Collaborative Research: Documenting N2 fixation in N deficient waters of the Eastern Tropical South Pacific

几项独立的地球化学和遥感证据表明，二氮（N2）固定可能与主要氧气最低区（OMZ）下游的地表沃茨水有关，特别是在热带南太平洋东部（ETSP）。然而，几乎没有直接证据支持这些推论。除了证实这些间接的评估，记录显着的N2固定在ETSP将提供深入了解两个长期存在的争议：海洋N预算是否平衡，所暗示的建模和古海洋学数据，如果是这样的话，如何增加和删除N的空间，从而在时间上耦合的过程？ 在这个项目中，南加州大学和迈阿密大学的研究人员将检验这一假设，即ETSP中的固定发生率等于或超过先前在更充分研究的地区（如亚/热带北大西洋的贫营养沃茨）中记录的固定率。如果按比例缩放到ETSP沃茨的表面积，这可能会增加额外的10-50 Tg N每年的输入到全球海洋N预算。 他们将在连续两年的初夏和夏末在ETSP进行两次巡航，使用互补的生物和地球化学工具评估N2固定作为地表沃茨新氮来源的定量意义。将在两个时间/空间尺度上评估N2固定率：每日/当地（瓶15 N2培养和漂浮沉积物捕集器）;和季节/区域（使用系泊沉积物捕集器和水柱TDN d15 N的d15 N预算）。这些估计提供了详细的观测潜在的N2固定在两个夏季，当利率预计将是最大的，以及长期观察较低的预期N2固定期。结合这些不同的估计将旨在确定该地区的N2固定是否有助于平衡海洋氮预算。 如果一切按计划进行，这项研究将确定在ETSP固定N2的定量重要性，以及这些以前没有记录的速率是否可以帮助解决海洋氮预算。影响包括海洋N循环的能力，以保持体内平衡，从而在冰期/间冰期的时间尺度上的全球C循环。 更广泛的影响：该项目将提供研究经验和机会，为博士后以及研究生。将有直接的互动和指导与研究生在实验室和邮轮的机会。此外，该项目将定期涉及本科生作为工作研究，并参加南加州大学地球生物学REU计划。拟议的活动将与NSF资助的COSEE-West南加州大学和加州大学洛杉矶分校计划的工作相结合。该中心包括一个由海洋学研究人员、K-12教育工作者、教育中心和大洛杉矶地区公众组成的网络。

Several independent lines of geochemical and remote sensing evidence suggest that dinitrogen (N2) fixation may be associated with surface waters downstream of major oxygen minimum zones (OMZs) and in particular in the Eastern Tropical South Pacific (ETSP). However, little direct evidence supports these inferences. Besides substantiating these indirect assessments, documenting significant N2 fixation in the ETSP would provide insight into two longstanding controversies: Is the marine N budget balanced, as implied by modeling and paleoceanographic data, and if so, how are the processes that add and remove N spatially, and thus temporally coupled? In this project researchers at the University of Southern California and the University of Miami will test the hypothesis that fixation occurs in the ETSP at areal rates that equal or exceed those previously documented in more well-studied regions such as the oligotrophic waters of the sub/tropical North Atlantic. If scaled to the surface area of ETSP waters, this could add an additional 10-50 Tg N per year of inputs to the global marine N budget. They will undertake two cruises in the ETSP during early and late summer in two consecutive years to assess the quantitative significance of N2 fixation as a source of new N to surface waters using complementary biological and geochemical tools. N2 fixation rates will be evaluated on two temporal/spatial scales: daily/local (bottle 15N2 incubations and floating sediment traps); and seasonal/regional (d15N budget using moored sediment traps and water column TDN d15N). These estimates provide detailed observations of potential N2 fixation during station occupation in two summer seasons, when rates are expected to be greatest, as well as prolonged observation over lower expected N2 fixation periods. A combination of these different estimates will aim to determine if N2 fixation in this region can help balance the marine N budget. If all goes as planned, this study will determine the quantitative importance of N2 fixation in the ETSP, and whether these previously undocumented rates can help resolve the marine N budget. Implications include the ability of the marine N cycle to maintain homeostasis, and thus the global C cycle on glacial/interglacial time scales. Broader Impacts: This project will provide research experience and opportunities for a postdoctoral associate as well as a graduate student. There will be direct interactions and opportunities for mentoring with graduate students in the laboratory and on cruises. Also, the project will routinely involve undergraduates as work-studies and participate in the USC Geobiology REU Program. The proposed activities will be integrated with the work of the NSF funded COSEE-West program to USC and UCLA. This Center involves a network of oceanographic researchers, K-12 educators, education centers and the general public in the greater Los Angeles area.