Comparison of methane concentration and stable carbon isotope data for natural samples analyzed by discrete sample introduction module - cavity ring down spectroscopy (DSIM-CRDS) and traditional methods

Frequently anticipated questions:

• What does this data set describe?
  1. How might this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  3. What similar or related data should the user be aware of?
• How reliable are the data; what problems remain in the data set?
  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
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  5. How can I download or order the data?
• Who wrote the metadata?

What does this data set describe?

1. How might this data set be cited?
   Pohlman, John W., and Casso, Michael, 20210827, Comparison of methane concentration and stable carbon isotope data for natural samples analyzed by discrete sample introduction module - cavity ring down spectroscopy (DSIM-CRDS) and traditional methods: data release DOI:10.5066/P99B34V1, U.S. Geological Survey, Reston, VA.

   Online Links:

   • https://doi.org/10.5066/P99B34V1
   • https://www.sciencebase.gov/catalog/item/60d60d72d34e960393674818

   Other_Citation_Details:

   Suggested Citation: Pohlman, J.W., and Casso, M., 2021, Comparison of methane concentration and stable carbon isotope data for natural samples analyzed by discrete sample introduction module - cavity ring down spectroscopy (DSIM-CRDS) and traditional methods: U.S. Geological Survey data release, https://doi.org/10.5066/P99B34V1.
   This data release is in support of: Pohlman, J.W., Casso, M., Magen, C., and Bergeron, E., 2021, Discrete sample introduction module (DSIM) for quantitative and isotopic analysis of methane and other gases by cavity ring-down spectroscopy: Environmental Science and Technology, https://doi.org/10.1021/acs.est.1c01386.

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -126.6787
   East_Bounding_Coordinate: 84.2079
   North_Bounding_Coordinate: 48.7896
   South_Bounding_Coordinate: 15.4462
   

3. What does it look like?

   https://www.sciencebase.gov/catalog/file/get/60d60d72d34e960393674818?name=DSIM-CRDS_system.png (PNG)

   Image of Michael Casso operating the DSIM-CRDS system on a ship during field work.

   https://www.sciencebase.gov/catalog/file/get/60d60d72d34e960393674818?name=DSIM-CRDS_data_plot.png (PNG)

   Plot of DSIM-CRDS data suite from analysis of oceanographic profile

4. Does the data set describe conditions during a particular time period?

   Calendar_Date: 2021

   Currentness_Reference:

   publication date

5. What is the general form of this data set?

   Geospatial_Data_Presentation_Form: tabular digital data
   

6. How does the data set represent geographic features?
   1. How are geographic features stored in the data set?
      This is a Point data set. It contains the following vector data types (SDTS terminology):
      • point
   2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.00001. Longitudes are given to the nearest 0.00001. Latitude and longitude values are specified in Decimal degrees. The horizontal datum used is World Geodetic System 1984.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257223563.
      

      Vertical_Coordinate_System_Definition:

      Depth_System_Definition:

      Depth_Datum_Name: local surface
      Depth_Resolution: 0.1
      Depth_Distance_Units: meters
      Depth_Encoding_Method: attribute values
      

7. How does the data set describe geographic features?

   DSIM_Environmental_Data_DSIM-IRMS_Comparison

   Comma Separated Value (.csv) and Excel Workboon (.xlsx) files containing data. Contains 51 data records. The first row is descriptive and not related to column headings. (Source: Producer Defined)

   Expedition

   Official names of the scientific expedition(s) during which the samples were collected (Source: Producer Defined)

   Value	Definition
   HRS15-12	The 12th expedition aboard the R/V Hugh R. Sharp in 2015, an investigation of Atlantic Margin methane hydrate dynamics. 09/06/2015 to 09/17/2015. FA-2015-005.
   IODP Expedition 311	Integrated Ocean Drilling Program Expedition 311, an investigation of methane hydrate distribution along a margin perpendicular transect of the northern Cascadia margin. 08/28/2005 to 10/28/2005
   NGHP-02	National Gas Hydrate Program Expedition 02, an assessment of gas hydrate along the eastern coast of India. 03/03/2015 to 07/28/2015

   Geographic_Location

   General oceanic location where each expedition was conducted (Source: Producer Defined)

   Value	Definition
   U.S. Atlantic Margin	Continental shelf and slope of the U.S. Atlantic margin from offshore Virginia to Long Island New York, United States
   Northern Cascadia Margin	Continental margin offshore of Vancouver Island, British Columbia Canada
   Indian Ocean	Western continental margin of the Indian Ocean at the Krishna-Godavari and Mahanadi basins

   latitude(dd)

   Latitudinal position in decimal degrees measured by the navigation system of the supporting research vessel where the samples were collected (Source: Producer Defined)

   Range of values
   Minimum:	15.4462
   Maximum:	48.7896
   Units:	decimal degrees
   Resolution:	.0001

   longitude(dd)

   Longitudinal position in decimal degrees measured by the navigation system of the supporting research vessel where the samples were collected. Negative values indicate the western hemisphere. (Source: Producer Defined)

   Range of values
   Minimum:	-126.6787
   Maximum:	84.2079
   Units:	decimal degrees
   Resolution:	.0001

   Site

   Expedition site name referring to a specific area within the Geographic_Location. (Source: Producer Defined)

   Value	Definition
   Hudson Canyon	Shelf incising submarine canyon on the US Atlantic margin offshore of New York U.S.
   Baltimore Canyon	Shelf incising submarine canyon on the US Atlantic margin offshore of Maryland U.S.
   Chincoteague Slope	A portion of the U.S. Atlantic margin continental slope offshore of Virginia U.S.
   U1329C	IODP drilling location near the shelf/slope break on the northern Cascadia margin offshore of Vancouver Island, British Columbia Canada
   Site X, Area Y	Scientific drilling locations where “X” is the site number specified during the Indian National Gas Hydrate Program Expedition 2 (NGHP-02) and “Y” is the alphanumeric specific permit area within the site

   Deployment_ID

   Sample collection Deployment_ID for the designated scientific expedition (Source: Producer Defined) Alphanumeric codes for describing the samples collected for a deployment at a specific location. The alphabetic portion describes the Sample_Type (further described by the "Type" attribute), and the numeric portion the order the sample was collected

   Type

   Description of the type and means of sample collection (Source: Producer Defined)

   Value	Definition
   Piston Core	A device that collects a continuous sediment core extending from the sediment water interface to meters below the sea floor
   Multicore	A device that collects multiple short sediment cores extending from the sediment water interface to less than 1 m below the sea floor
   CTD	Conductivity-Temperature-Depth profiler that was integrated with number of Niskin-type water sampling bottles used to collect water samples from discrete depths in the ocean
   APC	Advanced piston core (APC) used to collect ~ 10 m sediment core sections in the upper portion of a scientific drilling hole where the sediments are unconsolidated
   RCB	Rotary core barrel (RBC) used to collected ~10 ml sediment core sections in the lower portion of a scientific drilling hole where sediments are too consolidate for the APC
   PCS	Pressure core system (PCS) used to collect up to 3 m long sediment sections and maintain the in-situ reservoir pressure during recovery. Used frequently during gas hydrate studies to recover and maintain cores with gas hydrate intact for detailed physical and chemical property studies

   Collection_Date

   Calendar date (MM/DD/YEAR) the sample was collected (Source: Producer Defined)

   Range of values
   Minimum:	9/26/2005
   Maximum:	9/18/2015
   Units:	calendar date (MM/DD/YEAR)
   Resolution:	1

   Sample_ID

   Expedition specific sample identification code (Source: Expedition Curator Defined) A combination of alphanumeric characters used to uniquely identify samples collected during each expedition. The specific format varies but is consistent within each expedition report

   Sample_Type

   Description of the type of sample processed (Source: Producer Defined)

   Value	Definition
   Sediment pore water	Sediment from the core collected with a 5 ml cut-off syringe, placed in a 30 ml serum vial and capped with a stopper. After the addition of 5 ml brine and a 2 min agitation period, 5 ml gas was removed from the vial and analyzed
   Water column	900 ml samples collected in 1L syringes. 100 ml headspace added to the syringe and after a 2 min agitation period the gas was removed and analyzed
   Sediment void gas	Gas from expansion cracks in a sediment core extracted from a hole pierced in the core liner in a syringe and transferred to an evacuated 30 ml stoppered serum. The analyzed sample was removed from the vial
   Sediment pressure core sampler gas	Gas samples released from the pressure core were collected in a syringe and transferred to a 30 ml evacuated serum vial. The analyzed sample was removed from the vial

   Sample_Depth(m)

   Depth below sea surface for water samples for sample type Water Samples or depth below sea floor for sediment samples of types Sediment pore water, Sediment void gas and, Sediment pressure core sampler gas (Source: Producer Defined)

   Range of values
   Minimum:	0.32
   Maximum:	1033
   Units:	meter
   Resolution:	.01

   Analysis_Date

   Calendar date the sample was analyzed (Source: Producer Defined)

   Range of values
   Minimum:	9/9/2015
   Maximum:	3/15/2019
   Units:	Date DD/MM/YEAR

   DSIM_Method

   DSIM configurations used to process the sample (Source: Producer Defined)

   Value	Definition
   Loop B Load/Analysis	The sample was introduced into DSIM through Loop B and subsequently diluted and analyzed in the Loop B analysis configuration
   Loop B Load/Analysis	The sample was diluted by a factor of 10 in a syringe and then introduced into DSIM through Loop B and subsequently diluted and analyzed in the Loop B analysis configuration
   System Load/Analysis	The sample was diluted by a factor of 10 in a syringe and then introduced into DSIM through Loop B and subsequently diluted and analyzed in the Loop B analysis configuration
   System Load/Analysis	A 100 ml sample was loaded into the DSIM analytical loop and then analyzed without dilution in the System Analysis configuration
   Loop A Exp Load/Analysis	The sample was introduced into DSIM through Loop A and subsequently diluted and analyzed in the Loop A analysis with expansion volume enable configuration
   Loop B Load/Analysis	The sample was diluted by a factor of 10 in a syringe and then introduced into DSIM through Loop B and subsequently diluted and analyzed in the Loop B analysis configuration

   Meas_CRDS_CH4(ppm)

   Concentration of methane measured by the analyzer in parts per million by volume without calibration or dilution factors applied (Source: Producer Defined)

   Range of values
   Minimum:	13.84
   Maximum:	1981
   Units:	parts per million
   Resolution:	0.01

   Meas_CRDS_CH4(SD)

   1-sigma standard deviation of the measurement determined by averaging a 1-minute data interval (Source: Producer Defined)

   Value	Definition
   n/a	Data not recorded

   Range of values
   Minimum:	0.01
   Maximum:	53.72
   Units:	parts per million
   Resolution:	0.01

   Corr_CRDS_CH4(ppm)

   Methane concentration calibrated and corrected for dilution within DSIM. This concentration represents the in situ concentration of the sample (Source: Producer Defined)

   Range of values
   Minimum:	14.1
   Maximum:	875304.64
   Units:	parts per million
   Resolution:	0.01

   Corr_CRDS_CH4(stdev)

   1-sigma standard deviation of the calibrated and dilution corrected value (Source: Producer Defined)

   Range of values
   Minimum:	0.02
   Maximum:	4537.93
   Units:	nanomoles per liter (nM)
   Resolution:	0.01

   CRDS_d13CH4(‰)

   CRDS generated isotopic ration value (iCH4) expressed as a delta value (‰) relative the Vienna Pee Dee Belemnite standard (Source: Producer Defined)

   Range of values
   Minimum:	-90.29
   Maximum:	-39.82
   Units:	per mille
   Resolution:	0.01

   CRDS_d13CH4(stdev)

   1-sigma standard deviation of the standardized delta value (‰) determined from a one minute measurement interval (Source: Producer Defined)

   Range of values
   Minimum:	0.23
   Maximum:	3.79
   Units:	per mille
   Resolution:	0.01

   IRMS_d13CH4(‰)

   Isotope ratio mass spectrometry (IRMS) measurement expressed as a delta value (‰) relative the Vienna Pee Dee Belemnite standard (Source: Producer Defined)

   Range of values
   Minimum:	-89.44
   Maximum:	-41
   Units:	per mille
   Resolution:	0.02

   IRMS_Data_Source

   Location where IRMS value was measured or reported in the literature (Source: Producer Defined)

   Value	Definition
   WHOI IRMS Facility	Measured at the Woods Hole Oceanographic Institution stable isotope lab
   Pohlman and others (2009)	Values previously published in Pohlman and others (2009), Methane sources and production in the northern Cascadia margin gas hydrate system, Earth and Planetary Science Letters. doi:10.1016/j.epsl.2009.08.037

   DSIM _Environmental_Data_DSIM-GC_Comparison

   Comma Separated Value (.csv) and Excel Workboon (.xlsx) files containing data. Contains 10 data records. The first row is descriptive and not related to column headings. (Source: Producer Defined)

   Expedition

   Official names of the scientific expedition during which the samples were collected (Source: Producer Defined)

   Value	Definition
   HRS15-12	The 12th expedition aboard the R/V Hugh R. Sharp in 2015, an investigation of Atlantic Margin methane hydrate dynamics. 09/06/2015 to 09/17/2015. FA-2015-005.

   Geographic_Location

   General oceanic location where each expedition was conducted (Source: Producer Defined)

   Value	Definition
   US Atlantic Margin	Continental shelf and slope of the U.S. Atlantic margin from offshore Virginia to Long Island New York, United States

   latitude(dd)

   Latitudinal position in decimal degrees measured by the navigation system of the supporting research vessel where the samples were collected (Source: Producer Defined)

   Range of values
   Minimum:	15.4462
   Maximum:	48.7896
   Units:	decimal degrees
   Resolution:	.0001

   longitude(dd)

   Longitudinal position in decimal degrees measured by the navigation system of the supporting research vessel where the samples were collected. Negative values indicate the western hemisphere. (Source: Producer Defined)

   Range of values
   Minimum:	-74.2960
   Maximum:	-74.2960
   Units:	decimal degrees
   Resolution:	.0001

   Site

   Expedition site name referring to a specific area within the Geographic_Location (Source: Producer Defined)

   Value	Definition
   Hudson Canyon	Shelf incising submarine canyon on the U.S. Atlantic margin offshore of New York US
   Baltimore Canyon	Shelf incising submarine canyon on the U.S. Atlantic margin offshore of Maryland U.S.
   Chincoteague Slope	A portion of the U.S. Atlantic margin continental slope offshore of Virginia U.S.
   U1329C	IODP drilling location near the shelf/slope break on the northern Cascadia margin offshore of Vancouver Island, British Columbia Canada
   Site X, Area Y	Scientific drilling locations where “X” is the site number specified during the Indian National Gas Hydrate Program Expedition 2 (NGHP-02). And “Y” is the alphanumeric specific permit area within the site. within specific permit areas

   Deployment_ID

   Sample collection Deployment_ID for the designated scientific expedition (Source: Producer Defined) Alphanumeric code for a conductivity-depth-temperature (CTD) deployment at a specific location.

   CTD_ID

   Identifier for the CTD sample collected during the deployment (Source: Producer Defined) CTD: Conductivity-Temperature-Depth profiler equipped with number of Niskin-type water sampling bottles used to collect water samples from discrete depths in the ocean. The numeric indicator is the sample bottle number

   Sample_ID

   Expedition specific sample identification code (Source: Producer Defined) A combination of alphanumeric characters used to uniquely identify samples collected during each expedition. The specific format varies but is consistent within each expedition report

   BottomDepth(m)

   Total water depth(s) where samples were was collected as measured by ship sonar (Source: Producer Defined)

   Range of values
   Minimum:	370
   Maximum:	370
   Units:	meters (m)
   Resolution:	1

   SampleDepth(m)

   Water depth from which samples were collected as measured by the CTD pressure sensor (Source: Producer Defined)

   Range of values
   Minimum:	1.24
   Maximum:	373.00
   Units:	meters (m)
   Resolution:	0.02

   DateCollected(MM/DD/YYYY)

   Calendar date (MM/DD/YEAR) the sample was collected and analyzed (Source: Producer Defined)

   Range of values
   Minimum:	9/12/15
   Maximum:	9/12/15

   Corr_GC-CH4(nM)

   Concentration of sample (in nanomoles L-1) as measured with a gas chromatograph equipped with a flame ionization detector (GC-FID) (Source: Producer Defined)

   Range of values
   Minimum:	3.09
   Maximum:	74.67
   Units:	nanomoles per liter (nM)
   Resolution:	0.01

   Corr_CRDS-CH4(nM)

   Methane concentration calibrated and corrected for dilution within DSIM. This concentration represents the in situ concentration of the sample (Source: Producer Defined)

   Range of values
   Minimum:	2.68
   Maximum:	79.12
   Units:	nanomoles per liter (nM)
   Resolution:	0.01

   Corr_CRDS-CH4(SD)

   1-sigma standard deviation of the calibrated and dilution corrected value (Source: Producer Defined)

   Range of values
   Minimum:	0.01
   Maximum:	0.26
   Units:	nanomoles per liter (nM)
   Resolution:	0.01

   CRDS-d13C_CH4(‰)

   CRDS measured isotope ratio value (iCH4) expressed as a delta value (‰) relative the Vienna Pee Dee Belemnite standard (Source: Producer Defined)

   Range of values
   Minimum:	-87.18
   Maximum:	-44.84
   Units:	per mille
   Resolution:	0.01

   CRDS-d13C_CH4(SD)

   1-sigma standard deviation of the standardized delta value (‰) determined from a one-minute measurement interval (Source: Producer Defined)

   Range of values
   Minimum:	0.84
   Maximum:	12.85
   Units:	per mille
   Resolution:	0.01

   CRDS-CO2(ppm)

   Methane concentration calibrated and corrected for dilution within DSIM. This concentration represents the headspace gas equilibrium concentration in the extraction syringe (Source: Producer Defined)

   Range of values
   Minimum:	395.8
   Maximum:	715.4
   Units:	parts per million
   Resolution:	0.1

   CRDS-CO2(SD)

   1-sigma standard deviation of the calibrated and dilution corrected value (Source: Producer Defined)

   Range of values
   Minimum:	0.5
   Maximum:	3.9

   CRDS-d13C_CO2(‰)

   CRDS measured isotope ratio value (iCO2) expressed as a delta value (‰) relative the Vienna Pee Dee Belemnite standard (Source: Producer Defined)

   Range of values
   Minimum:	-12.05
   Maximum:	-9.28
   Units:	per mille
   Resolution:	0.01

   CRDS-iCO2(SD)

   1-sigma standard deviation of the standardized delta value (‰) determined from a one-minute measurement interval (Source: Producer Defined)

   Range of values
   Minimum:	0.49
   Maximum:	1.47
   Units:	per mille
   Resolution:	0.01

Who produced the data set?

1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
   • John W. Pohlman
   • Michael Casso
2. Who also contributed to the data set?
   Development of the DSIM was supported by the U.S. Geological Survey’s Gas Hydrates Project. Samples from the U.S. Atlantic margin were collected with support from USGS-DOE Interagency Agreements DE-FE0005806 and DE-FE0023495.We appreciate suggestions and technical support provided by Lee-Gray Boze and Sean Sylva.
3. To whom should users address questions about the data?
   John W. Pohlman

   Woods Hole Coastal and Marine Science Center

   Research Geochemist

   384 Woods Hole Rd

   Woods Hole, MA
   

   USA

   508-548-8700 x2213 (voice)

   jpohlman@usgs.gov

Why was the data set created?

How was the data set created?

1. From what previous works were the data drawn?
2. How were the data generated, processed, and modified?

   Date: 2021 (process 1 of 1)

   To evaluate the performance of the USGS-DSIM system for analysis of natural samples, dissolved methane concentration data are compared to those from gas chromatography-flame ionization detection (GC-FID), and d13C values are compared to those from isotope ratio mass spectrometry (IRMS). Comparisons of methane water column concentrations are from an oceanographic profile in an area of sea floor methane seepage on the US Atlantic Margin. Comparisons of d13C-CH4 are from the U.S. Atlantic margin water column, U.S. Atlantic margin sediment pore waters, sediment void gas from the northern Cascadia Margin and gas hydrate-bearing sediment pressure cores from the Indian Ocean. The comparisons encompass the variety, concentration range, and isotopic values aquatic scientists and gas geochemists collect and analyze.
   The concentration of the gas sample in the syringe to be analyzed, as estimated by the user, determines the manner by which the sample is processed by the DSIM-CRDS system. Low concentration samples (< 1000 ppmv) are analyzed in the "System Load" DSIM configuration to minimize dilution of the sample (>97% recovery), while higher concentration samples are quantitatively diluted using configurations that dilute the sample by factors of ~85 (Loop B Load/Analysis), ~215 (Loop A Load/Analysis) or ~1400 (Loop A Load/Analysis with Expansion. This approach enables to a user to analyze limited volume (5 - 100-ml) samples ranging six orders-of-magnitude from 100% analyte to the lower limit of instrument detection (2 ppmv) with a relative standard deviation of less than 1% for every configuration for concentration while also obtaining stable carbon isotopic data comparable to IRMS values when the sample concentration exceeds 10 ppmv for methane and 200 ppm for CO2. How the methane and CO2 concentration and stable carbon isotopic data are converted from instrument measurements to values calibrated against internationally recognized standards as fully described in Pohlman and others (2021). See citation below. Briefly, all measurements are corrected as slope and offset corrections obtained from linear regression analysis of the known standard concentrations and instrument measured values. Person who carried out this activity:
   

   John Pohlman

   USGS Woods Hole Coastal and Marine Science Center

   Research Geochemist

   USGS, 384 Woods Hole Rd

   Woods Hole, MA
   

   USA

   508-457-8700 (x2310) (voice)

   508-457-2310 (FAX)

   jpohlman@usgs.gov

3. What similar or related data should the user be aware of?
   Pohlman, John W., Casso, Michael, Magen, Cédric, and Bergeron, Emile, 2021, Discrete sample introduction module (DSIM) for quantitative and isotopic analysis of methane and other gases by cavity ring-down spectroscopy: Environmental Science and Technology unknown, ACS, Washington D.C..

   Online Links:

   • https://doi.org/10.1021/acs.est.1c01386

   Other_Citation_Details: The journal article these data support.
   

   Pohlman, John W., Kaneko, Masanori, Heuer, Verena B., Coffin, Richard B., and Whiticar, Michael, 20090926, Methane sources and production in the northern Cascadia margin gas hydrate system: Earth Planetary Science Letters Volume 287, Issues 3-4, Elsevier, Amsterdam.

   Online Links:

   • https://doi:10.1016/j.epsl.2009.08.037

   Other_Citation_Details:

   The citation is included because the original northern Cascadia margin IRMS data are part of this publication

   Collett, Timothy S., Boswell, Ray, Waite, William F., Kumar, Pushpendra, Roy, Sandip Kumar, Chopra, Krishan, Singh, Sunil Kumar, Yamada, Yasuhiro, Tenma, Norio, Pohlman, John, Zyrianova, Margarita, and NGHP Expedition 02 Scientific Party, 20191001, India National Gas Hydrate Program Expedition 02 Summary of Scientific Results: Gas hydrate systems along the eastern continental margin of India: Marine and Petroleum Geology Vol 108, Amsterdam, Elsevier.

   Online Links:

   • https://doi.org/10.1016/j.marpetgeo.2019.05.023

   Other_Citation_Details:

   The citation is included because the original Indian Ocean IRMS data are part of this publication

How reliable are the data; what problems remain in the data set?

1. How well have the observations been checked?
   The accuracy of each attribute is determined by that analysis specific to that attribute.
2. How accurate are the geographic locations?
   The horizonal positions (coordinates) were obtained from shipboard navigation systems from the following vessels: D/V CHIKYU for the Indian Ocean data; D/V Joides Resolution for the northern Cascadia margin data; and R/V Hugh R. Sharp for the U.S. Atlantic margin data. The horizonal positional accuracy for research vessels of that caliber are considered to be accurate to less than 1 m.
3. How accurate are the heights or depths?
   Vertical data from the water column are accurate to 0.1 m as limited by the sensitivity of the pressure sensor in the CTD. Vertical data from the sediments (meters below the sea floor) are accurate to <0.01 m for all samples.
4. Where are the gaps in the data? What is missing?
   With the exception of a limited number (2) of standard deviations for methane concentration measurements by the CRDS, the data presented is complete. The missing values were not recorded during data aquisition.
5. How consistent are the relationships among the observations, including topology?
   All data provided in this release were obtained by Michael Casso under the supervision of USGS Research Geochemist John Pohlman. The data match all details for the data provided in the cross-referenced manuscript (Pohlman et al., 2021). Each sample represents a unique identifier and the data fit within expected ranges for the environments sampled.

How can someone get a copy of the data set?

1. Who distributes the data set? (Distributor 1 of 1)
   
   GS ScienceBase

   U.S. Geological Survey

   Denver Federal Center, Building 810, Mail Stop 302

   Denver, CO
   

   United States

   1-888-275-8747 (voice)

   sciencebase@usgs.gov
2. What's the catalog number I need to order this data set? The dataset consists of two XLSX files and their comparable CSV formatted files. These files are DSIM_Environmental_Data_DSIM-IRMS_Comparison.xlsx, DSIM_Environmental_Data_DSIM-IRMS_Comparison.csv, DSIM_Environmental_Data_DSIM-GC_Comparison.xlsx, DSIM_Environmental_Data_DSIM-GC_Comparison.csv. The dataset also includes CSDGM metadata in XML format.
3. What legal disclaimers am I supposed to read?
   Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty.
4. How can I download or order the data?
   • Availability in digital form:

     Data format:	The dataset contains 2 data files - each in an XLSX and CSV format. Additionaly, CSDGM metadata describes the data files. in format XLSX
     Network links:	https://www.sciencebase.gov/catalog/file/get/60d60d72d34e960393674818 https://www.sciencebase.gov/catalog/item/60d60d72d34e960393674818 https://doi.org/10.5066/P99B34V1

     Data format:	The dataset contains 2 data files - each in an XLSX and CSV format. Additionaly, CSDGM metadata describes the data files. in format CSV
     Network links:	https://www.sciencebase.gov/catalog/file/get/60d60d72d34e960393674818 https://www.sciencebase.gov/catalog/item/60d60d72d34e960393674818 https://doi.org/10.5066/P99B34V1

   • Cost to order the data: None

Who wrote the metadata?

Dates:

Last modified: 19-Mar-2024

Metadata author:

John Pohlman

Woods Hole Coastal and Marine Science Center

Research Chemist

384 Woods Hole Road

Woods Hole, MA

US

508-548-8700 x2213 (voice)

whsc_data_contact@usgs.gov

Contact_Instructions:

The metadata contact email address is a generic address in the event the person is no longer with USGS. (updated on 20240319)

Metadata standard:

FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)