HR: 11:08h
AN: B22A-05 INVITED    [Abstracts]
TI: Origin, growth history and glacial-interglacial responses of a cold-water coral mound in NE Atlantic: Results from O-isotope and Sr-isotope stratigraphy in IODP Expedition 307
AU: * Sakai, S
AF: Institute for Frontier Research on Earth Evolution, JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061, Japan
AU: Kano, A
AF: Department of Earth and Planetary Systems Science, HIroshima Univ., 1-3-1 Kagamiyama, Higashihirosima, 739-8526, Japan
AU: Abe, K
AF: Graduate School of Life and Environmental Sciences, Univ. Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8572, Japan
AU: Browning, E
AF: Department of Geosciences, Univ. Massachusetts, 611 North Pleasant Street, Amherst, MA 01003-9297, United States
AU: Scientific Party, I
AB: Cold-water corals may cover as a large area as the better-known warm-water corals forming shallow reefs, and they occur in a variety of forms and settings, from small isolated colonies or patch reefs to giant mound structures such as those found west of Ireland. In May 2005, IODP Expedition 307 sailed to Challenger Mound, which is one of thousands of cold-water coral mounds in Porcupine Seabight, 150 km offshore of southwestern Ireland, and recovered the first complete section through to the base of a modern cold-water coral mound which is composed of up to 155 m of unlithified coral-bearing (Lophelia pertusa) sediments. The coral-bearing sediments lie on an angular unconformable surface above the lower-middle Miocene glauconitic siltstones and sandstones. Mound growth could have been continuous, and the repeated 10-m-scale alternations in lithology between lighter- colored calcareous layers (interglacials) and darker-colored clayey layers (glacials) could be essentially related to the glacial-interglacial cycles, which supported by correspondence of the two curves of O-isotopes of planktic foraminifers and natural Gamma radiation. O-isotope results of planktic foraminifers show cold-water coral L. pertusa, which are organisms sensitive to environmental change, were able to maintain a cold-water coral mound community (e.g. temperature remained above 4°C) under the latest Pliocene-Pleistocene glacial- interglacial changes. Sr-isotopic stratigraphy revealed that the section is divided into two growth stages at 23.6 mbsf, and mound of the first stage started growing on the mid-Miocene basement around 2.6 Ma, when Northern Hemisphere glaciation was intensified. The mound growth reached a maximum rate (24 cm/ky) around 2.0Ma, and ceased at 1.7Ma. The second stage (1.0-0.5 Ma) shows a lower growth rate (5 cm/ky). Corals require zooplanktons that tend to condense in density gradient of ~800 m deep developed between Eastern North Atlantic Water (ENAW) and the underlying Mediterranean Outflow Water (MOW). This oceanographic setting favorable for the coral growth has likely established with the intensified glaciation. The mound sediments contain 58 % of calcium carbonate. Even by evaluating with its optimum carbonate production rate (184 ton/year), contribution of the cold-water coral mounds in all oceans could be insignificant as a carbon sink.
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 3344 Paleoclimatology (0473, 4900)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting