In situ benthic fluxes from an intermittently active mud volcano at the Costa Rica convergent margin
In situ benthic fluxes from an intermittently active mud volcano at the Costa Rica convergent margin
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哥斯达黎加汇聚边缘间歇性活动泥火山的原位底栖通量
DOI：
10.1016/j.epsl.2005.03.009
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发表时间：
2005
影响因子：
5.3
通讯作者：
Rehder G
中科院分区：
文献类型：
--
作者：
Linke P;Wallmann K;Suess E;Hensen C;Rehder G
沿着哥斯达黎加外的侵蚀会聚边缘存在大量由泥底辟作用或泥火山作用建造的丘状构造。其中之一，Mound 12，一个间歇性活跃的泥火山，目前排放大量的水溶性物质和水。化学合成喷口群落、自生碳酸盐和水柱中的甲烷羽流都是这种活动的表现。海底通量测量是由部署在位于12号丘最活跃部分的喷口处的视频引导海底舱着陆器获得的。着陆器配备了4个独立的舱室，覆盖海底的相邻区域。通过对封闭的底层沃茨重复取样记录了底栖通量，同时在部署一天后用着陆器恢复了底层表层沉积物。其中一个室直接放置在一个活跃的通风口的中心，该通风口以细菌垫的出现为标志，而其他室位于同一通风系统的边缘，横向距离仅为40厘米。建立了一个输运-反应模型，并用于描述表层沉积物孔隙水的浓度分布和封闭底层水的时间演化。重复的模型运行显示，在喷口中心流速为10 cm yr− 1时，孔隙水和底栖生物室数据的拟合效果最好。底栖生物周转（底栖生物过滤器）强烈地改变了底层水的通量率。在细菌垫位置，来自下方的甲烷通量高达1032 μmol cm− 2 yr −1，其中588 μmol cm− 2 yr − 1在表层沉积物中被微生物聚生体以硫酸盐为末端电子受体氧化，440 μmol cm− 2 yr − 1渗入上覆底层水中。硫化物通过上升的流体（238 μmol cm− 2 yr −1）被输送到地表，并通过甲烷的厌氧氧化（AOM，588 μmol cm− 2 yr −1）在地表沉积物中形成。然而，硫化物并没有释放到底层水中，而是在沉积物/水界面被氧气和硝酸盐完全氧化。进入沉积物的氧和硝酸盐通量很高（分别为781和700 μmol cm− 2 yr −1），主要是由硫化物的微生物氧化驱动的。在喷口系统边缘的其他室中，底栖生物通量要低得多。因此，在其中一个室中记录到的甲烷和氧气通量分别只有28和89 μmol cm− 2 yr −1。我们的研究表明，甲烷的好氧氧化比甲烷的厌氧氧化效率低得多，因此，甲烷在沉积物中没有被AOM氧化，几乎完全释放到底层水中。因此，厌氧而不是好氧甲烷氧化在调节底栖甲烷通量方面发挥着主要作用。此外，我们表明，甲烷和氧通量在冷喷口网站可能会变化高达3个数量级的横向距离只有40厘米，表明流体流动和甲烷释放在海底的极端集中。
Along the erosive convergent margin off Costa Rica a large number of mound-shaped structures exist built by mud diapirism or mud volcanism. One of these, Mound 12, an intermittently active mud volcano, currently emits large amounts of aqueous dissolved species and water. Chemosynthetic vent communities, authigenic carbonates, and methane plumes in the water column are manifestations of that activity. Benthic flux measurements were obtained by a video-guided Benthic Chamber Lander (BCL) deployed at a vent site located in the most active part of Mound 12. The lander was equipped with 4 independent chambers covering adjacent areas of the seafloor. Benthic fluxes were recorded by repeated sampling of the enclosed bottom waters while the underlying surface sediments were recovered with the lander after a deployment time of one day. One of the chambers was placed directly in the centre of an active vent marked by the occurrence of a bacterial mat while the other chambers were located at the fringe of the same vent system at a lateral distance of only 40 cm. A transport-reaction model was developed and applied to describe the concentration profiles in the pore water of the recovered surface sediments and the temporal evolution of the enclosed bottom water. Repeated model runs revealed that the best fit to the pore water and benthic chamber data is obtained with a flow velocity of 10 cm yr−1at the centre of the vent. The flux rates to the bottom water are strongly modified by the benthic turnover (benthic filter). The methane flux from below at the bacterial mat site is as high as 1032 μmol cm−2yr−1, out of which 588 μmol cm−2yr−1is oxidised in the surface sediments by microbial consortia using sulphate as terminal electron acceptor and 440 μmol cm−2yr−1are seeping into the overlaying bottom water. Sulphide is transported to the surface by ascending fluids (238 μmol cm−2yr−1) and is formed within the surface sediment by the anaerobic oxidation of methane (AOM, 588 μmol cm−2yr−1). However, sulphide is not released into the bottom water but completely oxidized by oxygen and nitrate at the sediment/water interface. The oxygen and nitrate fluxes into the sediment are high (781 and 700 μmol cm−2yr−1, respectively) and are mainly driven by the microbial oxidation of sulphide. Benthic fluxes were much lower in the other chambers placed in the fringe of the vent system. Thus, methane and oxygen fluxes of only 28 and 89 μmol cm−2yr−1, respectively were recorded in one of these chambers. Our study shows that the aerobic oxidation of methane is much less efficient than the anaerobic oxidation of methane so that methane which is not oxidized within the sediment by AOM is almost completely released into the bottom water. Hence, anaerobic rather than aerobic methane oxidation plays the major role in the regulation of benthic methane fluxes. Moreover, we demonstrate that methane and oxygen fluxes at cold vent sites may vary up to 3 orders of magnitude over a lateral distance of only 40 cm indicating an extreme focussing of fluid flow and methane release at the seafloor.
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DOI：
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2003
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