The impact of ocean deoxygenation on iron release from continental margin sediments
The impact of ocean deoxygenation on iron release from continental margin sediments
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DOI：
10.1038/ngeo2162
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发表时间：
2014-06
影响因子：
18.3
通讯作者：
F. Scholz;J. McManus;A. Mix;C. Hensen;R. Schneider
中科院分区：
文献类型：
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作者：
F. Scholz;J. McManus;A. Mix;C. Hensen;R. Schneider
在海洋的高硝酸盐-低叶绿素区域，如秘鲁/洪堡洋流系统和邻近的赤道东太平洋，初级生产力受到微量营养素铁的限制。在秘鲁上升区内，生物可利用的铁从减少的大陆边缘沉积物中释放出来。这种海底来源的大小可能会随着氧气最小区域的范围或强度的波动而变化。在这里，我们表明，钼、铀和铁浓度的测量可以作为沉积铁释放的替代指标，并使用这个替代指标来评估过去140,000年来秘鲁上升流系统下海底的铁释放。我们观察到反硝化水平之间的耦合，如氮同位素、氧化的痕量金属替代品和沉积铁浓度所指示的。具体地说，上层海洋氧合作用差的时期的特点是沉积物中的铁保持更有效，对水柱的铁供应减少。我们将更多还原条件下的高效铁保留归因于表层沉积物中广泛存在的硫化物条件以及伴随而来的铁硫化物的沉淀。我们认为，从大陆边缘沉积物中释放铁在既不存在氧气也不存在硫化物的狭窄氧化还原窗口中是最有效的。因此，我们认为，秘鲁上升流区未来的除氧不太可能导致铁可获得性的增加，而在较弱的氧气最低区，部分除氧可能会增加铁的供应。
In the oceans’ high-nitrate–low-chlorophyll regions, such as the Peru/Humboldt Current system and the adjacent eastern equatorial Pacific, primary productivity is limited by the micronutrient iron. Within the Peruvian upwelling area, bioavailable iron is released from the reducing continental margin sediments. The magnitude of this seafloor source could change with fluctuations in the extension or intensity of the oxygen minimum zones,. Here we show that measurements of molybdenum, uranium and iron concentrations can be used as a proxy for sedimentary iron release, and use this proxy to assess iron release from the sea floor beneath the Peru upwelling system during the past 140,000 years. We observe a coupling between levels of denitrification, as indicated by nitrogen isotopes, trace metal proxies for oxygenation, and sedimentary iron concentrations. Specifically, periods with poor upper ocean oxygenation are characterized by more efficient iron retention in the sediment and a diminished iron supply to the water column. We attribute efficient iron retention under more reducing conditions to widespread sulphidic conditions in the surface sediment and concomitant precipitation of iron sulphides. We argue that iron release from continental margin sediments is most effective in a narrow redox window where neither oxygen nor sulphide is present. We therefore suggest that future deoxygenation in the Peru upwelling area would be unlikely to result in increased iron availability, whereas in weaker oxygen minimum zones partial deoxygenation may enhance the iron supply.