Decoupling of zinc and silicic acid in the subarctic northeast Pacific interior

Zinc (Zn) is an essential micronutrient for marine phytoplankton that plays a role in regulating community composition and may limit primary productivity in localized regions. Depth profiles of dissolved Zn throughout the world ocean are tightly correlated with dissolved silicic acid (Si). New and previously published data from the subarctic northeast Pacific show a decoupling of dissolved Zn and Si. Waters above 400-500 m depth are characterized by elevated Zn compared to Si and the global average. The oxygen deficient zone of the subarctic northeast Pacific is characterized by a dissolved Zn:Si trend with slopes below the global average. The deficit of Zn relative to Si in the oxygen-depleted water column is consistent with a specific removal process for dissolved Zn in the subarctic northeast Pacific oxygen deficient zone. We propose that this data adds to a growing body of evidence implicating the formation of solid Zn sulfides in low oxygen, particle-associated microenvironments as an important loss term in the oceanic Zn budget. Time series data indicate that dissolved oxygen concentrations are diminishing in the ocean interior, expanding and intensifying oxygen deficient zones, and model results predict this trend will continue in the future. An oxygen-sensitive removal process affecting dissolved Zn may impact global ocean productivity and carbon cycling due to the role of Zn in regulating community composition and even total primary productivity in select regions.