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

该项目在快速反应研究(RAPID)计划的支持下获得资金，以利用2023-2024年水年强到极强的厄尔尼诺/南方涛动(ENSO)预测，建立降水和溪流采样站的纵向阵列，以限制强ENSO事件的大气水增量氧-18、氚过剩和增量氧-17信号。研究人员将在一年的时间里每月对降水和溪水进行采样，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断面上的小河流水域的现场样本，并使用混合单粒子拉格朗日积分轨迹(HYSPLIT)模型模拟降水的来源和路径，同时使用空间统计方法生成美国西南部(美国)稳定同位素结果的等值线。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的巨大作用，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)将如何应对二氧化碳上升和气温上升仍存在很大的不确定性。有大量的研究数据研究了ENSO将如何随变暖而变化，使用了全球气候模型(GCM)对未来气候的预测和古气候记录，但这些数据缺乏约束。美国西南部水文气候及其与ENSO的联系的大部分古气候证据来自过去大气水氧同位素的替代记录，典型的假设是，较低的Delta O2-18对应于更多的冬季水分和向ENSO条件的转变。因此，测试美国西部水气候对变暖的敏感性及其与ENSO的联系的能力取决于限制ENSO与整个美国西部大气水增量OO18之间的关系。然而，这种因果联系对于可能主导未来气候的强ENSO事件并不成立。此外，目前还没有数据来了解ENSO如何修改氧-17值，这是一种很有希望的分析同位素工具，可以限制碳酸盐和粘土同位素档案中的水汽来源动态和蒸发效应的作用。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事件强度和频率的重建，这将有助于限制在未来预测所需的区域观察到的可变性范围。这项研究非常符合快速计划潜在的变革性、高风险和快速反应的研究需求。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.