A new study unveils the prevalence of plastics in the entire water column of an offshore plastic accumulation zone in the southern Atlantic Ocean and implicates the ocean interior as a crucial pool of ‘missing’ plastics. Results show that small microplastics are critical, underexplored and integral to the oceanic plastic inventory. In addition, findings show that weak ocean current systems contribute to the formation of small microplastics hotspots at depth, suggesting a higher encounter rate for subsurface particle feeders like zooplankton.