In Hawaii, living corals thousands of years old give clues to past climate change
Using radiocarbon dating and samples of deep-sea corals snipped from the floor of the Pacific Ocean by a submersible, researchers from Stanford and Lawrence Livermore National Laboratory have discovered that deep-sea corals growing off Hawaii are much older than previously thought—some as old as 4,000 years.
The surprise finding is important in two areas, said Stanford's Brendan Roark, a postdoctoral fellow in the lab of geological and environmental sciences Professor Robert Dunbar. Roark spoke about the research last week in Boston at the annual meeting of the American Association for the Advancement of Science (AAAS).
First, the finding suggests that harvesting of the oldest coral for jewelry should be banned by federal and local officials, he said. The long-lived corals grow so slowly that any level of harvesting is unsustainable; they take so long to grow that they simply cannot replace themselves fast enough to survive even minimal harvesting.
Second, a 4,000-year-old coral, having stood in the same place in the Pacific Ocean and imbibed of the waters for so long, holds within its skeleton clues about the conditions of the ocean over many centuries. Ancient coral may turn out to be the archives of the ocean, Roark said, a unique reference library of past climate changes that could prove useful in understanding future climate change.
The coral might further our understanding, for example, of how the oceans absorb carbon dioxide from the atmosphere.
"These organisms are the equivalent of the bristlecone pine in the deep ocean," he said. They are placed in jeopardy not only by coral harvesters but also by deep-sea trawling and long-line fishing. "Clearly a different frame of mind is needed," he said. "It's not a renewable resource."
Roark and his associates found that Gerardia, commonly known as gold coral, can live for at least 2,700 years. It grows in tree-like fashion to several meters in height. Even older is the deep-water black coral Leiopathes glaberrima. Another tree-like skeleton, it has life spans in excess of 4,000 years—some of these corals began growing just a few hundred years after the great pyramids were built in Giza and are still alive today.
At the AAAS meeting, Roark, a paleoceanographer, presented the results from a collaborative project focused on geochemical records of past oceanographic and climate variability, as recorded in six different species of deep-sea corals. The preliminary results suggest the possibility of reconstructing subsurface temperature variability and changes in ocean circulation.
Coral samples were collected in waters as deep as 1,500 feet at the Makapu'u deep-sea coral bed off the southeast coast of Oahu, Hawaii. Researchers went down in the Hawaii Undersea Research Laboratory's submersibles, Pisces IV and V.
Roark's co-authors are Stanford's Robert Dunbar and Tom Guilderson from the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory.