Plankton respiration in the northern South China Sea during summer and winter

摘要

Plankton respiration is an important part of the carbon cycle and significantly affects the balance of autotrophicassimilation and heterotrophic production in oceanic ecosystems. In the present study, respiration rates of theeuphotic zone plankton community (CReu), size fractionated chlorophyll a concentration (Chl a), bacterialabundance (BAC), and dissolved oxygen concentration (DO) were investigated during winter and summer in thenorthern South China Sea (nSCS). The results show that there were obvious spatial and temporal variations inCReu in the nSCS (ranging from 0.03 to 1.10 μmol/(L·h)), CReu in winter ((0.53±0.27) μmol/(L·h)) was two timeshigher than that in summer ((0.26±0.20) μmol/(L·h)), and decreased gradually from the coastal zone to the opensea. The distribution of CReu was affected by coupled physical-chemical-biological processes, driven by monsoonevents. The results also show that CReu was positively correlated with Chl a, BAC, and DO, and that BACcontributed the highest CReu variability. Furthermore, the results of the stepwise multiple linear regressionsuggest that bacteria and phytoplankton were the dominant factors in determining CReu (R2 = 0.82, p<0.05) in thenSCS. Based on this relationship, we estimated the integrated water column respiration rate (CRint) within 100 mof the investigated area, and found that the relationship between the biomass of the plankton community andrespiration may be nonlinear in the water column.