First high-resolution record of fossil corals shows climate change

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Fig. 1: Members of the IODP Expedition 389 science group looking at the cores in
Fig. 1: Members of the IODP Expedition 389 science group looking at the cores in the IODP core repository in Bremen at MARUM - Center for Marine Environmental Sciences at the University of Bremen. C: parker@ECORD_IODP

Hawaii: Environmental data from shallow-water corals provide a glimpse 500,000 years into the past

During the IODP Expedition 389 "Hawaiian Drowned Reefs" off the coast of Hawaii, scientists recovered a total of 426 meters of cores from the seafloor in water depths ranging from 130 to 1240 meters. After almost a month of intensive analysis work at the IODP core repository in Bremen at MARUM - Center for Marine Environmental Sciences at the University of Bremen in February 2024, the cores have now been opened and sampled in order to obtain information about sea level or climate change from these enormously important high-resolution archives. Geobiologist Theresa Nohl from the University of Vienna is also involved. The project was led by Jody Webster (School of Geosciences, University of Sydney, Australia) and Christina Ravelo (Ocean Sciences Department at the University of California, Santa Cruz, USA).

Corals store past environmental conditions in their skeletons. By analyzing fossil corals, valuable data about the past climate and reef conditions off the coast of Hawaii can be obtained. Specifically, the international team of scientists is measuring the extent of sea level changes over the past 500,000 years. The data will be used to answer questions such as why sea level and climate change over time and how coral reefs react to abrupt changes in sea level and climate. "This look into the past will give us valuable insights into the mechanisms of climate change, for example," explains Theresa Nohl.

"We have recovered a spectacular sequence of fossil coral reef deposits that will allow us to decipher in unprecedented detail how sea level, paleoclimate and the reef ecosystem have changed over the last 500,000 years, particularly during periods of rapid global change," said Jody Webster. "We are also pleased to have recovered many samples of fossil corals with distinctive growth rings, which will give us for the first time detailed records of monthly changes in oceanographic conditions in past periods that were different from today. The idea is to use this data to make predictions about future Pacific-wide climate changes," adds Christina Ravelo.

Geobiologist Theresa Nohl from the University of Vienna is part of the onshore phase of the expedition as a sedimentologist. She has also spent the past few weeks at MARUM - Center for Marine Environmental Sciences at the University of Bremen carrying out intensive sampling and descriptive work. "My research question concerns the conservation of various organisms. This means that I am investigating the extent to which physical and (microbially controlled) chemical changes have altered the reef terraces and surrounding sediment after deposition, what these changes mean for the reconstruction of ecosystem dynamics and sea level fluctuations, and how these reconstructions can be improved." The samples and analyses are promising so far.

about the expedition

The IODP Expedition 389 science team consists of 31 scientists from various disciplines from Australia, Austria, China, Denmark, France, Germany, India, Japan, the Netherlands, Spain, the UK and the USA, ten of whom sailed on board the multi-purpose vessel MMA Valour off the coast of Hawaii in September and October 2023 to collect the cores and data using a remote coring system. After the offshore phase, the entire science team met in February 2024 at the IODP core repository Bremen at MARUM - Center for Marine Environmental Sciences at the University of Bremen, Germany, to split, analyze and sample the cores and start evaluating the collected data. The scientists will continue to process the samples and data in their home laboratories over the next few years to decipher detailed information from this unique new material and associated data.

The expedition is being carried out by the European Consortium for Ocean Research Drilling (ECORD) as part of the International Ocean Discovery Program (IODP). The IODP is a publicly funded international marine research program supported by 21 countries that explores the Earth’s history and dynamics recorded in the sediments and rocks of the seafloor and monitors the subseafloor environment. Using multiple platforms - a unique feature of the IODP - scientists study the deep biosphere and ocean beneath the seafloor, environmental changes, processes and impacts, and the cycles and dynamics of the solid Earth.