Transient shifts in Bering Sea shelf phytoplankton size structure in response to wind‐induced mixing Limnology and Oceanography Letters

Phytoplankton community size structure is a key attribute that influences pelagic trophic energy transfer and the vertical flux of organic matter to benthic food webs. To capture the ephemeral scale of phytoplankton population size spectra we developed an approach, combining long-term survey datasets, machine learning modeling and 3 yr of high-resolution moored vertical profiler measurements. We show that larger phytoplankton (> 10 μm cell diameter) dominated the spring bloom throughout the water column, however, after the bloom, smaller cells (< 10 μm cell diameter) comprise 70–80% of the phytoplankton community in the surface mixed layer. In contrast, larger cells are predominantly present at depths near the mixed layer interface. However, intermittent wind mixing events results in enhanced pulses of net community production and larger phytoplankton in the upper ocean. Our findings highlight how transient seasonal and vertical shifts in phytoplankton size structure occur in response to variable oceanographic conditions. Grant no. NA20OAR4320271