NURP Project Summary


	In Situ Sampling of Outcropping Glacial and Glaciomarine Sediments and Sedimentary Bedforms in the Gulf of Maine (Year 1 of 1) Project Number: NAGL-95-01 Principle Investigators: Belknap, D. F., D. Schnitker, T. S. Bacchus, and R. Stea Region(s): Gulf of Maine

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Project Objectives:

There are two main goals to the proposed in situ submersible studies. The first is to observe and sample the deglacial sequence in outcrops around Georges Basin Tower and Wright Swell. We specifically seek to find stratification that is obvious on seismic profiles, but subtle in 7 cm diameter piston cores, and thus find opportunities for specific in situ sampling. We hope to sample steep walls by push core, and obtain materials for grain-size and micropaleontological analyses, as well as dating. The second goal is to continue to examine current-formed sand bedforms on the northern flanks of Georges Bank, to measure orientations and sizes, and to sample sediments for grain-size analysis. These data will be used to model flow conditions required for formation, and to compare to data from our 1990 and 1994 cruises.

Summary of Research:

Four sites were surveyed with seismic reflection profiling, sidescan sonar (in 1994), and/or fathometer to locate specific dive sites. Two dives were completed in the Johnson Sea Link I in each general area. Each dive consisted of traverses using video and still camera photography, as well as sampling with suction sampler, box cores, punch cores, and collection of individual rock samples. A CTD sampled salinity and temperature continuously during the dives. Sites include: 1) a bedrock high in the center of Georges Basin, with a cap of glacial and glaciomarine sediments, 2) sand wave fields on the northern flank of Georges Bank, 3) an outcropping of till, glaciomarine, and post-glacial sediments in Lindenkohl Basin on the flank of Wrights Swell, and 4) an outcrop of galciomarine sediments on Wildcat Knoll.

Results:

Submersible dives were conducted in the Johnson Sea Link I, a free-ranging submersible with one pilot, a rear-compartment crew member, and two scientists, capable of diving to 1000m. The Johnson Sea Link I is equipped with a low-light high-resolution color video system, exterior still photopgraphy, and remote sampling capability. More than 300 still photographs and 30 hours of videotapes archive the observations from 8 dives. Navigation was by ORE trackpoint navigation, a sonar interrogration technique, tied to the ships GPS navigation. Dives were conducted in excellent conditions of surface weather and underwater visibility. Summary notes, videotapes, and still photographs are archived at the University of Maine. Four categories of samples were taken using the hydraulic arm on the Johnson Sea Link I: rocks, push cores, suction samples, and box cores. Push cores, box cores, and rock samples were collected in sealed buckets on the carrousel system. Sediments were given preliminary descriptions when brought on ship, as noted in the cruise logbook., and then logged in detail at the UM sedimentology laboratory in August of 1995. More complete analysis of the sediment samples and cores has not yet been completed. Individual rocks up to 30 cm intermediate diameter were recovered at seven locations. Rocks have been photographed in original condition, and then cut with a diamond saw for prepatation of thin sections. Rock samples will be shared with Ralph Stea for a regional petrologic and geochemical analysis of glacial erratics. A Seabird conductivity, temperature and depth recorder was deployed aboard the Johnson Sea Link I on each dive. The thermal inertia of the submersible is likely to give results different from a freely deployed CTD, but these data my serve a preliminary guides for further research, and at a minimum identify several descrete water masses.

Benefits:

The deglaciation of the Gulf of Maine has left a variety of sediment types that reflect their glacial and glacial-marine environments of deposition. A primary reason for in situ observations and sampling is to calibrate and justify interpretations of remote sensing data. (In turn, the geophysical data is important for large-scale and long-distance mapping and correlation of environments.) In particular, we have observed stratification in glaciomarine sediments on a scale larger than available in cores. Second, our seismic data show a wedge of sediment at the toe of Georges Bank, with sand waves now shown to be oriented downslope. This reflects an important, previously unrecognized mechanism of sediment redistribution in the area, and may be the result of a previously undescribed physical oceanographic feature in the Gulf of Maine. In addition to these primary geolocial questions, redistribution of sediments by active currents may have a significant impact on benthic biological communities. Also, pollutants and dredge-spoil material may eventually be carried out of the coastal zone into the deeper basins of the Gulf of Maine. The general counterclockwise gyres of the deepwater flow in Gulf of Maine basins could carry pollutants from Massachussetts Bay, for example , to Wilkinson Basin and perhaps farther eastward. We are examining current-generated bedforms off Georges Bank and the degree of current alteration to the Georges Basin Tower as a measure of effectiveness of sediment transport in the southeastern Gulf of Maine. Last but not least, other beneficial aspects of this cruise include the international cooperation with Canadian scientists. Student education and field experience was provided to graduate and undergaduate students of three institiutions. This multifaceted approach benefited both scientific research and eduation.