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起着至关重要的作用。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。在巴拿马<e:1>，一个特别关切的问题是降雨对巴拿马运河<e:1>运作的影响。在巴拿马，降雨和河流流量(Q)密切相关，它们在运河的持续成功中起着至关重要的作用。巴拿马的总降雨量一直排在年降雨量前五名，但当发生重大干旱时，巴拿马运河管理局会限制船舶通行，以节约用水，使运河能够继续运营。巴拿马<s:1>在降水方面具有众所周知的季节性变化，雨季大约从5月持续到11月。然而，人们对更长时间尺度（几十年或几百年）的降雨变化知之甚少。此外，目前尚不清楚El Niño事件如何影响巴拿马的降雨，尽管有迹象表明El Niño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，而且往往是不可靠的——我们需要一个更长远的视角。珊瑚骨架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用品。该项目将使用珊瑚气候代用品以近月分辨率重建巴拿马太平洋沿岸<s:1>近300年来的水文变化。最终的结果将是一个多珊瑚、多代理记录，可用于识别干旱或厄尔尼诺Niño等事件的频率和强度。本项目资助女本科生8名，博士生1名。这个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，并将与巴拿马的水资源管理人员分享<e:1>。许多热带国家的降水量变化剧烈，具有极端的季节性。热带辐合带（ITCZ）的经向迁移是造成这种变化的主要原因，在北方夏季向北移动，在南方夏季向南移动。在太平洋，El Niño和其他约束较差的年代际和世纪尺度海洋-大气变率模式也决定了区域气候。在巴拿马，降雨和河流流量(Q)紧密耦合的国家，在考虑对巴拿马<e:1>运河的潜在影响时，了解水文变化是至关重要的，巴拿马运河的功能完全依赖于运河船闸和加通湖水库之间的水头差异。因此，异常水文条件（如干旱和洪水）发生的可能性必须明确界定。然而，缺乏热带水文（即降雨和Q）的长期仪器记录限制了我们对干旱和洪水复发间隔进行严格理解的能力。这些问题提出了以下问题：1)厄尔尼诺Niño南方涛动与巴拿马干旱和洪水<e:1>之间的关系是什么？2)我们能否确定与厄尔尼诺现象Niño无关的干旱和洪水年份？4)巴拿马的Q值是否存在多年代际或长期的长期变化？其中涉及哪些气候过程？初步结果表明，1984年在巴拿马太平洋沿岸Chiriquí湾（GoC） Secas岛采集的珊瑚岩心钡/钙（Ba/Ca）时间序列数据与附近两条主要河流的Q值具有显著的相关性。鉴于这些令人鼓舞的结果，我们将完成1707年Secas岛岩心的Ba/Ca分析，并分析2018年收集的新的GoC珊瑚岩心。Q的最终近月分辨复合Ba/Ca记录将从2018年延伸至1707年CE。通过对同一1mm样品的Ba/Ca和δ18O进行配对，我们可以分别评估近311年来GoC的盐度和海温变化。这些古q值和盐度重建将提供巴拿马水文气候的全面历史，可以用来追踪与平均条件的长期偏差。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。

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.