Diel vertical migration by zooplankton moves organic carbon between the sunlit surface and deeper waters, altering how much carbon the ocean stores. Research by Daniel K. Steinberg at Woods Hole Oceanographic Institution and Michael R. Landry at Scripps Institution of Oceanography frames this behavior as a key component of the biological pump, the suite of processes that transfer carbon from the surface to the ocean interior.
Mechanisms of carbon transport
During night-time feeding near the surface, migrating zooplankton ingest phytoplankton and suspended particles. By day they descend to depth to avoid visual predators, where they respire, excrete, and produce fecal pellets. These processes are collectively termed active transport because they move carbon against the gradient that would otherwise be set by passive sinking. R. S. Lampitt at the National Oceanography Centre has shown that active transport by migrating zooplankton can be comparable to or exceed some components of passive particle flux in certain regions, making it a non-negligible pathway for carbon transfer. The efficiency of this transport depends on species composition, size of organisms, and the depth and duration of their daytime residence.
Ecological and biogeochemical consequences
Active transport affects carbon sequestration by increasing the proportion of fixed carbon that reaches depths where it is isolated from the atmosphere on seasonal to millennial timescales. Deeper respiration and pellet production elevate oxygen demand and nutrient regeneration at depth, which can reshape local food webs and biogeochemical cycles. In nutrient-rich upwelling or coastal regions the interplay between migrating zooplankton and seasonal productivity can modulate fisheries productivity, with direct consequences for communities relying on small-scale and commercial fisheries. In polar and high-latitude seas, extreme seasonal light regimes alter migration patterns and therefore the timing and magnitude of carbon transfer, influencing regional carbon budgets.
Understanding and modeling DVM is essential because it introduces variability not captured by passive-sinking assumptions used in many global carbon estimates. Steinberg and Landry advocate integrating direct observations of zooplankton behavior and metabolism into biogeochemical models to improve sequestration estimates. As climate-driven changes in stratification, light penetration, and predator communities alter migration behaviors, the contribution of zooplankton to the ocean’s capacity to sequester carbon will likely change, with implications for global carbon budgets and the human societies that depend on marine resources.