When the explorer drills the ice to make a physical measurement of thickness, he will use the hole to lower a 4kg conductivity-temperature device (CTD) into the ocean below.

BBC: Arctic team targets key ice data

These days, thanks to global warming and a receding ice cover, the voyage is easier to complete, says explorer James Delgado, author of Across the Top of the World.

NPR: Warming Eases Northwest Passage, Author Says

The explorer, Marco Polo (1254-1324), is believed to have seen ice-creams being made during his trip to China and introduced them to Italy.

BBC: CBBC Newsround | ICE-CREAM | The origin of ice-cream

"Certainly this is not the passage of John Franklin, " a British explorer whose 1845 mission ended in the deaths of 129 men after their two ships were lost in the ice.

NPR: Warming Eases Northwest Passage, Author Says