Post-glacial microbialite formation in coral reefs of the Pacific, Atlantic, and Indian Oceans

Author(s)

Katrin Heindel, Daniel Birgel-Rennebeck, Benjamin Brunner, Volker Thiel, Hildegard Westphal, Eberhard F. Gischler, Simone Ziegenbalg, Guy Cabioch, Peter Sjövall, Jörn Ludwig Peckmann

Abstract

The occurrence of microbialites in post-glacial coral reefs has been interpreted to reflect an ecosystem response

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 fertilization

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 carbonates.

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 intrinsic

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 reduction

is represented by low d34S values of pyrite (-43 to -42‰) enclosed in the microbialites and, compared

to seawater sulfate, slightly elevated d34S and d18O 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 accumulation

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 different

geological settings, this comparative study suggests that a volcanic hinterland is not required for microbialite

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.

Organisation(s)

Department of Geology

External organisation(s)

Max-Planck-Institut für marine Mikrobiologie, Georg-August-Universität Göttingen, Leibniz Centre for Tropical Marine Research, Johann Wolfgang Goethe-Universität Frankfurt am Main, Institut de recherche pour le développement, SP Technical Research Institute of Sweden

Journal

Chemical Geology

Pages

117-130

No. of pages

14

ISSN

0009-2541

Publication date

2012

Peer reviewed

Yes

Austrian Fields of Science 2012

104015 Organic chemistry, 105105 Geochemistry, 106022 Microbiology, 105101 General geology

Sustainable Development Goals

SDG 2 - Zero Hunger, SDG 14 - Life Below Water

Portal url

https://ucrisportal.univie.ac.at/en/publications/8efd09e6-a71d-4759-8271-adfb5c2bdf34