It is called "body rucksack arctic" and is a huge junk.
By "body rucksack arctic", they mean the body of the "Rucksack Arctic", as opposed to the other components (frame, support straps, loop straps, shoulder straps). Your example is in beautiful condition.
Thanks for this Falklands pic. I'm researching the Berghaus influence and so far have only seen pics of marines using THIS particular rucksack during Operation Corporate. I've read in many places that marines were issued the SAS/Para Rucksack - but I've never seen a single pic to confirm this. I've long believed that marines used Berghaus rucksacks during this operation - but again have not yet seen a single picture to verify this.
There's a version with a neatly cut-down frame and this was often sold as the "SBS Canoe Bergen". Thanks Jame K, I didn't know that that was a SASS modification. Comparing the frames, they have the SAME NSN and it was this that made me realise that it was not an official item. It was terrible because the frame struts bash into your spine because they're not at the height they were designed to be at.