I very seriously doubt if Ark Royal is picking up nukes.
Firstly, the ONLY nuclear weapons in the UK inventory for the past 7-8 years has been the warheads on the Trident missiles, they cannot be delivered any other way, you don't just strap a warhead designed to be carried by a submarine launched missile on to an aircraft.
In any case, the RN Sea Harriers had their nuclear capability removed at the end of the Cold War, and the RAF Harrier GR.7's never had the capability.
Before the WE-177 air dropped nuclear weapons were retired in the mid 90's, the RAF Tornado and Jaguar aircraft were the primary carrier aircraft.
Also, although Ark Royal was intended for a long planned exercise in the far east, it is clearly intended for the Gulf. This is because the usual airgroup of RN and RAF Harriers have not been embarked, or the Airborne Early Warning Sea King helicopters, which would be normal for the kind of general deployment on exercises.
Instead, Ark Royal is to be a Commando carrier, the UK's dedicated Commando Carrier, HMS Ocean, is also going to the Gulf, but Ark Royal will carry more Commandos, their equipment, and more Sea King HC.4 assault choppers, plus more of the commandos own Lynx's probably.
Also, Ark Royal has had a 5 year long refit, and it has the most modern and extensive command and and control system fitted to a UK warship, so it will be the H.Q. and flagship of the UK forces in the region.
There is a precedent for this, during the last Gulf War the French took the airgroup off one of their carriers, replacing them with Marines and assault choppers.
During the Afghanistan campaign, HMS Ocean was relieved by Ark Royal's sister ship, HMS Illustrious, again in the Commando Carrier role.
With overwhelming USN and USAF, plus RAF combat aircraft in the region, to ensure air superiority as well as weapons delivery, (the RAF's Harriers will be operating from land, at least at first), the best use of an asset like Ark Royal is in it's secondary Commando/assault helicopter role as well as a floating H.Q. If the Ark Royal was operating way out at sea, rather than in the Gulf, beyond land based air power, it would be a different matter.
Ark Royal carrying nukes? Sounds like CND propaganda, does their already minimal credibility no good at all.
Clearly the US has requested extensive Royal Marine participation from the UK.