Long-range lateral transport of dissolved manganese and iron in the subarctic Pacific
Dissolved Mn and Fe are important micronutrients for marine microorganisms. In this work, we presented comprehensive distributions of dissolved Mn in the subarctic Pacific and compared our Mn data with those of dissolved Fe in the same region. Dissolved Mn and Fe exhibited a scavenged-type and nutrient-type vertical profile, respectively. Most of the dissolved Mn was in the soluble fraction, while dissolved Fe in seawater included colloidal organic ligands. In the surface waters of the Gulf of Alaska, Mn concentrations were high where salinity was low, suggesting a coastal source for Mn. Drawdowns of Fe and nitrate were observed along the salinity gradient. Both Mn and Fe were transported eastward, with log scale transport distances of 3600 km and 3300 km, respectively in the upper intermediate water, and 4700 km and 3400 km, respectively in the lower intermediate water. In the upper intermediate water, Mn showed a strong positive relationship with phosphate, suggesting that regeneration processes could supply Mn to these waters. However, mixing with water masses from the subtropical North Pacific reduced Mn concentration. High dissolved oxygen concentrations in these waters also increased the rate of Mn loss. The transport distance of Mn in the intermediate water of the subarctic Pacific was the highest in the Pacific region. Transport of dissolved Mn and Fe for large distances in the intermediate water could eventually fuel phytoplankton growth at the surface via upwelling processes.
GEOTRACES, trace metals, Gulf of Alaska, Alaska Stream, North Pacific Intermediate Water
53.591946N, 41.748757S, -129.697267E, -211.845712W