Stable Isotopes of Argon in Seawater: New Tracers of Deep Water Formation Processes

最近的研究表明，北大西洋的副热带模式水--十八度水（EDW）可能在设置副热带环流的营养库方面发挥重要作用。 研究结果表明，平流的EDW注入一个楔形的低营养水下的季节性温跃层在北大西洋副热带环流。此外，营养物耗尽的水团的存在可能会抑制生物对垂直过程的反应，这些垂直过程使营养物在整个亚热带环流中向上流动。这就提出了关于EDW如何以及何时耗尽营养物质以及信号如何输出到副热带环流的其余部分的重要问题：1）在水团形成期间，与无机营养物质的生物耗尽相关的时间尺度是什么？2)俯冲时EDW的营养盐浓度是多少？EDW的形成如何影响下游营养盐库和营养盐垂直通量？在这个项目中，杜克大学的研究人员将通过对EDW形成区域的营养测量来解决这些问题。幸运的是，NSF资助的一个实地项目CLIvar MOde水动力学实验（CLIMODE）目前正在加紧对EDW的形成，维持和破坏进行全面分析。虽然CLIMODE的观测计划是由一套测量，它目前缺乏任何地球化学成分。该项目将为CLIMODE观测方案增加营养物取样，以检验关于EDW对地下营养物储层影响的假设。具体而言，调查人员将在计划的水文调查中增加营养分析，并将在两个CLIMODE系泊系统中的每一个上安装一个硝酸盐传感器。前者将创建第一个横截面的营养物质在冬季的形成区域，而后者将提供一个前所未有的时间序列的硝酸盐内的亚热带gyrere.The总体目标，这项拟议的工作是进一步了解在何种程度上的水平平流的亚热带模式水影响地下营养水库和相应的营养物质的初级生产者。这样的理解是至关重要的，因为亚热带环流作为碳汇的作用取决于营养物质的可用性，以燃料的生物泵，从海洋表面去除有机碳，并保持有利的气-海梯度的二氧化碳分压所需的溶解度泵。此外，由于水的质量生产是众所周知的年际和十年的时间尺度上变化，建立亚热带模式沃茨和养分的可用性之间的联系，推进我们的初级生产力是如何影响气候变化的理解。就更广泛的影响而言，很明显，更好地了解地下营养库是如何补充和减少的，将有助于了解海洋如何作为碳汇。 该项目还将支持一名博士前研究生的研究。

ABSTRACTOCE-0526826Recent studies suggest that Eighteen Degree Water (EDW), the subtropical mode water of the North Atlantic, may play an important role in setting the nutrient reservoir of the subtropical gyre. The findings indicate that advection of EDW injects a wedge of low nutrient water beneath the seasonal thermocline in the North Atlantic subtropical gyre. Furthermore, the presence of the nutrient-depleted water mass may dampen the biological response to vertical processes that flux nutrients upwards throughout the subtropical gyre. This raises important questions regarding how and when the EDW is depleted in nutrients and how the signal is exported to the rest of the subtropical gyre: 1) What are the time scales associated with the biological depletion of inorganic nutrients during water mass formation? 2) What is the nutrient concentration of the EDW upon subduction? and 3) How does the formation of EDW impact the downstream nutrient reservoir and vertical nutrient fluxes? In this project, researchers at Duke University will address these questions with nutrient measurements in the formation region of the EDW. Fortuitously, an NSF-funded field program, CLIvar MOde water Dynamics Experiment (CLIMODE), is currently ramping up for a comprehensive analysis of the formation, maintenance and destruction of EDW. Though CLIMODE's observational program is comprised of a suite of measurements, it currently lacks any biogeochemical component. This project will provide for the addition of nutrient sampling to the CLIMODE observational program in order to test hypotheses concerning the impact of EDW on the subsurface nutrient reservoir. Specifically, the investigators will add nutrient analyses to the planned hydrographic surveys and will mount a nitrate sensor on each of two CLIMODE moorings. The former will create the first cross-section of nutrients during the winter in the formation region, and the latter will provide an unprecedented time series of nitrate within the subtropical gyre.The overall goal of this proposed work is to further the understanding of the degree to which the horizontal advection of a subtropical mode water impacts the subsurface nutrient reservoir and the corresponding availability of nutrients to primary producers. Such an understanding is crucial since the subtropical gyre's role as a carbon sink depends on the availability of nutrients to fuel the biological pump, remove organic carbon from the surface ocean, and maintain a favorable air-sea gradient in the partial pressure of carbon dioxide necessary for the solubility pump. Furthermore, since water mass production is known to vary on interannual and decadal time scales, establishing the link between subtropical mode waters and nutrient availability advances our understanding of how primary productivity is impacted by climatic variability. In terms of broader impacts, it is clear that an improved understanding of how the subsurface nutrient reservoir is replenished and diminished will aid the understanding of how the ocean acts as a carbon sink. The project will also support the research of a pre-doctoral graduate student.