Long‐Range Lateral Transport of Dissolved Manganese and Iron in the Subarctic Pacific

Abstract

AbstractDissolved manganese (dMn) and iron (dFe) are important micronutrients for marine microorganisms. In this study, we presented comprehensive distributions of dMn in the subarctic Pacific and compared our Mn data with those of dFe in the same region. dMn and dFe exhibited a scavenged‐type and nutrient‐type vertical profile, respectively. We also determined the size fractionation of Mn at two stations and found that most of dMn was in the soluble fraction, in contrast to dFe, which included colloidal organic particles. In the coastal surface waters of the Gulf of Alaska, Mn was supplied from a riverine source. Drawdowns of dFe, dMn, and macronutrient were observed along the salinity gradient. Both dMn and dFe were transported eastward, with log‐scale transport distances of 3,600 and 3,300 km, respectively in the upper intermediate water, and 4,700 and 3,400 km, respectively in the lower intermediate water. In the upper intermediate water, dMn showed a positive relationship with apparent oxygen utilization, suggesting that regeneration processes could supply dMn to these waters. However, mixing with water masses from the subtropical North Pacific reduced dMn concentration. High dissolved oxygen concentrations in these waters also increased the rate of dMn loss relative to the lower intermediate water. The transport distances of dMn found in this study were the highest in the Pacific region. This long‐range transport of dMn and dFe could eventually fuel phytoplankton growth at the surface via upwelling processes.