A call for refining the role of humic-like substances in the oceanic iron cycle
A call for refining the role of humic-like substances in the oceanic iron cycle
复制标题
呼吁完善类腐殖质物质在海洋铁循环中的作用
作者：
S. Rauschenberg;B. Twining
浮游植物的初级生产是大气二氧化碳被隔离在海洋中的主要途径，但这需要铁，而铁的供应稀缺。由于99%以上的铁与有机配体形成络合物，从而增加了铁的溶解度和微生物的利用率，因此了解控制配体动力学的过程是至关重要的。长期以来，腐植酸类物质中的配体对铁的络合作用一直被认为是重要的，但它们的作用从未以海洋学上一致的方式得到解释。在这里，我们展示了铁与电活性腐殖质在多个开阔海洋地点的共同变化，铁与腐殖质的比例随着深度的增加而增加。我们的结果与腐殖酸配体在整个水柱中构成铁结合配体池的很大一部分的情况一致。我们演示了腐植酸配体的浓度和结合能力如何限制最大溶解铁浓度，并总结了可能影响这些参数的关键过程。如果这种关系具有全球代表性，腐殖质可能会设定一个浓度门槛，以缓冲深海铁库存。这项研究突出了腐殖质数据的匮乏，迫切需要跨不同的海洋盆地，从表面到深度同时测量电活性腐殖质、溶解铁和铁结合配体。
Primary production by phytoplankton represents a major pathway whereby atmospheric CO 2 is sequestered in the ocean, but this requires iron, which is in scarce supply. As over 99% of iron is complexed to organic ligands, which increase iron solubility and microbial availability, understanding the processes governing ligand dynamics is of fundamental importance. Ligands within humic-like substances have long been considered important for iron complexation, but their role has never been explained in an oceanographically consistent manner. Here we show iron co-varying with electroactive humic substances at multiple open ocean sites, with the ratio of iron to humics increasing with depth. Our results agree with humic ligands composing a large fraction of the iron-binding ligand pool throughout the water column. We demonstrate how maximum dissolved iron concentrations could be limited by the concentration and binding capacity of humic ligands, and provide a summary of the key processes that could influence these parameters. If this relationship is globally representative, humics could impose a concentration threshold that buffers the deep ocean iron inventory. This study highlights the dearth of humic data, and the immediate need to measure electroactive humics, dissolved iron and iron-binding ligands simultaneously from surface to depth, across different ocean basins.