A modeling assessment of the role of reversible scavenging in controlling oceanic dissolved Cu and Zn distributions

The balance of processes that control elemental distributions in the modern oceans is important in understanding both their internal recycling and the rate and nature of their eventual output to sediment. Here we seek to evaluate the likely controls on the vertical profiles of Cu and Zn. Though the concentrations of both Cu and Zn increase with depth, Cu increases in a more linear fashion than Zn, which exhibits a typical "nutrient-type" profile. Both elements are bioessential, and biological uptake and regeneration has often been cited as an important process in controlling their vertical distribution. In this study, we investigate the likely importance of another key vertical process, that of passive scavenging on sinking particles, via a simple one-dimensional model of reversible scavenging. We find that, despite the absence of lateral or vertical water advection, mixing, diffusion, or biological uptake, our reversible scavenging model is very successful in replicating dissolved Cu concentration profiles on a range of geographic scales. We provide preliminary constraints on the scavenging coefficients for Cu for a spectrum of particle types (calcium carbonate, opal, particulate organic carbon, and dust) while emphasizing the fit of the shape of the modeled profile to that of the tracer data. In contrast to Cu, and reaffirming the belief that Zn behaves as a true micronutrient, the scavenging model is a poor match to the shape of oceanic Zn profiles. Modeling a single vertical process simultaneously highlights the importance of lateral advection in generating high Zn concentrations in the deep Pacific. Key Points A 1-D reversible scavenging model is applied to oceanic [Cu] and [Zn]Dissolved Cu is well described by the process of reversible scavengingDissolved Zn is not, reflecting its behaviour as a true nutrient-type element