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Spotlight on Sandy

USGS Scientists Conduct Comprehensive Seafloor Mapping off the Delmarva Peninsula



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U.S. Geological Survey (USGS) coastal and marine scientists continually work to provide information for improving the resilience of coastal habitat and infrastructure to future storms and sea-level rise. In the aftermath of Hurricane Sandy, which impacted the Northeast U.S. coast in the fall of 2012, new research efforts have been directed at mapping the seafloor, imaging materials on and beneath the seafloor, and collecting sediment samples to characterize the geologic and surficial sedimentary framework of the inner continental shelf along the Delmarva (Delaware, Maryland, and Virginia) Peninsula (see “Hurricane Sandy Response—Linking the Delmarva Peninsula’s Geologic Framework to Coastal Vulnerability” and “Linking Coastal Processes and Vulnerability—Assateague Island Regional Study”).

Area off the Delmarva (Delaware, Maryland, Virginia) Peninsula mapped by USGS scientists
Above: Area off the Delmarva (Delaware, Maryland, Virginia) Peninsula mapped by USGS scientists in June–July 2014. Blue lines are survey tracklines, along which the scientists collected swath bathymetry (seafloor depths), seismic-reflection profiles (cross-sectional views of materials beneath the seafloor), and acoustic-backscatter data (which give indications about seafloor materials and roughness). Red dots are sites where they collected sediment samples and bottom photographs. [larger version]

As part of this project, a group of USGS scientists and technologists who dubbed themselves “Team Delmarva” conducted a 40-day research cruise, from June 15 to July 25, 2014, aboard the motor vessel (M/V) Scarlett Isabella. The team collected sediment samples and geophysical data on seafloor depths and surface materials, plus images of sediment layers beneath the seafloor, that will provide new insights into the past, present, and potential future of this coastal system. Their findings will inform a variety of management applications, such as assessments of sand resources, habitats, and coastal vulnerability.

Some members of Team Delmarva on the deck of the motor vessel
Team Delmarva conducted operations 24-hours a day
Above: Some members of Team Delmarva on the deck of the motor vessel (M/V) Scarlett Isabella: (left to right) Laura Brothers, Alex Nichols, Emile Bergeron, Wayne Baldwin, Seth Ackerman, and Eric Moore. USGS photograph by Scott Horvath. [larger version]

Below: Team Delmarva conducted operations 24 hours a day. (Left to right) Dave Callahan (ship’s engineer) and USGS personnel Alex Nichols, David Foster, Charles Worley, and Emile Bergeron deploy the S-Boom seismic source the first night underway. USGS photograph by Rob Thieler. [larger version]

Led by geologists Laura Brothers and Rob Thieler of the USGS Woods Hole Coastal and Marine Science Center (Woods Hole, Massachusetts), the team acquired just over 4 terabytes of geologic and seafloor mapping data, along a linear distance of more than 4,500 kilometers (2,800 miles) and over an area of more than 3,200 square kilometers (1,200 square miles). The team used the latest technology to collect swath bathymetry (seafloor depths), seismic-reflection profiles (cross-sectional views of materials beneath the seafloor), acoustic backscatter (data that provide information about seafloor materials and roughness), water-column properties, and samples of seafloor sediment.

Researchers stand watch in the acquisition van
Above: Charles Worley (left) and Bill Danforth stand watch in the acquisition van, where monitors display data in real time. The broad red bar in the monitor Worley is facing, for example, is bathymetry (depth to seafloor) along the ship’s track; the uniform red color indicates a flat seafloor. USGS photograph by Rob Thieler. [larger version]

Such an effort required an extensive array of gear, including two seagoing lab vans, three winches, two instruments mounted on the side of the vessel, four instruments towed by the vessel, two underwater cameras, a sediment grab sampler, several navigation systems, and a suite of backups. Fortunately, the team had an excellent platform, the M/V Scarlett Isabella, that comfortably accommodated all the gear and personnel and was able to navigate the shallow water (minimum of approximately 8 meters [26 feet] water depth) of the inner shelf.

Researchers prepare a Van Veen grab sampler Researchers pull in a cable containing hydrophones
Above Left: Alex Nichols (left) and Wayne Baldwin prepare a Van Veen grab sampler for deployment. Baldwin is setting a camera that will photograph the sediment surface before and after the jaws of the sampler close around the sediment sample. USGS photograph by Laura Brothers. [larger version]

Above Right: (Left to right) Rob Thieler, Laura Brothers, and David Foster pull in a cable (“streamer”) containing hydrophones (underwater microphones) after completing a boomer seismic survey. USGS photograph by Alex Nichols. [larger version]

The new data provide a more detailed look than ever before at the geologic and geophysical properties of the area’s seafloor and underlying sediments. Swath bathymetry data were collected using a 234-kHz Submetrix sidescan sonar. A moving vessel profiler (designed to gather data at multiple depths while being pulled behind a moving ship) measured the velocity of sound traveling through the water column—information that is used to improve the accuracy of bathymetric data. Acoustic backscatter data, which give an indication of seafloor type (such as gravel, sand, or mud), were collected using the side-mounted Submetrix sonar and a towed Klein sidescan sonar. In addition to aiding in geologic interpretations of sediment type and texture, these data can be used in mapping and understanding benthic habitats. An Edgetech 512i high-resolution subbottom profiler imaged stratigraphy from the seafloor to approximately 20 to 40 meters (65 to 130 feet) beneath the seafloor, enabling geoscientists to map the sedimentary deposits and determine the volume of mobile sediment that may influence how the Delmarva coastline changes in response to storms and climate change. Another seismic-reflection system employing a multichannel hydrophone (underwater microphone) array and a new sound source called the “S-Boom” imaged even deeper stratigraphy, as much as approximately 100 meters (330 feet) below the seafloor. This boomer seismic system provided data that will help define the deeper geologic framework and sedimentary history of the Delmarva Peninsula.

Calm seas enable acquisition of particularly high-quality data
Above: Calm seas enable acquisition of particularly high-quality data. Here, the Scarlett Isabella is towing three pieces of equipment (left to right): 512i subbottom profiler (flanked by yellow pontoons); S-Boom (at end of blue cable extending from center of stern); and a hydrophone cable, or “streamer” (marked by orange buoy in distance). USGS photograph by Rob Thieler. [larger version]

The research cruise collected an impressive amount of data that will keep the team busy for months to come. Products expected to come out of this research, in addition to scientific publications, are regional bathymetric and acoustic-backscatter maps and other geospatial data products. These products lay the foundation for defining the geologic framework, which is critical to understanding coastal-change processes and vulnerability. This work is part of a long-standing, multipronged effort by the USGS Coastal and Marine Geology Program to conduct research that allows coastal stakeholders—including communities, landowners, and U.S. Department of the Interior agencies such as the National Park Service and U.S. Fish and Wildlife Service—to make scientifically informed coastal-management decisions.

Read a profile of co-chief scientist Laura Brothers in “This Woman ROCKS,” this issue. Learn more about USGS Delmarva research at “Hurricane Sandy Response—Linking the Delmarva Peninsula’s Geologic Framework to Coastal Vulnerability.”


Related Sound Waves Stories
Linking Coastal Processes and Vulnerability—Assateague Island Regional Study
March / April 2014
This Woman ROCKS
September / October 2014

Related Websites
Hurricane Sandy Response—Linking the Delmarva Peninsula’s Geologic Framework to Coastal Vulnerability
USGS

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in this issue:

Research
Natural Methane Seepage Is Widespread on the U.S. Atlantic Ocean Margin

Spotlight on Sandy
Field Investigations of Hurricane Sandy's Impacts on Fire Island, New York

Seafloor Mapping off the Delmarva Peninsula

#StrongAfterSandy—A Congressional Briefing Hosted by the USGS

This Woman ROCKS!

Fieldwork
Tripod Brings Data from the Deep Seafloor of the South China Sea

Instruments near Martha’s Vineyard Measure Seafloor Bottom Shear Stress

Coastal Streams in Central California Reflect the Region’s Drought

USGS Scientist Participates in National Geographic’s BioBlitz 2014

Outreach
Twenty Years of Ask-A-Geologist

Awards
Advancing Data Sharing Capabilities—2014 DeSouza Award

Staff & Center News
Postdocs Contributing to Climate-Change Studies

Feds Feed Families Food Drive

Publications
Sept. / Oct. Publications

Accessibility FOIA Privacy Policies and Notices

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