Observations of Zooplankton Diel Vertical Migration From High‐Resolution Surface Ocean Optical Measurements

We demonstrate that signal spikes in optical backscatter measurements provide information on the diel vertical migration patterns of oceanic zooplankton. During nighttime, we observed high frequency spikes in particulate optical backscatter coincident with increased acoustic backscatter from vertically migrating zooplankton. We used our measurements to examine the spatial patterns and daily timing of zooplankton migrations across the eastern Subarctic Pacific Ocean, demonstrating coherence of diel vertical migrations with regional hydrographic features. Vertical zooplankton migration was consistently observed in oligotrophic offshore waters but less apparent in higher productivity waters over the continental shelf, where bottom depth, hydrographic fronts, and plankton abundance influenced apparent zooplankton distributions. Our results suggest that spikes in optical backscatter data, which are normally removed during data processing, can be more fully exploited to examine marine zooplankton dynamics from autonomous measurement systems.