Eric Baccega / Female Harp seal (Phoca groenlandicus) surfacing at breathing hole looking at her pup, Magdalen Islands, Gulf of St Lawrence, Quebec, Canada, March.

Sven Zacek / View through glacier ice towards snow-covered mountains in Kongsfjorden fjord in Svalbard, Norway. June 2015.

Olga Kamenskaya / Young Baikal seal (Pusa sibirica) at breathing hole. Lake Baikal, Russia, April.

Olga Kamenskaya / Young Baikal seal (Pusa sibirica) at breathing hole. Lake Baikal, Russia, April.

Olga Kamenskaya / Man looking into ice hole dug for ice diving, Lake Baikal, Siberia, Russia, March. Model released.

Franco Banfi / Scuba diver under ice, surfacing to the hole, viewed from underneath, Arctic circle Dive Center, White Sea, Karelia, northern Russia March 2010. No release available.

Brent Stephenson / A large hole in an iceberg with icicles hanging. Yalour Islands, Antarctic Peninsula, Antarctica, December.

Chadden Hunter / Filming on the Antarctic sea-ice at the edge of a small hole. A cameraman gets a shock when a Killer whale (Orcinus orca) mother and calf explode out of the water in front of his face. Taken on locat...

Eric Baccega / Female Harp seal (Phoca groenlandicus) surfacing at a breathing hole in the sea ice, Magdalen Islands, Gulf of St Lawrence, Quebec, Canada, March 2012

Jeff Wilson / View through the porthole of science teams and Frozen Planet film crew working on the sea ice in the Bering Sea, Alaska, USA, March 2008. The film crew were in search of Spectacled eider ducks, temper...

Bryan and Cherry Alexander / Meltwater pouring off iceberg above hole. Scoresbysund Fiord, East Greenland, September 2005.

Steven Kazlowski / Aerial view of Ringed seals (Phoca hispida) on multi-layer ice (freshwater pans formed over many years where salt is squeezed out of the ice) with exit hole underneath ocean, Chukchi Sea, 20 miles off...