Biogeochemical Flows of Nitrogen in a Tropical Upwelling System (A CARIACO Time Series Project)

海洋氮循环在控制海洋生产力和其他元素（如碳）通量方面起着关键作用。重建这一重要循环如何随时间变化的能力在很大程度上取决于沉积物中的氮同位素记录，但在有机氮的形成和转移过程中有几个过程可能使这种分析复杂化。在国家科学基金会的支持下，CARIACO海洋时间序列站提供了委内瑞拉附近加勒比南部这一地区季节性涌升、营养物、表层生产力和输出通量之间关系的详细记录。在这项研究中，哥伦比亚大学拉蒙多尔蒂地球观测站的研究人员将调查表层生态学的几个方面，这些方面可能影响有机物质中的氮同位素特征，包括氮的吸收及其营养和垂直转移。除了良好的研究化学的Cariaco盆地，这项工作是基于一个初步的，为期两年的研究表明，氮（15 N）的同位素签名中的中型和大型浮游动物在冬季和夏季上升流期间增加，并类似的同位素签名的材料转移到底层沉积物陷阱。所观察到的协会表明，生产上升流的响应是一个关键事件，在营养交换，以及在输出通量。虽然这种双重作用是新的生产的标志之一，Cariaco时间序列提供了一个非常好的机会来评估两个主要的过程，可能会控制观察到的季节性同位素变化; 1）可变分馏过程中无机氮同化由于社会的变化，浮游植物;和2）可变同位素富集的有机物质由于营养转移的数量变化，它经历。在委内瑞拉和其他科学家的合作下，将对微型和微型浮游生物的大小类别以及硝酸盐中氮的同位素值进行明确的同位素取样，以便有可能检验这些假设。该项目还将评估通过缺氧氨氧化（anammox）途径去除化合氮的可能性。作为本研究的次要目标，还将评估有机碳（13 C）同位素丰度的变化。在更广泛的影响方面，该项目将与美国和委内瑞拉科学家合作，并将在学年期间和拉蒙特-多尔蒂大学本科生夏季研究经验（REU）计划期间为几名本科生的培训提供支持。 它还将扩大现有的中美洲合作组织时间序列网站（http：//www.imars.usf.edu/CAR/index.html），使教育界更容易获得数据，并指导学生开展课堂活动。

ABSTRACTOCE-063609The marine nitrogen cycle plays a critical role in controlling ocean productivity and the fluxes of other elements such as carbon. The ability to reconstruct how this important cycle has changed through time depends largely on nitrogen isotopic records in sediments, but there are several processes during the formation and transfer of organic nitrogen that can complicate this analysis. The NSF supported, CARIACO ocean time-series station has provided a detailed record of the relationships among seasonal upwelling, nutrients, surface productivity, and export flux in this region of the southern Caribbean off Venezuela. In this study, researchers at the Lamont Doherty Earth Observatory of Columbia University will investigate several aspects of surface layer ecology that could impact the nitrogen isotopic signature in organic material including nitrogen uptake and its trophic and vertical transfer. In addition to the well studied chemistry of the Cariaco Basin, this work is based on a preliminary, two-year study that indicated that the isotopic signature of nitrogen (15N) in the meso- and macrozooplankton increased in the winter and summer upwelling periods and were similar to the isotopic signatures of the material transferred to underlying sediment traps. The observed associations suggest that the elevated production in response to upwelling is a key event in both trophic exchange as well as in export flux. Although this dual role is one of the hallmarks of new production, the Cariaco time series provides an unusually good opportunity to evaluate two major processes that may control the observed seasonal isotopic variations; 1) Variable fractionation during inorganic nitrogen assimilation due to community changes in the phytoplankton; and 2) Variable isotopic enrichment of organic mater due to changes in the number of trophic transfers it undergoes. With the collaboration of Venezuelan and other scientists, explicit isotopic sampling of the nano- and microplankton size classes as well as of the isotopic value of nitrogen in nitrate will be done so that it will be possible to test these hypotheses. This project will also evaluate the possible removal of combined nitrogen by the anoxic ammonium oxidation (anammox) pathway. As a secondary goal of this study, the changes in the isotopic abundance of organic carbon (13C) also will be evaluated. In terms of broader impacts, the project will feature collaboration with both US and Venezuelan scientists and will provide support for the training of several undergraduate students both during the school year and during the summer research experiences for undergraduates (REU) program at Lamont-Doherty. It will also augment the existing CARIACO Time Series web site (http://www.imars.usf.edu/CAR/index.html) by providing better educational access to the data as well as directed student activities for classroom use.