URLhttps://www.bco-dmo.org/dataset/663937
Download URLhttps://www.bco-dmo.org/dataset/663937/data/download
Media Typetext/tab-separated-values
CreatedNovember 4, 2016
ModifiedNovember 2, 2017
StateFinal no updates expected
Brief DescriptionDescription and isotopic composition of the carbonate deposits in the Santa Elena Ophiolite (Costa Rica)

Acquisition Description

Santa Elena samples:
Sample preparation and mineralogy: Ultramafic basement rocks were sampled throughout the Santa Elena Ophiolite. Carbonate deposits associated with Mg-HCO3 and Ca-OH springs in the eastern part of the ophiolite were sampled at various locations within riverbeds. All analytical measurements and sample preparation of the Santa Elena peridotites and carbonates were performed at the Department of Geosciences at Virginia Tech. The carbonate samples were prepared by drilling out individual depositional layers of carbonates to reveal heterogeneities within different layers or crushed with an agate mortar for bulk rock analysis. Carbonate precipitates from the rivers were first dried at 40 degrees C in the oven. Before sample analyses all samples were homogenized by hand with the agate mortar. The mineralogy of the carbonates was then determined by X-ray diffraction on a Rigaku MiniFlex XRD using the powder diffraction analysis package PDXL.

Bulk rock powders were prepared for all the ultramafic rocks. To remove contamination from weathering, the outermost 1-2 cm of the rock samples were cut away. The samples were then cleaned in an ultrasonic bath prior to powdering them with a shatter box using an alumina dish. These bulk rock powders were subsequently analyzed for their carbon and sulfur geochemistry.

Carbon geochemistry: 
Carbon in these systems is typically detected as inorganic (e.g. carbonate carbon) or organic carbon. Organic carbon has also been referred to as reduced carbon or non-carbonate carbon. Here we refer to it as total organic carbon (TOC) even though the presence of traces of graphite and other reduced carbon species cannot entirely be excluded. Total carbon (TC) and total inorganic carbon (TIC) contents, d13C of TC, d13C of TOC and d13C and d18O of TIC were analyzed on the basement rocks, while only d13C and d18O of TIC were determined for the carbonate deposits and precipitates.

TC contents, d13CTC and d13CTOC were determined on a Vario ISOTOPE elemental analyzer (EA) coupled to an Isoprime 100 isotope ratio mass spectrometer (IRMS). For analyses of d13CTOC, bulk rock samples were reacted for three days with 3N HCl to remove all acid soluble carbon. They were then rinsed with H2O, dried at 40 degrees C in the oven and homogenized in the agate mortar. TC and TOC isotope values are reported in the standard delta notation relative to the Vienna-Pee Dee Belemnite (V-PDB) standard and calibrated to this scale using international [IAEA-CH-6 (sucrose; d13C = -10.449‰) and IAEA-CH-7 (polyethylene; d13C = -32.151‰)] and commercial standards [Elemental Microanalysis wheat flour; d13C = -27.21‰]. TOC was calculated from the difference between TC and TIC and errors are within 10% of the TOC contents. %TIC was calculated as TIC/TC*100. Reproducibility of d13CTC and d13CTOC is better than 0.1‰.

The d13CTIC and d18OTIC and TIC contents were analyzed on a MultiFlowGeo headspace sampler attached to an Isoprime 100 IRMS. Samples were prepared in septum vials, flushed with helium and acidified with phosphoric acid. Samples were then reacted for at least 3 hours at room temperature if no magnesite was present (as determined by XRD analysis). Magnesite-bearing samples were reacted for 72 hours at 90 degrees C. Carbon and oxygen isotope values are reported in the standard delta-notation relative to the Vienna-Pee Dee Belemnite (V-PDB) standard and calibrated to this scale using the international standards IAEA-CO-1 (marble; d13C = +2.492‰, d18O = -2.4‰), IAEA-CO-9 (BaCO3; d13C = -47.321‰, d18O = -15.6‰) and NBS18 (calcite, d13C = -5.014‰, d18O = -23.2‰). Reproducibility for the analysis of the samples was better than +/- 0.07‰ for d13C and better than +/- 0.3‰ for d18O. Reproducibility of TIC contents is typically better than 5%.

Processing Description

Detection limits:
Carbon contents: approximately100 ppm

BCO-DMO Processing:
- modified parameter names to conform with BCO-DMO naming conventions;
- repalced blanks (missing data) with "nd".

Instruments

Rigaku MiniFlex XRD [X-ray diffractometer]
Details
Instance Description (Rigaku MiniFlex XRD)

The mineralogy of the carbonates was then determined by X-ray diffraction on a Rigaku MiniFlex XRD using the powder diffraction analysis package PDXL.

Instruments that identify crystalline solids by measuring the characteristic spaces between layers of atoms or molecules in a crystal.

Vario ISOTOPE elemental analyzer [Elemental Analyzer]
Details
Instance Description (Vario ISOTOPE elemental analyzer)

TC contents, d13CTC and d13CTOC were determined on a Vario ISOTOPE elemental analyzer (EA) coupled to an Isoprime 100 isotope ratio mass spectrometer (IRMS). 

Instruments that quantify carbon, nitrogen and sometimes other elements by combusting the sample at very high temperature and assaying the resulting gaseous oxides. Usually used for samples including organic material.

Details
Instance Description (Isoprime 100)

TC contents, d13CTC and d13CTOC were determined on a Vario ISOTOPE elemental analyzer (EA) coupled to an Isoprime 100 isotope ratio mass spectrometer (IRMS). 

The d13CTIC and d18OTIC and TIC contents were analyzed on a MultiFlowGeo headspace sampler attached to an Isoprime 100 IRMS.

The Isotope-ratio Mass Spectrometer is a particular type of mass spectrometer used to measure the relative abundance of isotopes in a given sample (e.g. VG Prism II Isotope Ratio Mass-Spectrometer).

Parameters

sample_name [sample]
Details
sample_name
Sample name

unique sample identification or number; any combination of alpha numeric characters; precise definition is file dependent

lat [latitude]
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lat
Latitude; positive values = North

latitude, in decimal degrees, North is positive, negative denotes South; Reported in some datasets as degrees, minutes

lon [longitude]
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lon
Longitude; positive values = East

longitude, in decimal degrees, East is positive, negative denotes West; Reported in some datsets as degrees, minutes

description [sample_descrip]
Details
description
Sample description
text description of sample collected
sample_powder [sample_descrip]
Details
sample_powder
Sample powder
text description of sample collected
cc [unknown]
Details
cc
Mineral model percentages estimated from XRD spectra: XX: greater than or equal to 50%, X: 20-50%, O: 5-20%, T: < 5%
association with a community-wide standard parameter is not yet defined
mgs [unknown]
Details
mgs
Mineral model percentages estimated from XRD spectra: XX: greater than or equal to 50%, X: 20-50%, O: 5-20%, T: < 5%
association with a community-wide standard parameter is not yet defined
arg [unknown]
Details
arg

Mineral model percentages estimated from XRD spectra: XX: greater than or equal to 50%, X: 20-50%, O: 5-20%, T: < 5%

association with a community-wide standard parameter is not yet defined
qz [unknown]
Details
qz
Mineral model percentages estimated from XRD spectra: XX: greater than or equal to 50%, X: 20-50%, O: 5-20%, T: < 5%
association with a community-wide standard parameter is not yet defined
srp [unknown]
Details
srp

Mineral model percentages estimated from XRD spectra: XX: greater than or equal to 50%, X: 20-50%, O: 5-20%, T: < 5%

association with a community-wide standard parameter is not yet defined
del13C [unknown]
Details
del13C
Delta 13C
association with a community-wide standard parameter is not yet defined
del18O [unknown]
Details
del18O
Delta 18O
association with a community-wide standard parameter is not yet defined
Details
temp
Equilibration tempertures between fluid and magnesite; calculated after Aharon, 1988
water temperature at measurement depth

Dataset Maintainers

NameAffiliationContact
Esther M. SchwarzenbachFreie Universität Berlin
Shannon RauchWoods Hole Oceanographic Institution (WHOI BCO-DMO)

BCO-DMO Project Info

Project TitleIdentifying the controls on biological activity in serpentinites
AcronymControls on biological activity
URLhttps://www.bco-dmo.org/project/654267
CreatedAugust 18, 2016
ModifiedOctober 31, 2016
Project Description

Project description from C-DEBI:
Serpentinization – the hydrothermal alteration of ultramafic rocks – is a unique mineralogical process that results in H2 and CH4 – rich fluids that can support microbial communities. Using a combination of petrographic observations, bulk rock and in-situ sulfur isotope signatures of variably serpentinized peridotites from four different geotectonic environments we provide new constraints on the factors that support microbial activity. The studied samples overall suggest that redox conditions reflected by the presence of pyrite and pyrrhotite represent the fluid chemistry that favors microbial activity. This fluid chemistry, i.e., the prevailing hydrogen and sulfur fugacities of the fluid, are thereby correlated to high water-rock ratios and increased incorporation of seawater-derived species such as sulfate and carbonate. These species serve as major energy sources of microbial activity. In contrast, highly reducing conditions and limited fluid input limits or even prevents microbial activity within serpentinites due to insufficient availability of these species. Interaction with carbonate and sulfate-bearing meteoric waters is likely an essential process that supports microbial activity in continental serpentinization environments. Overall, this study shows that apart from fluid temperatures being within the limits of life, the fluid chemistry (redox conditions and availability of e.g. carbonate and sulfate) are the primary factors that control the presence or absence of microbial communities within serpentinizing peridotites. This study highlights the importance of combining bulk rock and in-situ stable isotope data with petrographic and mineralogical observations in order to better constraint the presence of microbial communities within the subsurface of peridotite-hosted hydrothermal systems.

Note: This project was funded by a C-DEBI Research Grant.

Project Maintainers
NameAffiliationRoleContact
Esther M. SchwarzenbachFreie Universität BerlinLead Principal Investigator
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