Modern carbonate mounds; Porcupine drilling on IODP Expedition 307

Author(s): Williams, Trevor; Kano, Akihiro; Ferdelman, Tim; Henriet, Jean-Pierre
Integrated Ocean Drilling Program, Expedition 307, Shipboard Scientific Party, Corpus Christi, TX
Author Affiliation(s): Primary:
Lamont-Doherty Earth Observatory, United States
Other:
Hiroshima University, Japan
Max Planck Institute for Marine Microbiology, Federal Republic of Germany
Ghent University, Belgium
Volume Title: 33rd international geological congress; abstracts
Source: International Geological Congress [International Geological Congress, Abstracts = Congrès Géologique International, Résumés, Vol.33; 33rd international geological congress, Oslo, Norway, Aug. 6-14, 2008. Publisher:], [location varies], International CODEN: IGABBY
Note: In English
Summary: Cold-water corals occur widely on the deep sea bed, and may cover as large an area as the better-known shallow warm-water corals. They can form giant mound structures such as those found in the Belgica Mound Province in the Porcupine Seabight, 100 km west of Ireland. The Belgica province is a spectacular landscape of 66 partly buried subconical mounds in water depths of 600-900 m, reaching up to 160 m high with slopes as steep as 45°. The surface of the mounds is known through swath bathymetry, remotely operated vehicle deployments, and shallow coring, but the internal composition and history of the mounds could only be speculated on until May 2005, when IODP Expedition 307 recovered the first complete section through to the base of Challenger Mound. Expedition scientists found that cold-water corals started to grow at this location about 2.6 Ma--the same time as the establishment of Northern Hemisphere glaciation and modern NE Atlantic water stratification. Subsequent mound growth was closely linked to the oceanographic regime. In addition to drilling Challenger Mound (Site U1317), Sites U1316 and U1318 recovered sequences downslope and upslope to establish the surrounding geological context. A total of 1400 m of sediment was recovered from these 3 sites during 12 days of drilling. We were able to demonstrate that such mounds are built and structurally supported by cold-water corals, rather than by microbially precipitated carbonate fueled by hydrocarbon seeps, as had previously been proposed. The branching coral skeletons buffered fine-grained sediments and constructed the remarkable 155 m high mound and stabilized the steep slopes. Cold-water corals are suspension feeders sensitive to changes in temperature and nutrient supply, yet they were able to maintain a deep-water mound community for a 1.5 Myr period under glacial/interglacial climatic change, waxing and waning with the prevailing oceanographic regime. Strontium isotope dating of corals and molluscs provided the age history of the mound, and the oxygen isotope record of benthic foraminifera has further refined it. The role of prokaryotes in diagenesis of layers in the mound is being investigated. Drilling on Expedition 307 provided insight into the much more ancient carbonate mud mounds in the geological record, which have a size and shape similar to the modern mounds of the Porcupine Seabight, but differ in their composition and early lithification. The abundance of modern mounds suggests that the fossil mounds may have formed in deeper water than is commonly supposed. There is also diversity among modern carbonate mounds. For example, at the northern end of the Porcupine Seabight there are thousands of smaller-scale coral mounds, the young mounds offshore of Morocco are found alongside mud volcanoes and methane seeps, and the algal mounds in the Florida Strait are different again. There remains much to be discovered by deep drilling of these fascinating geo-biological structures.
Year of Publication: 2008
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Anthozoa; Atlantic Ocean; Belgica Mound Province; Biogenic structures; Bioherms; Carbonate mounds; Challenger Mound; Cnidaria; Deep-sea environment; Drilling; Europe; Expedition 307; Foraminifera; IODP Site U1316; IODP Site U1317; IODP Site U1318; Integrated Ocean Drilling Program; Invertebrata; Ireland; Isotopes; Marine environment; Marine sediments; Modern; Mounds; Mud mounds; North Atlantic; Northeast Atlantic; Offshore; Porcupine Seabight; Protista; Sedimentary structures; Sediments; Shallow-water environment; Stable isotopes; Western Europe
Coordinates: N512300 N512300 W0114300 W0114300
N512300 N512300 W0114400 W0114400
N512600 N512600 W0113300 W0113300
Record ID: 2010054817
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