Marine snow surface production and bathypelagic export at the Equatorial Atlantic from an imaging float

Abstract. The marine biological carbon pump (BCP) plays a central role in the global carbon cycle, transporting carbon from the surface to the deep ocean and sequestering it for long periods. Sinking of surface-produced particles, known as the Biological Gravity Pump (BGP) constitutes the main component of the BCP. To study the BGP in the equatorial Atlantic upwelling region, a biogeochemical (BGC) Argo float equipped with an Underwater Vision Profiler 6 (UVP6) camera was deployed from July 2021 to March 2022. The float was recovered after its eastward drift from 23° W to 7° W along the equator, during which it conducted profiles to 2000 m depth every three days. For the first time in this oceanic region, in situ images and physical and biogeochemical data from a BGC-Argo float were acquired and analyzed in combination with satellite data. During the float trajectory, two blooms were recorded followed by two main export events of sinking aggregates that lasted for over a month, consistently reaching 2000 m depth. A Lagrangian approach was applied to investigate the production, transformation, and deep export of marine particles. Based on the characterization of the morphology of detritus within and outside of the plumes, five particle morphotypes with different sinking properties were detected. Small and dense aggregates were present throughout the water column while porous morphotypes, despite being larger, were predominantly concentrated in the surface layer. Export was driven by small and compact particles with higher particle abundance and flux during upwelling and export events. Our investigation reveals the stability of the equatorial Atlantic BCP system during this period, yielding an export efficiency of 6–7 % during and outside of export events. This study highlights the importance of using new technologies on autonomous platforms to characterize the temporal variability in the magnitude and functioning of the BCP.