Large benthic fluxes of dissolved iron in China coastal seas revealed by Ra-224/Th-228 disequilibria
Large benthic fluxes of dissolved iron in China coastal seas revealed by Ra-224/Th-228 disequilibria
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Ra-224/Th-228不平衡揭示中国近海溶解铁的大底栖通量
DOI：
10.1016/j.gca.2019.06.026
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发表时间：
2019
影响因子：
5
通讯作者：
Cai Pinghe
中科院分区：
文献类型：
--
作者：
Shi Xiangming;Wei Lin;Hong Qingquan;Liu Lingfeng;Wang Yuning;Shi Xueying;Ye Ying;Cai Pinghe
我们报告了基于最近发展的224ra /228Th不平衡方法的中国沿海底栖铁通量估算。底栖动物的铁通量具有相当大的时空变化，跨度超过4-5个数量级，从<10 µmol m−2d−1到~ 100 mmol m−2d−1。然而，我们发现在中国沿海有一个显著的趋势，即底栖铁通量随底深呈指数下降趋势。这种趋势可能是动能和化学结合能梯度在沿海海域达到顶峰的结果。同时，在100-150 μM溶解氧（DO）的狭窄氧化还原窗口内，底栖铁通量更频繁地出现。这一观察结果与早期的假设相矛盾，即大陆边缘沉积物的铁释放随着底部水体DO浓度的降低而增加。这可能反映了需氧量灌溉的妥协，其作用是促进底部沉积物中铁的释放，而溶解的铁（II）的再氧化导致更有效的铁在沉积物-水界面附近保留。值得注意的是，基于224ra /228Th不平衡的Fe底栖通量比由孔隙水浓度梯度法得出的通量大一个数量级。此外，在其他沿海海域，同位素估计值比基于传统孵育法（即底栖生物室法）的历史测量值高50至30倍。然而，我们对底栖铁通量的估计与基于一种新的二维成像技术的通量值大致一致。
We report benthic flux estimates of Fe from China coastal seas based on a recently developed224Ra/228Th disequilibrium approach. There were considerable temporal and spatial variabilities in benthic Fe fluxes, which spanned over 4–5 orders of magnitude, from <10 µmol m−2d−1up to ∼100 mmol m−2d−1. Nonetheless, we have identified a prominent trend in China coastal seas showing that benthic Fe fluxes tended to decline exponentially with bottom depth. This trend is probably a result of kinetic energy and chemically bound energy gradients that culminate in the coastal seas. In the meantime, large benthic Fe fluxes were more frequently observed within a narrow redox window of 100–150 μM dissolved oxygen (DO) in the bottom water. This observation contradicts an early assumption that iron release from continental margin sediments increases with decreasing DO concentration in the bottom water. It possibly reflects a compromise of oxygen-demanded irrigation that acts to enhance Fe release from bottom sediments, and re-oxidation of dissolved Fe(II) that results in more efficient Fe retention near the sediment-water interface. Notably, benthic fluxes of Fe based on224Ra/228Th disequilibria were one order of magnitude larger than those derived from the porewater concentration gradient method. Moreover, the isotopic estimates were >30 times higher than the historical measurements based on the traditional incubation method (i.e., the benthic chamber method) in other coastal seas. However, our estimates of benthic Fe flux were in general agreement with the reported flux value based on a new two dimensional imaging technique.