Russia is planning huge oil and gas developments in the Arctic Ocean off its northern coast – drilling that could threaten pristine wildlife habitats.
Large-scale production could begin in the next two decades, if the price of oil rises high enough.
Preliminary exploration has already begun, including in the Laptev Sea.
But scientists say the region is home to important, thriving populations of walrus and polar bears, which could be put at risk.
Biologists on the 2013 Laptev Expedition this summer have been trying to establish if the walruses and polar bears there are a unique group, in need of special protection. BBC journalists went with them to investigate the issue.
We flew to Khatanga, one of the most northerly towns in Siberia, and there we boarded a small boat, the Taimyr.
From Khatanga it was a two-day, 500km (310-mile) journey almost due north.