Bryan and Cherry Alexander / Inuit hunters trying to stop lead opening using their harpoons. Northwest Greenland, 1977.

Steven Kazlowski / An Inupiaq whaling crew prepare to paddle their seal skin boat / umiak, in an open lead in the Chukchi Sea, during spring whaling season, off the Arctic coastal village of Point Hope, Alaska, May 2008

Steven Kazlowski / Cape Thompson and an open lead in the pack ice, blown open by strong winds, indicating thinning sea ice conditions, 26 miles south of Point Hope, Arctic coast of Alaska, March 2008

Flip Nicklin / Narwhal (Monodon monoceros) group in ice break, Baffin Island, Nunavut, Canada

Steven Kazlowski / Silhouette of Inupiaq subsistence whalers at the edge of an open lead in the pack ice, looking for passing bowhead whales as the mid-day sun follows the horizon. Chukchi Sea, offshore from Barrow, Arc...

Steven Kazlowski / Silhouette of Inupiaq subsistence whalers at the edge of an open lead in the pack ice, looking for passing bowhead whales as the mid-day sun follows the horizon. Chukchi Sea, offshore from Barrow, Arc...

Steven Kazlowski / Inupiaq subsistence whaler stands on jumbled ice at the edge of an open lead in the pack ice to look for passing bowhead whales, during spring whaling season. Chukchi Sea, offshore from Barrow, Arctic...

Steven Kazlowski / Inupiaq subsistence whalers try to catch a bowhead whale (Balaena mysticetus) from their umiak in an open lead in the pack ice. Chukchi Sea, offshore from Barrow, Arctic coast of Alaska, April 2012.

Steven Kazlowski / Inupiaq subsistence whalers prepare to pull up a bowhead whale (Balaena mysticetus) catch along the edge of the open lead in the pack ice. Chukchi Sea, offshore from Barrow, Arctic coast of Alaska, Ap...

Steven Kazlowski / Inupiaq subsistence whalers break open a hole in the pack ice using a harpoon along the edge of an open lead, during spring whaling season, Chukchi Sea, offshore from Barrow, Arctic coast of Alaska

Steven Kazlowski / Inupiaq subsistence whaler stands on jumbled ice at the edge of an open lead in the pack ice to look for passing bowhead whales, during spring whaling season. Chukchi Sea, offshore from Barrow, Arctic...

Steven Kazlowski / Inupiaq subsistence whalers paddle their umiak, or bearded seal skin boat, to find passing bowhead whales traveling through the open lead, during spring whaling season. Chukchi Sea, offshore from Barr...

Steven Kazlowski / Inupiaq subsistence whalers bring their umiak - bearded seal skin boat - back onto the edge of an open lead in the pack ice, during spring whaling season. Chukchi Sea, offshore from Barrow, Arctic coa...

Steven Kazlowski / Inupiaq subsistence whalers in their umiak - bearded seal skin boat - watch a polar bear (Ursus maritimus) sow and cub travel along the edge of the open lead in the pack ice, during spring whaling sea...

Steven Kazlowski / Inupiaq subsistence whalers paddle their umiak - or bearded seal skin boat - and break thin ice forming in the open lead, allowing for passing bowhead whales during spring whaling season. Chukchi Sea,...

Steven Kazlowski / Inupiaq subsistence whalers get into their umiak - or bearded seal skin boat - in order to break thin ice forming in the open lead, allowing for passing bowhead whales during spring whaling season. Ch...

Steven Kazlowski / Inupiaq subsistence whaler at the front of an umiak - or bearded seal skin boat - spots a whale from the edge of an open lead in the pack ice during spring whaling season. Chukchi Sea, offshore from B...

Steven Kazlowski / Inupiaq subsistence whalers with an umiak - a bearded seal skin boat - wait at the edge of an open lead in the pack ice and look for whales. Chukchi Sea, offshore from Barrow, Arctic coast of Alaska,...

Bryan and Cherry Alexander / Inuit hunter harpooning Polar bear (Ursus maritimus) in a lead in Melville Bay, Northwest Greenland, 1986. 40 BELOW bookplate.

Bryan and Cherry Alexander / Group of Emperor penguins (Aptenodytes forsteri) stopping by a lead in the sea ice. Snow Hill Island, Antarctica, October.

Bryan and Cherry Alexander / Emperor penguins (Aptenodytes forsteri) stop before crossing a lead in the ice. Snow Hill Island, Antarctica, October.

Bryan and Cherry Alexander / Shard of clear ice, up-ended as the lead opens and closes with the tide. Antarctica, October 2006.

Bryan and Cherry Alexander / Polar bear (Ursus maritimus) picking her way across a lead on chunks of ice. Spitsbergen, Norway, 1993.

Bryan and Cherry Alexander / Polar bear (Ursus maritimus) caught in lead, watched by Husky (Canis familiaris). Northwest Greenland.

Bryan and Cherry Alexander / Inuit hunters in bearskin trousers hauling dead Polar bear (Ursus maritimus) out of lead. Northwest Greenland, 1980.

Bryan and Cherry Alexander / Husky (Canis familiaris) watching Polar bear (Ursus maritimus) caught in lead in the ice. Northwest Greenland.

Bryan and Cherry Alexander / Inuit hunter and Huskies (Canis familiaris) crossing lead. Melville Bay, Northwest Greenland, 1980.

Bryan and Cherry Alexander / Inuit hunter retrieving dead seal from lead. Northwest Greenland, 1980.

Bryan and Cherry Alexander / Inuit family and Huskies (Canis familiaris) using ice floe as raft to cross wide lead in late spring. Qaanaaq, Northwest Greenland, 1971.

Bryan and Cherry Alexander / Inuit elder fishing for Sculpin through lead in sea ice. Qaanaaq, Northwest Greenland.

Bryan and Cherry Alexander / Inuit family using ice floe as raft to cross wide lead in early summer. Qaanaaq, Northwest Greenland, 1971.

Bryan and Cherry Alexander / Inuit hunters hauling dead Polar bear (Ursus maritimus) out of lead at end of hunt, Northwest Greenland

Bryan and Cherry Alexander / Polar bear (Ursus maritimus) in lead snarling at Huskies (Canis familiaris), Northwest Greenland.

Bryan and Cherry Alexander / Inuit hunter Jacob Petersen jumping lead in summer sea ice, followed by Huskies (Canis familiaris). Qeqertat, Northwest Greenland, 1980

Steven Kazlowski / Beluga whale (Delphinapterus leucas) swimming in an open lead during spring migration, Chukchi Sea, Barrow, Arctic Alaska

Steven Kazlowski / Landscape of sea ice flowing through an open lead in the pack ice. This is potentially dangerous for Inupiaq whalers and hunters. If the ice should push up against the main pack, sections may break of...

Steven Kazlowski / Landscape of sea ice flowing through an open lead in the pack ice. This is potentially dangerous for Inupiaq whalers and hunters. If the ice should push up against the main pack, sections may break of...

Steven Kazlowski / Inupiaq subsistence whalers travel by skiff boat through an open lead in the pack ice during spring whaling season, Chukchi Sea, off the coastal village of Barrow, Alaska, USA. May 2009

Steven Kazlowski / Flock of Long tailed ducks (Clangula hyemallis) in flight over an open lead in the Chukchi Sea during spring migration, Barrow, Alaska.  

Steven Kazlowski / Large flock of King eider ducks (Somateria spectabilis) in flight through an open lead in the pack ice during spring migration, Chukchi Sea, off the Arctic coastal village of Barrow, Alaska, USA  

Steven Kazlowski / Bowhead whale (Balaena mysticetus) exhaling through blowhole, swimming through open lead in the pack ice during spring migration, Chukchi Sea, off shore from Barrow, Alaska  

Steven Kazlowski / Spring landscape of the midnight sun over an open lead in the pack ice in the Chukchi Sea, off shore from the arctic village of Barrow, Alaska. April 2009

Sue Flood / A bridge to cross a lead in the sea ice (with crossed flags to mark hazard) near Snow Hill Island, Weddell Sea, Antarctica November 2009

Doug Allan / Aerial view of Beluga whales (Delphinapterus leucas) travelling up lead, Lancaster Sound, Nunavut, Canadian high Arctic

Sue Flood / Lead or crack in sea ice near Ross Island, Antarctica, December 2008

Tui De Roy / Crabeater Seal (Lobodon carcinophagus) trio surfacing to breathe through fast ice lead, Admiralty Sound, Weddell Sea, Antarctica

Tui De Roy / Crabeater Seal (Lobodon carcinophagus) surfacing to breathe through fast ice lead, Admiralty Sound, Weddell Sea, Antarctica

Steven Kazlowski / An Inupiaq whaling crew at the edge of an open lead in the pack ice wait behind a snow blind and watch for passing whales during spring whaling season, off the Arctic coastal village of Point Hope, Ch...

Steven Kazlowski / Cape Thompson and an open lead in the pack ice, blown open by strong winds, indicating thinning sea ice conditions, 26 miles south of Point Hope, Arctic coast of Alaska, March 2008

Steven Kazlowski / Crack forming in pack ice over the Chukchi Sea, creating an open lead, blown open by strong winds, indicating thinning sea ice, near Point Hope, Alaska, March 2008

Steven Kazlowski / An Inupiaq whaling crew paddle their seal skin boat / umiak, in an open lead in the Chukchi Sea, during spring whaling season, off the Arctic coastal village of Point Hope, Alaska, May 2008

Steven Kazlowski / An Inupiaq seal skin boat / umiak at the edge of an open lead in the pack ice during spring whaling season, off the Arctic coastal village of Point Hope, Chukchi Sea, Alaska, May 2008

Steven Kazlowski / An Inupiaq whaling crew pulls in a Bowhead whale (Balaena mysticetus) catch at the edge of an open lead in the pack ice during spring whaling season, off the Arctic coastal village of Point Hope, Chuk...

Steven Kazlowski / Crack forming in the pack ice (blown open by strong winds, indicating thinning sea ice) over the Chukchi Sea, creating an open lead, outside the Arctic village of Point Hope, Alaska, April 2008

Steven Kazlowski / An Inupiaq whaling crew paddle their seal skin boat / umiak, in an open lead in the Chukchi Sea, during spring whaling season, off the Arctic coastal village of Point Hope, Alaska, May 2008

Steven Kazlowski / Sun behind storm clouds reflecting in open lead in pack ice, Chukchi Sea near Point Hope, Alaska, March 2008

Steven Kazlowski / Cape Thompson and an open lead in the pack ice, blown open by strong winds, indicating thinning sea ice conditions, 26 miles south of Point Hope, Arctic coast of Alaska, March 2008

Steven Kazlowski / Adult Beluga / White whales (Delphinapterus leucas) swim through an open lead in the pack ice during spring migration, off the Arctic coastal village of Point Hope, Chukchi Sea, Alaska, May 2008

Steven Kazlowski / An Inupiaq whaling crew waits at the edge of an open lead in the pack ice for passing Bowhead whales during spring whaling season, off the Arctic coastal village of Point Hope, Chukchi Sea, Alaska, Ma...

Steven Kazlowski / Person standing on Cape Thompson and an open lead in the pack ice, blown open by strong winds, indicating thinning sea ice conditions, 26 miles south of Point Hope, Arctic coast of Alaska, March 2008

Steven Kazlowski / An Inupiaq seal skin boat / umiak at the edge of an open lead in the pack ice during spring whaling season, off the Arctic coastal village of Point Hope, Chukchi Sea, Alaska, May 2008

Steven Kazlowski / An Inupiaq whaling crew prepare to paddle their seal skin boat / umiak, in an open lead in the Chukchi Sea, during spring whaling season, off the Arctic coastal village of Point Hope, Alaska, May 2008

Steven Kazlowski / An Inupiaq whaling crew paddle their seal skin boat / umiak, in an open lead in the Chukchi Sea, during spring whaling season, off the Arctic coastal village of Point Hope, Alaska, May 2008

Steven Kazlowski / King eider duck (Somateria spectabilis) flock in flight along the Arctic coast during spring migration, flying across an open lead in the pack ice on the Chukchi Sea off Barrow, Alaska, May

Steven Kazlowski / Landscape at the edge of an open lead in the pack ice, outside the Arctic village of Point Hope, Chukchi Sea, Alaska, May 2008

Steven Kazlowski / An Inupiaq whaling crew pulling in Bowhead whale (Balaena mysticetus) catch at the edge of an open lead in the pack ice during spring whaling season, off the Arctic coastal village of Point Hope, Chuk...

Steven Kazlowski / An Inupiaq whaling crew at the edge of an open lead in the pack ice wait behind a snow blind and watch for passing whales during spring whaling season, off the Arctic coastal village of Point Hope, Ch...

Steven Kazlowski / King eider duck (Somateria spectabilis) flock in flight along the Arctic coast during spring migration, flying across an open lead in the pack ice on the Chukchi Sea off Barrow, Alaska, May

Steven Kazlowski / An Inupiaq whaling crew at the edge of an open lead in the pack ice waiting behind a snow blind and watch for passing whales during spring whaling season, with a Beluga / White whale (Delphinapterus l...

Steven Kazlowski / Hopson One whaling crew with skin boat and whaling implements on the edge of a lead in the frozen Chukchi Sea, off Point Barrow, Arctic Alaska

Steven Kazlowski / Polar bear (Ursus maritimus) sow with subadult cub along the edge of an open lead on the frozen eastern Chukchi Sea, Arctic Alaska

Flip Nicklin / Narwhal (Monodon monoceros) pod in lead in pack ice, Baffin Island, Northwest Territories, Canada

Jim Brandenburg / Pressure ridges and lead in Arctic Ocean, Canada

Jim Brandenburg / Lead in pack ice, Ellesmere Island, Nunavut, Canada

Norbert Wu / Orca (Orcinus orca) travels down opening leads of ice, making deep dives under ice to hunt Antarctic cod, McMurdo Sound, Antarctica, sequence 2 of 4

Norbert Wu / Orca (Orcinus orca) travels down opening leads of ice, making deep dives under ice to hunt Antarctic cod, McMurdo Sound, Antarctica, sequence 1 of 4

Norbert Wu / Sea ice lead, sea ice splits to reveal long leads in summer, opening passages for marine life to travel through, McMurdo Sound, Antarctica

Norbert Wu / Sea ice lead, sea ice splits to reveal long leads in summer, opening passages for marine life to travel through, McMurdo Sound, Antarctica

Jim Brandenburg / Aerial view of pressure ridges and lead in ice, Arctic Ocean, Arctic

Jim Brandenburg / Pressure ridges and lead in Arctic Ocean, Arctic

Jim Brandenburg / Aerial view of lead in pack ice, Arctic Ocean, North Pole, Arctic

Norbert Wu / Weddell Seal (Leptonychotes weddellii) group gather around crack in sea ice, Antarctica

Norbert Wu / Orca (Orcinus orca) mother and calf spyhopping in icebreaker channel, must find open pockets of water to breathe, McMurdo Sound, Antarctica

Norbert Wu / Orca (Orcinus orca) surfacing at edge of ice, makes deep dives under ice to hunt Antarctic cod, Antarctica

Norbert Wu / Orca (Orcinus orca) pod resting at end of lead of ice, make deep dives under ice to hunt Antarctic cod, Antarctica

Norbert Wu / Orca (Orcinus orca) travels down opening leads of ice, making deep dives under ice to hunt Antarctic Cod, McMurdo Sound, Antarctica, sequence 4 of 4

Norbert Wu / Orca (Orcinus orca) travels down opening leads of ice, making deep dives under ice to hunt Antarctic Cod, McMurdo Sound, Antarctica, sequence 3 of 4

Flip Nicklin / Diver Glenn Williams swimimg under an open ice lead as tour group watches from above, Admiralty Inlet, Baffin Island, Canada

DOC WHITE / Lead - crack in ice floe - Canadian Arctic

Tui De Roy / Crabeater Seal (Lobodon carcinophagus) surfacing to breathe through fast ice lead, Admiralty Sound, Weddell Sea, Antarctica

Tui De Roy / Crabeater Seal (Lobodon carcinophagus) surfacing to breathe through fast ice lead, Admiralty Sound, Weddell Sea, Antarctica

Tui De Roy / Crabeater Seal (Lobodon carcinophagus) surfacing to breathe through fast ice lead, Admiralty Sound, Weddell Sea, Antarctica

Norbert Wu / Sea ice lead, sea ice splits to reveal long leads in summer, opening passages for marine life to travel through, McMurdo Sound, Antarctica

Jim Brandenburg / Pressure ridges and cracks in pack ice, Arctic Ocean

Jim Brandenburg / Pack ice, Arctic Ocean, North Pole, Arctic

Norbert Wu / Cracks in the sea ice form around islands and icebergs, Antarctica