Warming sea surface temperatures allowed the development of the Great Barrier Reef

The Great Barrier Reef (GBR)is a unique environment almost 300 times bigger than the next biggest barrier reef system. One of the key questions about this system is what conditions allowed the formation of this environment. Given the influence of Sea Surface Temperature (SST) on modern reef environments, it was originally assumed that it was related to changes in SST. However, there is a lack of SST records for the late Pleistocene for the area around the Great GBR. We used TEX₈₆^H to produce a new SST record starting at 900 ka from ODP Site 820 next to the northern GBR. Before MIS 17, summer SSTs were as low as 26-24 degrees during glacials. While reefs can persist at these temperatures, reef expansion is limited by the cold conditions. Then, there is an increase in temperature around MIS 17. This is followed by a period of relatively of stable SST between MIS 17-13, with glacial summer SSTs above 27 degrees. This period matches the establishment of the GBR at MIS 17 (700 ka) and then the development of the permanent reef system around MIS 13 (500 ka). This period of relatively stable SSTs might have allowed the system to develop and expand within a narrow window ideal for coral Reef growth, even during glacials. Therefore, our research suggests that major steps in the development of the Great Barrier Reef system are linked to changes in the SSTs.