The daily migration of small marine animals to oceanic depths intensifies oxygen depletion in low-oxygen waters of the open ocean, reports a paper published online this week in Nature Geoscience. The findings suggest that future changes in oceanic oxygen levels could alter the migratory patterns of these marine animals.

Daniele Bianchi and colleagues examined the depth to which marine animals dive during the day, using acoustic data obtained from across the globe between 1990 and 2011. They find that animals dive deeper when subsurface oxygen concentrations are high. In low oxygen areas, animals only migrate as far as the upper bounds of the low oxygen waters. Using a mathematical model, they show that the daily migration of small animals exacerbates oxygen loss in oxygen minimum zones of the ocean.