Global compilation of published gas hydrate-related bottom simulating reflections

Metadata also available as - [Outline] - [Parseable text] - [XML]

Frequently anticipated questions:

What does this data set describe?

Title:
Global compilation of published gas hydrate-related bottom simulating reflections
Abstract:
Bottom simulating reflections (BSRs) are seismic features that are imaged in marine sediments using high-energy, impulsive seismic sources such as air guns or generator-injector guns. BSRs often cut across sediment stratigraphy and are interpreted as marking the deepest depth at which gas hydrate can exist. Gas hydrate is a naturally occurring and widely distributed frozen form of water and gas (usually methane) stable at low temperatures (up to about 25 degrees Celsius [°C]) and intermediate pressures (those that usually correspond to greater than 500 meters water depth). BSRs have been mapped in all the world’s oceans, in inland seas (such as the Black Sea), and in Lake Baikal in Russia. This data release consists of a GeoPackage that compiles digitized BSR maps from published scientific papers and other sources into a single resource, with attribution to the original researchers. An associated spreadsheet provides the same descriptive information about each of the original BSR maps in a form accessible without opening the GeoPackage. A GeoPackage is an open-source, platform-independent, standards-based package of geospatial data for a geographic information system (GIS). To formulate the dataset, published BSR maps were georeferenced, digitized, and converted to a common geographic coordinate system, and the resulting files were assigned a quality factor based on characteristics of the original maps and the difficulty of georeferencing. As described in detail in the associated metadata, most maps had a single polygon or multiple polygons enclosing the area where BSRs were recognized by the original researchers. Some maps had only circles or ovals around areas interpreted as containing BSRs, and these geometric shapes were digitized for the database. A few maps indicated the precise segments of individual seismic lines where BSRs are identified, resulting in BSRs being digitized as polylines instead of polygons. Polygons for BSRs in the northern Gulf of Mexico and U.S. Atlantic margin are based on files provided for direct release (no georeferencing necessary) by the Bureau of Ocean Energy Management.
Supplemental_Information:
The compilation is not exhaustive of all bottom simulating reflections (BSRs) in the English-language scientific literature since some published maps lack sufficient features (e.g., coastlines) or geographic coordinates to allow them to be georeferenced for digitization of the BSRs. Especially at high latitudes, some published maps could not be included in the compilation since the original map was published in an unknown projection that caused the maps to be highly distorted once georeferenced. In some cases, the maps chosen for this compilation represent an updated, more complete, or more precise rendering of BSRs than available in alternate publications. The authors of this dataset may also have missed published references that contained digitizable BSRs from areas not currently represented in the database, and the contact for the dataset (Carolyn Ruppel, cruppel@usgs.gov) can be reached to provide such information for consideration for inclusion in an update planned for 2025. The date range given for "time period information" encompasses the range of dates over which the maps were published, not the dates over which the supporting seismic information for each published map was acquired or interpreted.
  1. How might this data set be cited?
    How, Amelia R., and Ruppel, Carolyn D., 20230202, Global compilation of published gas hydrate-related bottom simulating reflections: data release DOI:10.5066/P9IW5CL7, U.S. Geological Survey, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Woods Hole, Massachusetts.

    Online Links:

    Other_Citation_Details:
    Suggested citation: How, A.R., and Ruppel, C.D., 2023, Global compilation of published gas hydrate-related bottom simulating reflections: U.S. Geological Survey data release, https://doi.org/10.5066/P9IW5CL7.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -158.577649
    East_Bounding_Coordinate: 179.056773
    North_Bounding_Coordinate: 81.538744
    South_Bounding_Coordinate: -61.512652
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/63caaf8cd34e06fef14f3e2a?name=BSRbrowsegraphic.png (PNG)
    Image of global BSRs (red) included this release
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 01-Jan-1988
    Ending_Date: 31-Dec-2022
    Currentness_Reference:
    The date range given for "time period information" encompasses the range of dates over which the maps were published, not the dates over which the supporting seismic information for each published map was acquired or interpreted.
  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.
    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 0.0197427722. Longitudes are given to the nearest 0.0261514554. Latitude and longitude values are specified in Decimal seconds. The horizontal datum used is WGS_1984.
      The ellipsoid used is WGS_84.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    BSR_polygons
    polygon entries (single and multipart) for bottom simulating reflectors (BSRs), containing 51 records (Source: U.S. Geological Survey)
    fid
    Internal feature number. Whole numbers that are automatically generated. Number 42 is missing from the polygon features, resulting in non-sequential fid. (Source: QGIS)
    Range of values
    Minimum:1
    Maximum:52
    shpname
    Name of feature, in format of first author of original reference and year of publication followed by underscore and then a generalized area descriptor. Three locations have multiple bottom simulating reflection (BSR) polygon layers from the same references, but with characteristics appended after the geographic descriptor. "MH212009_Japan" layers are labelled "confirmed" (corresponding to the original map's "methane hydrate concentrated zones are confirmed partially by detailed surveys" shown in red polygons), "suggested" (corresponding to the original map's "characteristics of methane concentration are suggested in some areas" shown in navy blue polygons), "low" (corresponding to the original map's "characteristics of methane concentration are not recognized" shown in green polygons), and "unknown" (corresponding to the original map's "surveys are insufficient for the evaluation of methane hydrate" shown in light blue polygons). "Shedd2012_GulfofMexico" layers are labelled "continuous," "discontinuous," and "pluming" based on the BSR designations in the original publication. "BOEM2012_USAtlantic" layers are labelled "high" to indicate strong confidence in the existence of BSRs and "possible" to indicate lesser confidence in the BSRs, based on the original publication. "Kumar2014_India" layers are labelled "high," "medium," and "low" corresponding to red polygons (highly prospective for gas hydrates), green polygons (moderately prospective), and yellow polygons (low prospectivity) on the original map. (Source: Producer defined) ASCII text
    geometry
    Geometry of feature, with "polygon" indicating single or multipart polygon. (Source: Producer defined) ASCII text
    fileid
    Whole number identifying corresponding entry in Excel file. (Source: Producer defined)
    Range of values
    Minimum:1
    Maximum:51
    location
    Text field providing up to three location designations separated by dashes, starting with the most general and progressing to the most specific. For marine locations, the first designator refers to the appropriate ocean or basin. For onshore locations (permafrost or Lake Baikal), the first designator refers to the country. Some locations have a designator that includes a slash ("/"). This is the case for the Sea of Japan/East Sea or East Sea/Sea of Japan since this same body of water is referred to using both names, usually dependent on the nationality of the lead author of the associated reference. (Source: Producer Defined) ASCII text
    central_long
    Decimal degrees corresponding to the average of the minimum and maximum longitudinal extent of each polygon feature, with positive denoting east longitude and negative denoting west longitude. (Source: Producer defined)
    Range of values
    Minimum:-149.24153
    Maximum:176.41938
    Units:decimal degrees
    central_lat
    Decimal degrees corresponding to the average of the minimum and maximum latitudinal extent of each polygon feature, with positive denoting north latitude and negative denoting south latitude. (Source: Producer defined)
    Range of values
    Minimum:-61.13465
    Maximum:79.90192
    Units:decimal degrees
    minlong
    Decimal degrees corresponding to the minimum longitudinal extent of each polygon feature, with positive denoting east longitude and negative denoting west longitude. (Source: Producer defined)
    Range of values
    Minimum:-158.57649
    Maximum:173.78199
    Units:decimal degrees
    maxlong
    Decimal degrees corresponding to the maximum longitudinal extent of each polygon feature, with positive denoting east longitude and negative denoting west longitude. (Source: Producer defined)
    Range of values
    Minimum:-139.90657
    Maximum:179.05677
    Units:decimal degrees
    minlat
    Decimal degrees corresponding to the minimum latitudinal extent of each polygon feature, with positive denoting north latitude and negative denoting south latitude. (Source: Producer defined)
    Range of values
    Minimum:-61.51265
    Maximum:78.265099
    Units:decimal degrees
    maxlat
    Decimal degrees corresponding to the maximum latitudinal extent of each polygon feature, with positive denoting north latitude and negative denoting south latitude. (Source: Producer defined)
    Range of values
    Minimum:-60.75665
    Maximum:81.53874
    Units:decimal degrees
    reference
    Text field that contains the figure number and citation for the scientific work from which the bottom simulating reflectors (BSRs) are taken, including the digital object identifier (DOI) or URL when available. (Source: Producer Defined) ASCII text
    quality
    Whole number indicating subjective evaluation of the quality of the bottom simulating reflections (BSRs) shapefile generated for each feature in this data set, based on consideration of difficulties with georeferencing, whether the BSRs are truncated or too generalized in the original map, and related factors. (Source: Producer Defined)
    ValueDefinition
    1Denotes the best quality and is only used for files provided directly by the Bureau of Ocean Energy Management, already in geographic or projected coordinates (known projection).
    2Used for most BSRs based on the likelihood of imprecisions in georeferencing and digitizing.
    3Indicates the worst quality and is assigned for high latitude or other locations that were particularly difficult to georeference or for maps that provided only general indications about the location of BSR features (e.g., circles or ovals around areas with BSRs).
    comments
    Text field with additional notes about the original map or the georeferencing or digitization. Not all records have a comment. (Source: Producer Defined) ASCII text
    filegen
    Who generated the feature, in which year, and how. (Source: Producer Defined) ASCII text
    BSR_polylines
    polyline entries for bottom simulating reflectors (BSRs), containing 2 records (Source: U.S. Geological Survey)
    fid
    Internal feature number. Whole numbers that are automatically generated. (Source: QGIS)
    Range of values
    Minimum:1
    Maximum:2
    shpname
    Name of feature, in format of first author of original reference and year of publication followed by underscore and then a generalized geographic descriptor. (Source: Producer defined) ASCII text
    geometry
    Geometry of layer, with "polyline" indicating line features. (Source: Producer defined) ASCII text
    fileid
    Whole number identifying corresponding entry in Excel file. (Source: Producer defined)
    Range of values
    Minimum:52
    Maximum:53
    location
    Text field providing up to three location designations separated by dashes, starting with the most general and progressing to the most specific. The first designator refers to the appropriate ocean or basin. (Source: Producer Defined) ASCII text
    central_long
    Decimal degrees corresponding to the average of the minimum and maximum longitudinal extent of each polyline, with positive denoting east longitude and negative denoting west longitude. (Source: Producer defined)
    Range of values
    Minimum:-125.993959
    Maximum:150.02577
    Units:decimal degrees
    central_lat
    Decimal degrees corresponding to the average of the minimum and maximum latitudinal extent of each polyline, with positive denoting north latitude and negative denoting south latitude. (Source: Producer defined)
    Range of values
    Minimum:44.643149
    Maximum:52.409875
    Units:decimal degrees
    minlong
    Decimal degrees corresponding to the minimum longitudinal extent of each polyline, with positive denoting east longitude and negative denoting west longitude. (Source: Producer defined)
    Range of values
    Minimum:-127.423939
    Maximum:144.03115
    Units:decimal degrees
    maxlong
    Decimal degrees corresponding to the maximum longitudinal extent of each polyline, with positive denoting east longitude and negative denoting west longitude. (Source: Producer defined)
    Range of values
    Minimum:-124.563978
    Maximum:156.020391
    Units:decimal degrees
    minlat
    Decimal degrees corresponding to the minimum latitudinal extent of each polyline, with positive denoting north latitude and negative denoting south latitude. (Source: Producer defined)
    Range of values
    Minimum:40.280268
    Maximum:47.509814
    Units:decimal degrees
    maxlat
    Decimal degrees corresponding to the maximum latitudinal extent of each polyline, with positive denoting north latitude and negative denoting south latitude. (Source: Producer defined)
    Range of values
    Minimum:49.006031
    Maximum:57.309937
    Units:decimal degrees
    reference
    Text field that contains the figure number (where applicable) and citation for the scientific work from which the bottom simulating reflectors (BSRs) are taken, including the digital object identifier (DOI) or URL when available. (Source: Producer Defined) ASCII text
    quality
    Whole number indicating subjective evaluation of the quality of the bottom simulating reflections (BSRs) shapefile generated for each feature in this data set, based on consideration of difficulties with georeferencing, whether the BSRs are truncated or too generalized in the original map, and related factors. (Source: Producer Defined)
    ValueDefinition
    1Denotes the best quality and is only used for files provided directly by the Bureau of Ocean Energy Management, already in geographic or projected coordinates (known projection).
    2Used for most BSRs based on the likelihood of imprecisions in georeferencing and digitizing.
    3Indicates the worst quality and is assigned for high latitude or other locations that were particularly difficult to georeference or for maps that provided only general indications about the location of BSR features (e.g., circles or ovals around areas with BSRs).
    comments
    Text field with additional notes about the original map or the georeferencing/digitization. (Source: Producer Defined) ASCII text
    filegen
    Who generated the feature, in which year, and how. (Source: Producer Defined) ASCII text

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • How, Amelia R.
    • Ruppel, Carolyn D.
  2. Who also contributed to the data set?
    The bottom simulating reflections digitized for this release are published in the figure numbers (where applicable) in the references provided in the "reference" column of the GeoPackage attribute table and the Excel spreadsheet. DOE-USGS Interagency Agreement 89243320SFE000013 and the USGS Gas Hydrates Project (Energy Resources Program and Coastal and Marine Hazards and Resources Program) supported this research.
  3. To whom should users address questions about the data?
    Carolyn Ruppel
    U.S. Geological Survey, Northeast Region
    Research Geophysicist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2339 (voice)
    508-457-2310 (FAX)
    cruppel@usgs.gov

Why was the data set created?

This GeoPackage was formulated for the purpose of compiling polygons and polylines showing the locations of bottom simulating reflections (BSRs) likely associated with the presence of gas hydrates in marine sediments on global continental margins. The BSRs are primarily from published maps, with additional BSRs from online maps or digital files provided directly to the U.S. Geological Survey by the Bureau of Ocean Energy Management.

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: 01-Jun-2021 (process 1 of 8)
    STEP 1: In most cases, maps showing the areal extent of bottom simulating reflections (BSRs) were extracted from digital copies of published manuscripts as JPEG (Joint Photographic Exports Group) or PNG (Portable Network Graphics) files and named with the convention of lead author of the publication followed immediately by the publication year then an underscore symbol and the geographic location of the BSRs. Two maps (labelled "MH21" and "Praeg2018") were taken directly from websites. Files labelled "BOEM" and "Shedd2012" were provided in already digitized form by the Bureau of Ocean Energy Management (BOEM). Processing date indicates approximate date of first recent map extraction with the exception of a map digitized by Carolyn Ruppel in 2013 (Kvenvolden1990). Map extractions continued sporadically until January 2023. Person who carried out this activity:
    Carolyn Ruppel
    U.S. Geological Survey, Northeast Region
    Research Geophysicist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2339 (voice)
    508-457-2310 (FAX)
    cruppel@usgs.gov
    Date: 06-Aug-2021 (process 2 of 8)
    STEP 2: Each map was imported into a geographic information system using QGIS software (final version used QGIS 10.20.1 - Odense on a Windows 10 machine). Using coastlines (when available) and latitude and longitude control points (when indicated on the map), each map was georeferenced and the resulting shapefile saved. Processing date indicates approximate date of first georeferencing for the whole dataset. Processing continued sporadically until January 2, 2023, with some files reprocessed if the resulting shapefile did not credibly reproduce the original map. Person who carried out this activity:
    Amelia How
    U.S. Geological Survey, Northeast Region
    Research Geophysicist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2215 (voice)
    508-457-2310 (FAX)
    ahow@usgs.gov
    Date: 29-Dec-2022 (process 3 of 8)
    STEP 3: Digitized BSRs not in the WGS84 geographic coordinate system were converted to WGS84 using Esri ArcMap 10.7 on a Windows 10 machine. The files provided by the Bureau of Ocean Energy Management (see Step 1) were also converted from NAD83 to WGS84 as needed. Processing date indicates the first date on which files were converted. This processing step was finished in early January 2023. Person who carried out this activity:
    Carolyn Ruppel
    U.S. Geological Survey, Northeast Region
    Research Geophysicist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2339 (voice)
    508-457-2310 (FAX)
    cruppel@usgs.gov
    Date: 12-Jan-2023 (process 4 of 8)
    STEP 4: Shapefiles (originally 54) and an associated spreadsheet containing information about the quality of the georeferencing, the reference for the published bottom simulating reflections (BSRs), and comments related to the file were compiled for further processing. Using QGIS 3.16.7-Hannover running on a Windows 10 machine, each polygon shapefile (originally 52) and polyline shapefile (2) were checked for validity using the Vector Geometry tool – Check validity. Two polygons were found to have problems (Chand2012_Barents and Wang2022_SouthChinaSea), and these files were edited and repaired. Shapefiles that consisted of more than one polygon were combined into a single multipart polygon. This was accomplished using the tool Vector geometry – dissolve. As a result of this process, each shapefile contained only one feature. The same process was applied to the polyline shapefiles. Each shapefile was then edited to remove all attributes except the attribute id. A new text attribute was added “shpname” which was populated with the shapefile name prefix originally provided. Person who carried out this activity:
    VeeAnn A. Cross
    U.S. Geological Survey, Northeast Region
    Marine geologist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2251 (voice)
    508-457-2310 (FAX)
    vA.@usgs.gov
    Date: 12-Jan-2023 (process 5 of 8)
    STEP 5: Using the QGIS software referenced in Step 4, the polygon shapefiles were then merged into a single polygon shapefile using the Vector General tool – Merge vector layers. The output polygon shapefile was named merged_polygons.shp. The same procedure was followed for the 2 polyline shapefiles with the output shapefile named merged_polylines.shp Person who carried out this activity:
    VeeAnn A. Cross
    U.S. Geological Survey, Northeast Region
    Marine geologist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2251 (voice)
    508-457-2310 (FAX)
    vA.@usgs.gov
    Date: 12-Jan-2023 (process 6 of 8)
    STEP 6: Using the QGIS software referenced in Step 4, the polygon shapefile was then joined to the Excel spreadsheet containing additional information about the shapefiles (see Step 4) in order to bring over the additional attributes needed for the dataset. The join was accomplished using the Vector general tool – Join attributes by field value. The attribute in the shapefile to join to was shpname corresponding to the column in the Excel spreadsheet named "shapefile." The results were saved into a temporary layer in QGIS. This same join procedure was followed for the polyline merged shapefile and saved as a temporary layer in QGIS. Person who carried out this activity:
    VeeAnn A. Cross
    U.S. Geological Survey, Northeast Region
    Marine geologist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2251 (voice)
    508-457-2310 (FAX)
    vA.@usgs.gov
    Date: 12-Jan-2023 (process 7 of 8)
    STEP 7: Using the QGIS software referenced in Step 4, the polygon temporary layer was then exported to a GeoPackage using Export – Save feature as. Format – GeoPackage. Filename - BSR_GeoPackage.gpkg. Layer name – BSR_polygons. The polyline temporary layer was then exported to the same GeoPackage. Right-mouse click on the layer name – Export – Save feature as. Format – GeoPackage. Filename - BSR_GeoPackage.gpkg. Layer name – BSR_polylines. Person who carried out this activity:
    VeeAnn A. Cross
    U.S. Geological Survey, Northeast Region
    Marine geologist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2251 (voice)
    508-457-2310 (FAX)
    vA.@usgs.gov
    Date: 16-Jan-2023 (process 8 of 8)
    STEP 8: Using QGIS software 3.22.14 - Bialowieza on a Windows 10 machine, the attribute tables for the two layers in the GeoPackage were edited to delete unneeded or redundant columns, to resolve small errors in location descriptions, and to reorder the columns in the attribute table (using "processing > refactor"). In addition, the Excel file was reordered for better correlation with the order of the feature files within the layers for the GeoPackage, and the GeoPackage attributes pointing to the Excel file numbering were manually updated using QGIS. Edits were also made to increase the uniformity of the reference formats and to reduce the number of retained digits for some of the latitude and longitude entries. One record was removed due to low quality georeferencing and the map's being superseded by a co-located and more complete BSR map in another publication. This resulted in the fid within the attribute table being non-sequential (#42 is skipped), reduced the number of polygons to 51 and the total number of features to 53. The process date is the first date on which the files were edited to bring the GeoPackage and the Excel file into conformity. Person who carried out this activity:
    Carolyn Ruppel
    U.S. Geological Survey, Northeast Region
    Research Geophysicist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-458-8700 x2339 (voice)
    508-457-2310 (FAX)
    cruppel@usgs.gov
  3. What similar or related data should the user be aware of?
    Ruppel, Carolyn D., and Waite, William F., 20200604, Timescales and processes of methane hydrate formation and breakdown, with application to geologic systems: Journal of Geophysical Research vol. 125, e2018JB016459, American Geophysical Union (AGU), n/a.

    Online Links:

    Other_Citation_Details:
    Ruppel, C.D., and Waite, W.F., 2020, Grand challenge: Timescales and processes of methane hydrate formation and breakdown, with application to geologic systems: Journal of Geophysical Research Solid Earth, 125, https://doi.org/10.1029/2018JB016459
    Waite, William F., Ruppel, Carolyn D., Boze, Lee-Gray, Lorenson, Thomas D., Buczkowski, Brian J., McMullen, Katherine Y., and Kvenvolden, Keith A., 20200611, Preliminary global database of known and inferred gas hydrate locations: data release DOI:10.5066/P9LLFVJM, U.S. Geological Survey, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Waite, W.F., Ruppel, C.D., Boze, L-G., Lorenson, T.D., Buczkowski, B.J., McMullen, K.Y., and Kvenvolden, K.A., 2020, Preliminary global database of known and inferred gas hydrate locations: U.S. Geological Survey data release, https://doi.org/10.5066/P9llFVJM.

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

  1. How well have the observations been checked?
    The geographic accuracy of the digital bottom simulating reflection (BSR) locations in this dataset depends on (a) the accuracy of the BSR delineations in the original references; (b) the quality of the georeferencing and digitization that could be achieved for the files (all except BOEM2012 and Shedd2012) that required these processing steps; (c) decisions made about how to digitize the BSRs for this dataset. In addition, the dataset as a whole has an inaccuracy in that some known BSRs were not included owing to the difficulty of finding a map with sufficient features for georeferencing and digitizing.
    To assess the potential inaccuracy related to (a): The general criteria used to delineate BSRs in marine seismic data acquired with high-energy, impulsive acoustic sources having the frequency characteristics needed to image BSRs include such factors as: (1) negative polarity (reverse impedance, indicating higher over lower velocity sediments) reflections in marine sedimentary section within tens to hundreds of meters below the seafloor; (2) seismic reflections that sometimes roughly parallel the seafloor, consistent with their position at a depth where the hydrostatic pressure and temperature in the sediments correspond to the limit for gas hydrate stability conditions; and (3) seismic reflections that cut across stratigraphic layering, consistent with the reflections' marking a phase boundary, not a stratigraphic boundary, within the sediments. Other bottom simulating features are sometimes recognized in marine seismic data (e.g., the transition of quartz to opal-CT), but such features have different impedance and depth characteristics than BSRs associated with gas hydrates. For the published papers used as the source of maps for georeferencing and digitization of the BSRs, all had been subject to peer review, and gross misidentification of opal-CT features as hydrate-related BSRs is unlikely. There is considerable subjectivity in authors' delineations of BSRs on maps, especially when polygons are drawn encompassing areas in which the raw data indicate fragments of recognized BSRs along individual seismic lines. How much of the area does not contain BSRs within the polygons on original maps is unknown. For Mosher2011_EasternCanada, Bialis2022_BlackSea, and Minshull2020_Norway the BSRs in the original publications were respectively indicated only by circles, ovals, or small, nearly circular shapes on the original maps, meaning that more precise locations and/or spatial extents of BSRs are unknown. Polygons around areas containing BSRs in the original publications often have square edges (possibly correlating to the extent of the original seismic data) or are truncated at the edge of a map, and the original maps associated with BenAvraham2022_SouthAfrica and Neben1998_CelebesSea have question marks on parts of the BSR polygons. Some publications map BSRs not as polygons, but as line segments or points along seismic lines at the places where BSRs are recognized. The publications associated with Jin2003_SouthShetland and Kopp2002_Sumatra show squares over BSRs mapped on seismic lines, and the original maps for Trehu2022_Cascadia, Chi2006_Taiwan, Liu2006_Taiwan, Ohde2018_Nankai, and some others have BSR points along seismic lines. Especially for cases in which the published maps use a polygon to enclose an area where BSRs have been recognized, the delineation of the polygon is likely to represent the greatest inaccuracy in terms of where BSRs actually exist. Note that there are two or more maps for some locations in the dataset. Examples (not exhaustive list) include the Black Sea (Bialis2022_BlackSea, Ludmann2004_BlackSea, and Vasilev2002_BlackSea), the South China Sea (Li2013_SouthChinaSea and Wang2022_SouthChinaSea), Nankai (MH212009_Japan files and Ohde2018_Nankai), and offshore India (Kumar2014_India files and Prakash2010_IndiaEast) have two or more that features within the BSR_polygons layer within the GeoPackage. Users can compare the extent of the BSRs in these maps (in some cases, the BSR polygons will be seen to overlap) and note the differences, but no value judgment was placed by the dataset's authors on the relative accuracy of one of these maps over another.
    To assess the potential inaccuracy associated with (b): Georeferencing and digitizing BSRs from maps published over a period of more than 30 years in a wide range of journals and from many geographic areas are not the preferred method for compiling a global dataset, but rather the only method possible when the digital files are unavailable from the original authors. High-quality georeferencing was difficult for BSRs at high latitudes, for maps that were originally published in projections that distorted geometric relationships, and for maps lacking coastlines. The quality of digitization can vary from map to map as well, depending on slight variations in manually picking the points to digitize. It is not possible to quantitatively determine the degree of inaccuracy resulting from georeferencing and digitization, but georeferencing inaccuracies will almost always exceed digitizing inaccuracies.
    To assess the potential inaccuracy related to (c): Subjective decisions were made during the digitization process, especially when representing BSRs that appeared in the original published maps as points along seismic lines. For most published maps, polygons in the original were digitized as polygons, and polygons were not combined during digitization. For BSRs identified as points along seismic lines in references such as Chi2006_Taiwan, Liu2006_Taiwan, and Ohde2018_Nankai, polygons were drawn around areas where the BSR points were identified, and the polygon outlines were digitized. Trehu2022_Cascadia and Trehu2022_Hydrate Ridge come from the same published map, which has BSR points identified along seismic lines. For the former file, the points were combined into line segments where BSRs were present on the seismic lines and digitized as polylines. For Hydrate Ridge, which was densely covered by BSR points identified along seismic lines, a polygon was drawn encompassing the dense cluster of points and then digitized. When the dataset authors drew polygons for digitization around points or line segments where BSRs were recognized in original seismic data, this was done judiciously to ensure that large areas without BSR indicators would not be included within the polygons. However, drawing such polygons does introduce an additional inaccuracy.
    Note that the two entries associated with BOEM_USAtlantic were provided to the U.S. Geological Survey by the Bureau of Ocean Energy Management (BOEM) as digital coordinates, meaning that there is no inaccuracy associated with (b) or (c) for these BSRs. The entries associated with Shedd2012 were similarly provided by BOEM as shapefiles so that there is also no inaccuracy related to (b) or (c).
    BSRs are known to exist in some locations where no published map could be found or where published maps lacked features making it possible to georeference and digitize the maps. For example, BSRs exist offshore parts of Antarctica, but published maps could not be georeferenced for this dataset. BSRs are known to be far more extensive offshore eastern Canada than indicated by the one publication included in this dataset, but no maps have been published, perhaps because the underlying data described in the reference for Mosher2011_EasternCanada are proprietary.
  2. How accurate are the geographic locations?
    Spatial inaccuracy could result from a variety of factors discussed in detail in this metadata under geographic accuracy. Spatial inaccuracy could include problems with the accuracy of original information and with the digitization processes.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    The GeoPackage contains all of the BSRs that were successfully georeferenced and digitized and the additional files provided directly by the Bureau of Ocean Energy Management in geographic coordinates or as shapefiles.
  5. How consistent are the relationships among the observations, including topology?
    Except for the Kvenvolden1990 map digitized by Carolyn Ruppel in 2013, each of the original maps that required digitization was georeferenced and digitized using the same process and by the same researcher (A. How). In every case, features plotted from the resulting shapefiles overlapped the comparable features in the original maps in the geographic information systems software and had plausible latitudes and longitudes. When these features were plotted on a global map, they resembled the extent and morphology of the maps in the original publications. Polygons were verified to be closed shapes without extraneous components. Because this dataset combines a number of sources, overlapping polygons exist and are valid.

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 Not for use for navigation or scientific/resource planning. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations and to consult the original references for further information about the maps included in this compilation.
  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? The release contains the GeoPackage (USGS_DigitizedBSRs_GeoPackage.gpkg), the Excel file (USGS_DigitizedBSRs_table.xlsx), the browse graphic (BSRbrowsegraphic.png), and associated FGDC CSDGM metadata in XML format.
  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 as an open, portable, platform-independent GeoPackage. The user must have software capable of reading this format. Note that reading the GeoPackage in Esri software will show "geom" added as a second column by the software in the attribute table. The Excel file provided with the GeoPackage contains the attributes for the GeoPackage (without this additional column introduced by Esri software) in an alternate format and requires Microsoft Office software for access. 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: 02-Feb-2023
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)
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.
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/SB_data_release/DR_P9IW5CL7/USGS_DigitizedBSRs.faq.html>
Generated by mp version 2.9.51 on Mon Feb 6 10:15:51 2023