Dataset: AT15-40 Porewater Geochemistry

Name: Porewater geochemistry data for sediment samples that were included in the global seep survey conducted via Alvin dives from R/V Atlantis cruise AT15-40 in the Guaymas Basin in 2008
Published: 2015-11-12
Keywords: oceans

Cite This Dataset

DOI:10.26008/1912/bco-dmo.3675.1

Spatial Extent: N:27.0077 E:-111.408 S:27.0065 W:-111.4093

Temporal Extent: 2008-12-06 - 2008-12-15

Project:

Collaborative Research: Microbial Carbon cycling and its interactions with Sulfur and Nitrogen transformations in Guaymas Basin hydrothermal sediments (Guaymas Basin Interactions)

Microbial carbon and sulfur cycling in the hydrothermally altered sediments of Guaymas Basin (Guaymas Basin Vents)

Principal Investigator:

Andreas Teske (University of North Carolina at Chapel Hill, UNC-Chapel Hill)

Co-Principal Investigator:

Daniel B. Albert (University of North Carolina at Chapel Hill, UNC-Chapel Hill)

Barbara J. MacGregor (University of North Carolina at Chapel Hill, UNC-Chapel Hill)

Christopher S. Martens (University of North Carolina at Chapel Hill, UNC-Chapel Hill)

BCO-DMO Data Manager:

Shannon Rauch (Woods Hole Oceanographic Institution, WHOI BCO-DMO)

Version:

Version Date:

2015-11-12

Restricted:

Validated:

Yes

Current State:

Final no updates expected

Porewater geochemistry data for sediment samples that were included in the global seep survey conducted via Alvin dives from R/V Atlantis cruise AT15-40 in the Guaymas Basin in 2008

Abstract:

Porewater geochemistry of Guaymas Basin hydrothermal sediments (Southern Spreading segment, 27°00.44N and 111°24.55W, 2000 m water depth) including methane, CO2, and sulfate. During two R/V Atlantis cruises to Guaymas Basin, the association of Beggiatoa mats with hydrothermal seepage and the habitat preferences of various Beggiatoa types were investigated by geochemical and microbiological characterization of sediments underneath Beggiatoa mats in combination with temperature measurements down to 40 cm sediment depth. In particular, temperature profiles and corresponding sulfide, sulfate, dissolved inorganic carbon (DIC), delta 13C-DIC, methane, and delta 13C-methane gradients from mats exhibiting orange-to-white color transitions were examined to elucidate hydrothermal fluid delivery and/or tolerance associated with differently colored Beggiatoa types.

Expand/Collapse All

Archival Copy

Version Date	Archive	Persistent Identifier	Date Assigned
2015-11-12	Marine Biological Laboratory/Woods Hole Oceanographic Institution Library (MBLWHOI DLA)	10.26008/1912/bco-dmo.3675.1	2020-08-21

Description

Porewater geochemistry of Guaymas Basin hydrothermal sediments (Southern Spreading segment, 27°00.44N and 111°24.55W, 2000 m water depth) including methane, CO2, and sulfate.

During two R/V Atlantis cruises to Guaymas Basin, the association of Beggiatoa mats with hydrothermal seepage and the habitat preferences of various Beggiatoa types were investigated by geochemical and microbiological characterization of sediments underneath Beggiatoa mats in combination with temperature measurements down to 40 cm sediment depth. In particular, temperature profiles and corresponding sulfide, sulfate, dissolved inorganic carbon (DIC), delta 13C-DIC, methane, and delta 13C-methane gradients from mats exhibiting orange-to-white color transitions were examined to elucidate hydrothermal fluid delivery and/or tolerance associated with differently colored Beggiatoa types (McKay et al. 2012)

Methods & Sampling

Temperature profiling: Temperature profiles at the sampling site were recorded using Alvin’s external heatflow temperature probe, a 0.6 m titanium tube containing a linear heater and five thermistors (type 44032, Omega Engineering, Inc.) at 10 cm intervals along the length of the tube (McKay et al., 2012). When fully immersed in the sediment, this probe records five in-situ temperatures at the sediment/water interface, and at 10, 20, 30 and 40 cm sediment depth.

Geochemical Analyses: Sulfate concentration measurements were completed shipboard; after centrifuging sediment-filled 15 ml tubes, the overlying porewater was filtered through 0.45 um filters, acidified with 50 ul of 50% HCl and bubbled with nitrogen for 4 minutes to remove sulfide. Sulfate concentrations were then measured shipboard using a 2010i Dionex Ion Chromatograph (Sunnyvale, CA, USA) through Ag exchange columns (Dionex) so as to remove Cl (Martens et al., 1999). For sulfide, 1 ml porewater samples were combined with 0.1M zinc acetate and concentrations were analyzed spectrophotometrically on the ship (Cline 1969).

Headspace methane concentrations were determined onboard by standard gas chromatography with a flame ionization detector (FID), specifically using a HACH Carle Series 100 AGC Gas Chromatograph with a Alltech Molecular Sieve 5A packed column (80/100 mesh, 3.05 m length, 3.2 mm ID) and a 80 degree C isothermal temperature profile. Stable isotopic compositions of the same methane samples (core 4484-3) were measured post-cruise at UNC via gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) on a Finnigan MAT 252 Isotope Ratio Mass Spectrometer, using a HP 5890 Series II Gas Chromatograph with a HP Plot Q column (30 m length, 0.32 mm ID, 20 um film thickness) and a 30 degree C isothermal temperature profile. To measure DIC, 2 ml of unamended porewater from each sediment horizon were injected into evacuated serum vials (30 ml) and stored upside down at -20 degrees C. At UNC, the samples were thawed, and DIC was reacted to gaseous CO2 by adding 1 ml of a 30% phosphoric acid solution to each serum vial and shaking vigorously before GC analysis (Kelley et al., 1990). Stable isotopic values and concentrations of DIC were analyzed via coupled GC (Hewlett Packard 5890) and Isotope Ratio Mass Spectrometer (Finnigan MAT 252).

Data Processing Description

BCO-DMO Dataset Edits:
- Added dive_id, dive_target, month, day, year, lat and lon (shipfix and subfix), depth, and cruise_id columns;
- Parameter names were modified to conform to BCO-DMO conventions;
- Missing data was replaced with 'nd', indicating 'no data';
- 'DIC' and 'd13C_DIC' were notated as 'CO2' and 'delta 13C of CO2' in original data submission. Per correspondence with the PI, 'DIC' should replace 'CO2' in these parameter names. The samples were acidified so that all DIC (CO2 + HCO3- + CO3=) turns into CO2.

Data Files

File
porewater_geochemistry.csv (Comma Separated Values (.csv), 11.29 KB) MD5:9da455e9402ffc43c9850a5bf7b5c24f Primary data file for dataset ID 3675

More Information about this dataset

Funding Sources

Funding Source	Award Number
NSF Division of Ocean Sciences	OCE-0647633
NSF Division of Ocean Sciences	OCE-1357238

Deployments

Deployment	Synonyms	Start Date	Platform	Investigator
AT15-40		2008-12-05	R/V Atlantis	Andreas Teske (Chief Scientist)	data info
AT15-40_Alvin_Dives		2008-12-06	Alvin	Andreas Teske (Chief Scientist)	data info

Instruments

Alvin tube core

Supplied Description:

Instrument Type

Generic Name: Alvin tube core

Acronym: Tube Core

Generic Description:

A plastic tube, about 40 cm (16 inches) long, is pushed into the sediment by Alvin's manipulator arm to collect a sediment core.

Gas Chromatograph

Supplied Description:

The stable isotopic composition of methane and DIC was determined by GC/C/IRMS using a Hewlett Packard 5890 GC coupled to a Finnegan Mat 252 Isotope Ratio Mass Spectrometer (Hewlett Packard, Wilmington, DE, USA).

Instrument Type

Generic Name: Gas Chromatograph

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/LAB02/

Generic Description:

Instrument separating gases, volatile substances, or substances dissolved in a volatile solvent by transporting an inert gas through a column packed with a sorbent to a detector for assay. (from SeaDataNet, BODC)

Ion Chromatograph

Supplied Description:

Sulfate analyses were measured shipboard using a 2010i Dionex Ion Chromatograph (Sunnyvale, CA, USA) using Ag+ cation exchange columns (Dionex) to remove added Cl– ions as previously described (Martens et al., 1999).

Instrument Type

Generic Name: Ion Chromatograph

Generic Description:

Ion chromatography is a form of liquid chromatography that measures concentrations of ionic species by separating them based on their interaction with a resin. Ionic species separate differently depending on species type and size. Ion chromatographs are able to measure concentrations of major anions, such as fluoride, chloride, nitrate, nitrite, and sulfate, as well as major cations such as lithium, sodium, ammonium, potassium, calcium, and magnesium in the parts-per-billion (ppb) range. (from http://serc.carleton.edu/microbelife/research_methods/biogeochemical/ic.html)

Isotope-ratio Mass Spectrometer

Supplied Description:

Instrument Type

Generic Name: Isotope-ratio Mass Spectrometer

Acronym: IR Mass Spec; IRMS

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/LAB16/

Generic Description:

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

Date and time formats are described in python strftime() syntax.

Supplied Name	Supplied description	Supplied Units	Standard Name
dive_core_no	Dive-core number (first 4 digits represent dive, last 2 digits represent core).	dimensionless	core_id
dive_no	ID number of the Alvin dive.	dimensionless	dive_id
core_no	ID number of the core.	dimensionless	core_id
depth_target	Target depth.	meters	depth
shipfix_lat	Ship's latitude at start of dive, in decimal degrees (North = Positive).	decimal degrees	lat
shipfix_lon	Ship's longitude at start of dive, in decimal degrees (West = Negative).	decimal degrees	lon
subfix_lat	Latitude when submersible Alvin began its ascent, in decimal degrees (North = Positive).	decimal degrees	lat
subfix_lon	Longitude when submersible Alvin began its ascent, in decimal degrees (West = Negative).	decimal degrees	lon
month	Month that sampling occurred (01 to 12).	dimensionless	month
day	Day of month (01 to 31).	dimensionless	day
year	Four-digit year when sampling occurred.	dimensionless	year
cruise_id	Cruise ID number.	dimensionless	cruise_id
depth_core	Depth sampled within the core.	centimeters (cm)	depth_core
CH4	Porewater methane concentration in mM.	milliMolar (mM)	CH4
d13C_CH4	Stable carbon isotope ratio of methane (13C/12C ratio) in CH4 in sediment porewater samples.	o/oo	d13C
DIC	Concentration of DIC in mM. Note: the samples were acidified so that all DIC (CO2 + HCO3- + CO3=) turns into CO2.	milliMolar (mM)	DIC
d13C_DIC	Concentration of dissolved inorganic carbon in sediment porewater samples. Notes: units are milli-Molar; the samples were acidified so that all DIC (CO2 + HCO3- + CO3=) turns into CO2.	o/oo	d13C_DIC
sulfate	Concentration of sulfate in sediment porewater samples.	milliMolar (mM)	SO4

Status message

Database

Contribute Data

Dataset: AT15-40 Porewater Geochemistry