Total dissolved zinc in the upper water column of the subarctic North East Pacific

Abstract

Abstract Total dissolved Zn concentrations are reported for winter and summer along the E–W line P transect and for summer along S–N line Z transect extending from Ocean Station Papa (OSP; 50°N 145°W) to the respective shelf waters. Surface-water (10 m) concentrations ranged from 0.04 nM in the open ocean to 0.9 nM at the Canadian shelf station. A clear gradient is evident, with dissolved Zn concentrations decreasing with increasing distance from shore along the E–W transect in both summer and winter. No consistent trend was observed along the S–N transect. Low concentrations of Zn (0.05–0.07 nM) were observed in near-surface water at OSP in winter. The vertical distribution of dissolved Zn is oceanographically consistent, showing a silicon-like vertical profile. Concentrations of silicic acid and dissolved Zn at depth are higher than those at equivalent depths in the Atlantic, as expected from deep-water circulation patterns and build-up in concentration of these elements. Dissolved Zn/Si ratios in the upper 200 m indicate a trend of decreasing with distance from shore, which infers a decoupling between dissolved Zn and silicic acid in the upper ocean. We hypothesise that the silicon-like profile of dissolved Zn is a result of recycling from relatively biologically resistant organic particulate phases, that leads to profiles very similar to those of dissolved silicon. Other than at two stations where there is very high primary production, there is no apparent horizontal relationship between total dissolved Zn and chlorophyll a or production.