When marine organisms eat and grow they capture and store carbon, termed blue carbon. Polar seas have extreme light climates and sea temperatures. Their continental shelves have amongst the most intense phytoplankton (algal) blooms. This carbon drawdown, storage and burial by biodiversity is a quantifiable ‘ecosystem service’. Most of that carbon sinks to be recycled by microbes, but some enters a wider foodweb of zooplankton and their predators or diverse seabed life. How much carbon becomes stored long term or buried to become genuinely sequestered varies with a wide range of factors, e.g. geography, history, substratum etc. The Arctic and Antarctic are dynamic and in a phase of rapid but contrasting, complex physical change and marine organismal carbon capture and storage is altering in response. For example, an ice shelf calving a 5000 km2 iceberg actually results in 106 tonnes of additional blue carbon per year. Polar blue carbon increases have resulted from new and longer climate-forced, phytoplankton blooms driven by sea ice losses and ice shelf collapses. Polar blue carbon gains with sea ice losses are probably the largest natural negative feedback against climate change. Here the current status, variability and future of polar blue carbon is considered.