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

Abstract

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 air-sea 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.Published by Copernicus Publications on behalf of the European Geosciences Union.

Slow‐sinking particulate organic carbon in the Atlantic Ocean: Magnitude, flux, and potential controls

“…Microbial respiration of fast‐sinking POC flux is often found to be too slow to explain observed decreases in flux [ Belcher et al ., ] which suggests that zooplankton processing may have significant interactions with fast‐sinking particles. Several recent papers have concluded that zooplankton sloppy feeding [ Giering et al ., ], microbial gardening [ Mayor et al ., ], and zooplankton fragmentation [ Cavan et al ., ; Belcher et al ., ; Cavan et al ., ] may lead to the in situ production of slow‐sinking particles from fast‐sinking particles.…”

High‐Frequency Variability of Small‐Particle Carbon Export Flux in the Northeast Atlantic

“…While the observed seasonality in small‐particle transfer efficiency is likely driven in large part by changes in stratification, it may also reflect changes in particle consumption. For example, increased summertime zooplankton abundance and metabolism might reduce particle export through grazing activities (Cavan et al, ). Alternatively, the microbial community could display an increased abundance or increased remineralization rates due to increased temperatures observed in the upper mesopelagic in summer (Rivkin & Legendre, ).…”

Global evaluation of particulate organic carbon flux parameterizations and implications for atmospheric pCO2

“…For example, Mari et al [] show that transparent exopolymer particles (TEPs) accumulate in the surface microlayer and need to be ballasted to overcome its low density and to promote aggregation, which brings into question the classic view that TEP increases POC flux by promoting aggregation through its role as a “biological glue.” Attenuation of POC flux is also affected by surface processes that modify the character and lability of the POC that is exported. In this context, episodic events [ Lebrato et al , ; Smith et al , ], community structure [ Guidi et al , ; Guidi et al , ], and zooplankton processes [ Giering et al , ; Cavan et al , , ; Steinberg and Landry , ] are all likely important.…”