Styrofoam cups (not onions) were attached to the multi-corer before deployment.
After recovery, USGS tech Valerie holds up the bag “full” of shrunken cups.

On many research cruises, the science party creates fun souvenirs out of styrofoam cups decorated with Sharpies and then sent to the bottom of the ocean. In this case, they traveled to a depth of about 1,200 meters in a porous bag (in this case senior cook Mark relocated onions to donate to the cause) zip-tied onto the frame of the multi-corer. Styrofoam is approximately 90% air, so sending it to the crushing depths (in this case literally) squeezes that air out of the polysterene beads, condensing the material. What came back more closely resembles shot glasses, though some are a bit deformed due to uneven compression. Many were decorated with drawings of the ship, sea creatures, and the lat long position where the cups were shrunk.

Shrunken cup with scale markings, alongside
an un-shrunken cup and measuring tape.

On this trip someone had the great idea to add a scale to their cup. The length of the cup from the bottom to the lip is 7.2cm, or 2.8 inches. When these came back from their trip on the multi-corer, it had shrunk to just over half of that. Had they been sent even deeper, they would continue to shrink. I have some from other trips that were attached to a CTD rosette frame and traveled to 6,000 meters, and they are closer to the size of a thimble. 

Dr. Tony Rathburn from CSU Bakersfield organized the event today, bringing cups decorated by his non-oceanography inclined colleagues at the land-locked university. It added an element of whimsy to an otherwise routine day of coring operations and, as far as I know, these are the first shrunken cups available as souvenirs from R/V Sally Ride!