Ideas and perspectives: Is dark carbon fixation relevant for oceanic primary production estimates?

Abstract

About half of the global primary production (PP) is generated in the euphotic layer of the ocean. The 14C method developed by Steemann Nielsen (Nielsen, 1952) more than half a century ago has been the most frequently used method to determine PP in all aquatic systems. This method includes dark incubations to exclude the nonphototrophic dissolved inorganic carbon (DIC) fixation. The presence of significant dark DIC fixation rates has been habitually used to suggest the inaccuracy of the 14C method to determine autotrophic phytoplankton primary production. However, we suggest that the dark DIC fixation rates should be incorporated into global oceanic carbon production estimates since the total production of organic matter does not originate only from photosynthesis but also from other processes such as chemoautotrophic and anaplerotic processes. Here we analyzed data collected over almost 30 years from the longest available oceanic time series and calculated that the inclusion of dark DIC fixation would increase oceanic PP estimates by 5 %-22% when total dark DIC fixation is included or by 2.5 %-11% when only considering the nighttime DIC fixation.We conclude that dark DIC fixation should be included into global oceanic primary production estimates as it represents newly synthesized organic carbon (ca. 1.2-11 PgC yr-1) available for the marine food web.