Collaborative Research: GEOTRACES Atlantic Section Nitrate Isotope Measurements

合作研究：GEOTRACES 大西洋剖面硝酸盐同位素测量

• 批准号: 1138360
• 负责人: Karen Casciotti
• 金额: $ 20.94万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-03-01 至 2014-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1138360&HistoricalAwards=false
• 关键词: Collaborative; Research; GEOTRACES; Atlantic; Section

Nitrogen is one of the two major nutrients required universally by plankton in the ocean, and its availability can affect the ocean's ecology, productivity, and carbon cycle. While the cycling of fixed N in the ocean is in one sense emblematic of other nutrient cycles, it is also unique in that its largest input (N fixation) and output (denitrification) are biologically mediated, which renders the ocean N budget susceptible to complex biological feedbacks. It thus provides a platform for asking one of the core questions of global biogeochemical cycles: How is it that the actions of individual organisms and groups conspire with physicochemical conditions to produce a global Earth surface environment that has been continuously habitable for billions of years? The dominant terms in the oceanic fixed N input/output budget are poorly characterized, and we focus our attention here on N fixation. Developing robust estimates of the global rate and distribution of N fixation from "direct" shipboard measurements of N fixing activity is complicated by the inherent spatial and temporal variability of this biologically mediated flux. Thus, geochemical approaches for estimating N fixation inputs have come to the forefront. Currently, nitrate stable isotope measurements, which could provide an integrative estimate of N fixation on a regional or basin scale, are sparse in the Atlantic, being focused primarily in the Sargasso Sea. The GEOTRACES program provides a platform to put these data into a broader context through the illumination of basin-scale patterns. In this project researchers from Princeton University, Brown University, and the Woods Hole Oceanographic Institution will measure the d15N of nitrate in seawater and atmospheric samples collected as part of the GEOTRACES North Atlantic Section. Nitrate d15N is a GEOTRACES "core parameter" that will complement other measurements and will by itself provide important constraints on the oceanographic processes, including N fixation, lateral nitrate transport, low latitude N cycling, the effect of the North African upwelling regions on nutrient fluxes across the basin, and the exchange of fixed N with the Mediterranean. In addition to yielding such specific process-related insights, this work will provide one of the first cross-basin views of nitrate isotopes in the interior and will thus help to simply characterize the isotope signals of different interior water masses, including the Mode Waters, Antarctic Intermediate Water, Mediterranean Intermediate Water, Lower and Upper North Atlantic Deep Water, and Antarctic Bottom Water. Finally, the isotopic characterization of atmospheric nitrate deposition will inform our understanding of the N isotope budget and isotopic gradients of the North Atlantic. Combined, these measurements will yield insight into modern biogeochemical processes and will also provide first order background information for both modern physical oceanographic and paleoceanographic applications. As an example of the latter, studies of Atlantic sediments seek to reconstruct past changes in the rate of N fixation, based on the modern finding that N fixation appears to lower the d15N of thermocline nitrate in the Sargasso Sea. Progress in this paleoceanographic work relies on a more complete picture of nitrate d15N in the modern Atlantic. Broader impacts: The broader impacts of the proposed study include the mentoring of a postdoctoral investigator and the inclusion of undergraduates in state-of-the-art research. The project will also provide a high-quality nitrate isotope data set for the North Atlantic for use by the broader community.

氮是海洋中普兰克顿普遍要求的两种主要营养之一，其可用性会影响海洋的生态，生产力和碳循环。尽管从某种意义上说，固定n的循环是其他营养周期的象征，但它的独特之处在于，其最大的输入（N固定）和输出（硝化）是生物学介导的，这使海洋N预算对复杂的生物反馈很容易受到影响。因此，它提供了一个平台来询问全球生物地球化学周期的核心问题之一：单个生物体和群体的行为如何使用物理化学条件共​​谋产生一个全球地球表面环境，而这已经在数十亿年中持续不断地居住？海洋固定N输入/输出预算中的主要术语的特征很差，我们将注意力集中在N固定上。从N固定活动的“直接”船板测量值中，对N固定的全球速率和分布进行了强大的估计，这是由于该生物学介导的通量的固有空间和时间变异性而变得复杂。因此，用于估计N固定输入的地球化学方法已成为最前沿。当前，硝酸盐稳定的同位素测量值可以在大西洋上稀疏提供区域或盆地尺度上N固定的综合估计值，主要集中在Sargasso Sea。 GeoTraces程序提供了一个平台，可以通过照明盆地规模模式将这些数据置于更广泛的环境中。在这个项目中，普林斯顿大学，布朗大学和伍兹孔海洋学机构的研究人员将在海水和大气样本中测量硝酸盐D15N，作为地理位置北大西洋地区的一部分收集的大气样品。硝酸盐D15N是一种“核心参数”，它将对其他测量值进行补充，并将其本身对海洋学过程产生重要约束，包括n固定，硝酸盐外侧运输，低纬度N循环，北非下非上升区域对跨越盆地的营养浮肿的影响，以及固定的固定型均与固定的niitererranearnean。除了产生与过程相关的特定见解外，这项工作还将提供室内硝酸盐同位素的第一个跨冰淇淋视图之一，因此将有助于简单地表征不同内部水质量的同位素信号，包括模式水，包括南极的中间水，地中海中间水，下层和上层水，北部和北部的水和蚂蚁镇和蚂蚁，以及蚂蚁和蚂蚁镇和蚂蚁。最后，大气硝酸盐沉积的同位素表征将为我们了解北大西洋的N同位素预算和同位素梯度。这些测量结果结合在一起，将洞悉现代生物地球化学过程，还将为现代物理海洋学和古环摄影应用提供一阶背景信息。作为后者的一个例子，大西洋沉积物的研究试图重建固定速率的过去变化，基于现代发现，即N固定似乎降低了Sargasso Sea中硝酸盐的D15N D15N。这项古文化工作的进展取决于现代大西洋中硝酸盐D15N的更完整图片。更广泛的影响：拟议的研究的更广泛影响包括指导博士后研究者以及在最先进的研究中纳入本科生。该项目还将为北大西洋提供高质量的硝酸盐同位素数据集，以供更广泛的社区使用。