By Dr. Emma Wear, Postdoctoral Scholar, Flathead Lake Biological Station, University of Montana
June 9, 2018
One of the fun aspects of deep-sea oceanography is the chance to make shrunken Styrofoam cups. Many oceanographers have two or three of these pieces of art sitting around their offices as souvenirs of past cruises. We decorate Styrofoam cups with markers, attach them to the side of an instrument that we’re sending to the bottom of the ocean, and get them back several inches smaller than when they went overboard.
A decorated cup before and after it was sent down to 5,000 meters on a CTD cast on the abyssal plain, with a normal cup for scale. This cup shrunk from 13.5 centimeters tall to only 6.5 centimeters. Image courtesy of the DeepCCZ expedition. Download larger version (jpg, 1 MB).
These cups are meant to be educational as well as entertaining. We’re shrinking cups decorated by children to illustrate hydrostatic pressure. At the bottom of the deep sea, the weight of several thousand meters of overlying water exerts a great deal of pressure. On the abyssal plain at 5,000 meters where we’re sampling, the pressure is almost 500 times greater than the atmospheric pressure at sea level. This is the same increase in pressure with depth that SCUBA divers need to account for when planning their dives, but on a much larger scale.
It’s not just Styrofoam that feels this effect—our scientific equipment experiences the same hydrostatic pressure on the deep-sea floor. We can’t send down just any off-the-shelf thermometer or camera—we have to pay attention to how deep each instrument is designed to go. If an instrument is accidentally sent below its depth rating, it can implode. Our sensors and cameras are highly reinforced, typically in stainless steel or titanium housings, to protect against the effects of this extreme hydrostatic pressure. Even instruments that only spend a few minutes at depth, like the sensors on the CTD (conductivity, temperature, and depth) rosette that we use to collect water samples, are susceptible to pressure damage.
