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Biological uptake and reversible scavenging of zinc in the global ocean

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Science  06 Jul 2018:
Vol. 361, Issue 6397, pp. 72-76
DOI: 10.1126/science.aap8532

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Controlling zinc in the oceans

Zinc, a key micronutrient for marine phytoplankton, has a global distribution remarkably similar to that of silicic acid, even though Zn and Si have very different biogeochemical cycles. Weber et al. investigated why this is so by combining model calculations and observations. They found that biological uptake in the Southern Ocean and reversible scavenging of Zn onto sinking particles both affect the distribution of Zn in the ocean. Thus, Zn and Si distributions will be affected differently by future changes in ocean temperature, pH, and carbon fluxes.

Science, this issue p. 72

Abstract

Zinc (Zn) is a key micronutrient for marine phytoplankton, with a global distribution that is similar to silicic acid. The processes that govern this relationship, despite the very different biological cycling of Zn and silica, remain poorly understood. Here, we use diagnostic and mechanistic models to show that only a combination of Southern Ocean biological uptake and reversible scavenging of Zn onto sinking particles can explain the observations. The distinction between organic and adsorbed Zn can also reconcile the vertical distribution and mass balance of Zn isotopes, which previously appeared at odds. This holistic understanding explains the Zn deficiencies observed throughout the low-latitude ocean and implies a greater sensitivity of the marine Zn cycle to climate-driven changes in organic matter cycling than previously recognized.

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