Potential cobalt limitation of vitamin B12 synthesis in the North Atlantic Ocean

Abstract

While recent studies have confirmed the ecological importance of vitamin B12, it is unclear whether the production of this vitamin could be limited by dissolved Co, a trace metal required for B12 biosynthesis, but found at only subnanomolar concentrations in the open ocean. Herein, we demonstrate that the spatial distribution of dissolved B12 (range: 0.13–5 pmol L−1) in the North Atlantic Ocean follows the abundance of total dissolved Co (range: 15–81 pmol L−1). Similar patterns were observed for bacterial productivity (range: 20–103 pmol 3H leucine L−1 hr−1) and algal biomass (range: 0.4–3.9 μg L−1). In contrast, vitamin B1 concentrations (range: 0.7–30 pM) were decoupled from both Co and B12 concentrations. Cobalt amendment experiments carried out in low‐dissolved Co waters (∼20 pmol L−1) enhanced B12 production two‐fold over unamended controls. This study provides evidence that B12 synthesis could be limited by the availability of Co in some regions of the world ocean.