Assessing and extending the N2O record in the Vostok ice core

测量冰芯中的微量气体是重建大气成分的主要手段。在这些重建中隐含着两个潜在的假设：1)从冰芯中恢复的气泡记录了气泡形成时大气的组成；2)气泡的组成没有因冰盖内极长的储存期而受到损害。虽然有充分的证据表明，某些微量气体记录（如co2和CH4）可能没有受到损害，但从Vostok的第二个冰川终止期开始的异常氧化亚氮（N2O）测量结果被认为是硝化微生物在现场产生（N2O）的结果。这个三管齐下的试点项目将测试应用分子技术、微生物培养和生理分析以及同位素/地球化学测量相结合的可行性，以评估硝化细菌改变冰芯中氮物种的潜力。首先，我们打算证明我们的分子和微生物技术能够识别冰川冰中的硝化细菌。我们将通过将已知的嗜冷/耐寒硝化菌（如耐低温亚硝化单胞菌）的活培养物添加到一套融化的Vostok冰样品（不同的细胞浓度）中来证明这一点，这些样品将被重新冷冻。然后，我们将分子技术应用于这些“加标”样品，以建立我们的分子探针的检测限。我们还将开始从这些模型冰芯中富集培养物，以监测硝化生物随时间的生长和活动。最后，我们将采用不同的去污技术，以确保我们从冰芯中获得未受损害的样品，用于微生物工作。我们将尝试通过添加同位素标记的底物（15NH4）和监测标记物与N2O和NO2的结合来测量N2O的产生，并量化硝化器活性的温度依赖性。由于预计代谢率极低，我们计划建立一个持续3年的孵化期。最后，我们建议分析Vostok岩芯中N2O的元素和同位素组成，以确定我们在终止II中记录的异常行为是否在终止I中也很明显。我们将比较Vostok N2O记录与GISP II， Taylor Dome和GRIP冰芯的同期N2O记录。

Measurements of trace gas species in ice cores are the primary means for reconstructing the composition of the atmosphere. There are two underlying assumptions implicit in these reconstructions: 1) the bubbles recovered from the ice cores record the composition of the atmosphere at the time the bubbles were formed, and 2) the composition of the bubbles has not been compromised by the extremely long storage periods within the ice sheet. While there is ample evidence that certain trace gas records (e.g. CO2and CH4) have probably not been compromised, anomalous nitrous oxide (N2O) measurements from the penultimate glacial termination at Vostok are thought to be the result of in-situ (N2O) production by nitrifying microorganisms. This 3-pronged pilot project will test the feasibility of applying a combination of molecular techniques, microbial cultivation and physiological assays and isotopic/geochemical measurements in evaluating the potential for nitrifying bacteria to modify nitrogen species in an ice core. First we propose to demonstrate that our molecular and microbiological techniques are capable of identifying nitrifying bacteria in glacial ice. We will demonstrate this by adding live cultures of known psychrophilic/psychrotolerant nitrifiers (e.g. Nitrosomonas cryotolerans) to a suite of melted Vostok ice samples (varying cell concentrations) which will be refrozen. We will then apply our molecular techniques to these "spiked" samples to establish the detection limit for our molecular probes. We will also start enrichment cultures from these model ice cores to monitor the growth and activity of the nitrifying organisms over time. Finally, we will apply different decontamination techniques to insure we are getting uncompromised samples from the ice cores for the microbial work. We will attempt to measure N2O production and quantify the temperature dependence of the nitrifier activity by adding isotopically labeled substrate (15NH4) and monitoring the incorporation of the label into N2O and NO2. As the metabolic rates are expected to be extremely low, we plan to set up incubations that will extend over a ~3yr period. Finally, we propose to analyze the elemental and isotopic composition of N2O in the Vostok core spanning the last termination (Termination I) to see if the anomalous behavior we documented for Termination II is also apparent during Termination I. We will compare the Vostok N2O record with contemporaneous N2O records from the GISP II, Taylor Dome, and GRIP ice cores.