Distribution of dissolved zinc in the western and central subarctic North Pacific

Zinc (Zn) is an essential micronutrient for bacteria and phytoplankton in the ocean as it plays an important role in numerous enzyme systems involved in various metabolic processes. However, large-scale distributions of total dissolved Zn in the subarctic North Pacific have not been investigated yet. In this study, we investigated the distributions of total dissolved Zn to understand biogeochemical cycling of Zn in the western and central subarctic North Pacific as a Japanese GEOTRACES project.

Seawater samples were collected during the R/V Hakuho-maru KH-12-4 GEOTRACES GP 02 cruise (from August to October 2012), by using acid-cleaned Teflon-coated X-type Niskin samplers. Total dissolved Zn in seawater was determined using cathodic stripping voltammetry (CSV) after UV-digestion.

In this study, total dissolved Zn concentrations in the western and central subarctic North Pacific commonly showed Zn increase from surface to approximately 400–500 m, just above the oxygen minimum layer. However, in the western subarctic North Pacific, relatively higher Zn concentrations have also been observed at intermediate depths (800–1200 m), in comparison with those observed in deep waters. The relationship between Zn and Si in the western subarctic North Pacific showed that Zn is slightly enriched at intermediate depths. These results may indicate that there are additional sources of Zn to intermediate water of the western subarctic North Pacific.