Annual Variability of Particulate and Dissolved Primary Production in the Subtropical Coastal NW Pacific

Marine primary production is considered the ultimate organic carbon source in the ocean. Particulate primary production (PPP) is usually transferred to higher trophic levels through grazing, whereas dissolved primary production (DPP) may drive the microbial loop. This study investigated both PPP and DPP in the coast of the subtropical northwestern Pacific from January 2018 to March 2019. Total of 42 photosynthesis-irradiance (P^B-E) curves and photosynthetic parameters (maximum photosynthetic rate [P^B_m] and initial slope [α]) for PPP and DPP were obtained. The results showed that the P^B_m and α of the PPP were higher than those of the DPP. The P^B_m and α of the PPP ranged from 4.10 to 22.60 mgC (mgChl)^-1 h^-1 and from 0.0083 to 0.0541 mgC (mgChl)^-1 h^-1 (μE m^-2 s^-1)^-1, respectively. For the DPP, P^B_m and α ranged from 1.56 to 18.25 mgC (mgChl)^-1 h^-1 and from 0.0033 to 0.0198 mgC (mgChl)^-1 h^-1 (μEm^-2s^-1)^-1, respectively. The daily PPP was generally higher than DPP. The daily PPP ranged from 8.10 to 122.79 mgC m^-3 d^-1, while the daily DPP ranged from 2.84 to 98.55 mgC m^-3 d^-1. Daily PPP and DPP both peaked during the late summer and the early autumn, indicating irradiance could be an important controlling factor for primary production. However, the percentage of extracellular release (PER; ≡DPP/(DPP+PPP)) showed no significant seasonal difference in the range between 17 to 45%. The factors affecting the PER variations need further investigations.