Minimal offshore extent of ice-bearing (subsea) permafrost on the U.S. Beaufort Sea margin

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What does this data set describe?

Title:
Minimal offshore extent of ice-bearing (subsea) permafrost on the U.S. Beaufort Sea margin
Abstract:
The present-day distribution of subsea permafrost beneath high-latitude continental shelves has implications for sea level rise and climate change since the Last Glacial Maximum (~20,000 years ago). Because permafrost can be spatially associated with gas hydrate (which may be thermodynamically stable within the several hundred meters above and below the base of permafrost), the contemporary distribution of subsea permafrost also has implications for the persistence of permafrost-associated gas hydrate beneath shallow waters at high latitudes, particularly on margins that were not glaciated at the Last Glacial Maximum. On the U.S. Beaufort Sea margin offshore northern Alaska, researchers have sometimes assumed that contemporary subsea permafrost extends to the 100 meter isobath on the outer continental shelf. Using a compilation of more than 50,000 stacking velocities from ~100,000 line-km of industry-collected multichannel seismic reflection data acquired over 57,000 square kilometers of the U.S. Beaufort Sea continental shelf, we derive the average (bulk) velocity in the upper 750 milliseconds of two-way travel time (TWTT). An average velocity of 2000 meters per second (m/s) is used to delineate the offshore extent of ice-bearing permafrost that has not thawed since the end of the Last Glacial Maximum. The 2000 m/s velocity contour represented in this data release is within 37 km of the modern U.S. Beaufort shoreline and at water depths less than 25 m. The contour was determined as part of a study by Brothers, L. L., B. M. Herman, P. E. Hart, and C. D. Ruppel (2016), Subsea ice-bearing permafrost on the U.S. Beaufort Margin: 1. Minimum seaward extent defined from multichannel seismic reflection data, Geochemistry, Geophysics, Geosystems, 17, 4354–4365, doi:10.1002/2016GC006584. Direct borehole observations of ice-bearing permafrost in the same area as the 2000 m/s velocity contour from this data set are described in the associated work: Ruppel, C. D., B. M. Herman, L. L. Brothers, and P. E. Hart (2016), Subsea ice-bearing permafrost on the U.S. Beaufort Margin: 2. Borehole constraints, Geochemistry, Geophysics, Geosystems, 17, 4333–4353, doi:10.1002/2016GC006582. The placement of the 2000 m/s contour derived from seismic reflection stacking velocities is similar to, but not exactly the same as, the extent of subsea permafrost inferred based on earlier seismic refraction analyses of Brothers, L. L., P. E. Hart, and C. D. Ruppel (2012), Minimum distribution of subsea ice-bearing permafrost on the U.S. Beaufort Sea continental shelf, Geophys. Res. Lett., 39, L15501, doi:10.1029/2012GL052222.
Supplemental_Information:
The date range given for "time period information" is approximate and is meant to encompass the range of dates over which the original seismic data were acquired. In the first cross-referenced work, the original seismic data were described as being collected in the mid-1970s in the Beaufort Sea and onshore in the National Petroleum Research Reserve and the Arctic National Wildlife Refuge from 1977 to 1990. However, the permit numbers associated with the data indicate that the data were acquired only between 1977 and 1990. A subset of the data used in this study (e.g., scanned tiff images of the semblance based velocity analyses, the compiled results of the velocities picked from the semblance based analyses, processed seismic data, and navigation files) is available from the National Archive of Marine Seismic Surveys (NAMSS) https://walrus.wr.usgs.gov/NAMSS/. All of the other velocity data used in this study are available from the Bureau of Ocean Energy Management (BOEM) Alaska Region. Interested parties may submit Freedom of Information Act requests to BOEM with the permit number in order to obtain this information. The permit numbers (NAMSS ID is in parentheses where applicable) are: 77-25 (B-25-77-AK), 80-01, 80-03 (B-03-80-AR), 80-42, 81-02 (B-02-81-AR), 81-23 (B-23-81-AR), 82-59 (B-59-82-AR), 83-28, 84-37, 85-49, 87-04, 87-15 (B-15-87-AR), 90-05, and 90-15. The original list of permit numbers is provided in the Supporting Information published with Brothers, L. L., B. M. Herman, P. E. Hart, and C. D. Ruppel (2016), Subsea ice-bearing permafrost on the U.S. Beaufort Margin: 1. Minimum seaward extent defined from multichannel seismic reflection data, Geochemistry, Geophysics, Geosystems, 17, 4354–4365, doi:10.1002/2016GC006584. The Supporting Information can be accessed at http://agupubs.onlinelibrary.wiley.com/doi/10.1002/2016GC006584.
  1. How might this data set be cited?
    Brothers, Laura L., Ruppel, Carolyn D., Hart, Patrick E., and Herman, Bruce M., 2019, Minimal offshore extent of ice-bearing (subsea) permafrost on the U.S. Beaufort Sea margin: data release DOI:10.5066/P96FB9F7, U.S. Geological Survey, Coastal/Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Woods Hole, Massachusetts.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Brothers, L.L., Ruppel, C.D., Hart, P.E., and Herman, B.M., 2019, Minimal offshore extent of ice-bearing (subsea) permafrost on the U.S. Beaufort Sea margin: U.S. Geological Survey data release, https://doi.org/10.5066/P96FB9F7.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -157.0262
    East_Bounding_Coordinate: -140.5589
    North_Bounding_Coordinate: 71.9791
    South_Bounding_Coordinate: 69.4095
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/5c90f6d0e4b0938824547e4d?name=AlaskasubseaIBPF_USGS.png (PNG)
    Image of shapefile indicating location of 2000 m/s velocity contour, which is taken as a proxy for the minimal offshore extent of ice-bearing permafrost (subsea permafrost) on the U.S. Beaufort Sea margin.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 01-Jan-1977
    Ending_Date: 31-Dec-1990
    Currentness_Reference:
    source data
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: vector 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):
      • String (1)
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 6
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -147.0
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000.0
      False_Northing: 0.0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.6096
      Ordinates (y-coordinates) are specified to the nearest 0.6096
      Planar coordinates are specified in meters
      The horizontal datum used is North_American_Datum_1927.
      The ellipsoid used is Clarke_1866.
      The semi-major axis of the ellipsoid used is 6378206.4.
      The flattening of the ellipsoid used is 1/294.9786982.
  7. How does the data set describe geographic features?
    AlaskasubseaIBPF_USGS.shp
    polyline shapefile of minimal offshore permafrost extent (Source: U.S. Geological Survey)
    FID
    Internal feature number. (Source: Esri) Sequential unique whole numbers that are automatically generated. Because this is a polyline, the only FID is "0".
    Shape
    Feature geometry. (Source: Esri) Coordinates defining the feature. This feature is a polyline.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Brothers, Laura L.
    • Ruppel, Carolyn D.
    • Hart, Patrick E.
    • Herman, Bruce M.
  2. Who also contributed to the data set?
    The seismic data for this study and most of the stacking velocities were provided to the U.S. Bureau of Ocean Energy Management by companies that collected the original data. The data are now more than 25 years old and are in the public domain. The Bureau of Ocean Energy Management, DOE-USGS Interagency Agreement DE-FE0002911, and the USGS Gas Hydrates Project supported this research. Laura Brothers was also supported by a DOE National Energy Technology Laboratory/National Research Council Methane Hydrate Fellowship under DE-FC26-05NT42248 to conduct this research from 2010 to 2012.
  3. To whom should users address questions about the data?
    Laura Brothers
    U.S. Geological Survey, Northeast Region
    Research Geologist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2312 (voice)
    508-457-2310 (FAX)
    lbrothers@usgs.gov

Why was the data set created?

This shapefile was formulated for the purpose of delineating the 2000 meter per second (m/s) contour for average sediment velocities calculated for the first 750 milliseconds of two-way travel time from legacy seismic reflection records collected near the Alaskan coastline bordering the U.S. Beaufort Sea. The 2000 m/s averaged sediment velocity contour is interpreted as the contemporary seaward extent of ice-bearing permafrost (subsea permafrost) on the U.S. Beaufort Sea margin (Arctic Ocean) offshore northern Alaska.

How was the data set created?

  1. From what previous works were the data drawn?
    Industry seismic data provided to the Bureau of Ocean Energy Management -- Alaska Region (source 1 of 1)
    companies, various, 19901231, Seismic imagery and stacking velocities for private-sector seismic surveys onshore and offshore along the U.S. Beaufort Sea coastline.

    Type_of_Source_Media: Digital and/or Hardcopy
    Source_Contribution:
    various companies; see Supplemental Information in this metadata file for permit numbers corresponding to seismic data used for the first cross-referenced work, information about how to obtain the data, and alternate ways to access a subset of the data
  2. How were the data generated, processed, and modified?
    Date: 16-Apr-2014 (process 1 of 7)
    STEP 1: The stacking velocity was converted to an average bulk compressional velocity (Vave) using the Dix equation at the discrete picked times for each stacking velocity analysis. (processing date is approximate) Person who carried out this activity:
    Laura Brothers
    U.S. Geological Survey, Northeast Region
    Research Geologist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2312 (voice)
    508-457-2310 (FAX)
    lbrothers@usgs.gov
    Date: 16-Apr-2014 (process 2 of 7)
    STEP 2: A cubic spline was fitted to Vave at each velocity analysis location, from which Vave was interpolated to 750 milliseconds (ms) two-way travel time (TWTT). Note that 750 ms TWTT nominally corresponds to the uppermost ~600 meters (m) of section offshore and possibly up to ~1000 m for locations with permafrost. (processing date is approximate) Person who carried out this activity:
    Laura Brothers
    U.S. Geological Survey, Northeast Region
    Research Geologist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2312 (voice)
    508-457-2310 (FAX)
    lbrothers@usgs.gov
    Date: 16-Apr-2014 (process 3 of 7)
    STEP 3: In order to grid the Vave values at points evenly spaced in distance and then contour these values, the Vave value at each latitude and longitude (geographic coordinate system) from the previous step had to be ascribed to an x-y location in a planar coordinate system. Using ArcGIS, the original geodetic datum (NAD27) provided by the Bureau of Ocean Energy Management was retained, and the Vave value locations were converted to x-y locations in Universal Transverse Mercator zone 6N. UTM zone 6N is a Northern Hemisphere UTM zone bounded by 144 degrees West Longitude and 150 degrees West longitude and 0 degrees north latitude and 84 degrees north latitude. Note that, according to metadata in NAMSS (see Data Credit) for the original data acquisitions, the seismic surveys were mostly referenced to the NAD83 datum, even though some of the surveys preceded development of the NAD83 standard. It is not known if this description of the original data is correct. (processing date is approximate) Person who carried out this activity:
    Laura Brothers
    U.S. Geological Survey, Northeast Region
    Research Geologist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2312 (voice)
    508-457-2310 (FAX)
    lbrothers@usgs.gov
    Date: 16-Apr-2014 (process 4 of 7)
    STEP 4: Vave were gridded with 2 km node spacing in GeoFrame software, where they were smoothed with a two-pass biharmonic filter. (processing date is approximate; this step completed by Bruce Herman (retired) of the Bureau of Ocean Energy Management in Anchorage, Alaska)
    Date: 16-Apr-2014 (process 5 of 7)
    STEP 5: The variation in water depth across the shelf introduces a slight gradient in Vave (average velocity from 0 to 750 ms TWTT). Using the Dix Equation, the velocity of the sediment alone (Vsed) was therefore calculated using: (Vsed)^2 = [(Vave^2 x 750 ms) - (Vwc^2 x Twc)] / (750 ms - Twc), where Vwc is water column velocity (assumed 1475 m/s), and Twc is TWTT for the water column. This step was completed using Excel spreadsheets. (processing date is approximate) Person who carried out this activity:
    Laura Brothers
    U.S. Geological Survey, Northeast Region
    Research Geologist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2312 (voice)
    508-457-2310 (FAX)
    lbrothers@usgs.gov
    Date: 16-Apr-2014 (process 6 of 7)
    STEP 6: The resulting Vsed values were contoured in Esri ArcGIS and the 2000 m/s contour extracted to make the shapefile for this dataset.(processing date is approximate) Person who carried out this activity:
    Laura Brothers
    U.S. Geological Survey, Northeast Region
    Research Geologist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2312 (voice)
    508-457-2310 (FAX)
    lbrothers@usgs.gov
    Date: 06-Aug-2020 (process 7 of 7)
    Added keywords section with USGS persistent identifier as theme keyword. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
  3. What similar or related data should the user be aware of?
    Brothers, Laura L., Herman, Bruce M., Hart, Patrick E., and Ruppel, Carolyn D., 20161011, Subsea ice-bearing permafrost on the U.S. Beaufort Margin: 1. Minimum seaward extent defined from multichannel seismic reflection data: Geochemistry, Geophysics, Geosystems vol. 17, issue 11, pp. 4354-4365, American Geophysical Union (AGU), n/a.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Brothers, L. L., Herman, B. M., Hart, P. E., and Ruppel, C. D. ( 2016), Subsea ice-bearing permafrost on the U.S. Beaufort Margin: 1. Minimum seaward extent defined from multichannel seismic reflection data, Geochem. Geophys. Geosyst., 17, pp. 4354– 4365, doi:10.1002/2016GC006584.
    Ruppel, Carolyn D., Herman, Bruce M., Brothers, Laura L., and Hart, Patrick E., 20161104, Subsea ice-bearing permafrost on the U.S. Beaufort Margin: 2. Borehole constraints: Geochemistry, Geophysics, Geosystems vol. 17, issue 11, pp. 4333-4353., American Geophysical Union (AGU), n/a.

    Online Links:

    Other_Citation_Details:
    Ruppel, C. D., Herman, B. M., Brothers, L. L., and Hart, P. E. ( 2016), Subsea ice-bearing permafrost on the U.S. Beaufort Margin: 2. Borehole constraints, Geochem. Geophys. Geosyst., 17, pp. 4333–4353, doi:10.1002/2016GC006582.
    Brothers, Laura L., Hart, Patrick E., and Ruppel, Carolyn D., 20120807, Minimum distribution of subsea ice-bearing permafrost on the U.S. Beaufort Sea continental shelf: Geophysical Research Letters vol. 39, issue 15, L15501, American Geophysical Union (AGU), n/a.

    Online Links:

    Other_Citation_Details:
    Brothers, L. L., Hart, P. E., and Ruppel, C. D. ( 2012), Minimum distribution of subsea ice-bearing permafrost on the U.S. Beaufort Sea continental shelf, Geophys. Res. Lett., 39, L15501, doi:10.1029/2012GL052222.

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

  1. How well have the observations been checked?
    Because this dataset is not "observational," but rather "calculated," the accuracy is only as good as (a) the underlying stacking velocities, which were spot checked in the original studies and from which anomalous values were discarded; (b) the methods used to convert stacking velocities to average (bulk) velocities (Vsed) in the upper 750 ms of two-way travel time, which rely primarily on the widely-used Dix equation; (c) the Dix calculation used to infer the bulk velocity of the uppermost section of offshore sediments (Vave) after the water is stripped off (Equation 1 of the first cross-referenced work); and (d) contouring routines within ArcGIS software. Most of the inaccuracy in the location of 2000 m/s velocity contour as captured in this data release likely arises due to (b) in the list above, with (c) also contributing.
    To assess the potential inaccuracy related to (b): Based on a sensitivity analysis for determination of Vave from Equation (1) in the first cross-referenced paper (Brothers, L. L., B. M. Herman, P. E. Hart, and C. D. Ruppel (2016), Subsea ice-bearing permafrost on the U.S. Beaufort Margin: 1. Minimum seaward extent defined from multichannel seismic reflection data, Geochemistry, Geophysics, Geosystems, 17, 4354–4365, doi:10.1002/2016GC006584; see also process step 4 of this metadata file), a 5% inaccuracy in the determination of Vsed for an assumed water column two-way travel time TWC of 10 ms (~15 m water depth) and the 1475 m/s Vwc (water column velocity) adopted in the first cross-referenced paper will produce slightly more than a 5% deviation in Vave. Thus, a 100 m/s inaccuracy in Vsed could propagate as more than a 100 m/s inaccuracy in Vave. However, this inaccuracy would be on a point by point basis for the 50,000 stacking velocity points used in this analysis. The inaccuracy would have to be systematic amongst these 50,000 points for the contours of Vave in Figure 3 of the first cross-referenced paper to shift appreciably and for the position of the 2000 m/s contour that constitutes this shapefile to be affected.
    To assess the potential inaccuracy related to (c): Vave for a given bulk sediment velocity Vsed between the observed values of 1475 to 3110 m/s will vary by less then 1.3% for water column velocity (Vwc) between 1400 and 1500 m/s and for a deeper water (~75 m) part of the shelf (two-way travel time TWC for the water column = 100 ms). The largest variation is for these larger water depths and for the lowest assumed Vwc. A variation of 1% at 75 m water depth (outer shelf) is only ~19 m/s. Figure 3 of the first cross-referenced paper depicts a steep offshore gradient in Vsed, which is contoured at 100 m/s. The calculated maximum inaccuracy is therefoer only ~one-fifth of 100 m/s. Thus, uncertainties due to Vwc differing from the assumed value of 1475 m/s would not be significant.
  2. How accurate are the geographic locations?
    Spatial inaccuracy could result from attribution of stacking velocities to the wrong location by the companies that provided those data to the U.S. Bureau of Ocean Energy Management and/or from poor navigation of the original seismic data. No further information on spatial inaccuracy is available, and navigation for the original data is unknown. The horizontal positional information provided for the stacking velocities used for this study do correspond to locations along known seismic lines, which is a first-order indication that the positions are reasonable.
  3. How accurate are the heights or depths?
    Spatial inaccuracy could result from attribution of stacking velocities to the wrong location by the companies that provided those data to the U.S. Bureau of Ocean Energy Management and/or from poor navigation of the original seismic data. No further information on spatial inaccuracy is available, and navigation for the original data is unknown. The horizontal positional information provided for the stacking velocities used for this study do correspond to locations along known seismic lines, which is a first-order indication that the positions are reasonable.
  4. Where are the gaps in the data? What is missing?
    The shapefile was derived by contouring all Vave values determined from the original stacking velocities deemed to be within physically reasonable limits. No values of Vave were selectively discarded prior to contouring, nor were values changed.
  5. How consistent are the relationships among the observations, including topology?
    Each Vave used as the basis for contouring the entire dataset of Vave values to produce the shapefile was determined using the same process. As described in the first cross-referenced work, stacking velocities that were clearly anomalous were analyzed prior to their use in determining Vsed and thence Vave (see Process Steps) and discarded if the values were not physically reasonable. As a general example (not one specific to this dataset), if a stacking velocity were significantly lower than the speed of sound in water, this stacking velocity would be considered anomalous.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None. Please see 'Distribution Info' for details.
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
    United States

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? AlaskasubseaIBPF_USGS.zip: File contains the polyline feature class (AlaskasubseaIBPF_USGS.shp), the browse graphic (AlaskasubseaIBPF_USGS.png), and associated FGDC CSDGM metadata in XML,HTML, FAQ, and text formats.
  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 U.S. Geological Survey 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?
  5. What hardware or software do I need in order to use the data set?
    These data are available in Esri shapefile format. The user must have software capable of reading this format. The data are available for download in zip format, which requires software to extract the files from the zip archive.

Who wrote the metadata?

Dates:
Last modified: 06-Aug-2020
Metadata author:
Carolyn Ruppel
U.S. Geological Survey, Northeast Region
Research Geophysicist
384 Woods Hole Road
Woods Hole, MA
United States

508-458-8700 x2339 (voice)
cruppel@usgs.gov
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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