New Perspectives on Paleo-ENSO Conditions in Coastal Peru as Seen Through Short-Lived Bivalves

厄尔尼诺和拉尼娜事件统称为厄尔尼诺-南方涛动(ENSO)，是影响世界各地人们的气候和环境年际变化的最大来源。例如，厄尔尼诺现象在澳大利亚和东南亚造成干旱，同时在美国西海岸、厄瓜多尔和秘鲁产生破坏性洪水。拉尼娜现象产生相反的影响，两者都可能产生重大的经济和自然灾害影响。最近的研究已经确认了仪器记录中不止一种类型的ENSO事件，称为中太平洋、东太平洋或沿海厄尔尼诺事件，基于降雨量最大的地区。这些不同类型的厄尔尼诺现象可能解释了为什么从西太平洋、中太平洋和东太平洋重建的ENSO并不总是一致。此外，问题仍然存在，这种多样性的ENSO事件是发生在20世纪之前，当时气温较低，还是发生在之前的温暖时期。这个项目试图通过提供2800至2100年前秘鲁中北部的ENSO变化的新记录来填补我们对过去ENSO行为的了解空白，这是一个目前缺乏ENSO变化记录的关键地区和时间框架。我们对过去和现在的ENSO现象的了解对于完善用于预测未来气候条件的全球气候模型以及规划气候变化的短期和长期影响非常重要。该项目利用古气候学家和考古学家的专业知识，同时培训学生多学科方法，将开发一种新的重建方法，可用于其他贝壳材料丰富的地点。最终的产品将是秘鲁中北部的ENSO变化的新记录，时间跨度比现在早2800到2100年。研究地点是地平线早期(公元前800年至公元前100年)的三个考古遗址(凯兰、万巴乔和萨曼科)，都是秘鲁沿海内贝尼亚山谷早期城市社会的一部分。该项目使用了从这三个遗址内的几个考古单位挖掘出的两种短命双壳类物种(Donax obesulus和Mesodesma donacium)的贝壳。这两个物种有不同但互补的栖息地偏好(温暖与寒冷)，这使它们有助于捕捉厄尔尼诺和拉尼娜事件；然而，这两个物种都是短暂的(1至3年)。该项目不是建立单个ENSO事件的连续记录，而是根据贝壳内氧同位素测量的单个时间片的现代和考古标本重建季节性温度和盐度变化，类似于海洋沉积物岩心使用的单一有孔虫方法。综合考古数据将为沿海社会在很长一段时间内对ENSO变化的复原力或脆弱性提供一个重要的视角。该项目将支持两名相对较早就业的教师(一名女性)、一名研究生和一名或多名本科生，他们将在PIS过去的实验室(古气候和人类学研究)工作，该实验室将自然和社会科学家聚集在一起，促进跨学科合作。该奖项反映了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。

El Niño and La Niña events, collectively called El Niño-Southern Oscillation (ENSO), are the largest source of year-to-year climatic and environmental variability that affects people around the world. For example, El Niños cause droughts in Australia and Southeast Asia while producing damaging floods along the west coast of the United States, Ecuador and Peru. La Niñas produce the opposite effects and both can have significant economic and natural hazard impacts. Recent studies have identified more than one type of ENSO event in the instrumental record, called Central Pacific, Eastern Pacific, or Coastal El Niño events based on the region with greatest rainfall. These different types of El Niños may explain why ENSO reconstructions from the western, central, and eastern Pacific do not always agree. Furthermore, questions remain whether or not this diversity of ENSO events occurred before the 20th century when temperatures were cooler, or occurred during prior warm periods. This project seeks to fill a gap in our knowledge of past ENSO behavior by providing a new record of ENSO variability in north-central Peru for the period 2800 to 2100 years ago, a critical area and time frame currently lacking records of ENSO variability. Our understanding of past and present ENSO is important for refining global climate models used to forecast future climate conditions and in planning for short and long-term impacts from changing climate.This project leverages the expertise of paleoclimatologists and archaeologists while training students in a multidisciplinary approach that will develop a new reconstruction method that could be used in other locations with abundant shell material. The final product will be a new record of ENSO variability in north-central Peru spanning 2800 to 2100 years before present. The study sites are three Early Horizon (800 to 100 BCE) archaeological sites (Caylán, Huambacho, and Samanco), all part of an early urban society in the coastal Nepeña Valley, Peru. The project uses shells from two short-lived bivalve species (Donax obesulus and Mesodesma donacium) excavated from several archaeological units within these three sites. These two species have different but complementary habitat preferences (warm vs. cold) that make them useful to capture El Niño and La Niña events; however, both species are short-lived (1 to 3 years). Instead of building a continuous record of individual ENSO events, this project will reconstruct seasonal temperature and salinity variability from modern and archaeological specimens for individual time slices from intra-shell oxygen isotope measurements, similar to the single foraminifer approach used in marine sediment cores. The integration of archaeological data will provide a crucial perspective on the resilience or vulnerability of coastal societies to ENSO variability on long time periods. The project will support two relatively early career faculty (one female), a graduate student, and one or more undergraduates who will work in the PIs' PAST laboratory (Paleoclimate and Anthropology Studies), which brings natural and social scientists together to foster interdisciplinary collaboration.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.