Further evidence of diel vertical migration of copepods under Arctic sea ice during summer

ABSTRACT: We examined diel vertical variability of acoustic backscatter under sea ice during the midnight sun season at high latitude in the Canada Basin of the Arctic Ocean. Acoustic backscatter demonstrated that the dominant Arctic copepods (Calanus hyperboreus) consistently performed a distinct diel vertical migration (DVM) synchronized with the solar radiation cycle. DVM was mainly observed between 2 distinctive pycnocline layers at 25 and 45 m above the subsurface chlorophyll maximum (SCM) within Pacific summer water. Picophytoplankton (<2 μm) were mainly distributed within the SCM layer, whereas diatoms (>20 μm) were above the SCM layer. This indicated that light variation is a potential trigger for the DVM of Arctic copepods under sea ice, whereas the vertical depth of occurrence was primarily controlled by water mass stratification and food. This vertical behavior is significant to understanding how Arctic copepods adjust to their habitats relative to sea ice, water masses, and food sources in the dynamic environmental changes in the Arctic Ocean.