A Comparison of TCO2 and 14C Estimates of Primary Production

Phytoplankton form the base of the global marine carbon cycle. Measurements of primary production are integral to understanding fluxes between the atmosphere and both organic and inorganic carbon pools in the ocean. Virtually all measurements today are made using the carbon-14 (14C) uptake method, yet numerous uncertainties and procedural problems remain unresolved (Karl et al. 1998, Marra 2002). One source of error in the 14C method results from the metabolic activity of grazers, and could potentially be 100% of the measured production rate (Welschmeyer 2010). The purpose of this project was to directly test 14C methodology against an independent carbon-based method of photosynthesis which is also free of grazer-induced biases in order to examine the relationship between grazer metabolism and the observed 14C error. 14C uptake measurements were compared to measurements of gross primary production using the light-dark bottle technique and measuring the change in total inorganic carbon, TCO2, with a coulometer. The 14C technique was found to underestimate primary production by 41%, and a positive relationship between microzooplankton metabolic parameters and a 14C recycling error was observed. The results of this study imply that total global ocean primary production is significantly higher than currently estimated