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

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.