Chapter

Cold-Water Corals and Ecosystems

Part of the series Erlangen Earth Conference Series pp 1005-1020

C and O isotopes in a deep-sea coral ( Lophelia pertusa) related to skeletal microstructure

  • Dominique BlamartAffiliated withLaboratoire des Sciences du Climat et de l’Environnement (LSCE) Unité mixte de Recherche CEA-CNRS
  • , Claire Rollion-BardAffiliated withCRPG-CNRS
  • , Jean-Pierre CuifAffiliated withUniversité de Paris XI, Faculté des Sciences
  • , Anne Juillet-LeclercAffiliated 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
  • , Tjeerd C. E. van WeeringAffiliated withKoninklijk Nederlands Instituut voor Onderzoek der Zee (NIOZ)
  • , Jean-Pierre HenrietAffiliated withRenard Centre of Marine Geology, Gent University

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Abstract

Lophelia pertusa is a deep-sea scleractinian coral (azooxanthellate) found on the continental margins of the major world oceans. Built of aragonite it can be precisely dated and measured for stable isotope composition (C–O) to reconstruct past oceanic conditions. However, the relation between stable isotope and skeleton microstructures, i.e. centres of calcification and surrounding fibres, is crucial for understanding the isotopic patterns. Values for δ18O and δ13C in Lophelia pertusa were determined at a micrometer scale using an ion microprobe (SIMS - Secondary Ion Mass Spectrometry). In this coral species, centres of calcification are large (50 µm) and arranged in lines. The centres of calcification have a restricted range of variation in δ18O (−2.8 ± 0.3 ‰ (V-PDB)), and a larger range in δ13C (14.3 to 10.9 ‰ (V-PDB)). Surrounding skeletal fibres exhibit large isotopic variation both for C and O (up to 12 ‰) and δ13C and δ18O are positively correlated. The C and O isotopic composition of the centres of calcification deviate from this linear trend at the lightest δ18O values of the surrounding fibres. The fine-scaled variation of δ18O is probably the result of two processes: (1) isotopic equilibrium calcification with at least 1 pH unit variation in the calcification fluid and (2) kinetic fractionation. The apparent δ13C disequilibrium in Lophelia pertusa may be the result of mixing between depleted δ13C metabolic CO2 (respiration) and DIC coming directly from seawater. This study underlines the close relationship between microstructure and stable isotopes in corals. This relationship must also be taken into consideration for major elements like Mg and trace elements (U-Sr-Ba) increasing the reliability of the geochemical tools used in paleoceanography.

Keywords

Deep-sea corals SIMS stable isotopes isotopic disequilibrium Lophelia pertusa