Chapter

Cold-Water Corals and Ecosystems

Part of the series Erlangen Earth Conference Series pp 113-133

Deep-water corals of the northeastern Atlantic margin: carbonate mound evolution and upper intermediate water ventilation during the Holocene

  • Norbert FrankAffiliated withLaboratoire des Sciences du Climat et de l’Environnement (LSCE) Unité mixte de Recherche CEA-CNRS
  • , Audrey LutringerAffiliated withLaboratoire des Sciences du Climat et de l’Environnement (LSCE) Unité mixte de Recherche CEA-CNRS
  • , Martine PaterneAffiliated withLaboratoire des Sciences du Climat et de l’Environnement (LSCE) Unité mixte de Recherche CEA-CNRS
  • , Dominique BlamartAffiliated withLaboratoire des Sciences du Climat et de l’Environnement (LSCE) Unité mixte de Recherche CEA-CNRS
  • , Jean-Pierre HenrietAffiliated withRenard Centre of Marine Geology, Gent University
  • , David van RooijAffiliated withRenard Centre of Marine Geology, Gent University
  • , Tjeerd C. E. van WeeringAffiliated withKoninklijk Nederlands Instituut voor Onderzoek der Zee (NIOZ)

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Abstract

We present combined 230Th/U and 14C dating on deep-water corals from the northeastern North Atlantic in order to investigate coral growth and sedimentation on carbonate mounds, as well as past changes of intermediate water ventilation. Within European projects GEOMOUND and ECOMOUND reef forming Lophelia pertusa deep-water corals were raised from intermediate depth (∼610 to 888 m bsl) from top of carbonate mounds at southeast Rockall Bank and at Porcupine Seabight. XRD analyses, δ234U, and 230Th/232Th indicate negligible alteration of the investigated corals, i.e. open system U-series behavior. 230Th/U ages from coral specimens of the uppermost coral sequence of the investigated mounds range from today to 10,950 CAL yr BP, i.e. coral growth during the Holocene. A modern Lophelia gave a 230Th/U age of 1983±6 AD, close to the date of collection in 2001 AD. Deep-water coral growth is the driving process of sediment accumulation on the summit of carbonate mounds, with sediment accumulation rates in the order of ∼0.3 mm yr−1. However, coral growth is discontinuous and irregular, and complete coral sequences are frequently altered (dissolved) likely due to organic matter consumption by oxidizing pore fluids. Mound top sediments indicate the presence of corals over several glacial/interglacial cycles, but corals of glacial origin could not be identified on the investigated mounds.

Upper intermediate water Δ14C and reservoir ages (R) were reconstructed on 11 deep-water corals. Δ14C of −13±7 ‰ obtained on the coral dated to 1983 AD shows a significant lower value than the ones previously reported for the late 90’s (+27 ‰), but in agreement with seawater measurements performed in the early 80’s. Between 10,950 CAL yr BP and 420 CAL yr BP, R exhibit variations between as low as 240±110 yrs (at 5,440 CAL yr BP) to up to 750±230 yrs (at 10,450 CAL yr BP). However, most of the data (8 out of 10 corals) yield R between 400 and 600 yrs similar to previously reported pre-anthropogenic R values. Thus, the overall hydrographical pattern and surface to intermediate water CO2 exchange in the eastern North Atlantic was similar to the present day one.

Keywords

Deep-water corals carbonate mounds Northeast Atlantic Rockall-Bank Porcupine Seabight 230Th/U dating 14C Dating ocean ventilation