The Great Barrier Reef has migrated back and forth across the ocean floor in response to large sea-level fluctuations over the past 30,000 years, reports a paper published online this week in Nature Geoscience.

Over the past 30,000 years, sea level has varied dramatically as continental ice sheets expanded and waned. At the Last Glacial Maximum, about 21,000 years ago, sea level was about 120 metres lower than it is today.

Jody Webster and colleagues examined drill cores collected near the modern Great Barrier Reef to assess how the reef system responded to past sea-level changes. They identified five reef death events: two caused by the exposure of the reef as sea level fell, and three caused by drowning as sea level rose faster than the corals could grow. The final death event was hastened by high sediment fluxes 10,000 years ago, and led to the establishment of the reef in its modern location. The authors also found that, following each event, the reef was able to re-establish at a more suitable depth within hundreds to thousands of years. This suggests that the reef’s long-term resilience was supported by connections with nearby reefs that could repopulate the reef as it migrated.