On Wednesday we sent the CTD down to 6000 meters to sample the second deepest location in the Atlantic Ocean. We had arrived at the South Sandwich Trench, just 60 miles east of the South Sandwich Island Chain. Along with the sensors and sampling bottles on the CTD we included two mesh bags filled with a collection of Styrofoam objects. Whitney had arranged with Katie Harris (Colby ’08) for her students at the Epiphany School to send him decorated Styrofoam cups for the trip to the bottom. On the ship the “big kids” didn’t want to be left out of the fun, and soon all manner of expanded polystyrene was being cut, shaped, and decorated to create Great Belt memorabilia. The photographs show several before and after shots of the polystyrene objects. The objects shrink because Styrofoam is made from closed-cell, polystyrene beads that are 10% polymer and 90% air. At pressure the cells crush, expelling the air, and forming miniature polystyrene objects.
It was fascinating to watch the depth sounder display depths of only a few hundred meters near the South Sandwich Islands and then plunge to 7400 meters just 60 miles east of the islands. We had traveled over a classic oceanic trench. The South Sandwich Islands are being formed by active volcanism driven by plate tectonics. At the deep, South Sandwich Trench the South American Plate is being subducted below the South Sandwich Plate at a rate of 4 cm/year. The subduction drives the
ocean plate downward creating the ocean trench. Because tip of the subducted plate is pushed into the hot Asthenoshere, the oceanic plate melts at depth creating the magma that is forming the South Sandwich Island chain. Mt Belinda on Montegu Island has been persistently erupting since 2001. The South Sandwich Islands are still growing! Unfortunately, as we sailed through the island arc all we could see were the clouds forming over what we imagined were beautiful, glacier-covered mountains.