Physical Control of Atmospheric Carbon Dioxide Flux in Estuaries

该项目的总体目标是全面了解河口的物理和地球化学过程如何相互作用，以调节大气中的二氧化碳（CO2）交换。测量二氧化碳分压（pCO 2）和溶解氧（DO）在哈德逊河口从系泊阵列和船基调查，将被用来解决在时间和沿着和跨河口方向的变化。这些测量将包括溶解气体的表面和次表面分布，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从一个固定平台进行，该平台跨越海-气界面，位于近地表湍流可能受风、波浪和潮汐影响的位置，并受到垂直密度分层变化的显著影响。这些数据将提供一个定量模型的气体传输速度，这将被用来估计大气通量的空间分辨测量表面二氧化碳分压。据推测，通常推断在许多河口的上部区域的CO2的高释气强烈控制下的河口环流。这些测量将解决两个长期存在的研究需求，这两个需求导致河口CO2排放量存在很大的不确定性：1）表面pCO 2值的空间和时间异质性，以及2）约束不佳的气体传输速度。该研究解决了这两个基本的不确定性，这两个都是强烈调制的物理过程，和一个新的概念模型的气体交换，假设是适用于广泛的河口将进行测试。停泊的仪器将量化的重要性，在一系列的时间尺度，没有解决在大多数以前的研究。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的观测将严格量化的湍流之间的关系在水表面边界层和表面气体交换。这解决了一个具有重要社会意义的基本跨学科问题，并将显着改善河口二氧化碳排放量的估计。该项目将为一名研究生提供跨学科培训，他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共研讨会以及通过在国家会议上的发言传达给公众和科学受众以及感兴趣的利益相关者。几个社区大学的学生将获得经验，建设和测试新的科学传感器，这将是部署在哈德逊河。来自这些传感器的数据将在Beczak的城市河流中心展示，并用于为哈德逊河中心的游客开发教育材料。该项目将测试河口气体交换最大值（EGM）的概念模型，其位置主要由底层河口动力学控制。与河口最大浑浊带（ETM）类似，EGM的位置被假设为受盐限附近的向陆河口环流中的辐合控制，并且由于垂直密度分层阻止了次密度跃层沃茨与大气交换的呼吸需求而发生。这种对层结的依赖可能会导致春季和小潮之间的大气通量的大的不对称性，这可能从根本上控制沿河口位置的EGM。预计还将出现显著的跨河口变化，这可能是由横向上涌或分层中的强横向梯度驱动的。在光线有限的哈德逊河口，每两周的变化分层和混合可能会影响浮游植物的动态，这也可能有助于在大气exchanges.This奖项的时空变化反映了NSF的法定使命，并已被认为是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的支持。

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.