Cycling of redox-sensitive elements in a sandy subterranean estuary of the southern North Sea
Cycling of redox-sensitive elements in a sandy subterranean estuary of the southern North Sea
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DOI：
10.1016/j.marchem.2016.11.003
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发表时间：
2017-01
期刊：
影响因子：
3
通讯作者：
Anja Reckhardt;M. Beck;J. Greskowiak;B. Schnetger;M. Böttcher;M. Gehre;H. Brumsack
中科院分区：
文献类型：
--
作者：
Anja Reckhardt;M. Beck;J. Greskowiak;B. Schnetger;M. Böttcher;M. Gehre;H. Brumsack
金属和硫的循环在海滩沉积物中起着重要作用。我们研究了氧化还原敏感的金属锰，铁，U，Re，Mo和V，在关系到盐度，有机质，和硫循环内的地下河口的屏障岛沙海滩Spiekeroog岛，北方德国。孔隙水样品沿沿着一个跨海岸断面下降到5米以下的沉积物surface.Redox条件范围从好氧，接近沙丘的基础，以子缺氧向低水位线。我们证明，地球化学过程不仅改变了微量金属的孔隙水浓度，但也反映了O同位素-和溶解的SO 42 −的S同位素组成在较小程度上。陆地和海洋端元之间保守混合的偏差影响微量金属通量通过海底地下水排放到海洋。溶解的活性锰的存在可能会加速氧化还原反应，我们在浅层亚氧孔隙沃茨水中检测到了这种活性锰。SO 42-的O同位素组成的变化表明，在亚氧带中存在一个隐藏的S循环，该循环由Fe和Mn的循环提供燃料。海水循环通过上部海滩（潮间带的沙丘部分）的沉积物从溶液中去除U和V，但作为Mn、Fe、Re和Mo的来源进入海洋。孔隙水排放的护堤接近低水位线表现出较低的U，V，和Re浓度比邻近的海水。因此，这部分海滩是U、V和Re的汇，但却是Mn、Fe和Mo的源。由于缺乏溶解的硫化物，在孔隙水中没有发现明显的Mo亏损。从地下河口到海洋的净通量率估计为每天和每米海岸线，Fe为185 mmol，Mn为48 mmol，Mo为8.3 μmol，Re为− 24.7 nmol，U为− 8.6 μmol，V为− 24 μmol。这些通量包括来自岛上淡水透镜的淡水通量和通过海滩表面的海水循环。因此，地下河口作为V，U和Re汇，但作为Fe，Mn和Mo的来源，以邻近的海水。Spiekeroog海滩系统与岛屿的backbarrier潮滩边缘的溶解金属的净通量的第一次比较表明，潮滩面积可能是更重要的供应或从北海的金属去除。
The cycling of metals and sulfur plays an important role in beach sediments. We studied the redox-sensitive metals Mn, Fe, U, Re, Mo, and V, in relation to salinity, organic matter-, and sulfur cycling within the subterranean estuary of a barrier island sand beach on Spiekeroog Island, Northern Germany. Pore water samples were obtained along a cross-shore transect down to 5 m below the sediment surface.Redox conditions range from oxic, close to the base of the dune, to sub- to anoxic towards the low water line. We demonstrate that biogeochemical processes alter not only the pore water concentrations of the trace metals, but are also reflected by the O isotope- and to a minor degree the S isotope composition of dissolved SO42 −. The deviations from conservative mixing between terrestrial and marine endmembers influence trace metal fluxes into the ocean via submarine groundwater discharge. Redox reactions may be accelerated by the presence of dissolved reactive Mn, which we detected in shallow suboxic pore waters. Changes in the O isotope composition of SO42 −indicate a cryptic S cycle in the suboxic zone that is fueled by the cycling of Fe and Mn.Seawater circulation through sediments of the upper beach (duneward part of the intertidal zone) removes U and V from solution, but serves as a source for Mn, Fe, Re, and Mo to the ocean. Pore water discharging from a berm close to the low water line exhibits lower U, V, and Re concentrations than adjacent seawater. This part of the beach thus serves as a sink for U, V, and Re, but as a source for Mn, Fe, and Mo. No significant Mo depletion is found in the pore water, due to the lack of dissolved sulfide. Net flux rates from the subterranean estuary into the ocean are estimated to be 185 mmol for Fe, 48 mmol for Mn, 8.3 μmol for Mo, − 24.7 nmol for Re, − 8.6 μmol for U, and − 24 μmol for V per day and meter of shore line. These fluxes include freshwater flux from the island's freshwater lens and seawater circulation through the beach face. The subterranean estuary therefore serves as V, U, and Re sink, but as a source for Fe, Mn, and Mo to adjacent seawater.A first comparison of net fluxes of dissolved metals from the Spiekeroog beach system with the island's backbarrier tidal flat margins indicates that the tidal flat area might be of greater importance for the supply or removal of metals to/from the North Sea.