Antarctic sea ice is a critical component of the climate system and a
vital habitat for Southern Ocean ecosystems. Understanding the
underlying physical processes and improving Antarctic sea ice
predictability is of broad interest. Using model data, we investigate
sea ice and upper ocean predictability at interannual timescales in the
Weddell Sea region. We find that oceanic predictability is largely
confined to the Winter Water layer and responds to seasonal
modifications of the water column, mainly driven by sea ice processes.
Predictability depends not only on the depth of the Winter Water layer,
but also on how strongly stratified its base is. Predictability is lost
when warm Circumpolar Deep Water with no sea ice-related memory entrains
into the mixed layer. We show the strong dependence of sea ice
predictability on the local upper ocean vertical structure, which
suggests that both are likely to change in a warming climate.