Dullo, Wolf-Christian

Flögel, Sascha

IODP Expedition 307 Scientific Party

Liebetrau, Volker

Raddatz, Jacek

Rüggeberg, Andres

English

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Geophysical Research Abstracts,Vol. 11, EGU2009-2803-1, 2009EGU General Assembly 2009© Author(s) 2009Environmental control on cold-water carbonate mounds developmentA. Rüggeberg, V. Liebetrau, J. Raddatz, S. Flögel, W.-Chr. Dullo, and IODP Exp. 307 Scientific PartyLeibniz-Institute of Marine Sciences (IFM-GEOMAR), Paleoceanography, Kiel, Germany (arueggeberg@ifm-geomar.de)Cold-water coral reefs are very abundant along the European continental margin in intermediate water depths andare able to build up large mound structures. These carbonate mounds particularly occur in distinct mound provinceson the Irish and British continental margins. Previous investigations resulted in a better understanding of the cold-water coral ecology and the development of conceptual models to explain carbonate mound build-up. Two differenthypotheses were evoked to explain the origin and development of carbonate mounds, external versus internalcontrol (e.g., Freiwald et al. 2004 versus e.g. Hovland 1990). Several short sediment cores have been obtainedfrom Propeller Mound, Northern Porcupine Seabight, indicating that cold-water corals grew during interglacial andwarm interstadial periods of the Late Pleistocene controlled by environmental and climatic variability supportingthe external control hypothesis (e.g. Dorschel et al. 2005, Rüggeberg et al. 2007).The recent discovery of Dullo et al. (2008) highlights the impact and importance of the external (environmental)control hypothesis with coral growth and distribution following the structure of seawater density, i.e. the potentialdensity anomaly sigma-theta. This study evidences that all studied living coral reef sites of the NE Atlantic areoccurring in water masses with a specific density window of sigma-theta = 27.5 ± 0.15 kg/m3, whereas dead reefsare outside this density range. In order to transfer this idea to the paleo-record, we used the method of Lynch-Stieglitz (2001) and others for the determination of paleo-densities using stable oxygen isotope measurements(δ18O) on benthic foraminifera. The accuracy of the density reconstruction is well known for the Holocene, theLast Glacial Maximum, and past interglacials.With this knowledge we tested whether paleo-densities might be an important prerequisite for growth and devel-opment of cold-water coral reefs during the past interglacials and during mound initiation. δ18O records of benthicforaminifera from sediment cores of Propeller Mound indicate that paleo-density values have a similar range dur-ing interglacials and interstadials of the past 300 kyr as for the present-day settings. However, the method is onlyvalid for temperatures between 5° and 30°C. Therefore, mean glacial values of 27.8 kg/m3 are minimum estimatesconsidering possible glacial temperatures below 5°C, but are clearly offset to the living-coral-reef-density-range of27.35–27.65 kg/m3. We also tested this application on sediments from IODP Exp. 307 core 1317 C indicating thatseawater densities are in a similar range during mound initiation at around 2.6 Ma (Kano et al. 2007).References:Dorschel et al. (2005) Earth and Planetary Science Letters, 233: 33– 44.Dullo et al. (2008) Marine Ecology Progress Series, 371:165–176.Freiwald et al. (2004) UNEP-WCMC, p. 84.Hovland (1990) Terra Nova, 2: 8–18.Kano et al. (2007) Geology, 35(11):1051–1054.Lynch-Stieglitz (2001) Geochemistry Geophysics Geosystems, 2, doi: 10.1029/2001GC000208.Rüggeberg et al. (2007) International Journal of Earth Sciences, 96: 57–72

Environmental control on cold-water carbonate mounds development

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