Fossil coral reefs as a window into the past and future

Coral reefs are very sensitive to sea level and other changes in environmental conditions. As fossils they provide a record of past conditions over hundreds, thousands and millions of years of Earth’s history. There is, however, a discontinuity in the global record over the past 500,000 years, especially during periods of major and abrupt climate instability. The IODP Expedition 389 “Hawai’ian Drowned Reefs” focusses on this missing link and is led by Co-Chiefs scientists Professor Christina Ravelo (Ocean Sciences Department at the University of California, Santa Cruz, USA) and Professor Jody Webster (School of Geosciences, the University of Sydney, Australia).  

Prof Christina Ravelo: “The Hawai‘i fossil reefs are storytellers of the past climate and ocean changes and of the reef ecosystem responses to those changes. These stories can be unlocked through careful study of the fossils that we hope to recover.” 

Prof Jody Webster: “We hope that information recorded in the fossil reefs will help scientists make improved predictions about the rate and magnitude of sea-level rise, what impact global warming and cooling has on short-term climate phenomena like droughts, floods and marine heat waves, and how coral reef ecosystems respond to these changes.”

Dr Thomas Felis, head of the Coral Paleoclimatology group at MARUM – Center for Marine Environmental Sciences at the University of Bremen, is a member of the expedition team. “After previous coral reef drilling expeditions to the Great Barrier Reef and Tahiti in which I was involved, there is now the unique opportunity in Hawai‘i to go back much further into the past, hopefully up to half a million years”, says Thomas Felis. Felis also coordinates the DFG Priority Programme "Tropical Climate Variability & Coral Reefs" (SPP 2299), a Germany-wide collaborative network that aims to improve the understanding of climate variability in the tropical oceans and its impacts on coral reef ecosystems in a warming world. “I am very pleased that 4 researchers from our program have been invited to contribute to the IODP Expedition 389 to Hawai‘i.”

The expedition aims to recover cores from water depths between 134 and 1,155 meters at a maximum of twenty locations. Even though this will be the first time that a seafloor coring system will be deployed in this area, the anticipated sites are well studied. “We have a very good idea of what the seabed looks like off the coast of Hawai’i based on extensive mapping using underwater sonar, as well as footage and surface samples collected using submersibles and remotely operated diving robots by scientists over the past four decades”, says Jody Webster. “This information has helped us select the best places to carefully collect the cores that will deepen our understanding of the history of the reef system”, adds Christina Ravelo.

The University of Hawai’i is a partner institution for this expedition and has a strong tradition of science in coral reefs, littoral phenomena, and shoreline geology. Hawai’ian scientists have been studying sea level change and its impacts and have highlighted how this knowledge is important for formulating a mitigation and resilience strategy for the future. Prof Kenna Rubin, Inorganic Geochemist at the University of Hawai'i at Manoa, Department of Earth Sciences, has been involved in planning of the expedition from the beginning and will be a key participant.

Prof Kenna Rubin: “These detailed, high-resolution temporal and compositional records anticipated from this expedition will add greatly to our knowledge of responses to climate change, as well as helping scientists to better understand the volcanic subsidence history of the Big Island. The impacts of this research in Hawai’i will contribute to existing studies of sea level change as recorded here by coral reefs.”

The scientific objectives of the expedition aim to address questions on four main topics:

• To measure the extent of sea level change over the past half a million years
• To investigate why sea level and climate changes through time
• To investigate how coral reefs respond to abrupt sea level and climate changes, and
• To improve scientific knowledge of the growth and subsidence of Hawai’i over time.

The planning phase of the expedition includes intensive environmental observations and a comprehensive risk assessment.