Deep sea-corals reveal climate history
Our planet’s oceans have played a key role in its climate system, from the storage and transport of heat across the globe to the carbon cycle. One way to gain a new understanding of past climatic changes is through the collection of deep-sea coral skeletons. They do not have algal symbionts, unlike reef-forming corals found in shallow tropical areas, so are not limited to the photic zone or warm waters. The DEEP-SEA CORALS (Deep-sea coral geochemistry and climate: a focus on the history of the Southern Ocean) project used deep-sea corals for assessment of previous climatic conditions, and to understand factors affecting coral distribution. Few studies have previously used cold-water corals as paleoclimate archives due to the challenges involved in their collection. The calcium carbonate skeletons of deep-sea corals were collected during scientific deep-sea collection expeditions and were dated using the decay of uranium. The chemistry of the growth layers within the coral skeletons reflected external environmental conditions thus acting as a record of rapid climate change events in the ocean. Research papers were published that reviewed the current knowledge of deep-sea coral research, established new geochemical proxies and dating techniques for using deep-sea corals as climate archives. They also explored the past history of coral population dynamics in the Southern Ocean. In addition, the oceanic radiocarbon in the Southern Ocean was compared to the Equatorial Atlantic. It was shown, for the first, time, that the sub-surface ocean carbon cycle changes at the same time as atmospheric carbon dioxide levels even on centennial timescales. The ecological process studies enabled dating of corals, showing change in species composition over time. A new method developed for rapidly radio-dating uranium will allow quick dating of all the collected samples. The project also mapped present-day distributions of corals in the Southern Ocean and equatorial Atlantic to eventually provide an ecological interpretation of distribution changes. DEEP-SEA CORALS used corals to discern much about ancient climatic changes, thereby helping to reveal more about contemporary processes. The work will also aid protection of deep-sea habitats, and lead to improved policy outcomes.
