The MBIWE98 was carried out from
August 3 to September 2, 1998 and consisted of a moored array experiment and hydrographic surveys.
Sediment sampling and bottom photography was carried out in July 1999.
The moored array consisted of instrumented moorings deployed at 3 stations spaced across Massachusetts Bay
aligned along 55-245° T (fig. 1,
fig. 2, table 1). Site A, located about 5
from the western edge of Stellwagen Bank at 95 m water depth, was
placed to provide a description of the waves near the generation region. Site A was instrumented with
temperature and conductivity sensors at 10, 20, 30, 40 and 50 m deployed
on a surface mooring. Site B was located approximately
12 km from the western edge of Stellwagen Bank in the center of
Stellwagen Basin at 85 m water depth. Site B was heavily instrumented
from 10 m from the surface to 1 m above bottom
with an array of temperature, conductivity, current, light transmission and pressure instruments deployed
on a surface mooring, 2 subsurface moorings, and a bottom tripod
(fig. 3). One of the subsurface moorings at the
central site (B) was
a horizontal mooring to provide closely spaced measurements in both the horizontal and vertical. Site C
was located at 50 m water depth, just offshore of the transition from fine
to coarse-grained sediments. Measurements at Site C included temperature, conductivity, light transmission,
pressure, and current from sensors deployed on a surface and subsurface mooring and on a bottom tripod
(fig. 4). Time-series photographs of the sea floor
were also made at Site C from a camera mounted on the bottom tripod. In order to resolve the high-frequency
motions caused by the internal waves, instruments in the array sampled every 15 - 120 s,
depending on instrument type (table 1 (in .xls format) and
The horizontal mooring (fig. 5,
fig. 6) deployed at site B is a new technology, under development by
WHOI in cooperation with ONR, designed to provide closely spaced (order 20 m)
measurements in both the horizontal and vertical in the coastal ocean (Grosenbaugh and others, 2002).
The mooring consisted of a 160 m long horizontal wire tensioned between two 48" subsurface floats at 20 m below the surface. The floats are kept in position by anchors attached to each float and set at approximately a 45° angle. Along the horizontal wire, 5 vertical wires spaced 30 m apart supported temperature and conductivity sensors 5 m apart in the vertical from 20 to 45 m water depth. In addition, three current meters were mounted on the horizontal wire, one at the center, and one at each end 55 m from the central meter.
Moorings were also in place during MBIWE
at two additional sites in western Massachusetts Bay (fig. 1) as part of a long-term monitoring
program carried out by the USGS in cooperation with the Massachusetts Water Resources Authority
(Butman and others, 2004a). Instrumentation at site LT-A included an ADCP, subsurface mooring and a bottom tripod with current, temperature, conductivity, pressure, and light transmission. Instrumentation at site LT-B included an ADCP. The sampling rate of the near-bottom instruments at LT-A was 3.75 minutes;
the ADCP's at LT-A and LT-B sampled for 5 minutes
every 15 minutes.
Three hydrographic cruises were conducted during the moored array experiment to map the temperature,
salinity, and suspended-sediment fields across Massachusetts Bay. Sections of temperature and salinity
were made along a transect through the moorings (fig. 7)
on August 6 and August 20, 1998 on the FV Christopher Andrew,
and sections of temperature, salinity, and light transmission were made between August 31 and Sept. 2, 1998,
during mooring recovery, on the RV Argo Maine. Temperature and
salinity on the RV Argo Maine were measured with a
SeaBird 9/11CTD and light transmission with a 0.25 m path length Chelsea AlphaTrackA transmissometer.
The sea floor of Massachusetts Bay has been mapped using a multibeam sea floor mapping system
providing detailed bathymetry and backscatter intensity in the vicinity of the moorings
(Valentine and others 2003a, b, c, Butman and others, 2004b).
Bottom photographs, videos and sediment samples of the sea floor were obtained along the
MBIWE transect in July 1999 on the
FV Isabel S. These observations were made using the SeaBed
Observation and Sampling System (SEABOSS) (Valentine and others (2000), Blackwood and Parolski (2002)).
SEABOSS is equipped with two video cameras, a still camera, a pressure-depth sensor, and a modified
Van Veen sediment grab sampler. At each station, the SEABOSS was lowered to a target elevation
about 76 centimeters (30 inches) above the sea floor and the ship allowed to slowly drift,
typically for a few hundred meters. As the ship drifted, typically at a knot or less, bottom video
was recorded continuously and individual photographs of the sea floor were triggered remotely
based on the video available in real time at the surface. Typically 5-20 still photographs were
obtained at each station. At 76 centimeters above the bottom, the still photographs show a
76 x 51 centimeter area of the sea floor. At most stations, a single sample of the sediment was
obtained using the Van Veen sampler, typically at the end of the transect. At some locations,
cobbles and boulders on the sea floor made sampling impossible. The upper 2
cm of the sediment were skimmed from the grab sample and analyzed
for texture using the methods outlined in Poppe and others (2000). Photographs from these and
other stations in western Massachusetts Bay may be found in Gutierrez and others (2001).
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