Sulfur and oxygen isotope insights into sulfur cycling in shallow-sea hydrothermal vents, Milos, Greece

Geochemical Transactions

Research Article

Gregory K Druschel¹  Fotios-Christos A Kafantaris¹  William P Gilhooly²  Jan P Amend³  Roy E Price⁴  David A Fike⁵ 

[1] Department of Earth Sciences, Indiana University-Purdue University Indianapolis, Indianapolis, IN, USA;Department of Earth Sciences, Indiana University-Purdue University Indianapolis, Indianapolis, IN, USA;Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, USA;Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA;Department of Biological Sciences, University of Southern California, Los Angeles, USA;Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA;SUNY Stony Brook, School of Marine and Atmospheric Sciences, Stony Brook, NY, USA;Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, USA;

关键词: Palaeochori Bay;    Milos Island;    Shallow-sea hydrothermal vents;    Phase separation;    Sulfur isotopes;    Sulfate oxygen isotopes;    Anhydrite;    Sulfide oxidation;   

DOI  :  10.1186/s12932-014-0012-y

 received in 2014-01-27, accepted in 2014-07-22,  发布年份 2014

来源: Springer

【 摘 要 】

Shallow-sea (5 m depth) hydrothermal venting off Milos Island provides an ideal opportunity to target transitions between igneous abiogenic sulfide inputs and biogenic sulfide production during microbial sulfate reduction. Seafloor vent features include large (>1 m2) white patches containing hydrothermal minerals (elemental sulfur and orange/yellow patches of arsenic-sulfides) and cells of sulfur oxidizing and reducing microorganisms. Sulfide-sensitive film deployed in the vent and non-vent sediments captured strong geochemical spatial patterns that varied from advective to diffusive sulfide transport from the subsurface. Despite clear visual evidence for the close association of vent organisms and hydrothermalism, the sulfur and oxygen isotope composition of pore fluids did not permit delineation of a biotic signal separate from an abiotic signal. Hydrogen sulfide (H2S) in the free gas had uniform δ34S values (2.5 ± 0.28‰, n = 4) that were nearly identical to pore water H2S (2.7 ± 0.36‰, n = 21). In pore water sulfate, there were no paired increases in δ34SSO4 and δ18OSO4 as expected of microbial sulfate reduction. Instead, pore water δ34SSO4 values decreased (from approximately 21‰ to 17‰) as temperature increased (up to 97.4°C) across each hydrothermal feature. We interpret the inverse relationship between temperature and δ34SSO4 as a mixing process between oxic seawater and 34S-depleted hydrothermal inputs that are oxidized during seawater entrainment. An isotope mass balance model suggests secondary sulfate from sulfide oxidation provides at least 15% of the bulk sulfate pool. Coincident with this trend in δ34SSO4, the oxygen isotope composition of sulfate tended to be 18O-enriched in low pH (<5), high temperature (>75°C) pore waters. The shift toward high δ18OSO4 is consistent with equilibrium isotope exchange under acidic and high temperature conditions. The source of H2S contained in hydrothermal fluids could not be determined with the present dataset; however, the end-member δ34S value of H2S discharged to the seafloor is consistent with equilibrium isotope exchange with subsurface anhydrite veins at a temperature of ~300°C. Any biological sulfur cycling within these hydrothermal systems is masked by abiotic chemical reactions driven by mixing between low-sulfate, H2S-rich hydrothermal fluids and oxic, sulfate-rich seawater.

【 授权许可】

CC BY   
© Gilhooly et al.; licensee Chem Central 2014. This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.