Linking high latitude nutrient supply to export productivity and nitrogen cycling in the tropical Pacific across the Plio-Pleistocene

最近的工作证明了营养供应在推动赤道东太平洋出口生产力事件和刺激下游反硝化方面的重要性。然而，这种观点仅限于过去的3万年。在轨道时间尺度上，变化可能与高纬度南大洋倾覆率的变化有关。在百万年的时间尺度上，人们假设，由于全球变冷，通风温跃层的浅化加强了高纬度和低纬生物地球化学之间的联系。这项研究由罗德岛大学的一名研究人员领导，旨在了解营养物质供应、出口生产率、氧气需求和水柱反硝化的变化如何与长时间尺度上的海洋环流的大范围变化有关。更长的记录对于评估高纬度养分供应在推动低纬生物地球化学变化方面的重要性至关重要，并将提供对轨道时间尺度上发生的周期性变化和更长时间尺度变化的洞察。这项研究集中于两个关键问题：1)高纬度的营养供应在推动赤道东太平洋记录的高生产力事件中起什么作用？2)增加的出口和氧气需求在调节东热带太平洋水柱反硝化方面起什么作用？这项研究建立在现有的岩心下方数据的基础上，并添加了过去300万年来南大洋和热带太平洋的氮同位素和出口生产力记录。来自热带太平洋一系列地点的记录将产生反硝化变化的叠加记录和赤道东太平洋养分供应变化的估计。南大洋的记录将被用来估计模式水域起源地的预先形成的营养物质浓度。这些新记录将被纳入一个更大的国际合作项目，该项目旨在制定一幅连贯的图景，说明更新世气候驱动的环流变化如何影响全球氮和碳的循环。该项目也代表了在赤道太平洋东部建立完整的新生代养分循环和出口生产力历史的第一步。广泛的影响包括研究生的教育和培训、公共宣传活动以及与一名法国科学家的国际合作。

Recent work has demonstrated the importance of nutrient supply in driving export productivity events in the eastern equatorial Pacific and stimulating denitrification downstream. However, this view is limited to the last 30,000 years. On orbital timescales, variations likely relate to changes in overturning rate in the high latitude Southern Ocean. On million-year timescales, it is hypothesized that the shoaling of the ventilated thermocline, due to global cooling, strengthened the connection between high and low latitude biogeochemistry. This study, led by a researcher from the University of Rhode Island, seeks to understand how variations in nutrient supply, export productivity, oxygen demand, and water column denitification relate to large scale changes in ocean circulation on long timescales. Longer records are essential in order to evaluate the significance of high latitude nutrient supply in driving low latitude biogeochemical shifts, and will provide insight into both the cyclic changes occurring on orbital timescales and longer timescale shifts. The study focuses on two key questions: 1) What is the role of nutrient supply from high latitudes in driving documented episodes of high productivity in the eastern equatorial Pacific?, and 2) What is the role of enhanced export and oxygen demand in modulating water column denitrification in the eastern tropical Pacific? The study builds on available downcore data and add nitrogen isotope and export productivity records from the Southern Ocean and tropical Pacific across the last 3 million years. Records from a series of sites across the tropical Pacific will result in a stacked record of denitrification changes and an estimate of nutrient supply changes in the eastern equatorial Pacific. The Southern Ocean records will be used to estimate preformed nutrient concentrations at the origin of mode waters. The new records will be incorporated into a larger international collaboration that aims to develop a coherent picture of how climate-driven circulation changes in the Plio- Pleistocene impact the global cycling of nitrogen and carbon. This project also represents a first step toward developing a complete Cenozoic history of nutrient cycling and export productivity in the eastern equatorial Pacific.Broader impacts include education and training of a graduate student, public outreach activities, and international collaboration with a French scientist.