Collaborative Research: Multiyear autonomous measurement of N-loss in the ETNP ODZ

深海的几个区域自然地几乎不含氧气。 由于缺乏氧气，生活在这些地区的微生物的生活方式与含氧沃茨水中的微生物不同，它们消耗硝酸根离子而不是氧气进行呼吸。 使用硝酸盐进行微生物呼吸导致产生氮气，这被称为反硝化。 氮是控制植物生长的重要营养素;然而，尽管植物可以以硝酸盐的形式使用氮，但除了少数例外，它们不能使用氮气。关于海洋中发生了多少脱氮作用，是什么控制了它，以及它在时间和空间上如何变化，仍然存在许多不确定性。 传统的海洋脱氮研究受到船舶在海上的时间和他们可以观察的海洋相对较小的比例的限制。 我们的项目计划通过使用称为浮子的车辆来解决这个问题，这些车辆可以在海洋中自主运行三年或更长时间，因为它们随着水流漂流数百公里。 我们将为十个浮标配备传感器来测量氧气和氮气，这些浮标将被放置在墨西哥西部太平洋的缺氧地区。 这是海洋中最大的此类区域，我们有两年的原型浮子结果，验证了我们的方法。 这项研究很可能会改变我们对海洋脱氮的理解，并最终通过对海洋氮循环的预测以及在当前和未来条件下固定二氧化碳的能力更有信心而使整个社会受益。 使用商用技术的浮子系统的应用和进一步发展将直接有利于后续研究，并更广泛地展示使用水跟踪平台来解决困难的海洋学问题。这项研究的进展预计将延续到其他学科，包括海洋地球化学建模。 该项目包括外联活动、对早期职业科学家的支持和学生培训。 对于外展活动，调查人员计划配合完善的课后计划，为马萨诸塞州代表性不足的人群提供服务，并在华盛顿大学利用与花车相关的展示材料进行公开演讲。 尽管缺氧区只占海洋总体积的一小部分，但在调节全球海洋碳和氮循环方面发挥着重要作用，包括容纳全球30%至50%的固定氮损失。不幸的是，目前的不确定性，臭氧消耗区氮损失来自大量的时间和空间变化率，仍然采样不足的船基测量。虽然当地监管的氮损失的氧气和有机物的可用性是公认的，时间/空间变化的氮通量的物理强迫，如远程通风，季节性变化，和中尺度涡的影响可能是一个结果。了解物理强迫对氮损失的影响是如何通过氧和有机通量介导的，将需要充分了解任何未来ODZ扩张的原因和后果。为了提高我们对ODZ氮损失的理解，我们将开展一项为期多年的自主浮动观测计划，以解决有关ODZ中生物可利用氮损失的突出问题。 作为最大的开放水域和我们试点部署的区域，我们的行动区域将是东热带北部。太平洋（ETNP），我们的研究将在多年的时间内确定，在现场纳米级的氧气和生物氮的浮子配置文件跨越地理梯度的氧气和表面生产力。对于第一次，我们的研究也将确定在1至2周的拉格朗日浮子漂移沿着一个恒定的密度表面的氮浓度的变化，在原位氮损失率。在ETNP进行的为期2年的浮动部署试验证明了我们这样做的能力。重要的是，与先前的工作相比，我们的基于浮子的方法更紧密地将观测的频率和分布与生物源氮生产的预期变化相匹配，并且通过获取500个剖面，将显著增加该区域的数据密度。氮的漂移和1000 nM氧的配置文件。该奖项反映了NSF的法定使命，并已被认为是值得支持，通过评估使用基金会的学术价值和更广泛的影响审查标准。

Several regions of the deep ocean naturally contain almost no oxygen. Because of this lack of oxygen, microbes living in these regions live in ways that differ from those in oxygenated waters consuming nitrate ions instead of oxygen for respiration. Use of nitrate for microbial respiration results in the production of nitrogen gas which is called denitrification. The resulting removal of nitrate has consequences for the whole ocean as nitrogen is an important nutrient controlling plant growth; however, whereas plants can use nitrogen in the form of nitrate, they cannot, with a few exceptions, use nitrogen gas. There remains a number of uncertainties regarding how much denitrification occurs in the ocean, what controls it, and how it varies in time and space. Traditional studies of ocean denitrification have been limited by the time ships can be at sea and the relatively small proportion of the ocean they can observe. Our project plans to remedy this problem by using vehicles called floats that can operate autonomously in the ocean for three years or more as they drift with currents over hundreds of kilometers. We will outfit ten floats with sensors to measure oxygen and nitrogen gas which will be placed throughout the oxygen depleted region of the Pacific Ocean to the west of Mexico. This is the largest such region in the ocean from which we have two years of results from a prototype float which validated our approach. This study may well transform our understanding of ocean denitrification and ultimately benefit society as a whole through greater confidence in predictions of the ocean's nitrogen cycle and capacity to fix carbon dioxide under current and future conditions. Application and further development of float systems using commercially available technology will directly benefit successor studies, and more broadly showcase the use of water-following platforms to tackle difficult oceanographic problems. Advances from this study are expected to carry over to other disciplines including ocean biogeochemical modeling. Outreach activities, support for an early career scientist, and student training are included in the project. For the outreach activities, the investigators plan to tie into well-established after-school programs serving underrepresented populations in Massachusetts and established opportunities for public presentations using float related display materials at the University of Washington. Oxygen deficient zones (ODZs), despite constituting a small fraction of total oceanic volume, play important roles in regulating global ocean carbon and nitrogen cycles including hosting 30 to 50% of the global loss of fixed nitrogen. Unfortunately, current uncertainty in ODZ nitrogen loss derives from substantial temporal and spatial variability in rates that remain under-sampled by ship-based measurements. While local regulation of nitrogen loss by oxygen and organic matter availability are well accepted, temporal/spatial variability in the nitrogen flux is likely a result of the influence of physical forcings such as remote ventilation, seasonal variability, and mesoscale eddies. Understanding how the impact of physical forcings on nitrogen loss as mediated through oxygen and organic flux will be required to fully understand the causes and consequences of any future ODZ expansion. To improve our understanding of ODZ nitrogen loss, we will carry out a multiyear, autonomous float-based observational program to address outstanding questions regarding bioavailable nitrogen loss in ODZs. As the largest ODZ and region of our pilot deployments, our operation area will be the Eastern Tropical N. Pacific (ETNP) where our study will determine over a multi-year period, in-situ nM-level oxygen and biogenic nitrogen on float profiles spanning geographic gradients in oxygen and surface productivity. For the first time, our study will also determine in situ nitrogen loss rates from changes in nitrogen concentration during 1 to 2 week Lagrangian float drifts along a constant density surface. A pilot 2 yr float deployment in the ETNP documents our ability to do so. Critically, our float-based approach more closely matches the frequency and distribution of observations to the expected variability in biogenic nitrogen production as compared to prior work and will dramatically increase the data density for this region by acquiring 500 profiles/drifts for nitrogen and 1000 profiles for nM oxygen.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.