Collaborative Research: Reconstructing river discharge and hydrologic variability in Panama via coral geochemistry: Implications for management of the Panama Canal

河流和水文在热带生态系统中发挥着关键作用。它们影响气候的各个方面，帮助维持生命，并影响饮用水，粮食安全和经济等社会需求。在帕纳马，降雨对帕纳马运河运作的影响是一个特别令人关切的问题。在帕纳马，降雨量和河流流量（Q）密切相关，它们在运河的持续成功中发挥着至关重要的作用。帕纳马全国的降雨量一直位居年降雨量前五位，但当发生重大干旱时，巴拿马运河管理局会限制船只通行，以节约用水，使运河能够继续运行。帕纳马有一个众所周知的降水季节性变化，雨季从5月持续到11月。然而，人们对几十年或几个世纪的更长时间尺度上的降雨量变化知之甚少。此外，尚不清楚厄尔尼诺事件如何影响巴拿马的降雨量，尽管有迹象表明厄尔尼诺强度与干旱严重程度之间存在关系。这些问题很难解决，因为仪器数据，特别是河流流量记录，是短暂的，往往不可靠-我们需要一个长期的观点。珊瑚骨骼的化学成分可以保存气候条件和气候变化的记录;这些化学记录被称为气候代理。该项目将使用珊瑚气候代用指标，以近月分辨率重建帕纳马太平洋沿岸沿着过去约300年的水文变化。最后产品将是一个多珊瑚、多代理记录，可用于确定干旱或厄尔尼诺等事件的频率和强度。该项目包括支助8名女本科生和1名博士。学生.该项目的成果将纳入为初中和高中教育工作者举办的教学讲习班，并将与帕纳马的水资源管理人员分享。许多热带国家的降水量变化剧烈，具有极端的季节性。经向迁移的热带辐合带（ITCZ）在很大程度上负责这种变化，北移在北方夏季和南移在南方夏季。在太平洋，厄尔尼诺现象和其他约束不那么严格的十年和百年尺度的海洋-大气变化模式也决定着区域气候。在帕纳马，降雨量和河流流量（Q）紧密相连，在考虑对帕纳马运河的潜在影响时，了解水文变化是至关重要的，因为巴拿马运河的运作完全依赖于运河船闸和加通湖水库之间的水头差。因此，必须很好地定义异常水文条件（如干旱和洪水）的概率。然而，缺乏长期的热带水文仪器记录（即;降雨量和Q）限制了我们对干旱和洪水重复间隔的严格理解。这些问题提出了以下问题：1）厄尔尼诺南方涛动与帕纳马干旱和洪水之间的关系是什么？2)我们能确定与厄尔尼诺无关的干旱和洪水年份吗？（4）帕纳马的Q值是否存在多年或长期的长期变化？初步结果表明，钡/钙（Ba/Ca）的时间序列数据从1984年收集的珊瑚芯在Secas岛的奇里基湾（GoC）沿着太平洋沿岸的帕纳马有一个非常强的相关性与Q从附近的两条主要河流。鉴于这些令人鼓舞的结果，我们将完成对公元1707年塞卡斯岛核心的Ba/Ca分析，并分析2018年收集的新的GoC珊瑚核心。Q的最终近月分解复合Ba/Ca记录将从2018年延伸到1707 CE。通过在相同的1 mm样品上配对Ba/Ca和δ 18 O，我们可以分别评估GoC在过去311年中的盐度和海表温度变化。这些古Q和盐度重建将提供巴拿马水文气候的全面历史，可用于跟踪长期偏离平均条件。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估。

Rivers and hydrology play a critical role in tropical ecosystems. They impact aspects of climate, help to sustain life, and influence societal needs such as drinking water, food security, and economics. In Panamá, a specific concern is the impact of rainfall on the functioning of the Panamá Canal. Rainfall and river discharge (Q) are strongly linked in Panamá, and they play a crucial role in the sustained success of the canal. Rainfall totals across Panamá consistently place it in the top five countries for annual rainfall, but when major droughts occur, the Panama Canal Authority places restrictions on ship traffic to conserve water so that the canal can continue to operate. Panamá has a well-known seasonal variability in precipitation, with a wet season that lasts from about May through November. However, little is known about rainfall variation on longer time scales, on the order of decades or centuries. In addition, it is not clear how El Niño events may influence Panamanian rainfall, though there are suggestions of a relationship between El Niño strength and drought severity. These questions are hard to address because instrumental data, particularly river discharge records, are short and often unreliable – we need a longer-term perspective. The chemistry of coral skeletons can preserve records of climate conditions and climate variability; these chemical records are called climate proxies. This project will use coral climate proxies to reconstruct hydrologic variability along the Pacific Coast of Panamá over the past ~300 years at near-monthly resolution. The final product will be a multi-coral, multi-proxy record that can be used to identify the frequency and strength of events such as droughts or El Niño. This project includes support for 8 female undergraduates and 1 Ph.D. student. Results from this project will be incorporated into a teaching workshop for middle and high school educators and will also be shared with water resource managers in Panamá. Many tropical nations are subjected to intense variation in precipitation with extreme seasonality. Meridional migration of the Intertropical Convergence Zone (ITCZ) is largely responsible for this variability, with northward movement during the boreal summer and a southward shift during the austral summer. In the Pacific, El Niño and other less well constrained decadal and century-scale modes of ocean- atmosphere variability also dictate regional climate. In Panamá, a country whose rainfall and river discharge (Q) are tightly coupled, understanding hydrologic variability is of the utmost importance when considering the potential impacts on the Panamá Canal, whose functioning relies solely on hydraulic head differences between the canal locks and the Gatun Lake reservoir. Therefore, the probability of anomalous hydrologic conditions, such as drought and flooding, must be well defined. However, the lack of long instrumental records of tropical hydrology (i.e.; rainfall and Q) limits our ability to develop a rigorous understanding of drought and flood recurrence intervals. These issues raise the following questions: 1) What is the relationship between El Niño Southern Oscillation and droughts and flooding in Panamá? 2) Can we identify droughts and flood years that are not related to El Niño? And 4) Has there been multi-decadal or long-term secular changes in Q in Panamá and what climatic processes are involved? Preliminary results indicate that barium/calcium (Ba/Ca) time-series data from a coral core collected in 1984 at Secas Island in the Gulf of Chiriquí (GoC) along the Pacific Coast of Panamá has a remarkably strong correlation with Q from two major nearby rivers. Given these encouraging results, we will be completing the Ba/Ca analyses of the Secas Island core back to 1707 CE and to analyze a new GoC coral core collected in 2018. The final near- monthly resolved composite Ba/Ca record of Q will extend from 2018 to 1707 CE. By pairing Ba/Ca and δ18O on the same 1mm samples we can separately evaluate salinity and sea surface temperature changes in the GoC over the last 311 years. These paleo-Q and salinity reconstructions will provide a comprehensive history of Panamanian hydroclimate that can be exploited to track protracted deviations from average conditions.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.