As we enter our second day of CTD (conductivity, temperature and depth) measurements, here’s more on what we’re looking for and how we do it.
Dissolved oxygen is very important to animals and plants that live in the ocean. Fish, for example, are dependent on oxygen in the water the same as we are dependent on oxygen in the atmosphere. Too little oxygen (less than 1.4 mL/L) results in what is called a “hypoxic” situation, which can in turn result in fish kills, red tides and other problems.
Erik Quiroz, a Texas A&M University scientist who is studying dissolved oxygen aboard the Pisces, summarized the proper technique to obtain a water sample to test for dissolved oxygen.
“You attach a rubber tube to the opening on the Niskin bottle, and squeeze the air out,” he said. “I let the water flow slowly through the hose into a flask until it is about a third full, and then let the water flow faster, allowing the water to overflow the flask by about three times its volume. All these steps help prevent atmospheric oxygen from entering the water sample.” The next step is to add manganous chloride, sodium hydroxide and sodium iodide to stabilize the oxygen in the flask to further prevent contamination from the atmosphere.
We’re also looking for methane during this project because large quantities of it were released along with the oil when the Deepwater Horizon exploded and sank. If scientists find a large concentration of methane, it’s likely there is also oil in the area.
Molly Redmond, a researcher from the University of California Santa Barbara, demonstrated the technique for sampling methane.
“We use large syringes with stop-cocks to collect the water from the Niskin bottle so we don’t take in any atmospheric air, which would contaminate the sample,” she said. “You fill up the syringe, and then tap it so that any bubbles rise to the top, and then squirt them out. Sometimes you have to repeat this process a few times in order to get rid of all the bubbles.”
Later on, we’ll introduce you to some more of our scientists.