Can Polar Bears smell seals under 3 sheets of ice and from 40 miles away?

No. While they can smell seals under the ice, they cannot do it from such a great distance.

No. Polar bears can't smell seals UNDER ice at all. What polar bears do is to roam pack ice until their amazing sense of smell detects the presence of a seal breathing-hole at distance. The bear moves toward the hole. Having found it, the bear hunkers down at the hole. When a seal surfaces in the hole to breathe out (a fairly noisy event as well as being accompanied by BAD fish breath) the bear can reach in and haul the seal up. Food problem solved!

Pretty simple affair. As for the 40 mile thing... it's a myth. That is not to say the bear doesn't cover many miles seeking the scent of a seal hole. But the bear cannot take a deep breath, look to the Southeast, and say "Aha!!! Dinner awaits 40 miles away!"

polar Bear's can smell from 20 kiles away and 3 feet deep.