How do we know where to take a sediment core?

Cleverson Silva, our resident geophysics expert, keeps watch over the Seabeam and Chirp systems

5  March, 2010

It’s another slow day of surveying on the RV Knorr, but that doesn’t mean that we’re not accomplishing anything.  As the ship moves along a preplanned survey track, it is continuously collecting bathymetric data that can show us what the seafloor looks like.  High resolution mapping of this area is one of the objectives of this cruise.  The main objective, however, is to find a sediment sequence that can give us a continuous, undisturbed paleoclimate record of the past 30, 000-60, 0000 years.

In order to find an ideal location that is likely to have such a sedimentary record, we use the Seabeam and Chirp systems to collect information about the geometry of the surface and sub-surface sediments.  We are looking for a site with flat, horizontal deposition that is not subject to slumping or faulting, or any sedimentary process that would disturb sediments once they have been deposited.

Bathymetric map of seafloor while "mowing the lawn", or making a zig-zag ship track

The Sea Beam system is a multibeam echo sounder that produces high resolution bathymetric contour charts of swaths the seafloor, like the one seen here from one of our first surveys. The swaths of map track the path of the ship.

Bottom profile as recorded by the SeaBeam system

Sediment Profile in 1,175 meters water depth

The Sea Beam system also produces gray-scale swath maps (side scan sonar maps) of the seafloor terrain that can help us determine the bottom roughness and the nature of the bottom sediments.

Finally, the Chirp system is a single-channel, high frequency seismic system. It collects information about the sub-bottom sedimentary sequence. The output is in the form of a cross section of the sediments below the seafloor, showing bottom topography and the large-scale internal structure of the strata.

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