NOAA Teacher at Sea
Christine Hedge
Onboard USCGC Healy
August 7 – September 16, 2009
Mission: U.S.-Canada 2009 Arctic Seafloor Continental Shelf Survey
Location: Chukchi Sea, north of the Arctic circle
Date: August 10, 2009
Science and Technology Log
This trip is all about data collection. In addition to our main seafloor mapping mission, each day there are buoys, sensors, or weather balloons deployed each collecting important data to help us understand the Arctic environment. This ocean is a harsh place. The objects that are placed underwater to collect data (like the HARP instruments that were retrieved earlier this week) need to be able to withstand cold, salt, pressure, and for those on the surface, wind and waves. Designing such a device to work for long periods of time in the Arctic must take great engineering skills.
The pressure of the deep ocean is an amazing force. If you have ever lost your goggles in the deep end of a pool – you know that water pressure increases with depth. Water is much heavier than air (about 1000 times heavier). Any instrument sent to the bottom of the Arctic Ocean is under a column of water that literally squeezes it with massive weight. In fact, the weight of just a 10 meter thick slice of ocean is equivalent to the weight of the entire atmosphere. Of course there is a scientific name for this increase of pressure due to the weight of the water above you. It is called hydrostatic pressure.
A simple experiment to illustrate the type of forces these scientific instruments endure involves Styrofoam cups! In fact, yesterday folks were encouraged to decorate a Styrofoam cup. The cups were gathered into a mesh bag and sent down 3800 meters attached to a device, which measures the conductivity, temperature, and depth of the water as it descends (a CTD).
Styrofoam can be thought of as plastic netting filled with air. This is why it is such a good insulator and so light. If we squeeze it with our hands, we can make the netting tighter and the Styrofoam becomes tight balls of plastic. If we lower the Styrofoam cups to great depths within the ocean – just think of the huge amount of hydrostatic pressure they are under!!!
The cups went to a depth of 3800 meters and shrank from about 4 inches to less than 2 inches! The weight of the water above them squeezed the air from the Styrofoam and gave us teeny cups – the shape didn’t change much – just the size. When engineers build instruments to study the ocean – such forces must be considered carefully.
Something to Think About
Besides diving into a swimming pool, can you think of another place in your world where pressure changes impact the environment?
Personal Log
I’m getting used to the life on board a ship. The crew is very helpful. They point me in the right direction when I get lost (which happens a lot) and help me to find basic comforts such as ice, the gym, and the laundry. I am amazed at how many doors I have to open and close to get from one place to another. The doors, designed to withstand water and fire, are heavy and take some upper body strength when we are in windy conditions.
They can also be very noisy and since someone is always sleeping on a ship that operates 24/7 we need to be considerate and move through them quietly. The further north we go the calmer the water gets. It is a real treat to walk out on deck and see the water smooth as glass, the blue and white ice chunks, and nothing but sky in front of us.
