To investigate the balance between net photo- and heterotrophy throughout the Arctic autumn-winter-spring transition, we assessed the abundances of O2 and Ar in surface waters by means of membrane-inlet mass spectrometry . We derived biologically mediated O2 super-/undersaturation (ΔO2/Ar), reflecting the difference between gross primary production and the community’s combined autotrophic and heterotrophic respiration (i.e., ‘net community production’, NCP). We present first results on the magnitude of NCP over the autumn-winter-spring transition and extrapolate biological carbon drawdown and release. Further correlation with biological and chemical parameters assessed during MOSAiC is used to identify the controls on net community production and to better understand the ecological mechanisms that drive biogeochemical fluxes in the rapidly changing Arctic.