Around 700,000 years ago, summer temperatures off the coast of Australia rose from an average of 26 to around 29 degrees Celsius and hardly fell below this level in the subsequent cold periods. "This ideal warm window favoured rapid coral growth and impressively demonstrates how sensitively a reef reacts to temperature," summarises Gerald Auer from the Department of Earth Sciences at the University of Graz. As part of an international team led by Kiel University, he examined sediment samples from the Ocean Drilling Program from a borehole in the immediate vicinity of the Great Barrier Reef. Thanks to a new method, the researchers were able to reconstruct the climatic conditions using chemical fossils from these samples. "We were also able to show that extremely stable temperatures over several millennia were necessary for the Great Barrier Reef to form in the first place," adds Auer, who carried out the age dating of the drill core data as part of the study.
However, the further warming of the sea due to man-made climate change is now the greatest threat to the cnidarians. Summer temperature peaks of over 30 degrees trigger coral bleaching and jeopardise the existence of reefs. "Many coral species will not be able to migrate away from the overheated regions, as they find it difficult to adapt to the cold and low-light winters at higher latitudes," notes the researcher.
Publication
Benjamin Petrick, Lars Reuning, Alexandra Auderset, Miriam Pfeiffer, Gerald Auer, Lorenz Schwark: High sea surface temperatures were a prerequisite for the development and expansion of the Great Barrier Reef, 2024, Science Advances
DOI: 10.1126/sciadv.ado2058