causal link, however, is not well-established for strong ENSO events that may dominate climate in the future. Furthermore, there is currently no data to understand how ENSO modifies delta oxygen-17 values, which is emerging as a promising analytical isotopic tool to constrain the role of moisture source dynamics and evaporative effects in carbonate and clay isotope archives of paleoclimate.The potential broader impacts include supporting two graduate students and providing a long-term monitoring dataset for improving reconstructions of the strength and frequency of ENSO events in the past which will help constrain the range of variability observed in the region necessary for future forecasts. The research fits well into the potentially transformative, high risk, and quick-response research imperative of the RAPID program.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.