![]() ![]() However, the water layer underneath the sea ice, here defined as the ‘under-ice habitat’, is important for zooplankton, because microalgae growing in sea ice (‘ice algae’) may provide critical food supply, particularly during the polar night 23, 24. Furthermore, the foraging success of visual predators, such as fish and marine birds and mammals, depends on the interplay between the timing and depth range of the zooplankton’s vertical migration and light penetration depth 17, 18, 19.Įarlier studies using hydroacoustic measurements demonstrated that the vertical migration of Arctic zooplankton is particularly sensitive to low light intensities, but these studies were unable to resolve the top 20 m of the ice-covered ocean 9, 10, 20, 21, 22. Vertically migrating zooplankton act as an active biological carbon pump (also called a ‘lipid pump’ 14), accounting for 25–132% of the gravitational biological carbon pump driven by sinking particulate organic carbon 15, 16. Besides DVM, polar lipid-rich zooplankton perform an ontogenetic migration, spending the polar night in deep water to overwinter in dormancy 13. In the polar regions, winter-active zooplankton perform a seasonal vertical migration between greater depths during the polar day and shallow depths during the polar night 9, 10, 11, 12. Commonly, zooplankton ascend to the surface during the night to feed on plankton and descend to deeper waters during the day to avoid visual predators. The diel change in light intensity is the primary driver of the largest synchronized movement of organisms on Earth: the diel vertical migration of zooplankton 8 (DVM). The effects of the changing light field on higher trophic levels of the Arctic marine ecosystem, however, are not well understood. The increased light penetration is already causing profound changes to key ecosystem functions, such as enhanced primary production in the marginal shelf seas, and a shifting phenology of ice algae and phytoplankton blooms 4, 5, 6, 7. ![]() The shrinking and thinning sea-ice cover of the Arctic Ocean allows the sunlight to penetrate deeper into the water column and extend the sunlit period in subsurface waters 1, 2, 3. ![]()
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