How much do zooplankton and fine-scale processes matter for the ocean biological pump?

Abstract

The ocean biological carbon pump stores carbon away from the atmosphere through multiple pathways, including gravitational settling, physical transport, and organism vertical migration. Robust assessments of its magnitude remain challenging. Traditional approaches often quantify pathways separately, risking double-counting, missing high-frequency processes such as fine-scale physics and daily vertical migration over large scales, and emphasizing particulate carbon while overlooking non-particulate fluxes. Here, we apply a unified framework that quantifies all pathways simultaneously in a high-resolution (3 km) idealized North Atlantic model resolving seasonal biophysical dynamics, including zooplankton migration, from kilometer-scale fronts to regional biomes. We show that fine-scale physical and migrant pumps together contribute 15-20% of carbon storage. Their storage is dominated by non-particulate carbon fluxes (dissolved organic carbon transport, zooplankton respiration). Fine-scale dynamics modulate export depth and storage timescales both directly, through physical transport, and indirectly, by shaping fast-sinking carbon-rich filaments and controlling zooplankton migration depth. Adequately measuring and representing these pathways in next-generation observations and models is key to quantify carbon storage and its response to variability.