Right now it is only day three of the cruise and it is already more than I could ever have expected. I am working on the sediment team, which are the last samples collected at each station. The sediment is collected in a box corer (picture to come soon!) and is designed to bring up an undisturbed sediment water interface. What fascinates me about the box corer is it's use of gravity to collect the samples. The corer is a rectangular box, with two large jaw-like structures attached to the bottom. When the corer is sent down to the ocean floor the tightness of the line and the weight of the corer holds open the jaws; when the corer hits bottom and the line goes slack, a pin is released snapping together the jaws and scooping up the sediment. At the same time a piece slides over the top of the box, trapping the water above the sediment. Now, inside the box is a little piece of the ocean floor; about 10in of sediment covered by 8in of water. The interesting part is that the jaws snap closed so fast, that the line between the water and sediment is undisturbed. The box corer allows us to reach down and pick up a little piece of the ocean floor and with these samples we can study how mercury is released from this benthic environment.
To collect from the box corer a plastic cylinder with two open ends is gently pushed down into the sediment. Placing a stopper in the top end of the cylinder creates a vacuum and the tube can be pulled out with sediment and water intact.
The purpose of my experiment is to study how mercury is released from floor of the ocean. Right now I have three cores from station 2 along with 10L of sea water collected from 5 meters above the ocean floor. The cores are placed in an incubation chamber located on the upper deck of the ship. The chamber is black to keep the inside dark and chilled to around 8 degrees Celsius so that the sediment cores are in an environment similar to ocean floor. Inside the chamber, the sediment cores have special caps with a magnetic stirring bar to create a gentle movement in the water, that would be present in natural conditions. Every 8, 12, and 18 hours the water in the chamber is collected and frozen for analysis back in the lab. A time 0 sample is also collected to measure the initial content of mercury in the sample, before introduction to the sediment chamber. New pore water is placed in the chamber to restart the experiment until the next time period. By doing this I will be able to see first of all how much mercury is being released from the sediments, and I will also be able to see if the release is gradual or more sudden.
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