6 August, 2002
Fleece is my friend! When out on deck this morning in the cold wind and rain, my layers of fleece (pants, jacket, neck warmer and hat) combined with all my other cold weather gear kept me relatively warm. The cold weather and the darker morning hours (remember that this area will experience 24 hour darkness beginning in late November) were a reminder that “summer” is definitely on the way out here in the Arctic Ocean. At 2 AM this morning, we were finishing our sampling at East Hannah Shoal station #1. For my students at home at Essex High School, be sure to note the symbol, EHS #1. At EHS 2 and 3, the only sampling that was done was with an XCTD or expendable CTD. Some of those who had gone to sleep after sampling water from the CTD bottles at EHS 1, were panicked when they awoke to find we were at EHS 4. They were convinced they had missed sampling two stations when they had actually only been for the XCTD. Let me explain what happened.
Mark Stephens and Dan Schuller were the ones deploying the XCTD. At those sites, this is the only equipment in use, and it takes only a short time to gather the temperature and salinity data from it. Mark is an assistant scientist at the University of Miami Rosenstiel School of Marine and Atmospheric Science, and Dan is a graduate student there. They are working with David Kadko who was on the spring SBI cruise with Mark. Their work involves more of the radioisotopes I’ve talked about before. You might remember Rick Nelson and Sandor Mulsow’s work with thorium-234 (journal for July 23), Jackie Grebmeier’s work with a series of radioisotopes in the sediments (journal for July 27). Mark and Dan are working with three isotopes of radium to trace the water that comes off the shelf and moves into the basin. They are parcticularly interested in eddies that form near the shore.
An eddy is somewhat like the water that goes down our drain. It’s a circular water current which, in this area, can have different types of water in the core (the inside) and in the outer ring (the outside). Depending on where the eddy was formed (i.e. on the shelf break or off the shelf break), it will have different radium levels in the core and in the outer ring. By analyzing the water for radium isotopes, they can distinguish which water is which. That is because the radium isotopes give each type of water a recognizable ‘fingerprint.” Radium is parcticularly noticeable in water that comes off the shelf. Thorium (remember Rick and Sandor) is found in the sediments on the shelf, and it decays to radium which dissolves in the water that travels over the shelf. Thus water moving over the shelf receives an “injection” of radium. As the water moves further out, it loses radium at a known rate because it of radioactive decay. By analyzing the amount of radium isotopes along our transect, Mark and Dan can calculate the rate of water movement off the shelf.
How do they do this? First they collect a LOT of water! Since radium is found in such small amounts, they must collect all the water from an entire CTD cast. On that special cast, six bottles will collect at one depth and six at another. At deep stations, they will collect from four depths. In addition, they always collect surface water. This is far too much water to be transported, so they filter it through a fiber that is coated with manganese, a substance that picks up the radium. These fibers are then passed through a counter on board for some of the radium isotopes and then transported back to the University of Miami where they will be analyzed for the other radium isotopes, the ones that last longer before breaking down.
Mark and Dan are parcticularly interested in this East Hannah Shoal transect because this is an area where both CTD and radium data indicated a possible eddy during the spring cruise. The data wasn’t completely clear and other data even suggest a different conclusion. That’s why they are sampling all along the transect, and that’s why they are putting out many XCTDs along the way. If you look in the picture below, you will see that Mark looks like he is firing a gun off the stern. He’s actually firing the XCTD into the water. The XCTD is connected to the gun and the gun is connected to a computer which reads temperature and salinity data from it. Once they have their information, the XCTD is cut loose. The entire process is a great example of science in action – test and re-test until you collect enough data and eliminate enough variables to reach a conclusion. The spring cruise produced other data as well. They found out that their radium results were supported by the work of other scientists on board the spring cruise. Evidence suggests that shelf water moves offshore in a 50 – 150 meter depth range.
Talking to Mark and Dan I was struck once again by the wonderful interdisciplinary nature of science, parcticularly on this cruise. For example, other scientists are interested in the radium and XCTD data so that they can assign a rate to the various biological and chemical processes they are observing. Thus the sharing of data is strongly encouraged and shared through a ship computer network. Plots created while underway are also hung up in the main lab. All this data will be analyzed, combined and re-analyzed in order to get a better picture of what is happening to carbon as it moves through the Arctic Ocean. It’s a long and involved process that leads to conclusions that are strongly supported by the data.
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