I understand what a 'deterrence patrol' is. The idea is to go and hide underwater, coming near the surface only periodically, only long enough to extend a very long antenna and listen for the signal that 'all is still well'. If the sub ever surfaces and fails to hear that signal, it fires its entire warload at pre-designated targets.

The challenge is staying hidden, and the problem here is that these are big subs with big powerful nuclear reactors on board. Just moving around underwater, creates a 'bulge' on the surface that can be seen by satellites with the right radar. This is true wherever the sub operates, except when it operates under ice.

Hiding under ice also conceals the enormous thermal plume that is inherent with operating nuclear reactors.

Indeed, just moving around underwater, kills luminescent phyotplankton, which means that subs leave a 'glowing trail' behind them when they move (easier to hide under the ice).

They're there, alright, and the Russians know it, too.