Abstract

Very little is known about Southern Ocean under-ice phytoplankton, despite their suspected potential -- ice and stratification conditions permitting -- to produce blooms. Here we use a distributional approach to ask how sea ice and under-ice phytoplankton characteristics are related in the Southern Ocean, circumventing the dearth of co-located ice and phytoplankton data. We leverage all available phytoplankton data from Argo profiling floats, together with ice freeboard and lead data from ICESat-2, to describe co-variations over time. We calculate moments of the probability distributions of maximum chlorophyll, particulate backscatter, the depths of these maxima, ice freeboard, and ice thickness. Argo moments correlate moderately with ice variance, but not mean, perhaps implying that variable sea ice and leads provide more opportunities for light to reach phytoplankton. We discuss ecological implications of our results in the context of data limitations, and advocate for diagnostic models and field studies to test processes influencing under-ice phytoplankton.