Temporal and spatial variability of the carbon cycle in the east of China’s seas: a three-dimensional physical-biogeochemical modeling study

Abstract

In the east of China’s seas, there is a wide range of the continental shelf. The nutrient cycle and the carbon cycle in the east of China’s seas exhibit a strong variability on seasonal to decadal time scales. On the basis of a regional ocean modeling system (ROMS), a three dimensional physical-biogeochemical model including the carbon cycle with the resolution (1/12)°×(1/12)° is established to investigate the physical variations, ecosystem responses and carbon cycle consequences in the east of China’s seas. The ROMS-Nutrient Phytoplankton Zooplankton Detritus (NPZD) model is driven by daily air-sea fluxes (wind stress, long wave radiation, short wave radiation, sensible heat and latent heat, freshwater fluxes) that derived from the National Centers for Environmental Prediction (NCEP) reanalysis2 from 1982 to 2005. The coupled model is capable of reproducing the observed seasonal variation characteristics over the same period in the East China Sea. The integrated air-sea CO2 flux over the entire east of China’s seas reveals a strong seasonal cycle, functioning as a source of CO2 to the atmosphere from June to October, while serving as a sink of CO2 to the atmosphere in the other months. The 24 a mean value of airsea CO2 flux over the entire east of China’s seas is about 1.06 mol/(m2·a), which is equivalent to a regional total of 3.22 Mt/a, indicating that in the east of China’s seas there is a sink of CO2 to the atmosphere. The partial pressure of carbon dioxide in sea water in the east of China’s seas has an increasing rate of 1.15 μatm/a (1μtm/a=0.101 325 Pa), but pH in sea water has an opposite tendency, which decreases with a rate of 0.001 3 a–1 from 1982 to 2005. Biological activity is a dominant factor that controls the $${p_{C{O_2}air}}$$ in the east of China’s seas, and followed by a temperature. The inverse relationship between the interannual variability of air-sea CO2 flux averaged from the domain area and Nino3 SST Index indicates that the carbon cycle in the east of China’s seas has a high correlation with El Nino-Southern Oscillation (ENSO).