Andres M. Dominguez / Dove's-foot crane's-bill leaf (Geranium molle) and algae in ice with air bubbles, Sierra de Grazalema Natural Park, southern Spain, February.

Andres M. Dominguez / Ice and grass in frozen pond, Sierra de Grazalema Natural Park, southern Spain, January.

Kevin Schafer / Frozen gas bubbles beneath surface of frozen lake, Abraham Lake, Canadian Rockies, Alberta, Canada

Erlend Haarberg / Air bubbles frozen in ice, Helgeland, Nordland, Norway, November

Graham Eaton / Underwater view of a mountain lake with frozen surface, Llyn Idwal, Snowdonia NP, Gwynedd, Wales, UK, December

Chadden Hunter / Emperor penguins (Aptenodytes forsteri) males dive through openings in the sea ice to take their first swim in over 4 months as they have spent the bleak winter incubating their eggs. Cape Washington,...

Sven Zacek / Frozen bubbles captured in ice on the surface of lake. South Estonia, Europe, January 2008.

Graham Eaton / Under the ice scene of freshwater frozen lake. Llyn Dinas, Snowdonia, Wales, December 2010.

Edwin Giesbers / Air bubbles trapped in ice, the Netherlands

Kim Taylor / Water beetles (Dytiscus marginalis) and (Acilius sulcatus) clustered around an air bubble trapped beneath the ice of a frozen pond, digitally enhanced, Surrey, England

SIMON KING / Blue Ice on frozen lake with air bubbles, Antarctica.

Ingo Arndt / Bubbles caught in ice, Lake Baikal, Siberia, Russia