The oceans play an important role in the geochemical cycle of methyl bromide (CH3Br), the major carrier of O3-destroying bromine to the stratosphere. The quantity of CH3Br produced annually in seawater is comparable to the amount entering the atmosphere each year from natural and anthropogenic sources. The production mechanism is unknown but may be biological. Most of this CH3Br is consumed in situ by hydrolysis or reaction with chloride. The size of the fraction which escapes to the atmosphere is poorly constrained; measurements in seawater and the atmosphere have been used to justify both a large oceanic CH3Br flux to the atmosphere and a small net ocean sink. Since the consumption reactions are extremely temperature-sensitive, small temperature variations have large effects on the CH3Br concentration in seawater, and therefore on the exchange between the atmosphere and the ocean. The net CH3Br flux is also sensitive to variations in the rate of CH3Br production. We have quantified these effects using a simple steady state mass balance model. When CH3Br production rates are linearly scaled with seawater chlorophyll content, this model reproduces the latitudinal variations in marine CH3Br concentrations observed in the east Pacific Ocean by Singh et al. [1983] and by Lobert et al. [1995]. The apparent correlation of CH3Br production with primary production explains the discrepancies between the two observational studies, strengthening recent suggestions that the open ocean is a small net sink for atmospheric CH3Br, rather than a large net source. The Southern Ocean is implicated as a possible large net source of CH3Br to the atmosphere. Since our model indicates that both the direction and magnitude of CH3Br exchange between the atmosphere and ocean are extremely sensitive to temperature and marine productivity, and since the rate of CH3Br production in the oceans is comparable to the rate at which this compound is introduced to the atmosphere, even small perturbations to temperature or productivity can modify atmospheric CH3Br. Therefore atmospheric CH3Br should be sensitive to climate conditions. Our modeling indicates that climate-induced CH3Br variations can be larger than those resulting from small (+/- 25%) changes in the anthropogenic source, assuming that this source comprises less than half of all inputs. Future measurements of marine CH3Br, temperature, and primary production should be combined with such models to determine the relationship between marine biological activity and CH3Br production. Better understanding of the biological term is especially important to assess the importance of non-anthropogenic sources to stratospheric ozone loss and the sensitivity of these sources to global climate change.

中文翻译：

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溴甲烷：海洋来源、海洋汇和气候敏感性

海洋在甲基溴 (CH3Br) 的地球化学循环中发挥着重要作用，甲基溴是破坏 O3 的溴进入平流层的主要载体。海水中每年产生的 CH3Br 的数量与每年从自然和人为来源进入大气的数量相当。生产机制未知，但可能是生物学的。大多数 CH3Br 通过水解或与氯化物反应就地消耗。逃逸到大气中的那部分的大小没有受到很好的限制；海水和大气中的测量已被用来证明大量的海洋 CH3Br 流入大气和一个小的净海洋汇。由于消耗反应对温度极为敏感，微小的温度变化对海水中 CH3Br 浓度的影响很大，因此，关于大气和海洋之间的交换。净 CH3Br 通量也对 CH3Br 生产速率的变化敏感。我们使用简单的稳态质量平衡模型量化了这些影响。当 CH3Br 生产率与海水叶绿素含量成线性比例时，该模型再现了 Singh 等人在东太平洋观察到的海洋 CH3Br 浓度的纬度变化。[1983] 和 Lobert 等人。[1995]。CH3Br 生产与初级生产之间的明显相关性解释了两项观测研究之间的差异，加强了最近关于公海是大气 CH3Br 的小型净汇而不是大型净源的建议。南大洋被认为是大气中 CH3Br 的一个可能的大型净来源。由于我们的模型表明大气和海洋之间 CH3Br 交换的方向和大小对温度和海洋生产力极其敏感，而且由于海洋中 CH3Br 的产生速率与该化合物被引入到海洋中的速率相当。大气，即使对温度或生产力的微小扰动也可以改变大气 CH3Br。因此大气 CH3Br 应该对气候条件敏感。我们的模型表明，气候引起的 CH3Br 变化可能大于由人为来源的微小 (+/- 25%) 变化引起的变化，假设该来源占所有输入的不到一半。未来对海洋 CH3Br、温度、初级生产应与此类模型相结合，以确定海洋生物活动与 CH3Br 生产之间的关系。更好地理解生物学术语对于评估非人为来源对平流层臭氧损失的重要性以及这些来源对全球气候变化的敏感性尤为重要。