Gentoo penguin, Petermann Island, Antarctica (© Paul Souders/DanitaDelimont.com/Alamy)

Penguins thrive in some of Earth's coldest waters. Today's image shows a gentoo penguin beneath a vault of shimmering blue ice, its sharp silhouette etched against the frozen world around it. Penguin Awareness Day, observed on 20 January, shines a spotlight on the birds that bring life, noise and personality to Earth's iciest coastlines.