Final Report Summary - CACH (Reconstructing abrupt Changes in Chemistry and Circulation of the Equatorial Atlantic Ocean: Implications for global Climate and deep-water Habitats) The Earth has experienced large, abrupt and complex climate shifts through geologic time. For example, ice core records show that glacials had lower atmospheric pCO2 and cooler temperatures than today, and that the last deglaciation was punctuated by large, abrupt millennial-scale climate events. The ocean is a key component of this climate system, transporting heat around the globe as well as playing a key role in the carbon cycle. This project combined oceanographic fieldwork, geochemical laboratory analyses and modelling to examine the nature of these interactions between the oceans and climate as well as the environmental pressures on deep-water habitats.In 2013 the project launched a research expedition across the Atlantic Ocean using specialist underwater vehicles to explore the deep sea. The interdisciplinary team of scientists on board recovered detailed maps, images and samples including seawater, sediments and deep-sea corals. Deep-sea corals are found in all of the ocean basins, at depths from a few metres down depths greater than 5,000m. The chemistry of the growth layers within the coral skeletons can reflect the external environmental conditions in which they grow, thus preserving a record of rapid climate events in the ocean similar in temporal resolution to the atmospheric records preserved in ice cores. We used a variety of techniques to analyse the skeletal remains of these corals, establishing both when they grew, and what they could tell us about the history of the oceans. We found that the deep ocean is a very dynamic environment, with large scale shifts in its circulation that occurred rapidly, and at the same time that carbon dioxide in the atmosphere increased as the Earth warmed. We were also able to detect melting of the major ice sheets of the glaciation from changes in the chemistry of the corals – thus linking oceans, atmospheres and land processes. We have also been able to use chemical analyses of sediment cores collected on the expedition to show that the deep ocean circulation of the Atlantic behaved in a remarkably coherent way during the deglaciation, relieving concerns that our understanding of the past ocean comes from only a few sites. Beyond the implications of our scientific results for understanding climate, we have also made progress across a range of fields. Working with ecosystem modellers, we have examined the major controls on the communities that live on isolated seamounts. We also developed new methods for examining litter and microplastics in marine environments. Indeed, we were the first to show that microfibres are being ingested by deep-sea animals, far from land. The samples and data from the project are continuing to be used at the University of Bristol and beyond, leaving a legacy of scientific discovery for the future.
