Variations in sediment production of dissolved iron across a continental margin not dominated by major upwelling or riverine inputs
Variations in sediment production of dissolved iron across a continental margin not dominated by major upwelling or riverine inputs
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DOI：
10.1016/j.marchem.2020.103750
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发表时间：
2020-03-20
期刊：
影响因子：
3
通讯作者：
Taillefert, Martial
中科院分区：
文献类型：
--
作者：
Eitel, Eryn M.;Owings, Shannon M.;Taillefert, Martial
尽管铁对形成海洋生产力模式的影响不可否认，但这种限制性营养素的不同来源对海洋的相对重要性仍在辩论中。虽然全球估计数表明，海底向海洋输入的铁量很大，但大多数研究都调查了受到涌升或大量河流输入影响的大陆边，这些环境并不代表大多数海洋。此外，报告大陆坡沉积物中溶解铁浓度的研究数量有限，尽管事实上，大陆架边缘和大陆隆起之间的这些区域占全球海洋沉积表面积的5%以上。由于Fe 2+在含氧沃茨中的快速氧化和Fe（III）产物的溶解度差，传统上认为铁的沉积通量可以忽略不计。最近的认识，三价铁可能是稳定在溶液中的有机配位体在氧化过程中的沉积物-水界面附近的建议，一个显着的分数的溶解铁池可能存在的形式下的有机铁（M）的配合物，最终可能会达到上覆的沃茨。在这项研究中，铁的形态和地球化学的重要性，确定在完整的沉积物岩心沿着一个横断面横跨整个大陆边缘附近的海角了望，北卡罗来纳州，一个地区不占主导地位的上升流或河流输入，是最被动的大陆边缘的代表。扩散摄氧量（DOU）和溶解的Fe 2+和有机Fe（III）络合物的最大扩散通量从沿海区的大陆架下降，保持低的货架和上大陆坡，但反弹到达到最大值，在中坡沉积物中的Fe（III）氧化物的浓度是最高的沿着断面。反过来，DOU下降，溶解铁低于检测较低的斜坡沉积物，表明中坡沉积物代表沉积中心，其中Fe（III）氧化物和有机物可能会积累。孔隙水硫酸盐和硫化物浓度以及单独的沉积物培养证实，硫酸盐还原不会大大影响铁在这些沉积物中的循环。溶解有机铁（III）在这些大陆边缘沉积物的生产可能是受有氧氧化的存在下，天然有机配位体附近的沉积物-水界面，异化铁还原，或化学氧化的Fe（II）络合天然有机配位体的组合。通量的Fe 2+和有机-Fe（III）配合物的沉积物-水界面没有观察到。然而，Fe 2+和有机-Fe（III）络合物进入这些沉积物的氧化带的扩散通量（
Despite the undeniable effect of iron on shaping patterns of ocean productivity, the relative importance of the different sources of this limiting nutrient to the ocean is still under debate. Although global estimates indicate that the benthic input of iron to the oceans is significant, most studies have investigated continental margins exposed to either upwelling or large riverine inputs, environments that are not representative of the majority of the oceans. Additionally, the number of studies that report dissolved iron concentrations in continental slope sediments is limited, despite the fact that these regions between the shelf edge and the continental rise make up > 5% of the sedimentary surface area of the global ocean. The sedimentary flux of iron has traditionally been considered negligible due to the rapid oxidation of Fe2+ in oxic waters and poor solubility of the Fe(III) product. The recent realization that ferric iron may be stabilized in solution by organic ligands during oxidation near the sediment-water interface suggests that a significant fraction of the dissolved iron pool may be present under the form organic-Fe(M) complexes that could eventually reach the overlying waters. In this study, the speciation and biogeochemical importance of iron was determined in intact sediment cores along a transect across the entire continental margin near Cape Lookout, North Carolina, a region not dominated by upwelling or riverine inputs that is representative of most passive continental margins. Rates of diffusive oxygen uptake (DOU) and maximum diffusive fluxes of both dissolved Fe2+ and organic-Fe(III) complexes decreased from the coastal zone to the continental shelf, remained low on the shelf and the upper continental slope, but rebounded to reach a maximum in mid-slope sediments where concentrations of Fe(III) oxides were the highest along the transect. In turn, DOU decreased and dissolved iron was below detection in lower-slope sediments, indicating that mid-slope sediments represent depocenters where Fe(III) oxides and organic matter may accumulate. Pore water sulfate and sulfide concentrations as well as separate sediment incubations confirmed that sulfate reduction does not greatly influence the cycling of iron in these sediments. The production of dissolved organic-Fe(III) in these continental margin sediments is likely regulated by a combination of aerobic oxidation in the presence of natural organic ligands near the sediment-water interface, dissimilatory iron reduction, or chemical oxidation of Fe(II) complexed to natural organic ligands. Fluxes of Fe2+ and organic-Fe(III) complexes across the sediment-water interface were not observed. However, diffusive fluxes of Fe2+ and organic-Fe(III) complexes into the oxic zone of these sediments (