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THE MAINE EVENT: FALL 2003 Predation by Gelatinous Zooplankton in the Gulf of Maine MISSION DISPATCH 6 • Monday, September 15, 2003 Location: Oceanographer Canyon (40° 17'N, 68° 07'W) Dispatch by Harry Breidahl - Marine Education Society of Australasia [MESA] Our second day at Oceanographer Canyon and expectations of productive dives are high. At present the seas are calm and the air is warm but the weather forecast does not sound promising. Hurricane Isabel is approaching from the southeast and we anticipate that our time at this location may soon be curtailed. The submersible dove at 1 pm with scientist Chuck Jacoby and sub pilot Dan Boggess in the acrylic sphere and graduate student Aino Hosia joined by sub crew Jim Pierce in the aft aluminum chamber. As with the sub dive last night, dive 3445 for JSL II reached 2,700 feet (820 meters) in depth. The results were equally valuable, providing plenty of living animals for the experiments on board. 
The next dive is the one that I have been waiting for. It is my turn to squeeze into the small aft chamber and travel to the bottom of Oceanographer Canyon. This dive was special for me because I had brought a collection of styrofoam cups that Australian school children had decorated. Taking foam cups down on the outside of a submersible is a simple, but effective way of demonstrating how pressure increases with depth. There are many ways to measure pressure but the most simple way is to say the pressure at sea level is 1 atmosphere (1 atmosphere = 1 kg/sq cm or 14 lbs/sq inch). For every 10 meters (33 feet) a sub descends, 1 atmosphere of pressure is added by the mass of water above it. At 10 m the pressure is 2 atmospheres, at 20 m it is 3 atmospheres and so on as we travel down. By 800 m the pressure is 81 atmospheres - that is 80 times greater that the pressure at the surface or 81 kg/sq cm. 
This increase in pressure is why submersibles, such as
JOHNSON SEA-LINK II (JSL) , need to be so strong. The occupants inside the
two chambers are safe because the walls are thick enough to resist the incredible pressure. However, anything on the outside
of these two chambers is subject to the increase of pressure with depth. With our cups, the pressure is enough to crush the
air bubbles inside the foam. This action shrinks the cups to tiny versions (roughly 4 times smaller) of the original cups.
JSL II dive 3446 was a great thrill for me. I dove in the other JOHNSON-SEA-LINK (JSL I) last year but managed to forget how small the aft chamber really is. No matter how cramped the chamber, the whole experience of plunging to 800 m below the waves into a dark, cold, hyperbaric world is an experience never to be forgotten. There is so much life down there and most of it is rarely seen and quite bizarre. 
As soon as we returned to the surface and transported the midwater animal cargo (another collection of siphonophores and other
gelatinous creatures called ctenophores and medusae) into the wet lab we checked the condition of the cups. The colorful patterns
that many of the children back home in Australia had written or drawn (in waterproof ink of course) on the cups had shrank along with
the cups themselves. The colored sections seemed to shrink less and create all manner of beautiful patterns on the cups. The plan is for me to take
the cups back to Australia and send them to the children who created them.
By the end of the day it became clear we needed to move closer to shore. The forecast of strong winds and high waves means we will not be able to launch the submersible or the traditional sampler gear (nets and bottles). So, we have to leave this canyon site as soon as we secure (tie-down) all the equipment. The current plan is to dive for a day at Wilkinson Basin and then steam into the safe harbor at Gloucester, Massachusetts. Fun facts for the day • The deeper the ocean the greater the pressure. At the surface air pressure is 14 lbs/sq inch that = 1 kg/sq cm = 1 atmosphere. • For every 33 feet (10 meters) add one kg of water or 1 atmosphere so at : > Surface = 1 atmosphere > 10 m = 2 atmospheres > 20 m = 3 atmospheres > 50 m = 6 atmospheres > 100 m = 11 atmospheres > 800 m = 81 atmospheres > 1000 m = 101 atmospheres   |  |
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