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Cold-Water Corals, Habitats, and Paleoclimate in the Drake Passage, Southern Ocean
Kathryn Scanlon and Dann Blackwood of the U.S. Geological Survey (USGS) Woods Hole Science Center in Woods Hole, Massachusetts, participated in a research cruise to study cold-water coral habitats and paleo-oceanographic conditions in the Drake Passage between Antarctica and the southern tip of South America. The 37-day research cruise, part of a cooperative program with Laura Robinson, a geochemist from the Woods Hole Oceanographic Institution (WHOI), and Rhian Waller, a coral biologist from the University of Hawai‘i, was carried out onboard the icebreaker Nathaniel B. Palmer during April and May 2008. Cruise funding was from the National Science Foundation (NSF) Office of Polar Programs (OPP) Antarctic Sciences (grant ANT-0636787), awarded to Robinson and Waller. The cruise brought together experts in coral ecology, habitat geoscience, and sea-floor mapping, as well as paleoclimate, to start building a coherent picture of the long-term temporal and spatial distributions of deep-sea corals in the Southern Ocean.
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Above left: Coral team braves the wind for a group shot on deck. Front row, left to right: Rhian Waller (University of Hawai‘i), Kathy Scanlon (USGS), Tina van de Flierdt (Imperial College London), Kate Hendry (University of Oxford). Back row, left to right: Marshall Swartz (WHOI), Taryn Noble (University of Cambridge), John Swartz (University of Pittsburgh), Laura Robinson (WHOI), Dann Blackwood (USGS), and Daniel Wagner (University of Hawai‘i). [larger version]
Above right: The five main areas where we mapped cold-water-coral habitat and collected specimens for paleoclimate studies. Sars Seamount, another seamount we dubbed "Interim," and the slope area off Burdwood Bank were mapped with multibeam sonar for the first time. We also collected multibeam bathymetry on the slope north of Elephant Island and along a segment of the Shackleton Fracture Zone, where some previous mapping had been done. [larger version]
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The Southern Ocean is an important part of the global climate system, but our knowledge of its history is limited by a scarcity of well-dated records. The skeletons of deep-sea corals can record information on past climate, and deep-sea corals are found both living and as fossils in Antarctic waters. During the cruise, we used multibeam sonar to map the sea-floor topography of continental slopes, fracture zones, and seamounts in order to identify likely areas for cold-water-coral habitat. We also collected long transects of overlapping sea-floor photographs by using TOWCAM, a deep-towed camera sled owned and operated by WHOI, to gain high-resolution information about the habitats. We then used small research trawls and dredges to collect living and fossil corals.
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Above left: Dann Blackwood (USGS, left) and Marshall Swartz (WHOI, right) prepare to deploy TOWCAM, a camera sled designed to photograph the sea floor in deep-water areas. The sled was towed about 4 m above the sea floor and took photographs every 10 seconds for several hours at a time. These data will be used with the newly collected multibeam bathymetry and biological specimens to characterize deep-water habitats in the Drake Passage. Photograph by John Swartz (University of Pittsburgh). [larger version]
Above center: Working conditions in the Drake Passage in the Southern Hemisphere's late autumn were challenging. The deck of the icebreaker Nathaniel B. Palmer was frequently awash with icy water during deployments and retrievals of sampling gear. Photograph by Dann Blackwood (USGS). [larger version]
Above right: (Left to right) Rhian Waller (University of Hawai‘i), Laura Robinson (WHOI), and Kathy Scanlon (USGS) examine a handful of sediment and broken coral just scooped out of a trawl net on deck. Photograph by Dann Blackwood (USGS). [larger version]
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We will use the multibeam bathymetry, photographs, and specimens collected (representing at least 36 species of coral) to characterize cold-water-coral habitats in the Drake Passage. This improved understanding will help constrain the distribution and requirements of cold-water corals in other, less severe environments. Ongoing efforts are currently underway to protect cold-water corals in many places around the world, including Oculina and Lophelia reefs off Florida and the Carolinas, respectively, and coral gardens off Alaska.
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Above left: The solitary cold-water coral Desmophyllum dianthus was the holy grail of this research cruise. The large (max approx 10 cm long) skeletons are easy to work with, are widely distributed in the world's oceans, and have a well-understood growth pattern, making dating and geochemical analysis easier. We collected a few live specimens and numerous fossil specimens from water depths between 600 and 1,800 m. In one dredge from Sars Seamount, we collected three whole fossil Desmophyllum dianthus coral skeletons and numerous fragments. The dark-brown coating on the skeletons is manganese oxide, which must be carefully removed before the corals can be dated. Its thickness suggests that these specimens may be older (by as much as tens of thousands of years) than some of the other specimens we collected. Photograph by Dann Blackwood (USGS). [larger version]
Above right: In addition to Desmophyllum dianthus, we obtained several other species of scleractinian, octocoral, and stylasterid cold-water corals, including these Balanophyllia sp. The three fossil specimens, each approximately 2 to 3 cm in diameter, are presumed to be of different ages. These and other species will be dated to determine the distribution of cold-water corals over time. Photographs by Dann Blackwood (USGS). [larger version]
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The fossil corals will be dated, and we will make geochemical analyses of their skeletons to reconstruct the history of the Antarctic Circumpolar Current, allowing us to address the role of the Southern Ocean in climate change over tens of thousands of years.
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| Above: Icebergs viewed from the icebreaker Nathaniel B. Palmer. Photographs by Dann Blackwood (USGS). [larger version]
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More information about the cruise, including additional photographs by Dann Blackwood, can be viewed on the cruise Web site.
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 August 2008
in this issue:
cover story:
Corals, Habitats, and Paleoclimate in the Drake Passage
Scientists and the Media: Impacts of Sea-level Rise
USGS NWRC Celebrates National Women's History Month
USGS Promoted at National Science Teachers Association Conference
Field Trip for Association of American Geographers Meeting
USGS Modeling Conference
New Poster Depicts Complex Bathymetry in Northern Monterey Bay
August 2008 Publications List
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U. S. Department of the Interior | U.S. Geological Survey
