Benthic Dissolved Silicon and Iron Cycling at Glaciated Patagonian Fjord Heads.
Benthic Dissolved Silicon and Iron Cycling at Glaciated Patagonian Fjord Heads.
复制标题
底栖式硅和铁循环在冰川的巴塔哥尼亚峡湾头处。
DOI：
10.1029/2022gb007493
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发表时间：
2022-11
影响因子：
5.2
通讯作者：
Hendry, Katharine R.
中科院分区：
文献类型：
--
作者：
Ng, Hong Chin;Hawkings, Jon R.;Bertrand, Sebastien;Summers, Brent A.;Sieber, Matthias;Conway, Tim M.;Freitas, Felipe S.;Ward, James P. J.;Pryer, Helena V.;Wadham, Jemma L.;Arndt, Sandra;Hendry, Katharine R.
关键词：
冰川融水向下游生态系统提供来自风化基岩的硅（Si）和铁（Fe）。然而，这些营养物质到达海洋的程度是由峡湾系统中溶解的Si和Fe的底栖生物循环的性质所调节的，因为在峡湾的顶部会快速沉积活性颗粒。在这里，我们通过沉积物孔隙水的地球化学分析，包括Si和Fe同位素（δ30Si和δ56Fe），以及Si的反应-输运模型，研究了四个巴塔哥尼亚峡湾头两种营养物质的底栖循环。与开放海洋沉积物（通常<0.001 mmol m−2 day−1）相比，峡湾沉积物中溶解铁的高扩散通量（高达0.02 mmol m−2 day−1）是由冰川来源的活性铁相的还原性和非还原性溶解所支持的，这反映在孔隙水δ56Fe（−2.7至+0.8‰）的范围内。相比之下，峡湾沉积物中溶解Si的扩散通量（0.02 ~ 0.05 mmol m−2 day−1）相对较低（典型的海洋值为0.1 mmol m−2 day−1）。在Fe(II) - Fe（III）氧化还原边界附近观察到高孔隙水δ30Si（高达+3.3‰），这可能与Fe（III）矿物相对溶解Si的去除有关，这与高沉积速率一起导致Si在采样点的低扩散通量。我们的研究结果表明，早期成岩作用促进了溶解铁的释放，但抑制了冰川峡湾头部溶解硅的释放，这对理解这些营养物质沿峡湾系统的下游运输具有重要意义。示意图显示了底栖铁和硅循环的耦合，以及由此推断的易还原性铁（氧）氢氧化物供应的空间差异和峡湾站点之间孔隙水平流的强度。在上部沉积物相对氧化的条件下，硅在铁（氧）氢氧化物上的吸附和无定形铁-硅相的共沉淀发生，而在含铁区，随着铁的还原性溶解，硅被释放回溶液。颜色较亮的圆圈和实心轮廓代表固相结合的Si和Fe（III）相，而颜色较浅的圆圈和虚线轮廓代表溶解的Si和Fe2+相。
Glacier meltwater supplies silicon (Si) and iron (Fe) sourced from weathered bedrock to downstream ecosystems. However, the extent to which these nutrients reach the ocean is regulated by the nature of the benthic cycling of dissolved Si and Fe within fjord systems, given the rapid deposition of reactive particulate fractions at fjord heads. Here, we examine the benthic cycling of the two nutrients at four Patagonian fjord heads through geochemical analyses of sediment pore waters, including Si and Fe isotopes (δ30Si and δ56Fe), and reaction‐transport modeling for Si. A high diffusive flux of dissolved Fe from the fjord sediments (up to 0.02 mmol m−2 day−1) compared to open ocean sediments (typically <0.001 mmol m−2 day−1) is supported by both reductive and non‐reductive dissolution of glacially‐sourced reactive Fe phases, as reflected by the range of pore water δ56Fe (−2.7 to +0.8‰). In contrast, the diffusive flux of dissolved Si from the fjord sediments (0.02–0.05 mmol m−2 day−1) is relatively low (typical ocean values are >0.1 mmol m−2 day−1). High pore water δ30Si (up to +3.3‰) observed near the Fe(II)‐Fe(III) redox boundary is likely associated with the removal of dissolved Si by Fe(III) mineral phases, which, together with high sedimentation rates, contribute to the low diffusive flux of Si at the sampled sites. Our results suggest that early diagenesis promotes the release of dissolved Fe, yet suppresses the release of dissolved Si at glaciated fjord heads, which has significant implications for understanding the downstream transport of these nutrients along fjord systems. Schematic shows the coupling of benthic Fe and Si cycling, and the inferred spatial difference in the supply of easily reducible Fe (oxy‐)hydroxides and the intensity of pore water advection between the fjord sites. Adsorption of Si onto Fe (oxy‐)hydroxides and co‐precipitation of amorphous Fe‐Si phases occur under relatively oxic conditions in the upper sediments, while Si is released back to solution following the reductive dissolution of Fe in the ferruginous zone. Circles with brighter colors and solid outlines represent solid‐bound Si and Fe(III) phases, while circles with lighter colors and dashed outlines represent dissolved Si and Fe2+ phases.