Records using themekt "Coastal and Marine Ecological Classification Standard"

Results are color-coded by center: PCMSC SPCMSC WHCMSC

Marsh Shorelines of the Massachusetts Coast from 2013-14 Topographic Lidar Data

The Massachusetts Office of Coastal Zone Management (CZM) launched the Shoreline Change Project in 1989 to identify erosion-prone areas of the Massachusetts coast. Seventy-six maps were produced in 1997 depicting a statistical analysis of shoreline change on ocean-facing shorelines from the mid-1800s to 1978 using multiple data sources. In 2001, a 1994 shoreline was added. More recently, in cooperation with CZM, the U.S. Geological Survey (USGS) delineated a new shoreline for Massachusetts using color aerial ortho-imagery from 2008 to 2009 and topographic lidar data collected in 2007. This update included a marsh shoreline, which was defined to be the tonal difference between low- and high-marsh seen in ortho-photos. Further cooperation between CZM and the U.S. Geological Survey (USGS) has resulted in another update in 2018, which includes beach shorelines, marsh shorelines and dune parameters, all of which were calculated from 2013-14 topographic lidar data. This metadata file describes the marsh shoreline that is part of the 2018 update. The marsh shoreline was defined to be the steep slope found at the seaward edge of the marsh vegetation. This definition was used because the marsh edge is the preferred shoreline indicator for computing rates of change and making position forecasts.

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

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.

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

A discrete sample introduction module (DSIM) was developed and interfaced to a cavity ring-down spectrometer to enable measurements of methane and CO2 concentrations and 13C values with a commercially available cavity ring-down spectrometer (CRDS). The DSIM-CRDS system permits the analysis of limited volume (5 - 100-ml) samples ranging six orders-of-magnitude from 100% analyte to the lower limit of instrument detection (2 ppm). We demonstrate system performance for methane by comparing concentrations and 13C results obtained by the DSIM and traditional methods for a variety of sample types, including low concentration (nanomolar) seawater and high concentration (> 90%) natural gas. The expansive concentration range the CRDS is able to analyze while being packaged in a field-portable analytical system greatly enhances functionality for investigating methane and CO2 dynamics, as well as other gases measured by laser absorption spectroscopy.

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Global compilation of published gas hydrate-related bottom simulating reflections

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.

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Modeled surface waves from winds in South San Francisco Bay

A model application using the phase-averaged wave model SWAN was developed to simulate wind waves in South San Francisco Bay, California, between May 30, 2021, and May 19, 2022. This data release describes the development of the model application, provides input files suitable for running the model using Delft3D version 4.04.01, and includes output from the model simulations in netCDF format.

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