The start of the Great Barrier Reef is a result of the increased stability of Temperatures in the Mid to Late Pleistocene.

The Great Barrier Reef is a unique environmental resource threatened by future climate change. However, it has always been unclear how this ecosystem developed in the Mid to Late Pleistocene. Work has shown that the reef developed between ~ 600-500 ka during MIS 15-13, although some records suggest a start at MIS 11 at 400 ka. There is a lack of Sea Surface Temperature (SST) records for this time for the area around the Great Barrier Reef. Furthermore, the few existing SST records do not show temperature changes during these key periods, leading researchers to suggest that factors other than temperature, such as sea-level change or sediment transport, explain the start of the reef. We used the TEX₈₆ proxy to produce a new SST record starting at 900 ka from ODP Site 820. This core is located next to the northern Great Barrier Reef. In this new record, there are SST changes that seem to match both dates for the start of the Great Barrier Reef. First, there is a period of stable SST between 700-500 ka, with no glacial cooling during this time. This could promote the development of a reef system during this time, allowing the reef more time to evolve from isolated smaller reefs to a continuous barrier reef. However, there is some suggestion based on facies analyses that even though the barrier system developed around MIS 15, the modern coral reef system was not yet fully established. Our records show that glacial temperatures during MIS 14 still are similar to SSTs from records further south. However, this trend shifts around MIS 11 when glacials became warmer. In fact, while before MIS 11, SST at ODP 820 was colder than records from the Western Pacific Warm Pool, afterwards SST was either the same or sometimes warmer than at these sites. Also, unlike other nearby records, the difference in SSTs between glacials and interglacials is reduced after MIS 11. This suggests that the northern Coral Sea might have been protected from the extremes of glacial temperature changes after the MPT. This process might have allowed the development of a continuous coral reef system by encouraging the growth of reefs 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. Our SST record suggests that SST changes are the primary driver of reef development and other non-SST factors are less important.