The evolution of the Great Barrier Reef: a decade of progress & future directions.

Predicting how the Great Barrier Reef (GBR) will respond in the face of future global climate changes is both poorly constrained and controversial. This relates to our incomplete understanding of how reef systems respond to environmental changes but also the lack of baseline data — particularly on centennial to millennial time scales. The recent declines in coral coverage across much of the GBR in the past 30 years, along with the massive bleaching and mortality following the 2016 and 2017 events, has brought these issues around coral reef resilience/demise into sharp focus. The study of the evolution of the GBR over past 500-600 ka can provide unique insights about how this iconic reef system responded to abrupt and major environmental changes over a range of spatio-temporal scales. Over the past decade considerable progress has been made in the analysis of new and existing fossil coral reef cores, including those recovered from the edge of continental shelf of the GBR, in water depths between 50 to 130 m by the International Ocean Discovery Program (IODP) Expedition 325 (Great Barrier Reef Environmental Changes). Together, these cores are revealing exciting information about past sea level, climate and environmental changes but also crucial new insights into how the GBR responded to these perturbations. In this seminar, I will present a synthesis of all available geomorphic, sedimentologic, biologic, geochemical, dating and numerical stratigraphic modeling information. I will discuss the nature and timing of the reef initiation and demise events, while documenting the corresponding changes in reef communities, growth rates and paleoenvironmental conditions at each major stage of the GBR’s 500-600 kyr history. Finally, I will also highlight the exciting potential of the next major IODP coral reef drilling project - Expedition 389 (Hawaiian Drowned Reefs) off the island of Hawai’i likely to be scheduled in the current phase of IODP (2019-23).