Post-glacial microbialite formation in coral reefs of the Pacific, Atlantic, and Indian Oceans Katrin Heindel a, b, ⁎, Daniel Birgel b , Benjamin Brunner c , Volker Thiel d , Hildegard Westphal e , Eberhard Gischler f , Simone B. Ziegenbalg b , Guy Cabioch g, 1 , Peter Sjövall h , Jörn Peckmann b a MARUM ‘Center for Marine Environmental Sciences’, University of Bremen, 28359 Bremen, Germany b Department for Geodynamics and Sedimentology, University of Vienna, 1090 Vienna, Austria c Max Planck Institute for Marine Microbiology, 28359 Bremen, Germany d Geoscience Center, Georg-August University of Göttingen, 37077 Göttingen, Germany e Leibniz Center for Tropical Marine Ecology, 28359 Bremen, Germany f Institute of Geosciences, Goethe-University, 60438 Frankfurt am Main, Germany g IRD, Centre d'Ile de France, 93143 Bondy CEDEX, France h SP Technical Research Institute of Sweden, Chemistry and Materials Technology, 501 15 Borås, Sweden abstract article info Article history: Received 2 November 2011 Received in revised form 3 February 2012 Accepted 10 February 2012 Available online 21 February 2012 Edited by U. Brand Keywords: Microbial mat Coral reef Sulfate-reducing bacteria EPS-mineralization Fertilization Volcanic hinterland The occurrence of microbialites in post-glacial coral reefs has been interpreted to reflect an ecosystem re- sponse to environmental change. The greater thickness of microbialites in reefs with a volcanic hinterland compared to thinner microbial crusts in reefs with a non-volcanic hinterland led to the suggestion that fer- tilization of the reefal environment by chemical weathering of volcanic rocks stimulated primary productivity and microbialite formation. Using a molecular and isotopic approach on reef-microbialites from Tahiti (Pacific Ocean), it was recently shown that sulfate-reducing bacteria favored the formation of microbial car- bonates. To test if similar mechanisms induced microbialite formation in other reefs as well, the Tahitian microbialites are compared with similar microbialites from coral reefs off Vanuatu (Pacific Ocean), Belize (Caribbean Sea, Atlantic Ocean), and the Maldives (Indian Ocean) in this study. The selected study sites cover a wide range of geological settings, reflecting variable input and composition of detritus. The new lipid biomarker data and stable sulfur isotope results confirm that sulfate-reducing bacteria played an intrin- sic role in the precipitation of microbial carbonate at all study sites, irrespective of the geological setting. Abundant biomarkers indicative of sulfate reducers include a variety of terminally-branched and mid chain-branched fatty acids as well as mono-O-alkyl glycerol ethers. Isotope evidence for bacterial sulfate re- duction is represented by low δ 34 S values of pyrite (-43 to -42‰) enclosed in the microbialites and, com- pared to seawater sulfate, slightly elevated δ 34 S and δ 18 O values of carbonate-associated sulfate (21.9 to 22.2‰ and 11.3 to 12.4‰, respectively). Microbialite formation took place in anoxic micro-environments, which presumably developed through the fertilization of the reef environment and the resultant accumula- tion of organic matter including bacterial extracellular polymeric substances (EPS), coral mucus, and marine snow in cavities within the coral framework. ToF-SIMS analysis reveals that the dark layers of laminated microbialites are enriched in carbohydrates, which are common constituents of EPS and coral mucus. These results support the hypothesis that bacterial degradation of EPS and coral mucus within microbial mats favored carbonate precipitation. Because reefal microbialites formed by similar processes in very differ- ent geological settings, this comparative study suggests that a volcanic hinterland is not required for micro- bialite growth. Yet, detrital input derived from the weathering of volcanic rocks appears to be a natural fertilizer, being conductive for the growth of microbial mats, which fosters the development of particularly abundant and thick microbial crusts. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Microbialites (microbial carbonates) represent the first fossil evi- dence of life on Earth, and microbial mats forming microbialites were ubiquitous for almost 85% of Earth's history (Grotzinger and Knoll, 1999). Microbialites are organosedimentary deposits, which form by the activity of benthic microbial communities (e.g., Golubic, Chemical Geology 304-305 (2012) 117–130 ⁎ Corresponding author at: Department for Geodynamics and Sedimentology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria. Tel.: + 43 1 427753443; fax: +43 1 42779534. E-mail address: katrin.heindel@univie.ac.at (K. Heindel). 1 Guy Cabioch, our esteemed colleague, passed away much too early, shortly before the submission of this manuscript. Guy was a renowned reef geoscientist who has made a lasting impact on his field of research. He will be greatly missed. 0009-2541/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.chemgeo.2012.02.009 Contents lists available at SciVerse ScienceDirect Chemical Geology journal homepage: www.elsevier.com/locate/chemgeo