Diel dynamics of zooplankton fecal pellet flux revealed by integrated in situ imaging observations and modeling

Abstract

The contribution of sinking fecal pellets to the biological carbon pump depends on pellet properties, producer abundance, and the depth and timing of pellet production, which can be modulated by diel vertical migration. We examined diel variability in zooplankton fecal pellet flux in the subarctic Northeast Pacific using two image‐based tools: the Underwater Vision Profiler (UVP5) and upward‐facing cameras (GelCam) on a surface‐tethered sediment trap array. We classified three morphologically distinct fecal pellet types across both platforms: long fecal pellets from crustaceans, tabular pellets from salps, and ellipsoid pellets from appendicularians. This enabled complementary estimates of pellet abundance, modeled carbon content, and flux. Daily composites revealed distinct diel patterns in three zooplankton groups and their associated pellet flux. A simple model linking vertical migration with pellet production, sinking, and attenuation reproduced the observed temporal variability. Together, these results highlight how diel behavior and physiology impact vertical carbon transport.