To reveal the effect of solar irradiation on the biogeochemical cycling of trace metals in the open ocean, the photodecomposition of organic iron- and copper-binding ligands was examined in an experiment using filtered seawater collected from a deep layer of the East China Sea. Six days of natural solar irradiation caused a significant decrease in the concentrations of both ligands, along with the loss of fluorescent dissolved organic matters. The relative decrease of iron-binding ligands, which are considered to be mainly composed of humic substances, was larger than that of copper-binding ligands or humic-like fluorescence. This may be attributable to relatively high photoreactivity of hydrophilic fluvic acids, which have higher affinity to ferric ions. Surprisingly, an accumulation of both iron- and copper-binding ligands was observed in the dark control bottles, but without a significant change in the fluorescence of humic-like substances. In conclusion, the upwelling of deep seawater into the sunlit surface layer can result in the rapid loss of the complexation capacity for both iron and copper ions. The stronger ligands for both metals, which were readily decomposed by sunlight irradiation, appears to have a similar composition, suggesting that competition could be important to determine the solubility and bioavailability of iron and copper.

为了揭示太阳辐射对公海中痕量金属的生物地球化学循环的影响，在一项实验中，使用了从东海深层收集来的海水对有机铁和铜结合配体的光分解进行了研究。六天的自然太阳辐射导致两种配体的浓度显着下降，同时荧光溶解的有机物也损失了。铁结合配体（主要由腐殖质组成）的相对减少量大于铜结合配体或类似腐殖质的荧光。这可以归因于亲水性氟酸的较高的光反应性，其对三价铁离子具有较高的亲和力。出奇，在黑暗对照瓶中观察到铁和铜结合配体的积累，但是腐殖质样物质的荧光没有明显变化。总之，深层海水上升到日光照射的表层会导致铁离子和铜离子的络合能力迅速丧失。两种金属的较强配体（很容易被阳光照射分解）似乎具有相似的组成，这表明竞争对于确定铁和铜的溶解度和生物利用度可能很重要。