Li/Mg systematics in scleractinian corals: Calibration of the thermometer

Montagna, Paolo; McCulloch, Malcolm; Douville, Eric; Correa, Matthias López; Trotter, Julie; Rodolfo-Metalpa, Riccardo; Dissard, Delphine; Ferrier-Pagès, Christine; Frank, Norbert; Freiwald, André; Goldstein, Steve; Mazzoli, Claudio; Reynaud, Stephanie; Rüggeberg, Andres; Russo, Simone; Taviani, Marco

doi:10.1016/j.gca.2014.02.005

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Journal article

Li/Mg systematics in scleractinian corals: Calibration of the thermometer

Montagna, Paolo Istituto di Scienze Marine, Consiglio Nazionale delle Ricerche, Bologna, Italy - Laboratoire des Sciences du Climat et de l’Environnement, Gif-sur-Yvette, France
McCulloch, Malcolm The UWA Oceans Institute and School of Earth and Environment, The University of Western Australia - ARC Centre of Excellence in Coral Reef Studies, The University of Western Australia
Douville, Eric Laboratoire des Sciences du Climat et de l’Environnement, Gif-sur-Yvette, France
Correa, Matthias López GeoZentrum Nordbayern, Universität Erlangen-Nürnberg, Germany
Trotter, Julie The UWA Oceans Institute and School of Earth and Environment, The University of Western Australia
Rodolfo-Metalpa, Riccardo CoRéUs, Institut de Recherche pour le Développement, Centre IRD de Noumea, New Caledonia
Dissard, Delphine The UWA Oceans Institute and School of Earth and Environment, The University of Western Australia - ARC Centre of Excellence in Coral Reef Studies, The University of Western Australia
Ferrier-Pagès, Christine Centre Scientifique de Monaco, Principality of Monaco
Frank, Norbert Institut für Umweltphysik, Universität Heidelberg, Germany
Freiwald, André Senckenberg am Meer, Abteilung für Meeresforschung, Südstrand 40, D-26384 Wilhelmshaven, Germany
Goldstein, Steve Lamont-Doherty Earth Observatory, Columbia University, USA
Mazzoli, Claudio Dipartimento di Geoscienze, Università degli Studi di Padova, Italy
Reynaud, Stephanie Centre Scientifique de Monaco, Principality of Monaco
Rüggeberg, Andres Dept. of Earth Sciences, University of Fribourg, Switzerland
Russo, Simone Institute for Environment and Sustainability, Joint Research Centre, Ispra, Italy
Taviani, Marco Istituto di Scienze Marine, Consiglio Nazionale delle Ricerche, Bologna, Italy

01.05.2014

Published in:

Geochimica et Cosmochimica Acta. - 2014, vol. 132, p. 288–310

English We show that the Li/Mg systematics of a large suite of aragonitic coral skeletons, representing a wide range of species inhabiting disparate environments, provides a robust proxy for ambient seawater temperature. The corals encompass both zooxanthellate and azooxanthellate species (Acropora sp., Porites sp., Cladocora caespitosa, Lophelia pertusa, Madrepora oculata and Flabellum impensum) collected from shallow, intermediate, and deep-water habitats, as well as specimens cultured in tanks under temperature-controlled conditions. The Li/Mg ratios observed in corals from these diverse tropical, temperate, and deep-water environments are shown to be highly correlated with temperature, giving an exponential temperature relationship of: Li/Mg (mmol/mol) = 5.41 exp (−0.049 * T) (r² = 0.975, n = 49). Based on the standard error of the Li/Mg versus temperature correlation, we obtain a typical precision of ±0.9 °C for the wide range of species analysed, similar or better than that of other less robust coral temperature proxies such as Sr/Ca ratios.The robustness and species independent character of the Li/Mg temperature proxy is shown to be the result of the normalization of Li to Mg, effectively eliminating the precipitation efficiency component such that temperature remains as the main controller of coral Li/Mg compositions. This is inferred from analysis of corresponding Li/Ca and Mg/Ca ratios with both ratios showing strong microstructure-related co-variations between the fibrous aragonite and centres of calcification, a characteristic that we attribute to varying physiological controls on growth rate. Furthermore, Li/Ca ratios show an offset between more rapidly growing zooxanthellate and azooxanthellate corals, and hence only an approximately inverse relationship to seawater temperature. Mg/Ca ratios show very strong physiological controls on growth rate but no significant dependence with temperature, except possibly for Acropora sp. and Porites sp. A strong positive correlation is nevertheless found between Li/Ca and Mg/Ca ratios at similar temperatures, indicating that both Li and Mg are subject to control by similar growth mechanisms, specifically the mass fraction of aragonite precipitated during calcification, which is shown to be consistent with a Rayleigh-based elemental fractionation model.The highly coherent array defined by Li/Mg versus temperature is thus largely independent of coral calcification mechanisms, with the strong temperature dependence reflecting the greater sensitivity of the K_d^Li/Ca partition coefficient relative to K_d^Mg/Ca. Accordingly, Li/Mg ratios exhibit a highly coherent exponential correlation with temperature, thereby providing a more robust tool for reconstructing paleo-seawater temperatures.

Faculty

Faculté des sciences et de médecine

Department

Département de Géosciences

Language