Methyl Bromide Cycling by Marine Phytoplankton and Associated Bacterioplankton

摘要近二十年来，由于人们对大气中臭氧浓度下降的担忧，研究人员开始寻找除氟氯烃以外能破坏臭氧的化合物。其中一种化合物是甲基溴（CH3Br），目前认为它是平流层中Br的最大来源。甲基溴及其衍生自由基在全球范围内可破坏5-10%的平流层臭氧，在区域范围内则可破坏更多。对对流层CH3Br的主要自然来源似乎是海洋、生物生产和随后的海气交换；野火导致的生物质燃烧的输出是未知的。人为来源包括生物质燃烧、汽车尾气，主要是熏蒸。模型预测，全球人为排放占总排放量的25-54%，其余为自然排放。这清楚地表明了自然资源的重要性。大气中CH3Br的主要损失是光解作用、海气交换、土壤和植物的表面损失以及土壤中的生物降解。大气中甲基溴的浓度似乎正以每年3%（+1%）的速度增加。由于其人为来源，目前存在一项建议，以大幅减少其作为熏蒸剂的使用，从而减少其向大气的输入。这种减少将影响对大气的自然和人为影响之间的平衡。这种减少将影响大气中CH3Br浓度的自然和人为影响之间的平衡。海洋在控制对流层甲基溴负荷方面起着重要而复杂的作用。海面可以作为大气的源和汇。为了确定海气交换中溶解的CH3Br的净可用性，必须了解所涉及的各个隔间和机制。本研究将在实验室和实地评估海洋浮游植物生产CH3Br的程度和速率，以确定甲基溴在海洋中循环的机制的相对重要性。

9618533 9617680 MATRAI ABSTRACT Concern about declining ozone concentrations in the atmosphere in the last two decades has led researchers to look for compounds that destroy ozone, other than chlorofluorocarbons. One such compound is methyl bromide (CH3Br) which is presently believed to be the largest source of Br in the stratosphere. Methyl bromide and derived radicals can destroy 5-10% of stratospheric ozone on a global basis and more on a regional basis. The major natural source of CH3Br to the troposphere appears to be marine, biogenic production and subsequent sea-air exchange; the output from biomass burning due to wildfires is unknown. Anthropogenic sources include biomass burning, automobile exhaust, and, mainly, fumigation. Models predict a global anthropogenic contribution of 25-54% of total emissions, the remainder being the natural contribution. This clearly indicates the importance of natural sources. The principal losses for atmospheric CH3Br are photolysis, air-sea exchange, surface losses to soils and plants, and biological degradation in soils. atmospheric concentrations of methyl bromide appear to be increasing at a rate of 3% (+1%) per year. Due to its anthropogenic sources, a proposal currently exists to drastically curtail its use as a fumigant and thus reduce its input to the atmosphere. This reduction would affect the balance between natural and anthropogenic effects on the atmosphere. This reduction would affect the balance between natural and anthropogenic effects on the atmospheric concentration of CH3Br. The oceans play an important and complex part in controlling the tropospheric burden of methyl bromide. Sea surface can act both as a source and a sink to the atmosphere. To determine the net availability of dissolved CH3Br for air-sea exchange, the various compartments and mechanisms involved must be understood. This study will assess the extent and rate of CH3Br production by marine phytoplankton in the laboratory and in the field in o rder to determine the relative importance of the mechanisms by which methyl bromide cycles in the oceans.