The behaviour of aluminium, manganese, iron, cobalt, and lead in the subarctic Pacific Ocean: boundary scavenging and temporal changes

Abstract

Aluminium (Al), manganese (Mn), iron (Fe), cobalt (Co), and lead (Pb) are trace metals that exhibit significant scavenging tendencies in the oceans. This study presents the full-depth distributions of the dissolved (d) and labile particulate (lp) fractions of these five elements in the subarctic Pacific Ocean, obtained during the GEOTRACES Japan KH-17-3 cruise. Along the 145° W meridional transect, the d and lp species of Al, Mn, Fe, and Co reflected fluvial supply from Alaska and benthic input from the continental shelf. We estimated that the boundary-scavenging zone has a width of approximately 250 km off Alaska. Along the 47° N zonal transect (GEOTRACES GP02 Line), we found input of trace metals from the Okhotsk and Bering Seas in the west, contrasting to the limited input of trace metals due to boundary scavenging in the east. The hydrothermal activity of the Juan de Fuca Ridge influenced the distribution of deep-water trace metals at the easternmost station, CL-21. Temporal change in the vertical profiles of dPb in the middle of the subarctic gyre highlighted a decline in anthropogenic Pb emissions from 2005 to 2017. Temporal change of the vertical profiles of Al, Mn, and Fe at 47° N, 160° E from 2011 to 2017 indicates the influence of the Great East Japan Earthquake. In particular, lp trace metals were brought by tsunami and ocean circulation in 2011, and decreased over time through scavenging.