Wild, Christian, Rixen, Tim, Sánchez-Noguera, Celeste, Merico, Agostino, Jimenez, Carlos, Cortés, Jorge and Naumann, Malik S (2015) A carbonate platform associated with shallow cold methane seeps in Golfo Dulce, Pacific Costa Rica. Galaxea, Journal of Coral Reef Studies, 17 (1). pp. 13-14. DOI https://doi.org/10.3755/galaxea.17.13.

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Abstract

Galaxea, Journal of Coral Reef Studies 17: 13-14(2015)Marine methane seeps are typically observed in cold, anoxic and organic-rich deep-sea environments, such as in the Black Sea, where methane emissions fuel the authigenic accretion of calcium carbonate structures via microbial sulphate reduction and anaerobic methane oxidation (Michaelis et al. 2002). For shallow tropical waters, methane seeps are only known from hydrothermal vents (Nakamura et al. 2006). Here, we report about our recent discovery of a cold methane seep in warm (ca. 29°C) and O2-saturated (97-100%) Golfo Dulce (8.496450°N, 83.262610°W) that is located at the Southern Pacific coast of Costa Rica, Central America.In January 2012, we observed gas emissions from a carbonate platform (ca. 100 m2 in area) formed about 2 m above muddy sediments at 10 m water depth. This carbonate platform exhibited live cover by the encrusting scleractinian coral Porites lobata (Fig. 1a, b), and frequent occurrence of typical reef-associated taxa, such as gorgonian corals and calcifying green algae (Fig. 1c, d). Collection and subsequent positive flame tests of the odourless (H2S-negative) gas samples revealed their high methane content (Fig. 1e, f). This qualitative finding was subsequently confirmed by quantitative gas-chromatographic analyses showing methane contents of >85%. The methane seep, although located in a seismically active zone, was clearly not associated with hydrothermal vents as confirmed by water temperatures of 28-31°C measured in the water streaming out from the platform. This water in contrast to the overlying O2-saturated water column, exhibited very low O2 concentrations of 5 μM to below detection limit (0.5 μM) as monitored continuously using O2 microsensors (OxMicro, Presens) that were placed within the methane emitting pores in the carbonate platform.First mass-spectrometric stable carbon (C) isotope measurements of the carbonate platform crust samples revealed δ13C signatures of -47 to -51‰ that indicate their origin from anaerobic oxidation of methane coupled with authigenic carbonate formation. These observations and preliminary analytical findings may thus provide first indication of a potential interplay of authigenic and biogenic reef accretion processes occurring at shallow cold methane seep sites.

Document Type: Article
Research affiliation: Affiliations > Not ZMT
Biogeochemistry and Geology > Carbon and Nutrient Cycling
Ecology
Theoretical Ecology and Modelling > Systems Ecology
Refereed: Yes
Open Access Journal?: No
DOI etc.: https://doi.org/10.3755/galaxea.17.13
ISSN: 1883-0838
Date Deposited: 06 Aug 2019 15:58
Last Modified: 01 Oct 2020 12:59
URI: http://cris.leibniz-zmt.de/id/eprint/2495

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