Marine snow — dead phytoplankton, fecal pellets and aggregated detritus — sinks out of the sunlit surface layer and is the ocean's biological carbon pump. Each particle's terminal settling velocity follows Stokes' law:
v = 2·g·r²·(ρp − ρw) / (9·μ)
with g = 9.81 m/s², seawater density ρw = 1027 kg/m³, dynamic viscosity μ = 1.88×10⁻³ Pa·s, particle radius r and excess density Δρ = ρp − ρw set by the sliders above (real aggregates are porous, so Δρ is tens to a few hundred kg/m³, not a solid-particle density).
While it sinks, bacteria respire the organic carbon. Directly measuring that decay particle-by-particle is impractical at sea, so oceanographers fit the empirical Martin curve to sediment-trap flux data:
F(z) = F(100)·(z / 100)^−b for z ≥ 100 m
F(100) is the export flux just below the euphotic zone (100 m) and b (≈0.6–1.2 in the real ocean, average ≈0.86) sets how fast flux attenuates with depth — a small b means efficient transfer to the deep ocean, a large b means most carbon is remineralized in the twilight zone. Each particle here carries mass m(z) = m₀·(z/100)^−b, so the population's flux profile reproduces the Martin curve directly instead of faking it — the "Live measured" curve on the chart is built from the particles actually on screen, with natural particle-to-particle scatter (real aggregates vary in size and lability), and it converges on the analytic Martin prediction.
- Left pane — the water column in cross-section: brighter/larger dots are more massive (more carbon remaining), fading dots have been mostly remineralized.
- Flux chart — F(z)/F(100) vs depth: the smooth line is the analytic Martin prediction, the dotted line is measured live from the particles in the column.
- Seafloor tally — the percentage and flux that actually survive to the base of the column, i.e. what is permanently sequestered rather than respired back to CO₂ in the water column.