Microbial activity and carbonate isotope signatures as a tool for identification of spatial differences in methane advection: a case study at the Pacific Costa Rican margin

Krause, Stefan, Steeb, Philip, Hensen, Christian, Liebetrau, Volker, Dale, Andrew W., Nuzzo, Marianne and Treude, Tina (2014) Microbial activity and carbonate isotope signatures as a tool for identification of spatial differences in methane advection: a case study at the Pacific Costa Rican margin Biogeosciences (BG), 11 . pp. 507-523. DOI 10.5194/bg-11-507-2014.

[img]
Preview
Text
bg-11-507-2014.pdf - Published Version

Download (3903Kb) | Preview
[img]
Preview
Text
bg-11-507-2014-supplement.pdf - Supplemental Material

Download (270Kb) | Preview

Supplementary data:

Abstract

Subduction of the oceanic Cocos plate offshore Costa Rica causes strong advection of methane-charged fluids. Presented here are the first direct measurements of microbial anaerobic oxidation of methane (AOM) and sulfate reduction (SR) rates in sediments from the two mounds, applying radiotracer techniques in combination with numerical modeling. In addition, analysis of carbonate δ18O, δ13C, and 87Sr / 86Sr signatures constrain the origin of the carbonate-precipitating fluid. Average rates of microbial activities showed differences with a factor of 4.8 to 6.3 between Mound 11 [AOM 140.71 (±40.84 SD); SR 117.25 (±82.06 SD) mmol m−2 d−1, respectively] and Mound 12 [AOM 22.37 (±0.85 SD); SR 23.99 (±5.79 SD) mmol m−2 d−1, respectively]. Modeling results yielded flow velocities of 50 cm a−1 at Mound 11 and 8–15 cm a−1 at Mound 12. Analysis of oxygen and carbon isotope variations of authigenic carbonates from the two locations revealed higher values for Mound 11 (δ18O: 4.7 to 5.9‰, δ13C: −21.0 to −29.6‰), compared to Mound 12 (δ18O: 4.1 to 4.5‰, δ13C: −45.7 to −48.9‰). Analysis of carbonates 87Sr / 86Sr indicated temporal changes of deep-source fluid admixture at Mound 12. The present study is in accordance with previous work supporting considerable differences of methane flux between the two Mounds. It also strengthens the hypothesis of a predominantly deep fluid source for Mound 11 versus a rather shallow source of biogenic methane for Mound 12. The results demonstrate that methane-driven microbial activity is a valid ground truthing tool for geophysical measurements of fluid advection and constraining of recent methane fluxes in the study area. The study further shows that the combination of microbial rate measurements, numerical modeling, and authigenic carbonate analysis provide a suitable approach to constrain temporal and spatial variations of methane charged fluid flow at the Pacific Costa Rican margin.

Document Type: Article
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > SFB 574
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
DOI etc.: 10.5194/bg-11-507-2014
ISSN: 1726-4170
Related URLs:
Projects: FLOWS, SFB574, Future Ocean
Contribution Number:
ProjectNumber
SFB 574270
Expeditions/Models:
Date Deposited: 13 Jan 2014 09:53
Last Modified: 24 Jul 2015 11:29
URI: http://eprints.uni-kiel.de/id/eprint/22495

Actions (login required)

View Item View Item

Document Downloads

More statistics for this item...