Great Barrier Reef records climate changes

SYDNEY - The relics of the Great Barrier Reef could give hints to a “tipping point” that could trigger a catastrophic climate change in future.

An international team jointly led by Jody Webster and Yosuke Yokoyama of the Universities of Sydney and Tokyo, respectively, is analysing sediment cores drilled by the research ship, the Greatship Maya, across the Great Barrier Reef last year.

The scientists are using the reef as a record of sea level fluctuations and climate change from the peak of the last Ice Age, about 21,000 years ago, to the first two millennia of the current warm Holocene epoch, which started about 12,000 years ago.

Coral reefs are markers of sea level. Coral gets its energy from photosynthetic algae in a symbiotic relationship with it, according to a Sydney statement.

When the sea level gets too high, less sunlight is captured by the algae, and the reef dies. Dead reefs form systems of terraces, ridges and pinnacles, the dates of which reveal sea level changes.

Scientists want to pin down the timing and impact of abrupt sea level rise when ice sheets melted in the past, in order to make predictions about the greenhouse future.

The behaviour of the ice sheets is among the big unknowns of climate science. If the West Antarctic ice sheet melted, the impact would be catastrophic, leading to a five to six metre sea level rise and send ocean circulation awry.

The team took cores of extinct coral reef and sediment from 34 holes drilled during an expedition to the Great Barrier Reef mounted by the Integrated Ocean Drilling Programme, a multi-million-dollar international research effort to explore the ocean floor.

Australian team members are dating the relict reefs using the radiocarbon and uranium-thorium techniques on the calcium carbonate coral exoskeletons.