The distribution and characteristics of suspended particulate matter in the Palau-Caroline seamount area of the western tropical Pacific Ocean

Abstract

Suspended particulate matter (SPM) plays an important biogeochemical role in aquatic systems, and assessing SPM spatial trends during the current climate change period is important. In the autumn of 2018, seawater samples were collected from depths of 1, 20, 50, 100and 200 m in the water column at 62 stations within the Palau-Caroline seamount area in the western tropical Pacific Ocean. The SPM concentration was measured to assess spatial variability. The particulate nitrogen (PN) concentration, particulate organic carbon (POC) concentration, and δ¹³C_POC were measured at 30 stations to assess spatial variability and the source of the suspended particulate organic matter (POM). The SPM concentration ranged from 0 to 1.18 mg/L, with an average value of 0.18 ± 0.20 mg/L, which is consistent with the results of previous studies in the ocean. Marked variation was observed in the SPM distribution. High SPM concentrations were observed around the seamount area, indicating that the seamount significantly influenced the distribution of the SPM. The POC concentrations decreased with depth, whereas the PN concentrations did not exhibit a clear distribution pattern. This difference in distribution suggested that the sources, cycling pathways and other controlling geochemical processes differed between POC and PN. The C/N ratios were notably low, ranging from 0.4 to 8.3, with an average of 2.0 ± 1.6. The δ¹³C_POC values ranged from −27.7 ‰ to −23.4 ‰, showing clear stratification with higher (less negative) values in the upper water column. The distribution characteristics of POC, PN, δ¹³C_POC, and the C/N ratio indicate that small phytoplankton may influence the POM characteristics of the upper water column. The POM collected in the study area appears to be derived mainly from in situ biological production.