by Kathy Scanlon

In May and June 2011, U.S. Geological Survey (USGS) marine geologist Kathy Scanlon participated in a 34-day research cruise on the icebreaking research vessel Nathaniel B. Palmer in the Drake Passage between Antarctica and South America. This was the second and final cruise of a project begun in 2008 with geochemist Laura Robinson of the Woods Hole Oceanographic Institution (WHOI) and the University of Bristol, U.K., and biologist Rhian Waller of the University of Maine.

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Also participating in the cruise was Shannon Hoy, an undergraduate at the College of Charleston, who was funded by the CARIS software company to help with the acquisition and processing of multibeam bathymetric (seafloor depth) data. Hoy received special training from CARIS before the cruise. After the cruise, she continued to work with Scanlon on the multibeam bathymetric data as a guest student at the WHOI and USGS offices in Woods Hole, Massachusetts.

The main objectives of the cruise were

1. to use a multibeam sonar system to complete bathymetric mapping of areas partly mapped in 2008 and to map new areas of the Drake Passage;
2. to identify present and past distributions of deep-sea corals by taking digital photographic images of the seafloor and collecting live and fossil specimens (a scientific paper that analyzing the distributions revealed in our 2008 data was published January 2011 in PLoS ONE); and
3. to collect fossil cold-water coral skeletons, which are useful as archives of oceanographic history.

Corals build their skeletons out of ingredients in seawater and thus record the distinctive chemistry of the water masses in which they grow. Using uranium-series dating techniques and radiocarbon analyses of our fossil specimens, we can reconstruct radiocarbon profiles of seawater masses over time for the past approximately 40,000 years.

The cruise was highly successful. Little time was lost due to weather conditions, which can be extremely harsh in the Southern Ocean during the late fall to early winter. We collected more than 14,000 fossil solitary scleractinian (stony coral) skeletons, 4,210 trackline-kilometers of multibeam bathymetric data, and more than 20,000 seafloor photographs, as well as several sediment cores, thousands of biological specimens, and water samples from each of six CTD (conductivity-temperature-depth) deployments.

The coral, water, and sediment samples, together with those collected in 2008, will enable us to put new constraints on the past extent of air-sea gas exchange, polar water-column stratification, and flux of Southern Ocean-sourced deep water to the rest of the world's oceans. Data from this cruise will allow the first systematic study of these constraints and of the environmental controls on deep-water coral biogeography in the Drake Passage, as well as enable us to test hypotheses linking processes in the Southern Ocean to climate change.