The biological carbon pump moves organic carbon fixed by phytoplankton near the surface down into the deep ocean, where it is stored away from the atmosphere for centuries. Most models emphasise the gravitational pump — sinking marine snow. This simulation isolates a separate, active mechanism: the migrant (zooplankton) pump.
Diel vertical migration (DVM):
night: z(t) → z_surface (feed in the productive mixed layer)
day: z(t) → z_deep (descend below the mixed-layer depth, MLD)
Carbon export flux below MLD:
F_migrant = N · R · (1 − f_MLD) · Δt
N = migrating population density
R = mass-specific respiration + excretion rate at depth
f_MLD = fraction of the population still above the MLD
Δt = residence time at depth per cycle
Each simulated copepod follows a smoothed sinusoidal depth trajectory synchronized to a compressed day/night clock. At night it swims into the lit, food-rich surface layer; at dawn it dives below the mixed-layer depth (dashed line) and spends the day there, respiring CO₂ and excreting faecal pellets and dissolved organic carbon that never return to the surface within that cycle — carbon exported from the atmosphere-exchanging layer entirely through animal locomotion, not sinking.
- Migration amplitude — how deep the population descends; deeper excursions export carbon further below the mixed layer, where it is more likely to be sequestered long-term.
- Respiration rate at depth — scales metabolic CO₂ release per individual while below the MLD (temperature- and species-dependent in real oceans).
- Migrant pump flux readout — instantaneous carbon export rate, computed only while population is below the MLD, matching the flux equation above.
- Population size — total instanced copepods; larger swarms increase total flux at fixed per-capita respiration, as in real biomass-scaled estimates.
Field estimates (Steinberg et al., Bianchi et al.) put the migrant pump at roughly 10–40% of the gravitational (sinking) pump's carbon export in many ocean regions — a real, measurable, and still actively studied contributor to the ocean's role as a carbon sink.