Evaluation of the Particulate Inorganic Carbon Export Efficiency in the Global Ocean

Abstract. The oceanic carbonate pump corresponds to the production and the sinking of particulate inorganic carbon (PIC) thanks to calcified planktonic organisms. In this study, global estimates of PIC standing stock, production derived from ocean colour and calcified taxa contribution were combined with PIC flux observation from short-term sediment traps deployed during the last decades covering the global ocean. Coccolithophores are the main planktonic calcified group in the euphotic zone, with a significant seasonal blooming pattern and an important latitude dependant seasonal response. The present study highlights that the PIC production in the euphotic zone and the pelagic PIC flux varied among oceanic regions, depth and season. Based on a geographic matchup between the PIC flux from sediment traps and remote sensing climatology observation, correlation between net primary production (NPP) of particulate organic carbon (POC) in the euphotic zone and PIC flux is revealed. However, PIC production in the euphotic zone is not correlated with PIC flux at global scale, but only for delimited ocean basin such as in the North Atlantic and the Southern Ocean. Despite lower PIC production and PIC/POC ratios in the euphotic zone, temperate and subpolar areas are more efficient to export PIC compared to equatorial and subtropical areas (higher PIC production and PIC/POC ratios in the euphotic zone). The plankton phenology seems to be an important driver of PIC export efficiency (PIC E_eff) and PIC transfer efficiency (PIC T_eff). This study suggests that the 'packaging factor' corresponding to the vehicle of the biological carbon pump (marine snow aggregates, fecal pellets) and the plankton network (e.g. zooplankton community, microbial loop) determine the PIC export efficiency and the PIC transfer efficiency.