Abstract
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.
Highlights
[2] The factors that control the distribution of trace metals are of prime importance to the biogeochemistry of the oceans [Bruland and Lohan, 2003], including the potential control these micronutrients exert on the intermediate timescale carbon cycle [Morel et al, 2003; Morel and Price, 2003]
The likely importance of biological uptake was quickly recognized in vertical profiles of dissolved Cd, which are conspicuously similar to those of the major nutrients [Boyle
The extent to which passive scavenging and biological uptake control depth profiles of trace metals in the ocean is of fundamental importance to their marine chemistry, since it controls both their recycling within the water column and the nature and rate of the eventual output from the dissolved pool to the sediment
Summary
[2] The factors that control the distribution of trace metals are of prime importance to the biogeochemistry of the oceans [Bruland and Lohan, 2003], including the potential control these micronutrients exert on the intermediate timescale carbon cycle [Morel et al, 2003; Morel and Price, 2003]. Bacon and Anderson [1982] considered a spectrum of scavenging models, from irreversible uptake to reversible exchange, in their attempt to explain the vertical distributions of dissolved and particulate Th isotopes They conclude that the close to linear increase in concentration of both phases with depth is consistent with continuous exchange of Th between seawater and particle surfaces, so-called “reversible scavenging.”. The extent to which passive scavenging and biological uptake control depth profiles of trace metals in the ocean is of fundamental importance to their marine chemistry, since it controls both their recycling within the water column and the nature and rate of the eventual output from the dissolved pool to the sediment. Though biological cycling is clearly implicated in controlling Zn depth profiles, the extent to which scavenging contributes to the dissolved [Zn] pattern remains an open question
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