Rising seas had surprising effect

Sea-level changes caused by melting ice sheets were behind the formation of Australia’s Great Barrier Reef, new research reveals.

It also shows climate change could cause unexpected changes to coastlines, many of which are already home to communities incredibly vulnerable to the rising tides.

The study, published today in international science journal Nature Geoscience and led by University of Canterbury researchers, has provided new insights into the origins of Australia’s K’gari (Fraser Island) and its neighbouring reef system.

But Jamie Shulmeister, head of the university’s earth and environment department, said when and why the two significant landscape features formed had been poorly understood until now.

Researchers discovered K’gari was created during a period of global climate change about 800,000 years ago, when ‘‘rising sea levels associated with melting ice sheets triggered large volumes of sand to be released on the east Australian coast north of Brisbane’’.

Shulmeister said this process created a massive field of sand dunes, which eventually became the Cooloola Sand Mass and nearby K’gari in Queensland.

‘‘The creation of K’gari also acted as a groyne, preventing sediment from being transported north of the island which provided the clear waters and conditions needed for coral growth in the area that now forms the southern and central parts of the Great Barrier Reef.’’

The research team studied sediment and soil samples from coastal dunes on the Cooloola Sand Mass and K’gari using a dating technique which estimated the last time the quartz-rich sand sediments were exposed to light.

The discovery explains why the Great Barrier Reef formed only around half a million years ago, despite Australia having conditions appropriate for reef growth for much, much longer.

Shulmeister said the findings had implications for future climate change scenarios, because they demonstrated that rising sea levels could cause coastlines to respond in ways apparently unconnected to the sea-level rise itself.

Sea-level rise is already expected to have significant implications for New Zealand, as well as its Pacific neighbours.

In September, Statistics NZ released 120 years of coastal data from 1901 to 2020, capturing an acceleration in the rising tides as the planet heats.

On the shores of Christchurch, Wellington and Dunedin, sea-level rise crept up twice as fast during the last 60 years, compared to the 60 years before. As the sea rises, homes will increasingly be at risk of flooding and damage, and coastal communities could be cut off during natural disasters – and may eventually have to retreat.