Isotope fractionation between dissolved and suspended particulate Fe in the oxic and anoxic water column of the Baltic Sea
Isotope fractionation between dissolved and suspended particulate Fe in the oxic and anoxic water column of the Baltic Sea
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DOI：
10.5194/bg-10-233-2013
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发表时间：
2012-04
期刊：
影响因子：
4.9
通讯作者：
M. Staubwasser;R. Schoenberg;F. Blanckenburg;S. Krüger;C. Pohl
中科院分区：
文献类型：
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作者：
M. Staubwasser;R. Schoenberg;F. Blanckenburg;S. Krüger;C. Pohl
通过波罗的海东哥特兰盆地缺氧水体的深度剖面，分析了铁同位素比值和溶解铁浓度（Fe dis，SPM）。结果表明，整个铁质层的δ 56 Fe分布有一个急剧的梯度，在富氧深盆中δ 56 Fe分布= −0.4‰，在富氧上层水柱中δ 56 Fe分布= p 0.3 ‰。同位素梯度与Fe分布的强浓度梯度相重叠，在Fe SPM中出现浓度最大值，δ 56 Fe SPM值低于δ 56 Fe分布。这些特征表明，在典型的氧化沉淀过程中，在氧化还原界面上，从溶液到悬浮的铁羟基氧化物（Fe IOH）的轻铁同位素的优先损失。总分馏的标志是Δ 56 FeIOH-Fe（II）（aq）> 0‰.这种差异似乎是海洋水柱中反应动力学主导的同位素交换的结果，而不是其他地方氧化Fe沉淀通常推断的平衡分馏。高残留δ 56 Fe分布在氧化-含铁界面上方和整个好氧水柱中，表明从海洋还原性沃茨输出到好氧开放水柱中的任何潜在溶解Fe都富集重同位素。在Fe硫化物饱和度以上的深层轻度富氧水柱中，δ 56 Fe SPM随深度降低的趋势和一般较低的δ 56 Fe分布与海洋缺氧沉积物剖面中通常观察到的趋势相当，在海洋缺氧沉积物剖面中发生微生物还原性Fe溶解。缺氧海盆中氧化还原循环铁的同位素组成主要反映了外部通量和内部循环强度之间的平衡，外部通量使组分趋向地壳δ 56 Fe值，内部循环强度使δ 56 Fe值趋向负值。
Fe isotope ratios and concentrations of dissolved Fe (Fe dis , SPM ) were analyzed from a depth profile through the anoxic Eastern Gotland Basin water column, Baltic Sea. Results show a sharp gradient in δ 56 Fe dis across the ferruginous layer with δ 56 Fe dis = −0.4‰ in the euxinic deep basin and δ 56 Fe dis = p0.3‰ in the oxic upper water column. The isotopic gradient overlaps with a strong concentration gradient of Fe dis , a concentration maximum in Fe SPM and lower δ 56 Fe SPM values than δ 56 Fe dis . These features indicate preferential loss of light Fe isotopes from solution to suspended iron-oxyhydroxides (Fe IOH ) during typical oxidative precipitation across the redox interface. The sign of the overall fractionation, Δ 56 Fe IOH -Fe(II)(aq) 56 Fe IOH -Fe(II)(aq) > 0‰. The difference appears to be the result of isotope exchange dominated by reaction kinetics in the marine water column, rather than equilibrium fractionation generally inferred for oxidative Fe precipitation elsewhere. High residual δ 56 Fe dis immediately above the oxic–ferruginous interface and throughout the oxic water column suggests that any potential dissolved Fe export from marine reducing waters into the oxic open water column is enriched in the heavy isotopes. In the deep, mildly euxinic water column above the level of Fe sulfide saturation, a decreasing δ 56 Fe SPM trend with depth and a generally low δ 56 Fe dis are comparable to trends generally observed in marine anoxic sediment profiles where microbial reductive Fe dissolution occurs. The isotope composition of the redox-cycled Fe inventory in anoxic marine basins mainly reflects the balance between external fluxes, driving the composition towards crustal δ 56 Fe values, and intensity of internal recycling, driving δ 56 Fe towards negative values.