~143 Gt C/year
||del Giorgio PA, Duarte CM. Respiration in the open ocean. Nature. 2002 Nov 28 420(6914):379-84 DOI: 10.1038/nature01165 p.379 right column top paragraphPubMed ID12459775
|| Duarte CM, Agusti S. The CO2 balance of unproductive aquatic ecosystems. Science. 1998 Jul 10 281(5374):234-6  Williams, P. J. LeB. The balance of plankton respiration and photosynthesis in the open ocean. Nature 394, 55–57 (1998)PubMed ID9657712
||Primary source  abstract: "Here [investigator] use[s] an analysis of depth-integrated measures of production and respiration from five open-ocean regions to show that, in the upper 100 m of the water column, biological production generally exceeds consumption."
||P.379 right column top paragraph: "Rates of respiration in the surface layer of the ocean are typically high, with average values of about 1.2 g C/m^2/day (primary sources), which, if extrapolated over the 290×10^6 km^2 of the open ocean, represent a global respiration of about 143 Gt C/yr." Gt C=Giga tonnes C=10^9 tonnes of Carbon