Does anybody know if it's possible to create a round map frame in QGIS Map Composer to create circumpolar maps?
There's currently no out-of-the-box functionality for this in Print Composer. As a work-around, you can add graticules as a separate layer and label their end points, like here:
For a full how to, see https://anitagraser.com/2016/05/01/how-to-create-round-maps-in-print-composer/
(Example uses data from http://www.quantarctica.org/)