the August issue of Outside magazine has a good story about an American expedition into the Arctic Ocean in late 1880's
to make a long story short the writer talks about following the story to Wrangel Island off the Russian coast.
he meets the Russian ranger who lives on the island,just one of four along with lots and lots of Polar bears.the preserve ranger just has a can of pepper spray and a flare gun on is belt,no AK47.
so that sort of gives me the impression that the spray and a good bam from a flare gun is enough to drive off a bear,a big nasty one!