27 May 2004

Joined: 23 Mar 2004 Posts: 87

May 27, 2004 Thursday
6:00 PM Alaska time

Around 2 AM this morning I was notified that we were going to use a rock dredge to obtain encrusting algal and animal species from the rocks on the seafloor. The rock dredge weighs over 400 pounds. It has a metal framework and a heavy chain basket that reminds me of an enlarged, medieval chain mail dress. In theory, the rock dredge’s metal framework is dragged along the bottom of the seafloor while the chain basket follows behind collecting rock specimens. The openings in the chain are rather large so that fine particles and small pebbles can pass through but cobble-sized rocks cannot.

At approximately 2:30 AM the dredge was hooked to a winch wire and lowered into the Chukchi Sea until it reached the seafloor. Roughly 650 meters of wire was paid out over the next half hour as the ship drifted away from the dredge. When the winch pulled in the wire, the dredge was pulled along the seafloor toward us.

The collected sample was quite different than we expected. Instead of cobble-sized rocks encrusted with animals and coralline algae, we collected a basketful of clay-like mud sediments. Never allowing an opportunity to escape, we sifted through the mud for benthic animals. We found clams, polychaete worms, priapulids, brittle stars, a snail and a sponge.

It took quite a while to clean the deck after sampling. We used a push broom, a “snow” shovel and a water hose. After the clean-up Susan and Craig began identifying the collected specimens. We finished sampling and cleaning just after 5:30 AM.

Rock dredge being lowered into the Chukchi Sea at the East Hanna Shoals 0.5 station.

Surprise…a mud sample collected by the
“rock dredge”. Craig Aumack is using a low-pressure wash to separate the
mud from the organisms. Susan Schonberg is ready with a collection pan
to gather the animals as they become exposed in the sample. Susan and
Craig are both from University of Texas Marine Science Institute.

To see photographs taken by Steve Roberts of UCAR/JOSS, click here.