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

几个独立的地球化学和遥感证据表明，二氮（N2）固定可能与主要氧最小带（OMZs）下游的地表水有关，特别是在东热带南太平洋（ETSP）。然而，几乎没有直接证据支持这些推论。除了证实这些间接评估之外，记录ETSP中显著的氮固定将为两个长期存在的争议提供见解：海洋氮收支是否平衡，正如模型和古海洋学数据所暗示的那样，如果是这样，那么增加和减少氮的过程在空间上是如何耦合的，从而在时间上是如何耦合的？在这个项目中，南加州大学和迈阿密大学的研究人员将测试ETSP中固定发生的面积速率等于或超过先前在研究更充分的地区（如亚热带/热带北大西洋的少营养水域）记录的假设。如果按比例计算到ETSP水域的表面，这可能会为全球海洋N预算增加每年10-50 Tg N的输入。他们将在连续两年的夏初和夏末在ETSP进行两次巡航，利用互补的生物和地球化学工具，评估氮固定作为地表水新氮来源的定量意义。N2固定率将在两个时间/空间尺度上进行评估：每日/局部（瓶15N2孵卵和浮动沉积物陷阱）；以及季节/区域（使用系泊沉积物陷阱和水柱TDN d15N的d15N预算）。这些估计提供了在两个夏季站位期间潜在氮固定的详细观测结果，这两个夏季预计氮固定率最高，以及在较低的预期氮固定期进行长期观察。这些不同估算的组合将旨在确定该地区的氮固定是否有助于平衡海洋氮收支。如果一切按计划进行，这项研究将确定ETSP中N2固定的定量重要性，以及这些先前未记录的速率是否有助于解决海洋N预算问题。其含义包括海洋氮循环维持内部平衡的能力，从而在冰期/间冰期时间尺度上确定全球碳循环。更广泛的影响：该项目将为博士后和研究生提供研究经验和机会。将有直接的互动，并有机会指导研究生在实验室和游轮。此外，该项目将定期涉及本科生作为勤工俭学，并参与南加州大学地球生物学REU计划。拟议的活动将与美国国家科学基金会资助的南加州大学和加州大学洛杉矶分校COSEE-West项目的工作相结合。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的公众组成的网络。

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.