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U.S. Geological Survey Open-File Report 2010–1150

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


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Thumbnail image of figure 1 and link to larger figure. A map of the location of bathymetric and backscatter surveys completed in Long Island Sound.
Figure 1. Location of the H11997 study area and other bathymetric and backscatter surveys completed in Long Island Sound.

The U.S. Geological Survey (USGS), in cooperation with National Oceanic and Atmospheric Administration (NOAA) and the Connecticut Department of Environmental Protection (CT DEP), is producing 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. 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). Therefore, detailed maps and interpretations of the sea floor are needed to evaluate the extent of adverse impacts and to provide information that can be used for future resource management.

The purpose of this report is to release the imagery, digital terrain models (DTMs), an interpretive data layer, and data derived from multibeam echosounder data collected offshore in eastern Long Island Sound during NOAA survey H11997, and photographic and textural data from 28 stations occupied to verify these acoustic data during USGS cruise 2010-015-FA. This study area forms a 133.7 square kilometer (km²), east-northeasterly-trending, roughly parallelogram-shaped area that extends along the thalweg axis of eastern Long Island Sound (fig. 1). In addition, an extension of the multibeam echosounder data off the study area's northwest corner covers the Cornfield Shoals Disposal Site (Wiley, 1996). Basic data layers provided in this report include raster grids and sun-illuminated imagery of sea-floor topography and an interpretive layer that shows the distribution of geologic features on the sea floor. This report also includes data from sediment grain-size analyses and a gallery of still photographs of the seabed that were used to verify interpretations based on the bathymetric data.

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 on the distribution of benthic habitat; (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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