Role of zooplankton in determining the efficiency of the biological carbon pump

• Published in: Biogeosciences
• Main Authors: Cavan, EL, Henson, SA, Belcher, A, Sanders, R
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus GmbH 2017
• Subjects: Earth Sciences; Oceanography; Biological Oceanography; Pacific; Southern Ocean; North Atlantic
• Online Access: https://doi.org/10.5194/bg-14-177-2017; http://ecite.utas.edu.au/116303

The efficiency of the ocean's biological carbon pump (BCP eff here the product of particle export and transfer efficiencies) plays a key role in the airsea partitioning of CO 2 . Despite its importance in the global carbon cycle, the biological processes that control BCP eff are poorly known. We investigate the potential role that zooplankton play in the biological carbon pump using both in situ observations and model output. Observed and modelled estimates of fast, slow, and total sinking fluxes are presented from three oceanic sites: the Atlantic sector of the Southern Ocean, the temperate North Atlantic, and the equatorial Pacific oxygen minimum zone (OMZ). We find that observed particle export efficiency is inversely related to primary production likely due to zooplankton grazing, in direct contrast to the model estimates. The model and observations show strongest agreement in remineralization coefficients and BCP eff at the OMZ site where zooplankton processing of particles in the mesopelagic zone is thought to be low. As the model has limited representation of zooplankton-mediated remineralization processes, we suggest that these results point to the importance of zooplankton in setting BCP eff , including particle grazing and fragmentation, and the effect of diel vertical migration. We suggest that improving parameterizations of zooplankton processes may increase the fidelity of biogeochemical model estimates of the biological carbon pump. Future changes in climate such as the expansion of OMZs may decrease the role of zooplankton in the biological carbon pump globally, hence increasing its efficiency.