Copper, in seawater, is predominantly bound by organic ligands of unknown composition. Complexation has been thermodynamically characterized using synthetic ligand competition experiments which assumes equilibrium among all chelators within the system. However, equilibration times are constrained by wall loss issues with the synthetic ligands. Here, a solvent extraction methodology, was utilized to avoid the wall-loss problems. Using an exceptionally high concentration of a strong copper chelator, oxine (8-hydroxyquinoline), at least six hours of equilibration time is required to reach steady state between the competing ligand and the labile copper in seawater. This is much longer than equilibration times used in previously published works. Our method was optimized by using samples from GEOTRACES expeditions in the North Pacific and North Atlantic Oceans. Surprisingly, 60–90% of the copper was not exchangeable with oxine under these conditions. We define this fraction as “inert”, and these data, which include profiles as deep as 1000 m in the North Pacific, suggest that this is a widespread feature. Our results suggest that there are two distinct pools of labile and inert copper, rather than an assemblage of similar complexes with incremental differences in stability constants. The results have important implications for the marine geochemistry of copper and its bioavailability. Complexation has been shown to limit copper bioavailability and influences scavenging and residence time. Moreover, a basic paradigm of copper speciation methodologies, that even strong Cu complexes are relatively labile, is likely incorrect.

海水中的铜主要与成分未知的有机配体结合。已经使用合成配体竞争实验在热力学上表征了络合，该实验假设系统内所有螯合剂之间达到平衡。然而，平衡时间受到合成配体壁损失问题的限制。在这里，使用溶剂萃取方法来避免壁损失问题。使用超高浓度的强铜螯合剂 oxine（8-羟基喹啉），至少需要 6 小时的平衡时间才能在海水中的竞争配体和不稳定铜之间达到稳态。这比以前发表的作品中使用的平衡时间长得多。我们的方法通过使用来自北太平洋和北大西洋 GEOTRACES 探险的样本进行了优化。令人惊讶的是，在这些条件下，60-90% 的铜不能与 oxine 交换。我们将这一部分定义为“惰性”，这些数据包括北太平洋深达 1000 米的剖面，表明这是一个普遍存在的特征。我们的结果表明，存在两个不同的不稳定和惰性铜池，而不是稳定性常数存在增量差异的相似复合物的组合。结果对铜的海洋地球化学及其生物利用度具有重要意义。已显示络合会限制铜的生物利用度并影响清除和停留时间。此外，铜物种形成方法的基本范例，