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U.S. Geological Survey Open-File Report 2013–1060

Sea-Floor Geology and Topography Offshore in Northeastern Long Island Sound


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Thumbnail image of figure 1 and link to larger figure. A map of the location of bathymetric surveys completed in Long Island Sound.
Figure 1. Index map showing the locations of the National Oceanic and Atmospheric Administration H12012 study area and the other bathymetric and backscatter surveys completed in Long Island Sound by NOAA and by the U.S. Geological Survey and the Connecticut Department of Energy and Environmental Protection.

The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Connecticut Department of Energy and Environmental Protection (CT DEEP), has produced detailed maps of the sea floor in Long Island Sound (fig. 1). The current phase of this cooperative research program is directed toward studies of sea-floor topography and its effect on the distributions of sedimentary environments and benthic communities. Because anthropogenic wastes, toxic chemicals, and changes in land-use patterns resulting from residential, commercial, and recreational development have stressed the environment of the sound and caused degradation and potential loss of benthic habitats (Koppelman and others, 1976; Long Island Sound Study, 1994), detailed maps and interpretations of the sea floor are needed to evaluate the extent of adverse impacts and to manage resources wisely in the future. The present study covers an elongate 52.9 km² area in northeastern Long Island Sound (fig. 1).

The purpose of this report is to make available the bathymetric imagery and digital terrain models (DTMs) derived from multibeam echosounder data collected in northeastern Long Island Sound during NOAA survey H12012 and the data and interpretive data layers from 21 bottom sampling and photography stations occupied to verify interpretations of these acoustic data. Basic data layers provided in the report include raster grids and sun-illuminated imagery of sea-floor topography. These datasets are provided as part of this report online and on DVD-ROM in Esri raster-grid and GeoTIFF formats in order to facilitate access, compatibility, and utility. Also provided are interpretive data layers that show the distribution of sedimentary environments and geologic features on the sea floor. Presented supplemental and verification data include sediment grain-size analyses and a gallery of still photographs of the seabed.

These bathymetric, interpretive, and verification datasets serve many purposes, including (1) defining the topographic variability of the sea floor, which is one of the primary controls of benthic habitat diversity; (2) improving our understanding of the oceanographic processes that control the distribution and transport of bottom sediments and the distribution of benthic habitats and associated infaunal community structures; and (3) providing a detailed framework for future research, monitoring, and management activities. These datasets also serve as base maps for subsequent sedimentological, geochemical, and biological observations, because precise information on topography and environmental setting is important for the selection of sampling sites and for accurate extrapolation and interpretation of point measurements.

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