The effect of plankton vertical migration on primary productivity in a warmer more stratified ocean

Kristian Spilling, Aditya Nayak, Per Juel Hansen, Matthew Johnson, Stefan Simis

Marine primary production sustains ocean ecosystems and plays a central role in regulating the global carbon cycle. Current projections suggest that ocean warming will enhance water stratification, limiting the resupply of inorganic nutrients to surface waters, and consequently reduce primary production. This view neglects possible biological feedback mechanisms such as vertical migration by plankton communities. Through active vertical movements, both photosynthetic organisms and their grazers transport nutrients from depth to the surface, effectively functioning as a biological nutrient pump. While the existence of these processes is well established, translating vertical migration into quantitative nutrient fluxes at ecosystem or regional scales remains a major challenge. Here, we synthesize the current understanding of vertical migration in both primary producers and grazers and assess its potential to shape nutrient transport in the ocean. We argue that vertical migration will have implications for nutrient cycling in a warmer, more stratified ocean. Specifically, any climate-driven shifts in plankton community composition towards taxa better capable of vertical migrating may diminish the projected decrease in primary production. Finally, we discuss how recent technological advances provide new opportunities to quantify this biological nutrient pump and improve predictions of its role in future ocean scenarios.