Received this cover from Svalbard Norway today. It was post marked "Tempelfjorden". The Tempel Fjord is about 60km East of Longyearbyen. In the winter a schooner, the Noorderlicht, remains in the fjord icebound and acts as a tourist stop for people on dog sled or snow mobile tours out of Longyearbyen. On the ice next to the ship is a mail box where tourists can mail post cards. Apparently the mail is transported back to Longyearbyen by dog sled, hence the "Polar Dog Mail" cancellation mark.
I received this cover in July when the ship is not frozen in the ice. Was my cover post marked at Tempelfjorden? Not likely. My guess is that it was actually cancelled in Longyearbyen since that's where I originally sent it to.