Abstract. In this study, we evaluate the performance of Nanjing University of Information Science and Technology Earth System Model, version 3 (hereafter NESM v3) in simulating the marine biogeochemical cycle and CO2 uptake. Compared with observations, NESM v3 reproduces reasonably well the large-scale patterns of upper ocean biogeochemical fields including nutrients, alkalinity, dissolved inorganic, chlorophyll, and net primary production. The model also reasonably reproduces current-day oceanic CO2 uptake, the total CO2 uptake is 149 PgC from 1850 to 2016. In the 1ptCO2 experiment, the NESM v3 produced carbon-climate (γ=-7.9 PgC/K) and carbon-concentration sensitivity parameters (β=0.8 PgC/ppm) are comparable with CMIP5 model results. The nonlinearity of carbon uptake in the NESM v3 accounts for 10.3% of the total carbon uptake, which is within the range of CMIP5 model results (3.6%~10.6%). Some regional discrepancies between model simulations and observations are identified and the possible causes are investigated. In the upper ocean, the simulated biases in biogeochemical fields are mainly associated with the shortcoming in simulated ocean circulation. Weak upwelling in the Indian Ocean suppresses the nutrient entrainment to the upper ocean, therefore reducing the biological activities and resulting in underestimation of net primary production and chlorophyll concentration. In the Pacific and the Southern Ocean, high-nutrient and low-chlorophyll result from the strong iron limitation. Alkalinity shows high biases in high-latitude oceans due to the strong convective mixing. The major discrepancy in biogeochemical fields is seen in the deep Northern Pacific. The simulated high concentration of nutrients, alkalinity and dissolved inorganic carbon water is too deep due to the excessive deep ocean remineralization. Despite these model-observation discrepancies, it is expected that the NESM v3 can be employed as a useful modeling tool to investigate large scale interactions between the ocean carbon cycle and climate change.
Marine biogeochemical cycling and oceanic CO<sub>2</sub> uptake simulated by the NUIST Earth System Model version 3
