The men - and dogs - who patrol northern Greenland

The Sirius Patrol is how Denmark maintains its claim to north-east Greenland and its untapped mineral wealth - mining technology is not advanced enough yet to exploit it in such harsh conditions.

So each autumn, six dog sledge teams set out to patrol this vast icy expanse, each manned by two soldiers from the Danish Special Forces.

Frozen Planet is broadcast on BBC One on Wednesday 30 November at 2100 GMT, or catch up on iPlayer.