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Sediment Grab Sampling on the New Jersey Continental Margin

Dates: September 7 - September 13, 1998

PI's: John Goff, Hilary Olson, University of Texas Institute for Geophysics

Additional Participants: Laurie Schuur (UTIG Student), Jamie Austin (UTIG), Graham Moss (UTIG Post Doc), and Don Monteverde (NJGS employee and Rutgers student)

R/V Onrust Crew: Steve Cluett (Captain), Mark Wiggins

Funding Agency: Joint Oceanographic Institutions, Site Survey Augmentation Award

Read our article (brief) for the July, 1999 issue of the JOI Newsletter and about more recent exploits collecting CHIRP seismic reflection data in this same region. Hilary Olson's slide show documents how samples are collected onboard ship.

Background

The sediment grab sampling work conducted aboard the R/V Onrust (SUNY Stonybrook) this September was the first of a two-part field experiment on the New Jersey continental margin. The second part will consisted of CHIRP seismic reflection, conducted in June, 1999. The grab sampling work has several goals:

1. Provide geotechnical support for proposed jack-up drilling sites along the Mid-Atlantic Transect corridor, which are in water depths that are too shallow for operation of the R/V Joides Resolution.
2. Provide ground-truth information (primarily grain size analysis) for the backscatter intensity map produced earlier for the Office of Naval Research's STRATAFORM program.
3. Through grain size and foraminiferal analyses, investigate present-day sedimentary processes associated with bedforms on the Holocene transgressive sand sheet.

Location map for grab sampling work on New Jersey Margin. Contours, plotted at 5 m intervals, are derived from NOAA
compilation of available hydrographic data. Overlain image is the sidescan backscatter data from the ONR STRATAFORM
swath mapping experiment in 1996. Stars indicate proposed jack-up drilling sites. Yellow symbols indicate planned grab
site locations - over 300 grabs in all. Barnegat Inlet is at the upper left corner of Figure.

Close-up view of planned grab sample (yellow dots) locations in the vicinity of the proposed drill site at MAT2 (star).
Image is shaded bathymetry (illumination angle from NE). ~N-trending bedforms are ribbons, with relief generally <1 m.

Sidescan backscatter of same region shown above. Higher backscatter values (lighter shades) are on east-facing
(seaward-facing) ribbon slopes. If higher backscatter is indicative of greater grain sizes, this observation could
indicate that the ribbons are transverse-to-flow with predominantly west-directed (shoreward) currents in this region.

Field Work

Our original plan was to conduct the CHIRP seismic over one 2.5 day leg just prior to Labor Day weekend, and then grab sampling field work during two 2.5-day legs following Labor Day, transiting in and out of Barnegat Light, NJ. The CHIRP leg was postponed to October due to hurricane activity. The grab sampling also got off to a less than auspicious start - the first major cold front of the season pushed temperatures into the low 50's along the coast, with winds up to 25 kts and seas to 6' - difficult, if not impossible circumstances under which to conduct grab sampling on a small ship (the Onrust is 60' long). The winds subsided to reasonable conditions after 2.5 days of waiting. Fortunately, once on site the grab sampling went extremely efficiently - thanks to the tremendous crew aboard the Onrust, the hard work of the science party, and the ease of use of the van Veen grab sampler (generously loaned by the USGS, Woods Hole). Despite the late start, we collected all planned grab samples (more than 300), both primary and secondary sites, and finished more than a half day before planned. The samples have been transferred to UTIG where they await processing and analysis (washing, drying, sifting, grain size distribution analysis, and foraminifera analysis).

Photo Gallery - click on thumb nail to get full size photo and caption: