The response of coral reef systems to sea level rise: how/why do reefs drown?

Fossil coral reefs provide important evidence about the former positions of sea level in space and time due to their geological preservation and suitability for dating. Of particular interest is the use of submerged coral reefs to: (1) reconstruct the timing, rate and magnitude of sea level rise to better understand the dynamic behaviour of past ice sheet melting, and (2) assess the impact of sea level rise and associated environmental changes that cause coral reef drowning (i.e. inability to keep pace with sea-level rise). Understanding how and why coral reefs drown is vital to the recognition and quantification of rapid sea-level rise associated with meltwater pulses (MWP’s) that have been controversially linked to the catastrophic collapse of ice sheets in the past. Studies of drowned fossil reefs from Barbados, Tahiti, Huon Peninsula, Hawaii and elsewhere have produced a broadly consistent picture of ice melt, reflecting eustatic change since the Last Glacial Maximum (LGM). However, despite the International Ocean Drilling Program (IODP) expeditions to Tahiti (Exp. 310), and more recently the Great Barrier Reef (GBR) (Exp. 325) extending these records, considerable uncertainty remains concerning the details, nature and impact of deglacial meltwater pulses on coral reef systems. These studies have shown that the sensitivity of reefs to rapid sea-level rise varies considerably, with some reefs drowning while others do not. In this seminar, I present a synthesis of key geomorphic, sedimentologic, biologic, geochemical, dating and numerical stratigraphic modeling data from submerged coral reefs around the world and explore the issue of how and why coral reefs drown. Focusing on the GBR, I will investigate the nature and timing of successive reef demise events, and argue that the synergistic effects of sea level rise (i.e. poor water quality) have been crucial in ultimately causing reef drowning and demise over the past 30,000 years. Finally, I will also highlight the exciting potential of the latest IODP reef expedition (Exp. 389 - Hawaiian Drowned Reefs) to address these questions that was recently drilled offshore Hawai’i (Aug-Oct, 2023).