A landmark international study by the Great Barrier Reef has shown that the world's largest reef system has suffered five deaths in the past 30,000 years, mainly due to sea-level changes and related environmental changes.
For millennia, the reef has adapted to sudden changes in the environment by traveling over the seabed as the oceans rose and fell away.
The study was published today in Nature Geoscience by University of Sydney Associate Professor Jody Webster is the first of her kind to reconstruct the evolution of the reef over the last 30 millennia in response to larger, abrupt environmental changes.
Associate Professor Webster from the University's School of Geosciences and Geocoastal Research Group said it remains an open question as to whether its resilience will be sufficient to survive the current global decline in coral reefs.
"Our study shows that the reef was able to jump back from past death events during the last glaciation and de-icing," he said. "However, we found it also very sensitive to increased sediment input, which is important given current land-use practices."
The study used data from geomorphic, sedimentological, biological and dating information from fossil reef cores at 16 locations in Cairns and Mackay
The study covers the time before the "last glacial maximum" about 20,000 years ago in the ocean
History of Deaths
When sea levels sank in the millennia before that time, there were two widespread deaths (about 30,000 years ago and 22,000 years ago) caused by the exposure of the reef to the air, known as subaerial exposure. During this time, the reef moved seaward to keep up with the sinking sea level.
During the defrost period after the last glacial maximum, there were two more reefed events before about 17,000 and 13,000 years ago rapid sea-level rise. These were accompanied as the reef moved landward, trying to keep up with rising seas.
Analysis of core samples and sediment flow data indicates that these reef death events from sea-level rise were likely associated with a sharp increase in sediment.
The last reef-death event some 10,000 years ago, before the emergence of the modern reef some 9000 years ago, was associated with no known abrupt sea-level rise or "meltwater pulse" during de-icing. Rather, it appears to be associated with a massive increase in sediment and reduced water quality with a general increase in sea level.
The authors suggest that the reef could re-establish itself over time due to the continuity of coral reef habitats and coral algae and the reef's ability to migrate laterally between 0.2 and 1.5 meters per year.
However, Professor Webster said that it would be unlikely that this rate would suffice the current rates of sea surface temperature increase, sharp decline in coral cover, annual coral bleaching or decrease in water quality, and increased sediment flow since to survive the European settlement.
"I have great concerns regarding the ability of the reef to its present form to survive the pace of change caused by the many current burdens and those projected in the near future," he said.
Associate Professor Webster said that earlier studies showed a temperature increase of the ocean surface by several degrees over a period of 10,000 years. However, current forecasts of changes in sea surface temperature are about 0.7 degrees in a century.
"Our study shows that the reef not only responds to sea level changes but has also been particularly sensitive to sediment flows in the past. In the current period, we need to understand how primary industry practices affect sediment input and reef water quality influence, "he said.
Unravel the role of climate for the evolution of sediments and reefs over millennia
Jody M. Webster et al., Response of the Great Barrier Reef to Sea Level and Environmental Changes in the Last 30,000 Years, Nature Geoscience (2018). DOI: 10.1038 / s41561-018-0127-3