Biocomplexity: Collaborative research: Oceanic N2 fixation and global climate

海洋氮（N2）固定最近被确定为海洋氮(N)循环的重要组成部分，并可能通过向上层水柱提供新的氮源直接影响海洋中大气CO2的封存。将氮气转化为活性氮的原核微生物是浮游生态系统的一个独特的子组成部分，并表现出各种复杂的动力学，包括微生物联合体和共生的形成，有时还会出现大规模的繁殖。越来越多的证据表明，铁（Fe）的有效性可能是这些浮游海洋重氮营养体的关键控制因素。铁传递到上层海洋的主要途径是通过粉尘沉积。因此，N2固定物可能直接参与气候系统的全球反馈，这些反馈也可能在许多不同的时间尺度上表现出复杂的动力学。假设的反馈机制将包括以下组成部分：世界海洋中氮的固定速率可以对大气中温室气体二氧化碳（CO2）的浓度产生影响，时间尺度从几十年（地表生物地球化学的变化）到几千年（氮固定和反硝化平衡产生的总NO3 -储量的变化）。大气中的二氧化碳浓度影响气候。反过来，气候系统可以通过控制Feon粉尘的供应和影响上层海洋的分层来影响海洋中N2的固定速率。人类也在这个反馈循环的当前表现中发挥着直接的作用，通过他们对尘埃产生的影响，通过沙漠边缘的农业，以及我们自己向大气中排放的二氧化碳。这些影响的循环性质可以导致反馈系统，特别是在较长的时间尺度上。这个由安东尼·迈克尔斯博士领导的跨学科合作研究小组将研究这个系统的每一个组成部分，然后对假设的反馈过程进行建模。由于这个系统的各个部分的相互作用，围绕着能够固定N2的原核微生物的独特行为和生物地球化学，这个反馈回路应该在各种时间尺度上表现出复杂的行为。在这项研究中，我们将进行一系列有针对性的实验和实地观测，以了解和参数化这一全球过程的每个部分，包括尘埃沉积对海洋N2固定的直接控制。这样的理解将为在数年到数千年的时间尺度上研究这个系统的复杂动力学的建模过程提供依据。建模过程将通过与海洋时间序列研究和沉积物岩心提供的海洋生物地球化学随时间变化的数据进行比较来评估。

BIOCOMPLEXITY: OCEANIC N2 FIXATION AND GLOBAL CLIMATE Oceanic nitrogen (N2) fixation has recently been identified as a significant part of theoceanic nitrogen (N) cycle and may directly influence the sequestration of atmospheric CO2 inthe oceans by providing a new source of N to the upper water column. The prokaryoticmicroorganisms that convert N2 gas to reactive N are an unique subcomponent of planktonicecosystems and exhibit a variety of complex dynamics including the formation of microbialconsortia and symbioses and, at times, massive blooms. Accumulating evidence indicates thatiron (Fe) availability may be a key controlling factor for these planktonic marine diazotrophs.The primary pathway of Fe delivery to the upper oceans is through dust deposition.N2 fixers may therefore be directly involved in global feedbacks with the climate systemand these feedbacks may also exhibit complex dynamics on many different time-scales. The hypothesized feedback mechanisms will have the following component parts: The rate of N2fixation in the world's oceans can have an impact on the concentration of the greenhouse gas,carbon dioxide (CO2), in the atmosphere on time-scales of decades (variability in surfacebiogeochemistry) to millennia (changes in the total NO3 - stock from the balance of N2 fixationand denitrification). CO2 concentrations in the atmosphere influence the climate. The climatesystem, in turn, can influence the rate of N2 fixation in the oceans by controlling the supply of Feon dust and by influencing the stratification of the upper ocean. Humans also have a direct rolein the current manifestation of this feedback cycle by their influence on dust production, throughagriculture at the margins of deserts, and by our own production of CO2 into the atmosphere.The circular nature of these influences can lead to a feedback system, particularly on longer time-scales. This collaborative and interdisciplinary group of investigators, led by Dr. Anthony Michaels, will study each of the components of this system and then to model the hypothesized feedback processes. Because of the interaction of the various parts of this system, keyed around the unique behavior and biogeochemistry of the prokaryotic microorganisms that can fix N2, this feedback loop should exhibit complex behaviors on a variety of time-scales. In this research, we will conduct a targeted series of experiments and field observations to understand and parameterize each of the pieces of this global process including the direct control of marine N2 fixation by dust deposition. This understanding will then feed a modeling process that examines the complex dynamics of this system on time-scales of years to millennia. The modeling process will be evaluated by comparison with data on the time-dependent behavior ofocean biogeochemistry as available from ocean time-series studies and sediment cores.