Physical Control of Atmospheric Carbon Dioxide Flux in Estuaries

该项目的总体目标是全面了解河口物理和生物地球化学过程如何相互作用以调节大气二氧化碳（CO2）交换。通过系泊阵列和船舶调查测量哈德逊河河口的二氧化碳分压（pCO2）和溶解氧（DO），将用于解决时间和沿河口和跨河口方向的变化。这些测量将包括地表和地下溶解气体的分布，它们的分布将与垂直密度分层和河口环流的变化有关。直接协方差大气CO2通量和水柱湍流测量将在一个固定平台上进行，该平台横跨海气界面，在该位置，近地面湍流可能受到风、波和潮汐的影响，并受到垂直密度分层变化的显著修改。这些数据将为气体传输速度提供一个定量模型，该模型将用于从空间分辨的地表二氧化碳分压测量中估计大气通量。据推测，在许多河口的上部区域通常推断出的二氧化碳高放气量是由潜在的河口环流强烈控制的。这些测量将解决两个长期存在的研究需求，这两个需求导致了河口二氧化碳排放的巨大不确定性：1)地表二氧化碳分压值的时空异质性；2)气体传输速度约束不佳。该研究解决了这两个基本的不确定性，这两个不确定性都受到物理过程的强烈调节，并且将测试假设适用于广泛河口的气体交换的新概念模型。系泊仪器将在一系列时间尺度上量化时间变率的重要性，这在大多数以前的研究中没有得到解决。直接协方差大气CO2通量测量结合水柱湍流、波浪和垂直密度分层观测，将严格量化水表面边界层湍流与地面气体交换之间的关系。这解决了一个具有重要社会意义的基本跨学科问题，并将大大改善对河口二氧化碳排放的估计。这个项目将为研究生提供跨学科的培训，他们将参与项目的各个方面。这项研究的结果将通过由关注哈德逊河科学和环境问题的组织主办的公开研讨会以及在国家会议上的演讲，传达给公众和科学听众，以及感兴趣的利益相关者。一些社区大学的学生将获得建造和测试新的科学传感器的经验，这些传感器将部署在哈德逊河上。来自这些传感器的数据将显示在贝扎克的城市河流中心，并用于为哈德逊河中心的游客制作教育材料。该项目将测试一个概念模型，即存在一个河口气体交换最大值（EGM），其位置主要由潜在的河口动力学控制。与河口浊度最大值（ETM）类似，EGM的位置被假设由靠近盐极限的向陆地的河口环流中的辐合控制，并且由于垂直密度分层阻止了次斜斜水的呼吸需求与大气交换而发生。这种对分层的依赖可能会导致春潮和小潮之间大气通量的巨大不对称，这可能从根本上控制EGM沿河口的位置。预计还会有显著的河口变异性，可能是由侧向上升流或强烈的横向分层梯度驱动的。在光照受限的哈德逊河河口，分层和混合的两周变化可能影响浮游植物的动力学，这也可能导致大气交换的时空变化。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。

The overarching goal of this project is to develop a comprehensive understanding of how physical and biogeochemical processes interact in estuaries to modulate atmospheric carbon dioxide (CO2) exchange. Measurements of the partial pressure of CO2 (pCO2) and dissolved oxygen (DO) in the Hudson River estuary from a moored array and from ship-based surveys, will be used to resolve variability in time and in the along- and across-estuary directions. These measurements will include both the surface and sub-surface distribution of dissolved gases, and their distribution will be related to variations in vertical density stratification and estuarine circulation. Direct covariance atmospheric CO2 flux and water column turbulence measurements will be made from a fixed platform that spans the air-sea interface at a location where near surface turbulence is likely impacted by wind, waves, and tides, and is significantly modified by variations in vertical density stratification. These data will provide a quantitative model for the gas transfer velocity, which will be used to estimate atmospheric fluxes from the spatially resolved measurements of surface pCO2. It is hypothesized that the high outgassing of CO2 commonly inferred in the upper regions of many estuaries is strongly controlled by the underlying estuarine circulation. The measurements will address two long-standing research needs that contribute to the large uncertainties in estuarine CO2 emissions: 1) spatial and temporal heterogeneity in surface pCO2 values, and 2) poorly constrained gas transfer velocities. The research addresses these two fundamental uncertainties, both of which are strongly modulated by physical processes, and a new conceptual model for gas exchange that is hypothesized to be applicable to a wide range of estuaries will be tested. Moored instrumentation will quantify the importance of temporal variability at a range of time scales, not resolved in most previous studies. Direct covariance atmospheric CO2 flux measurements combined with observations of water column turbulence, waves and vertical density stratification will rigorously quantify the relationship between turbulence in the aqueous surface boundary layer and surface gas exchange. This addresses a fundamental interdisciplinary problem of significant societal importance and will significantly improve estimates of CO2 emissions from estuaries. This project will provide interdisciplinary training for a graduate student, who will be involved in all aspects of the project. Results from this research will be communicated to the public and scientific audiences, and to interested stakeholders through public seminars hosted by organizations that focus on Hudson River scientific and environmental issues and through presentations at national meetings. Several community college students will gain hands on experience building and testing new scientific sensors, which will be deployed in the Hudson River. Data from these sensors will be displayed at the Center for the Urban River at Beczak and used to develop educational materials for visitors to this center on the Hudson River.This project will test the conceptual model that there is an estuarine gas exchange maximum (EGM), whose location is controlled primarily by the underlying estuarine dynamics. Analogous to the estuarine turbidity maximum (ETM), the location of the EGM is hypothesized to be controlled by the convergence in the landward estuarine circulation near the limit of salt and occurs because vertical density stratification prevents the respiratory demand of sub-pycnocline waters in from exchanging with the atmosphere. This dependence on stratification will likely result in large asymmetries in atmospheric flux between spring and neap tides, which may fundamentally control the along-estuary location of the EGM. Significant across-estuary variability also is expected, potentially driven by lateral upwelling or strong lateral gradients in stratification. In the light-limited Hudson River estuary, fortnightly variations in stratification and mixing likely influence phytoplankton dynamics, which also may contribute to the spatial and temporal variations in atmospheric exchange.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.