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| Value | Definition |
|---|---|
| Shells | Shell Zone areas have significant coverage of carbonate shells. For Buzzards Bay, shell zones were mapped where high densities of slipper shells (Crepidula fornicata) cover the seafloor. These zones are primarily mapped by identifying high acoustic backscatter in areas where surficial sediments are fine grained and verified with bottom photographs. Areas identified include the central Buzzards Bay basin near Quicks Hole, outside of Red Brook Harbor, within and around bathymetric channels north of Penikese Island. Other areas of high concentrations of shell material likely exist but are not identifiable without bottom photographs to verify these areas. |
| Range of values | |
|---|---|
| Minimum: | 0.040702 |
| Maximum: | 7.83683 |
| Units: | square kilometers |
| Resolution: | 0.00001 |
This sea-floor physiographic zone was created from geophysical and sample data collected from Buzzards Bay, and is used to characterize the sea floor in the area. Physiographic zone maps are important data layers for marine resource managers charged with protecting fish habitat, delineating marine boundaries, and assessing environmental change due to natural or human impacts. The physiographic zone, shell zone, was mapped separate from all other physiographic zones to avoid overlapping polygons, which would cause issues with the topology editing.
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Are there legal restrictions on access or use of the data?
- Access_Constraints: None
- Use_Constraints:
- Not to be used for navigation. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS) as the source of this information. Additionally, there are limitations associated with qualitative sediment mapping interpretations. Because of the scale of the source geophysical data and the spacing of samples, not all changes in sea floor texture are captured. The data were mapped between 1:5,000 and 1:20,000, but the recommended scale for application of these data is 1:25,000. Not all digitized sea floor features contained sample information, so often the sea floor texture is characterized by the nearest similar feature that contains a sample. Conversely, sometimes a digitized feature contained multiple samples and not all of the samples within the feature were in agreement (of the same texture). In these cases the dominant sediment texture was chosen to represent the primary texture for the polygon. Samples from rocky areas often only consist of bottom photographs, because large particle size often prevents the recovery of a sediment sample. Bottom photo classification can be subjective, such that determining the sediment type that is greater than 50% of the view frame is estimated by the interpreter and may differ among interpreters. Bottom photo transects often reveal changes in the sea floor over distances of less than 100 m and these changes are often not observable in acoustic data. Heterogeneous sea floor texture can change very quickly, and many small-scale changes will not be detectable or mappable at a scale of 1:25,000. The boundaries of polygons are often inferred based on sediment samples, and even boundaries that are traced based on amplitude changes in geophysical data are subject to migration. Polygon boundaries should be considered an approximation of the location of a change in texture.
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
| Data format: | WinZip version 14.5 file contains qualitatively derived polygons that define sea floor physiographic zones for Buzzards Bay, MA and the associated metadata in format Shapefile (version ArcMap 9.3.1) Esri Polygon Shapefile Size: 0.5 |
|---|---|
| Network links: |
https://pubs.usgs.gov/of/2014/1220/GIS_catalog/PhysiographicZones/BuzzardsBay_ShellZones.zip https://pubs.usgs.gov/of/2014/1220/ofr2014-1220-data_catalog.html https://dx.doi.org/10.3133/ofr20141220 |
These data are available in Environmental Systems Research Institute (Esri) shapefile format. The user must have software capable of importing and processing this data type.
