|
Moorings Deployed in the Hudson Shelf Valley, Offshore New York
 |
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
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.
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 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.
|
 |
January 2000
in this issue:
cover story:
Hudson Valley Shelf
CMG/WRD Co-op
Marine Facility Hosts Science Journalists
Co-op Research Open House
GIS Day '99
GD Managers Visit St. Pete
WHFC Visitors
WHFC Arrivals
January Publications List
|
U. S. Department of the Interior | U.S. Geological Survey
