Tiantian Ge, Chunle Luo, Peng Ren, Hongmei Zhang, Hongtao Chen, Zhaohui Chen, Jing Zhang and Xuchen Wang

Published in Frontiers in Marine Science, June 2022

Dissolved organic carbon (DOC) in the ocean is one of the largest reduced and exchangeable organic carbon pools on Earth and plays important roles in carbon cycling and biogeochemical processes in the ocean. Here, we report the concentrations and distributions of DOC in water samples collected along a meridional transect in the western North Pacific (NP) Ocean in November 2019. Concentrations of DOC ranged from 33-102 μM, were higher in surface water, decreased rapidly with depth to 1,000 m, and then remained relatively constant. The labile fraction of DOC accounted for 20-40% of the surface bulk DOC and was respired very rapidly in the upper 200 m depth. The semi-labile fraction of DOC accounted for 15-20% of the surface bulk DOC and was exported downward and turned over at water depths of 200-2,000 m. The formation of NP Intermediate Water (NPIW) in the Kuroshio Extension (KE) region is a major process carrying some surface semi-labile DOC down. The Low concentrations of DOC (33-44 μM) were present in the entire water column below 1,000 m along the transect in the NP. Primary production and microbial consumption played major roles in the concentration and distribution of DOC in the euphotic zone, and hydrodynamic mixing and circulation of different water masses appear to be dominant factors controlling the distribution and dynamics of DOC in the deep water of the western NP.

Fig. (A) Map of the study region plotted using Ocean Data View (ODV, Schlitzer, 2015) and the sampling transect stations of line P1 (red dots) in the northwestern North Pacific in November 2019. (B) Plot of sampling depth at the sampling transect stations of line P1. Seawater samples were collected for the full water depth at 7 stations (blue dots) and for only the upper 2,000 m at 19 stations (yellow dots).

Ge, T., Luo, C., Ren, P., and et al. 2022. Dissolved Organic Carbon along a Meridional Transect in the Western North Pacific Ocean: Distribution, Variation and Controlling Processes. Front. Mar. Sci., 9, https://doi.org/10.3389/fmars.2022.909148