Collaborative Research: Field and Modeling Studies of the Magnitude and Variability of 234-Th Based Estimates of POC Export Flux and Remineralization in the Upper Ocean

合作研究：基于 234-Th 估计的 POC 输出通量和上层海洋再矿化的幅度和变异性的现场和建模研究

• 批准号: 0327693
• 负责人: Adrian Burd
• 金额: --
• 依托单位: University of Georgia Research Foundation Inc
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-12-15 至 2008-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0327693&HistoricalAwards=false
• 关键词: Collaborative; Research; Field; Modeling; Studies

ABSTRACTOCE-0327721 / OCE-327644 / OCE-0327693The magnitude of the flux of biogenic particulate organic carbon (POC) exported from the surface waters of the world ocean and remineralized at depth is critical to constraining models of the global carbon cycle, yet remains controversial. Over the past decade, 234Th has been increasingly used as a tracer to estimate POC export from the euphotic zone by multiplying the depth-integrated 234Th flux by the POC/234Th ratio of sinking particles. The accuracy of this technique is highly dependent on the natural variability in the POC/234Th ratio and 234Th flux, yet the significance of this variability to estimates of POC export remains uncertain. The global distribution of 234Th-derived POC export fluxes can vary by 2-10 times or more due solely to variability in the POC/234Th ratio and procedures used to estimate the 234Th flux. Thus, despite over a decade of research, our understanding of the magnitude and variability of 234Th-derived POC export fluxes, and the dominant controlling mechanisms, is not well constrained.In this project field, researchers at the University of Rhode Island, Texas A & M University, and University of Georgia will conduct field and modeling studies to address the following major question: How accurate are 234Th-based estimates of POC export flux from the euphotic to the mesopelagic zone, what are the dominant mechanisms controlling 234Th scavenging and export, and how can this tracer technique be improved? They have two working hypotheses designed to address this central question. Hypothesis 1: Regional variability in the magnitude of 234Th-derived POC export is determined by differences in particle source/organic chemical composition and food web structure. Hypothesis 2: Particle-particle interactions and differential biogeochemical recycling of organic C and 234Th controls POC/234Th ratios and hence the magnitude of 234Th-derived POC export and remineralization. The research strategy is to combine new and existing measurements of sediment trap and particle size-fractionated 234Th, POC and specific organic compounds in the upper ocean (~0-500 m) with newly developed particle coagulation models to validate, test and further develop the proposed working hypotheses. Samples will be collected from three study sites characterized by distinct differences in food-web structure and particle export (Mediterranean, Arctic, NW Atlantic) and designed to provide maximum information on the mechanisms controlling POC/234Th ratios and POC export and remineralization. Model development and testing is a key aspect of the project and serves to guide and validate the field observations and provide information on mechanisms of 234Th estimates upper ocean POC export and remineralization.The intellectual merit of the proposed research bears on a number of national and international carbon cycle research programs (JGOFS, VERTIGO, DYFAMED, CARBOCEAN). Specifically, this proposal has broad intellectual implications for previous and currently NSF funded projects that use (or have used) 234Th to measure POC export fluxes from the upper ocean. For example, POC fluxes obtained during the JGOFS program may need to be revised, and future investigations of the mesopelagic, which will depend on accurate determination of the particle flux entering this region of the ocean, may need to take the results of this work into account. The results could also have implications for the SCOR/IGBP OCEANS initiative of improved understanding of the global ocean carbon cycle.

从世界海洋的表面沃茨输出并在深度处被同化的生物源颗粒有机碳（POC）的通量的大小对于约束全球碳循环的模型是至关重要的，但仍然存在争议。在过去的十年里，234 Th越来越多地用作示踪剂，通过将深度积分的234 Th通量乘以下沉颗粒的POC/234 Th比来估计真光层的POC输出。这种技术的准确性是高度依赖于在POC/234 Th比率和234 Th通量的自然变异，但这种变异的重要性，以估计POC出口仍然不确定。 234 Th导出的POC输出通量的全球分布可以变化2-10倍或更多，这仅仅是由于POC/234 Th比率的变化和用于估计234 Th通量的程序。因此，尽管经过十多年的研究，我们对234 Th衍生的POC输出通量的大小和变化以及主要控制机制的理解并没有得到很好的限制。在这个项目领域，罗得岛大学、德克萨斯A& M大学和格鲁吉亚大学的研究人员将进行实地和模拟研究，以解决以下主要问题：基于234 Th的POC输出通量从真光层到中层的估计有多准确，控制234 Th清除和输出的主导机制是什么，以及如何改进这种示踪技术？ 他们有两个工作假设，旨在解决这个中心问题。假设1：234 Th来源的POC输出的大小的区域差异是由颗粒源/有机化学成分和食物网结构的差异。假设二：颗粒-颗粒的相互作用和有机C和234 Th的差异地球化学循环控制POC/234 Th比率，因此234 Th衍生的POC输出和再矿化的幅度。研究战略是结合联合收割机新的和现有的测量沉积物陷阱和颗粒粒度分级234 Th，POC和特定的有机化合物在海洋上层（~0-500米）与新开发的颗粒凝聚模型，以验证，测试和进一步发展所提出的工作假设。样本将从三个研究地点收集，其特征在于食物网结构和颗粒输出（地中海，北极，西北大西洋）的明显差异，并旨在提供最大的信息控制POC/234 Th比率和POC输出和再矿化的机制。模型开发和测试是该项目的一个关键方面，并用于指导和验证现场观测，并提供有关234 Th估计上层海洋POC输出和再矿化机制的信息，拟议研究的智力价值与一些国家和国际碳循环研究计划（JGOFS，VERTIGO，DYFAMED，CARBOCEAN）有关。具体而言，这一建议具有广泛的知识影响，以前和目前的NSF资助的项目，使用（或已使用）234 Th测量POC输出通量从上层海洋。例如，在JGOFS计划期间获得的POC通量可能需要修订，未来对中层的调查将取决于对进入这一海洋区域的粒子通量的准确确定，可能需要考虑到这项工作的结果。这些结果也可能对SCOR/IGBP海洋倡议产生影响，以提高对全球海洋碳循环的认识。