Vertical migration of the ocean’s deep scattering layer affects the health of the planet

Abstract

The vertical transport of carbon, termed the biological pump, mitigates the effects of climate change by sequestering 25% of the carbon dioxide emitted by fossil fuel use each year. The nightly vertical movement of millions of zooplankton, fishes, squid, and shrimp that make up the deep scattering layer may account for as much as half of this carbon sequestration but this process remains poorly parameterized. We use a stationary echosounder deployed at ∼1000 m depth complemented by video imaging and environmental DNA sampling to describe the vertical migration of mesopelagic micronekton in Monterey Bay, California from the darkness of the deep sea to the bounty of food at the surface over 30 months. Vertical migration at this site showed as many patterns as have been described globally, with drastic changes in the proportion of animals migrating, the extent of migration, and the species involved. Patterns were consistent only over periods of a few days even as mobile sampling showed synchrony in patterns throughout the mesopelagic zone of the bay. These results provide critical information for incorporating the effects of this largest migration on Earth on predictions of future climate.