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People sorting coral bits in a room.
Photo Credit: Laura Robinson
Scientists and technicians aboard the research vessel Laurence M. Gould dry, sort and pack the multitude of coral fossils collected from deep-sea dredges along Cape Horn. The corals' hard skeletons contain chemical signatures that “record” some of the ocean properties at the time of their growth.

Cold corals

Scientists venture into the Drake to learn more about benthic ecosystem and climate change

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Visiting the underwater world of corals in the Southern Ocean isn’t exactly like a tropical vacation.

Consider that the stretch of water between the tips of South America and the Antarctic Peninsula, where some of these cold-water corals are found, is one of the most inhospitable in the world. Frequent storms and strong seafloor currents make it a difficult place for researchers to retrieve samples. The marine organisms exist at depths from hundreds to thousands of meters — a deep and dark realm rarely explored until recently.

“Down in the Southern Ocean, very little is known about the cold-water corals that live there,” said Rhian Waller External Non-U.S. government site, a co-principal investigator on a project to study the spatial and temporal diversity, distribution and propagation of coral species in the frigid seas between continents.

But learning more about the biogeography of the different coral species was only part of the goal for a five-week research expedition to the Drake Passage earlier this year. [See expedition blog, Corals in the Drake Passage External Non-U.S. government site.] It turns out that deep-water corals are also an excellent way to learn about the past conditions of the ocean and overall climate as it existed thousands of years ago.

People work on the deck of a ship.
Photo Credit: Kate Hendry
David Case, Sandy Alesowrth and Chris Roy recover the dredge used to collect live and fossil corals from the seafloor.

“The nice thing about corals … for studying climate is that we can date them very accurately,” said Laura Robinson External Non-U.S. government site, chief scientist on the research cruise aboard the Nathaniel B. Palmer External U.S. government site and co-principal investigator on the project with Waller.

Together, the two scientists and their team of students and international collaborators spent the early weeks of the Antarctic winter trawling and dredging for samples of both live and dead corals from seamounts rising up from the ocean floor or along the relatively shallow continental slopes.

The biologists aboard the ship recovered more than 11,000 individual samples, mainly in the order octocoralia (also known as soft corals), including what may turn out to be a few new species.

Just as importantly, the scientists deployed a couple of different camera systems from the ship to image the seafloor. The TowCam External Non-U.S. government site, pulled behind the Palmer, “flies” only about five meters off the seafloor, recording about 2,000 images at each deployment. The DropCam, as the name implies, falls straight to the seafloor while the ship is stopped, snapping pictures only two meters from the bottom.

Waller’s team will analyze the images back in the lab to identify species, information the scientists can use to map distribution and diversity between South America and the Antarctic Peninsula.

Crabs on the ocean floor.
Photo Courtesy: Laura Robinson and Rhian Waller
A photo taken at 900 meters depth by the DropCam on Interim Seamount shows red crabs and other benthic marine fauna.

“We’ll be able to track where certain species end — whether they fully cross the Drake Passage, or whether they’re only found at certain locations,” explained Waller, an assistant research professor at the University of Maine’s Darling Marine Center External Non-U.S. government site.

“The photography and sample sections go side-by-side, really, for the biology side of this project,” she added. “We see so much more in the photographs than we do in the collections, but often we can’t really identify what we have in the photograph unless we have a sample.”

The paleoceanographers, led by Robinson, are more interested in the fossil corals brought aboard the ship for the information they can provide about past ocean conditions and even ocean circulation.

Cold-water corals build hard skeletons made of calcium carbonate that contain chemical signatures that “record” some of the chemical and physical properties of the waters in which they grew. The uranium in the calcium carbonate decays into thorium, a process that allows the researchers to date the coral material very accurately — almost as well as glaciologists who use ice cores to reconstruct past climate.1 2   Next