Data and calculations to support the study of the sea-air flux of methane and carbon dioxide on the West Spitsbergen margin in June 2014

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What does this data set describe?

Title:
Data and calculations to support the study of the sea-air flux of methane and carbon dioxide on the West Spitsbergen margin in June 2014
Abstract:
A critical question for assessing global greenhouse gas budgets is how much of the methane that escapes from seafloor cold seep sites to the overlying water column eventually crosses the sea-air interface and reaches the atmosphere. The issue is particularly important in Arctic Ocean waters since rapid warming there increases the likelihood that gas hydrate--an ice-like form of methane and water stable at particular pressure and temperature conditions within marine sediments--will break down and release its methane to the overlying ocean. Some researchers have even proposed the possibility of an Arctic methane catastrophe characterized by wholesale breakdown of gas hydrates in marine sediments and release of the methane to the atmosphere as climate warms. This dataset collected on the West Spitsbergen margin during U.S. Geological Survey Coastal and Marine Geology Program Field Activity 2014-013-FA, which was carried out in conjunction with the University of Tromso and the GEOMAR Helmholtz Centre for Ocean Research Kiel on the R/V Helmer Hanssen, records 30-second-gridded methane and carbon dioxide concentrations in near-surface seawater and the atmospheric marine boundary layer, the carbon-13 isotopic composition of methane and carbon dioxide in the near-surface waters, and also environmental parameters (e.g., seawater salinity, wind speed, water and air temperatures). The results of calculations required to determine the sea-air flux of methane and carbon dioxide are also provided.
Supplemental_Information:
Additional information regarding the field activity can be obtained from: https://cmgds.marine.usgs.gov/fan_info.php?fan=2014-013-FA
  1. How might this data set be cited?
    Ruppel, Carolyn, Pohlman, John, and Casso, Michael, 2017, Data and calculations to support the study of the sea-air flux of methane and carbon dioxide on the West Spitsbergen margin in June 2014: data release DOI:10.5066/F7M906V0, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Ruppel, C., Pohlman, J., and Casso, M., 2017, Data and calculations to support the study of the sea-air flux of methane and carbon dioxide on the West Spitsbergen margin in June 2014: U.S. Geological Survey data release, https://doi.org/10.5066/F7M906V0.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: 5.20419
    East_Bounding_Coordinate: 10.82283
    North_Bounding_Coordinate: 78.76130
    South_Bounding_Coordinate: 78.20683
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/58cc3750e4b0849ce97dcec5?name=gasflux_basemap.jpg (JPEG)
    Browse graphic of the data point locations of the sea-air flux of methane and carbon dioxide on the West Spitsbergen margin.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 21-Jun-2014
    Ending_Date: 27-Jun-2014
    Currentness_Reference:
    ground condition
  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 Vector data set. It contains the following vector data types (SDTS terminology):
      • Entity point (17473)
    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 1/298.257.
  7. How does the data set describe geographic features?
    Attribute Table
    Table containing attribute information associated with the data set. (Source: U.S. Geological Survey)
    daynumber
    integer number representing the number of the day within the year 2014 (Source: U.S. Geological Survey)
    Range of values
    Minimum:172
    Maximum:178
    Units:day number within current year
    date
    date of data collection (Source: Producer defined)
    Range of values
    Minimum:6/21/2014
    Maximum:6/27/2014
    Units:month/day/year
    seconds_in_day
    seconds within day, after gridding at 30 second intervals (Source: Producer defined)
    Range of values
    Minimum:30
    Maximum:86340
    Units:seconds
    ship_lat
    30-second interpolated latitude as determined by ship's navigation system (Source: Producer defined)
    Range of values
    Minimum:78.20683
    Maximum:78.76130
    Units:decimal degrees north
    ship_long
    30-second interpolated longitude as determined by ship's navigation system (Source: Producer defined)
    Range of values
    Minimum:5.20419
    Maximum:10.82283
    Units:decimal degrees east
    ship_sog
    30-second interpolated ship's speed over ground, as determined by ship's navigation system (not used in any calculations) (Source: Producer defined)
    Range of values
    Minimum:0.
    Maximum:10.8
    Units:knots
    ship_truewind
    30-second interpolated ship's determination of true wind speed (Source: Producer defined)
    Range of values
    Minimum:0.7
    Maximum:11.8
    Units:meters per second
    airmar_lat
    latitude measured by internal Airmar PB200 GPS; no data value is 999. (not used in any calculations) (Source: Producer defined)
    Range of values
    Minimum:78.2068
    Maximum:78.7613
    Units:decimal degrees north
    airmar_long
    longitude measured by internal Airmar PB200 GPS; no data value is 999. (not used in any calculations) (Source: Producer defined)
    Range of values
    Minimum:5.2033
    Maximum:10.8232
    Units:decimal degrees east
    baropress
    barometric pressure measured by Airmar PB200 (Source: Producer defined)
    Range of values
    Minimum:1.01
    Maximum:1.03
    Units:atmospheres of pressure
    airT
    air temperature measured by the Airmar PB200 (Source: Producer defined)
    Range of values
    Minimum:-1.2
    Maximum:9.5
    Units:degrees C
    ch4watlo
    methane concentration in near-surface seawater (high precision, from CRDS 2201i), used in calculations when this value was less than 15 parts per million (Source: Producer defined)
    Range of values
    Minimum:1.90
    Maximum:11.13
    Units:parts per million
    ch4wathi
    concentration of methane in near-surface seawater (high range from CRDS 2201i; only used in calculations if ch4watlo is greater than 15 parts per million, which it never was for this dataset); no data value 999 (Source: Producer defined)
    Range of values
    Minimum:2.01
    Maximum:11.26
    Units:parts per million
    co2wat
    concentration of carbon dioxide in near-surface seawater (from CRDS 2201i) (Source: Producer defined)
    Range of values
    Minimum:201.80
    Maximum:415.51
    Units:parts per million
    co2iso
    δ13C of carbon dioxide in near-surface seawater (from CRDS 2201i); no data value 999. (Source: Producer defined)
    Range of values
    Minimum:-7.9
    Maximum:2.5
    Units:per mil
    ch4iso
    δ13C of methane in near-surface seawater (from CRDS 2201i); no data value 999. (Source: Producer defined)
    Range of values
    Minimum:-57.5
    Maximum:-46.0
    Units:per mil
    watvapwat
    water content of dried gas stream from near-surface seawater (from CRDS 2201i) (Source: Producer defined)
    Range of values
    Minimum:0.014
    Maximum:0.054
    Units:percentage
    corrch4wat
    (calculated) methane concentration in near-surface seawater after correction for lab calibration on standard gases applied to ch4watlo (Source: Producer defined)
    Range of values
    Minimum:1.95
    Maximum:11.33
    Units:parts per million
    laggedCH4
    (calculated) corrected methane concentration in near-surface water (corrch4wat) time-lagged to account for instrument's response (598 seconds for rise time and 1196 seconds when concentrations are decreasing), using the method of Kodovska et al. (2016; see cross-reference). (Source: Producer defined)
    Range of values
    Minimum:-1.36
    Maximum:12.20
    Units:parts per million
    laggedCH4sm
    (calculated) time-lagged methane concentrations in the near-surface waters (laggedCH4) smoothed using a Savitsky-Golay filter to eliminate spikes and non-physical values (e.g., negative values created by the mathematical calculation for the lagging); these values are the ones propagated through to methane flux calculations (Source: Producer defined)
    Range of values
    Minimum:1.86
    Maximum:11.66
    Units:parts per million
    corrco2wat
    (calculated) carbon dioxide concentration in near-surface seawater after correction for lab calibration on standard gases was applied to co2wat (Source: Producer defined)
    Range of values
    Minimum:210.62
    Maximum:436.26
    Units:parts per million
    corrch4iso
    (calculated) δ13C in methane in near-surface seawater after correction for lab calibration on standard gases was applied to ch4iso; no data value 999 (Source: Producer defined)
    Range of values
    Minimum:-51.0
    Maximum:-39.2
    Units:per mil
    corrco2iso
    (calculated) δ13C in carbon dioxide in near-surface seawater after correction for lab calibration on standard gases was applied to co2iso; no data value 999 (Source: Producer defined)
    Range of values
    Minimum:-11.9
    Maximum:-0.7
    Units:per mil
    airch4
    methane concentration in air (from CRDS 2301f) (Source: Producer defined)
    Range of values
    Minimum:1.84
    Maximum:1.98
    Units:parts per million
    airco2
    carbon dioxide concentration in air (from CRDS 2301f); values greater than ~410 ppm that have been retained in the spreadsheet can be caused by contamination from smokestack emissions; very large values replaced by no data value 999 (not propagated in calculations) (Source: Producer defined)
    Range of values
    Minimum:379.87
    Maximum:701.83
    Units:parts per million
    corrch4air
    (calculated) methane concentration in air after correction of airch4 using the results of the lab calibration on standard gases (Source: Producer defined)
    Range of values
    Minimum:1.86
    Maximum:2.00
    Units:parts per million
    corrco2air
    (calculated) carbon dioxide concentration in air after correction of airco2 for lab calibration on standard gases (Source: Producer defined)
    Range of values
    Minimum:391.88
    Maximum:724.08
    Units:parts per million
    watvapair
    water content of dried air sample (from CRDS 2301f) (Source: Producer defined)
    Range of values
    Minimum:0.18
    Maximum:0.36
    Units:percentage
    ysiwatT
    temperature of seawater fed into the laboratory, as measured by the YSI EXO2 sonde (Source: Producer defined)
    Range of values
    Minimum:3.31
    Maximum:6.57
    Units:degrees C
    ysisal
    salinity of seawater fed into the laboratory, as determined by the YSI EXO2 sonde; no data value 999. (when needed for calculations, 999 replaced by values at adjacent measurements) (Source: Producer defined)
    Range of values
    Minimum:33.8
    Maximum:34.8
    Units:practical salinity units (psu)
    ysipH
    pH of seawater fed into the lab, as measured by the YSI EXO2 sonde; no data value 999. (not used in calculations) (Source: Producer defined)
    Range of values
    Minimum:8.00
    Maximum:8.36
    Units:pH units
    ysiDO
    dissolved oxygen in seawater fed into the lab, as measured by the YSI EXO2 sonde; no data value 999 (not used in calculations) (Source: Producer defined)
    Range of values
    Minimum:9.83
    Maximum:12.69
    Units:milligram per liter
    ysiDOsat
    percent saturation of seawater with respect to oxygen, as calculated by the YSI EXO2 sonde based on measurement of ysiDO; no data value 999 (not used in calculations) (Source: Producer defined)
    Range of values
    Minimum:98.27
    Maximum:126.24
    Units:percentage of saturation
    ysifDOM
    fluorescent dissolved organic matter in seawater fed into the lab, as measured by the YSI EXO2 sonde (not used in calculations); no data value 999 (Source: Producer defined)
    Range of values
    Minimum:-1.58
    Maximum:-0.96
    Units:quinine sulfate units (QSU), where 1 QSU = 1 part per billion of quinine sulfate, which has fluorescence properties similar to that of organic matter; no data value 999 (not used in calculations)
    ship_hullwatT
    temperature of seawater measured with hull-mounted sensor on ship (Source: Producer defined)
    Range of values
    Minimum:2.69
    Maximum:6.31
    Units:degrees C
    OstCoeff
    (calculated) Ostwald coefficient (Source: Producer defined)
    Range of values
    Minimum:0.03590
    Maximum:0.04094
    Units:dimensionless
    ch4_SatAnom
    (calculated) saturation anomaly (% departure from saturation value) for methane in near-surface waters (Source: Producer defined)
    Range of values
    Minimum:-0.4
    Maximum:522.9
    Units:percentage
    SchmidtNo
    (calculated) Schmidt number (Source: Producer defined)
    Range of values
    Minimum:1406.23
    Maximum:1739.62
    Units:dimensionless
    gasvel_mday
    (calculated) gas transfer velocity (Source: Producer defined)
    Range of values
    Minimum:0.02
    Maximum:5.37
    Units:meters per day
    ch4airequil_nM
    (calculated) concentration of dissolved methane in equilibrium with the measured atmospheric methane concentration (Source: Producer defined)
    Range of values
    Minimum:3.00
    Maximum:3.45
    Units:nanomoles per liter
    ch4flux_umolm2day
    (calculated) sea-air methane flux (Source: Producer defined)
    Range of values
    Minimum:-0.027
    Maximum:31.928
    Units:micromole methane per square meter per day
    ch4flux_mgm2day
    (calculated) sea-air methane flux (Source: Producer defined)
    Range of values
    Minimum:-4.0e-04
    Maximum:5.1e-01
    Units:milligram of methane per square meter per day
    WaterConc_ch4nM
    (calculated) concentration of methane in near-surface seawater (Source: Producer defined)
    Range of values
    Minimum:3.19
    Maximum:20.44
    Units:nanomolar
    Ko_co2
    (calculated) carbon dioxide solubility coefficient (Source: Producer defined)
    Range of values
    Minimum:0.0430
    Maximum:0.0574
    Units:dimensionless
    gastrans_co2
    (calculated) sea-air gas transfer coefficient for carbon dioxide (Source: Producer defined)
    Range of values
    Minimum:0.20
    Maximum:54.45
    Units:dimensionless
    co2flux_mmolm2day
    (calculated) sea-air flux of carbon dioxide (Source: Producer defined)
    Range of values
    Minimum:-113.80
    Maximum:3.92
    Units:millimoles of carbon dioxide per square meter per day, using corrected carbon dioxide concentration value in air; no data value 999 corresponds to intervals when air CO2 values were set to 999 because they were out of range (e.g., in the smokestack emissions)
    co2flux_407ppm
    (calculated) sea-air flux CO2 (Source: Producer defined)
    Range of values
    Minimum:-100.97
    Maximum:4.73
    Units:millimole of carbon dioxide per square meter per day, using an assumed carbon dioxide concentration in air of 407 parts per million
    Entity_and_Attribute_Overview:
    This table contains data re-sampled at 30 second intervals and the associated calculations for the study of sea-air methane (CH4) and carbon dioxide (CO2) fluxes at seep sites and background sites on the West Spitsbergen (Svalbard) margin, based primarily on data acquired by the U.S. Geological Survey in June 2014 aboard the R/V Helmer Hanssen. The U.S. Geological Survey data are supplemented by shipboard data recorded by the R/V Helmer Hanssen. The description of the procedure for combining and gridding the data sets at 30 second intervals, smoothing of data as necessary, and completing calculations related to determining sea-air methane and carbon dioxide fluxes is provided in the Supporting Information to Pohlman and others (2017; see cross-reference)
    The data were originally recorded by several instruments operating continuously and producing data at different, uneven time intervals: Ship's navigation, ship-determined true winds, and hull-mounted temperature readings; Airmar navigation (used only as a rough check on ship's navigation), air temperature, and barometric pressure (more information about parameters available at: http://www.airmartechnology.com/uploads/installguide/PB200UserManual.pdf).
    YSI EXO2 sonde environmental parameters (water temperature, salinity, pH, dissolved oxygen, and fluorescent dissolved organic matter) of near-surface seawater pumped through the ship's seawater feed system into the laboratory (more information about parameters measured at: https://www.ysi.com/File%20Library/Documents/Manuals/EXO-User-Manual-Web.pdf.
    Picarro cavity ring-down spectrometer G-2201i analyses of the concentration of methane and carbon dioxide and the δ13C of methane and carbon dioxide in headspace gas extracted from near-surface seawater pumped through the ship's seawater feed system into the laboratory and then dried before measurement; and Picarro cavity ring-down spectrometer G-2301f analyses of the concentration of methane and carbon dioxide in air samples that were dried before analysis.
    The table also contains calculations related to the determination of sea-air flux of methane and carbon dioxide in the study area.
    Entity_and_Attribute_Detail_Citation:
    The entity and attribute information was generated by the individual and/or agency identified as the originator of the data set. Please review the rest of the metadata record for additional details and information.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Carolyn Ruppel
    • John Pohlman
    • Michael Casso
  2. Who also contributed to the data set?
    Data acquisition partially sponsored by the U.S. Department of Energy (DOE) through USGS-DOE interagency agreements DE-FE0002911 and DE-FE0005806. The Centre for Arctic Gas Hydrate, Environment and Climate (CAGE) at University of Tromso, as well as the Research Council of Norway, provided access to the R/V Helmer Hanssen for this cruise and also contributed navigation and other shipborne data.
  3. To whom should users address questions about the data?
    U.S. Geological Survey
    Attn: Carolyn Ruppel
    Research Geophysicist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA
    USA

    (508) 548-8700 x2339 (voice)
    (508) 457-2310 (FAX)
    cruppel@usgs.gov

Why was the data set created?

The data were collected at shallow and deepwater seeps and in background (no seep) areas on the West Spitsbergen margin for the purpose of determining the rate of methane and carbon dioxide exchange (flux) across the sea-air interface. Determining sea-air gas fluxes requires combining various datasets in space and time. This analysis uses the ship's navigational parameters, a hull-mounted seawater temperature sensor, and wind speed sensors; an Airmar PB200 weather station to provide a check on the ship's navigational parameters and record air temperature; two Picarro cavity ring-down spectrometers that measure the concentration of methane (CH4) and carbon dioxide (CO2) in (dried) samples of headspace gas obtained from near-surface seawater and in samples of air within the atmospheric marine boundary layer; and a YSI EXO2 sonde that measure physical and chemical parameters for the near-surface seawater pumped into the lab. The dataset also reports on the stable carbon (δ13C) isotopic composition of methane and carbon dioxide in the near-surface waters as measured by one of the Picarro cavity ring-down spectrometers. Such isotopic data can be used to infer the processes that led to the formation of methane and carbon dioxide (for example, microbial processes). The data have been combined, gridded at 30 second intervals and edited to remove periods when the instruments were being calibrated with lab standards or when data streams were disrupted. This results in non-continuous shiptracks and non-continuous times in the file. Once edited, the data were used to calculate a variety of values related to sea-air gas flux, including the saturation anomaly for methane in near-surface waters, sea-air flux of methane and carbon dioxide expressed in a variety of units, and various intermediate constants (Schmidt number, Ostwald coefficient) needed for sea-air flux calculations.

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: 2016 (process 1 of 2)
    The following text in this processing step and the next one describes the acquisition and processing sequence for the data and is only slightly modified from that in the Supporting Information for Pohlman and others, 2017 (see cross-reference). Much of the text here and in the next processing step is used verbatim.
    The navigational data, meteorological parameters, water environmental parameters, and gas concentrations were collected by different instruments and correlated based on time stamping or acquisition of the data on a single computer with a program that provides a single, continuous time stamp based on a Network Time Protocol (NTP). Navigational data (latitude and longitude) and meteorological data (true wind speed) were recorded at 60 second intervals in the R/V Helmer Hanssen’s digital log files. The ship’s position is determined using various global positioning system (GPS) receivers. The ship’s positional data were checked against independently-recorded GPS fixes recorded by a U.S. Geological Survey (USGS) receiver on an Airmar PB200 meteorological station and logged using Hypack navigational software or native Hyperterminal logging on laptop computers. In most case, the positional information recorded by the ship and by the Airmar PB200 GPS was found to be within a few meters, except during sharp turns.
    The ship’s meteorological sensors are located on top of the bridge, at an estimated 22.4 m above the water line. Although the U.S. Geological Survey independently recorded meteorological parameters using Airmar PB200 Weather Station at several positions on the ship, the true windspeed data obtained from these deployments were not reliable, possibly owing to problems with the directional calibration of the Airmar instrumentation. Because the standard method for determining sea-air flux depends on the square of the windspeed, small oscillations or quality problems in the true windspeed data are magnified by the flux calculation. The ship’s true windspeed record was therefore retained for use in flux calculations.
    Near-surface water temperature for this study was measured in two ways. First, a hull-mounted temperature sensor is part of the R/V Hanssen’s standard instrument package, with data recorded at 60 second intervals in the navigation files. Second, the temperature and salinity of the water pumped onto the ship's laboratory via the seawater feed were measured by a YSI EXO2 sonde just before the sample was injected into the equilibrator that forms the front-end to the USGS Gas Analysis System (USGS-GAS), which consisted of a 2201i cavity ringdown spectrometer that received headspace gas from a Weiss-type equilibrator. The nominal difference between these two water temperature measurements is ~0.4 °C for this dataset and represents warming of the water during transport to the YSI EXO2 sonde through the ship’s pipes. Various corrections applied to gas concentrations determined with the CRDS are carried out using the water temperature recorded by the YSI EXO2 sonde. Calculations that refer to the state of near-surface waters (e.g., Schmidt number) employ the hull-mounted water temperature determination.
    Concentrations of methane and carbon dioxide were measured with a Picarro G-2201i cavity ring-down spectrometer for near-surface water and a Picarro G-2301f cavity ring-down spectrometer for air. The G-2201i sequentially measures methane and carbon dioxide concentrations for 12C and 13C, in addition to water vapor. Concentrations are determined from the 12C absorption spectrum for those species, and δ13C values are determined from the ratio of the 13C/12C spectra. The measured concentration and δ13C values of methane and carbon dioxide for the G-2201i and the G-2301f, as appropriate, were corrected using a slope and offset correction based on a linear best-fit regression between the measured values and standards of known concentration and isotopic content. The slopes and offsets for the concentration calibration were determined from Air Liquide certified gas standards that contained 1.21, 2.01 and 30 parts per million methane, and 198, 348 and 500 parts per million carbon dioxide (± 5%). Concentrations standards were analyzed at least once per day during the expedition.
    The shipboard laboratory component of the surface water analysis element of the USGS Gas Analysis System consists of a seawater feed, a YSI EXO2 sonde, a Weiss-type equilibrator, a single-channel air-handler and a Picarro G-2201i cavity ring-down spectrometer. The intake of the seawater pump was located 3 meters below the waterline of the bow. Based on the characteristics of the shipboard plumbing and a pumping rate of 20 liters per minute seawater to the wet lab, the water samples required 22.5 seconds to traverse the distance between the pump intake at the bow and equilibrator in the shipboard laboratory. A split of the water pumped through the tubing from the seawater intake was directed to the YSI EXO2 sonde, which measured water temperature, salinity, and other parameters (e.g., pH, dissolved oxygen and fDOM). A second split of the flow sprayed into the equilibrator. Gas in the equilibrator was circulated continuously at a rate of 2 liters per minute through the single-channel air-handler, where it was dried and a fraction (80 milliliters per minute) fed continuously through the G-2201i. Gas exiting the cavity ring-down spectrometer was returned to the main circulation loop of the air handler and equilibrator. The 22.5 second lag was applied to the YSI data to correlate them with the correct spatial location. Transport time from the equilibrator to the cavity ring-down spectrometer added another delay of 30 seconds. Thus, the cavity ring-down spectrometer values were time-shifted by a total of 52.5 second to place them at the correct spatial position in near-surface waters. Accurate determination of the time-offset between when a parcel of water was sampled from surface water and when gas from that parcel was analyzed by the cavity ring-down spectrometer was necessary to realistically map the areas of high dissolved gas concentrations.
    The Picarro G-2301f cavity ring-down spectrometer measures methane and carbon dioxide concentrations and water vapor pressure. At the beginning of the expedition and prior to initiating the key surveys, the leak rate of the closed-loop gas analysis system that includes the Picarro G-2201i cavity ring-down spectrometer was measured. Tests were conducted by injecting 50 milliliters of a 1000 part per million methane certified gas standard into the 1.5 liter analytical loop with the equilibrator sealed at the base. The change in methane concentration over time (i.e., the leak rate) was then monitored. Measured leak rates of 0.060 and 0.048 part per million per minute for system-diluted concentrations of 32.0 and 29.9 parts per million methane equate to system turnover times of 533 and 623 minutes, respectively. By comparison, the time constant with the equilibrators in operation was much shorter at 598 seconds (see below). The much greater leak rate turnover time means that system leakage did not meaningfully affect the methane concentrations measured in the equilibrator during this expedition. To facilitate point-by-point calculation of sea-air gas fluxes, all time-corrected data were combined onto a common 30 second time grid.
    Processing took place over time, 2014-2016. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Carolyn Ruppel
    Research Geophysicist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA
    USA

    (508) 548-8700 x2339 (voice)
    (508) 457-2310 (FAX)
    cruppel@usgs.gov
    Date: 2016 (process 2 of 2)
    Relevant data columns from the navigation and CRDS files and from the serial feed log files were extracted using Unix command line processing, yielding separate files for geographic position and some meteorological parameters, the cavity ring-down spectrometer near-surface water and atmospheric boundary layer data, the YSI EXO2 sonde data, and other meteorological parameters. The data were read in with Matlab (version R2015B) routines, with a Savitsky-Golay filter applied to smooth some of the datasets where rapid oscillations could propagate through calculations and create nonphysical results, particularly in the determination of sea-air flux. The Savitsky-Golay filter is fast and retains more of the recorded signal than other filtering approaches. The Matlab version of the Savitsky-Golay filter was implemented here using a third-order polynomial and smoothed datasets on their original, uneven time grids over different-duration time windows, depending on the degree of oscillatory behavior in the original data. For example, air concentration data were smoothed with a 51-point filter (generally less than 2 minutes), water concentration data with a 31-point filter (31 minutes), hull-mounted temperatures with an 11-point filter (11 minutes), and δ13C values for CH4 and CO2 in near-surface waters, which constituted the noisiest dataset, with a 501-point filter (~20 minutes).
    Once the data were read in and smoothed, they were interpolated for each day of the cruise at common 30 second intervals using Matlab. Only navigation data and ship-supplied parameters (e.g., temperature of water at the hull) were recorded less frequently than 30 seconds. After gridding at 30 seconds, the interpolated data were written into spreadsheets where they were edited for quality control.
    Prior to determining the sea-air flux, concentrations measured by the cavity ring-down spectrometers were corrected to account for the delay related to time required for the headspace of the equilibrator to reach equilibrium with the incoming water. Four laboratory-based tests were conducted in 2014 and one shipboard-based test was carried out in 2015 to derive the time constant representing the amount of time required for the system to increase to e (exponential number = 2.71828) times its initial value when the ship enters an area of elevated methane. From these analyses, the estimated delay time is 598 seconds for the rising methane case, and this was doubled to 1196 seconds for times when concentrations are decreasing. The decreasing concentration scenario represents the time required for re-equilibration to 1/e of the highest value measured in an area of elevated methane.
    Following the method of Kodovska et al. (2016; see cross-reference), the lag correction was applied to the already-corrected methane values from the near-surface water measurements. To remove spikes and negative values caused by overcorrection of the data using this approach, the results were smoothed by 51 points (25 minutes) for the data acquisition on most days and by 71 points (35 minutes) for data acquisition on June 25, 2014. Given the greater solubility of carbon dioxide (and the faster response of the instrumentation), it was not necessary to lag-correct those data. The measured carbon dioxide values are assumed to be in equilibrium.
    Processing took place over time, 2014-2016. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Carolyn Ruppel
    Research Geophysicist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA
    USA

    (508) 548-8700 x2339 (voice)
    (508) 457-2310 (FAX)
    cruppel@usgs.gov
  3. What similar or related data should the user be aware of?
    Pohlman, John W., Greinert, Jens, Ruppel, Carolyn, Silyakova, Anna, Vielstadte, Lisa, Casso, Michael, Mienert, Jurgen, and Bunz, Stefan, 2017, Enhanced CO2 uptake at a shallow Arctic Ocean seep field overwhelms the positive warming potential of emitted methane: Proceedings of the National Academy of Sciences of the United States doi:10.1073/pnas.1618926114.

    Online Links:

    Kodovska, Fenix Garcia-Tigreros, Sparrow, Katy J., Yvon-Lewis, Shari A., Paytan, Adina, Dimova, Natasha T., Lecher, Alanna, and Kessler, John D., 2016, Dissolved methane and carbon dioxide fluxes in Subarctic and Arctic regions: Assessing measurement techniques and spatial gradients: Earth and Planetary Science Letters Volume 436, 15 February 2016, Pages 43–55.

    Online Links:


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

  1. How well have the observations been checked?
    All parameters were checked to ensure that they were within physically reasonable ranges. Sources of inaccuracies can include: bad satellite fixes (ship's navigation and Airmar positional data), icing on the Airmar PB200 (air temperature--no icing experienced on this cruise), high water content remaining in the dried headspace gas stream injected into the Picarro cavity ring-down spectrometer G-2201i (ch4watlo, ch4wathi, co2wat) or in the gas flowing from the atmospheric intake to the Picarro cavity ring-down spectrometer G-2301f (airch4, airco2), and sensors out of calibration for the YSO EXO2 sonde (ysipH, ysiDO, and ysifDOM).
    Gridding the data at 30 second intervals and smoothing selected datasets also can introduce inaccuracies. For example, for ship's speed over ground within the range of 4 knots to 10 knots could produce maximum horizontal inaccuracy of up to ~30 meters and ~75 meters (half the distance that the ship moves in 30 seconds), respectively, as a result of gridding and interpolation.
    The ship's hull-mounted temperature sensor has an accuracy of +/- 0.002 degrees Celsius and a resolution of 0.0001 degrees Celsius. YSI EXO2 parameters have the following accuracy and resolution: SALINITY (measured in practical salinity units, converted from electrical conductivity internally in the sonde using Standard Method 2520 (www.standardmethods.org): accuracy 1% of conductivity measured in milliSiemens per centimeter; resolution 0.01 milliSiemens per centimeter; WATER TEMPERATURE: accuracy +/- 0.01 degrees Celsius; resolution 0.00 degrees Celsius; pH (unitless): accuracy +/- 0.2 pH units; resolution 0.01 pH units; DISSOLVED OXYGEN (milligrams per liter), measured optically: accuracy +/- 0.1 milligrams per liter; resolution 0.01 milligrams per liter; FLUORESCENT DISSOLVED ORGANIC MATTER (quinine sulfate units): accuracy--not applicable; resolution: 0.01 quinine sulfate units.
    Accuracy of the cavity ring-down spectrometers (CRDS) was determined empirically based on 13 analyses of certified gas standards. For the Picarro cavity ring-down spectrometer G-2201i, the methane and carbon dioxide concentration measurements have accuracy of +/- 0.01 parts per million and 4.4 parts per million, respectively. The δ13C carbon isotopic measurements on methane and carbon dioxide have accuracy of +/- 2 parts per mil and +/- 1.5 parts per mil, respectively. For the Picarro cavity ring-down spectrometer G-2301f, the methane and carbon dioxide concentrations have accuracy of +/- 0.01 parts per million and +/- 0.7 parts per million, respectively. For both instruments, the water vapor determination has accuracy of 0.004%.
  2. How accurate are the geographic locations?
    Horizontal accuracy of Furuno GP-500/GP-300 global positioning system and the Furuno FSN 70 satellite navigation system used by the R/V Helmer Hanssen is not known, but is expected to be within 10 m. Estimated maximum horizontal inaccuracy that could be introduced by gridding recorded positions at 30 second time intervals is 30-75 meters for ship's speed over ground of 4 to 10 knots, respectively.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    Completeness_Report: The data have been combined, gridded at 30 second intervals and edited to remove periods when the instruments were being calibrated with lab standards or when data streams were disrupted. This results in non-continuous shiptracks and non-continuous times in the file. Otherwise, the data set is considered complete for the information presented, as described in the abstract and logical consistency report. Users are advised to read the rest of the metadata record carefully for additional details.
  5. How consistent are the relationships among the observations, including topology?
    30 second interval times may not be continuous. The data for each day were individually gridded at this time interval, and the gridding routine normally does not have enough data at the beginning and end of each day to start and end at the first and last (respectively) time intervals for a given day. Data corresponding to time intervals when the Picarro cavity ring-down spectrometer instruments were undergoing calibration with standard gases were removed, as were data recorded when the ship was oriented with air intakes for the Picarro cavity ring-down spectrometer G-2301f within the ship’s smokestack exhaust. In limited instances, missing values for seawater salinity and seawater temperature (mostly from the YSI EXO2) were replaced with data from adjacent time intervals. For other YSI EXO2 parameters, missing data were replaced by no data values (999.0) Data lines were also deleted or no data values (999.0) used when the carbon isotopic data for methane were positive or less than -90 per mil or when those for carbon dioxide were large positive or negative values. Such spurious isotopic data were sometimes recorded after testing of concentration standards.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None.
Use_Constraints:
None. Users are advised to read the data set's metadata thoroughly to understand appropriate use and data limitations.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? gasfluxdata_spitsbergen2014.csv and gasfluxdata_spitsbergen2014.xlsx
  3. What legal disclaimers am I supposed to read?
    Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 19-Apr-2017
Metadata author:
U.S. Geological Survey
Attn: Carolyn Ruppel
Research Geophysicist
Woods Hole Coastal and Marine Science Center
Woods Hole, MA
USA

(508) 548-8700 x2339 (voice)
(508) 457-2310 (FAX)
cruppel@usgs.gov
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/data_release/DR_F7M906V0/gasfluxdata_spitsbergen2014_meta.faq.html>
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