I open my cabin door and see the island. We’ve come to map the islands. Four low wooded islands in the central northern Great Barrier Reef. Four of some 1000 islands that, together with 2900 individual reefs, make this vast land-sea-scape.

These islands were mapped 45 years ago by Sarah’s grand-supervisor—her PhD supervisor’s supervisor—and 45 years before that by his grand-supervisor. We’re here to document change. The islands aren’t terra firma. They migrate slowly through time. The ocean’s swell—specifically the dominant south-easterly—moves the islands, particle by particle, north-westward.