74 / 2024-09-05 19:12:04

Distribution and Influencing Factor of Manganese in Western North Pacific Subtropical Gyre

GEOTRACES,Manganese,North Pacific Subtropical Gyre,distribution,influencing factor

Research on the biogeochemical cycling of materials in oligotrophic oceans, such as North Pacific Subtropical Gyre (NPSG), has been a vibrant field of study for several decades, while observational data on trace metals is scarce in the NPSG. Manganese (Mn) is a crucial element tracing multiple processes and exhibits significant scavenging tendency in the oceans. The distribution of dissolved Mn (dMn) was studied in the western NPSG (wNPSG) during GEOTRACES GP09 cruise (April to June 2019). The distribution of dMn in the surface layer showed regional characteristics, with the average concentration of 1.44±0.51 nM (n=142), and the highest dMn value, i.e., 2.68±0.75 nM (n=13) north of Luzon Strait. Based on the calculation, atmospheric wet deposition and photo-reduction dissolution instead of dry deposition supported surface dMn concentration in the open ocean. Dissolved Mn concentrations in the intermediate water (potential density within 26.6-27.4 kg/m³) showed significant correlation (r=0.82, p<0.05) with salinity, indicating the distributions of dMn in the intermediate water of wNPSG were controlled by the mixing of North Pacific Intermediate Water and modified Antarctic Intermediate Water. Deep water (>1500 m) dMn concentrations were low (<0.2 nM) in many wNPSG regions. Anomalous dMn enrichment (1.00~3.75 nM) from 2000 m to near bottom 3400 m is observed in the Mariana Trough and nearby region, presumably indicating the influence of hydrothermal plumes emanating from the active hydrothermal vents Alice Spring. A localized increase in dMn and correlated weak Ce negative anomalies and low Yb/Nd ratios hints that dMn input from the particle resuspension and release in Luzon Strait where Pacific deep water entering South China Sea.