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Fieldwork

Moorings Deployed in the Hudson Shelf Valley, Offshore New York


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map of mooring locations in Hudson Shelf Valley
Figure 1. Map showing location of moorings deployed in the Hudson Shelf Valley and adjacent shelf. Moorings A, B, C, and F form a transect along the axis of the valley from an area of contaminated sediments (A and B) to an area of relatively uncontaminated sediments (C and F). Moorings D and E are located upstream and downstream of the valley in the flow pattern driven by strong northeast winds associated with winter storms.
The U.S. Geological Survey is conducting a study of the transport and fate of sediments and associated contaminants in the New York Bight. As part of this study, a 5-day cruise was carried out December 3-7 aboard the R/V Oceanus to deploy a 6-element moored array to investigate the resuspension, transport and deposition of sediments in the vicinity of the Hudson Shelf Valley (Figure 1) during winter conditions. The Hudson Shelf Valley is a sink for fine-grained sediments and associated contaminants and also a conduit for transport of sediments across the shelf. Geochemical observations have shown elevated levels of contaminants in the sediments at the head of the valley, and as far as 100 km down-valley. Multibeam bathymetric and backscatter surveys of the valley, maps of contaminant distribution, and numerical modeling of the wind-driven currents provided the framework for selection of mooring locations.

The moored array experiment is the final phase of the New York project and is designed to address the role of winter storms in the following two hypotheses:

  • Sediments on the shelf and in the valley will be a source of polluted material that will further disperse and contaminate the lower valley

  • The contaminated sediments on the shelf and in the valley will remain in place

tripod deployment
Figure 2. Tripod being lifted off the deck for deployment. For recovery from the ocean bottom, the ball on the top of the tripod system is released by an acoustic command and pulls a line to the surface.
The long-term observations will provide a description of currents and document near-bottom processes, and will be used for development and verification of a coupled 3-D numerical hydrodynamic and sediment-transport model.

Instrumented tripods (Figure 2, left) that rest on the sea floor and measure near bottom-current, temperature, salinity, pressure, and turbidity, as well as current throughout the water column (using Acoustic Doppler Current Profilers), were deployed at each site. Tripods at sites A, B, and D were also equipped with a time-lapse bottom camera, and Acoustic Backscatter Sensors (ABS) that measure profiles of sediment concentration in the bottom 1 m using high-frequency sound. The tripod at Site A was further equipped with a time-series sediment sampler, a laser-particle sizing system, and a laser-particle sizer/settling tube. A large lighted surface buoy was also deployed to mark each site for fishermen.

Loading the R/V Oceanus
Figure 3. Tripods and surface buoys loaded on R/V Oceanus for deployment in the New York Bight and Hudson Shelf Valley. Three sizes of tripod-mounted bottom-instrument systems were used depending on the quantity and type of instruments to be deployed.
In addition to deploying the bottom tripod systems, video surveys were conducted at each site to characterize the sea floor, and conductivity-temperature-depth profiles were obtained along the valley axis and parallel to the valley to the east and west to map the water structure in and adjacent to the valley.

The cruise was delayed two days due to weather and a malfunctioning bow thruster that was repaired prior to sailing. Warm and calm weather on December 4 and 5 changed this potentially cold, rough, and challenging winter cruise into just a challenging cruise. Oceanus (Figure 3, right) proved an outstanding platform for the tasks at hand. Brad Butman, Courtney Harris, and Peter Traykovski (Woods Hole Oceanographic Institution) are co-principal investigators leading this field experiment. Cruise participants included Brad, Courtney, and Peter, along with Dann Blackwood, Jon Borden, Jessica Cote, Jane Denny, Ben Gutierrez, Jason Hyatt, Marinna Martini, Ellen Mecray, Marilyn ten Brink, Rick Rendigs, and Dave Walsh.

Rick Rendigs fills sediment trap
Rick Rendigs fills sediment trap with solution to preserve the sample just prior to deployment.
Thanks and congratulations to Marinna, Jon, and Jessica for preparing a large number of complex instrument systems, to Dann for mobilizing and tirelessly operating the bottom video system, to Rick for preparing the suspended-sampler, to Ellen for organizing the grab sampling operation, and to Dave, Jason, and Ben for assisting with instrument systems. Thanks to everyone who made this cruise a success. The array will be recovered in April.

For more information on USGS projects addressing contaminants and seafloor characterization in the New York Bight, see the USGS Fact Sheets Mapping the Seafloor of the New York Bight and Contaminants and Marine Geology in the New York Bight.


Related Web Sites
Mapping the Seafloor of the New York Bight
U.S. Geological Survey (USGS) Fact Sheet
Contaminants and Marine Geology in the New York Bight
U.S. Geological Survey (USGS) Fact Sheet

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