Setting Off to Explore the Depths
By Gwenn Hennon and Matthew Harke
For the past few days, we have been loading the gear and setting up our lab on the R/V Kilo Moana. We have to secure everything down to the benches to prevent equipment from falling and being damaged in rough seas.
Yesterday, we set sail at 8am, rounded the Island of O’ahu, and headed north into the blue waters of the North Pacific Subtropical Gyre. We are currently in transit, but this gives us time to test equipment and make sure everything is in order by the time we reach our first station. It also gives us time to help with the many shipboard operations. After a hearty breakfast of eggs, bacon, tater tots, and coffee, we had the opportunity to help deploy a “towfish” from a boom extending out 15 meters off the starboard side of the boat. Since this was the first deployment of its kind on this vessel, there were a lot of hands to help. Matt is the guy in the blue hard hat.
A towfish is a device which looks like a torpedo. The towfish is tethered to the boat and lowered into the water with the boom. It then “swims” through the water while the ship is under way, allowing us to take continuous samples. The team is trying to collect trace metal samples, and so they attached a trace metal-clean hose to the towfish to pump water as far from the ship as possible.
One difficulty with working on a large steel ship is that it “leaks” a lot of iron (as well as other metals) into the water. If you care about measuring iron levels in the water, you need to find a way to get away from the ship, and this method seems to do the trick. After a successful deployment and refueling at lunch, we also helped deploy and recover an underway CTD off the stern of the vessel. CTD stands for conductivity, temperature, and depth. This device allows us to profile the eddy as we transit across, giving us an in-depth look at the physical structure of the eddy. This will allow us to more accurately target water features when we stop to collect water later on. Each deployment lasts around 15 minutes and involves dropping the underway CTD off the back of the boat, letting it sink to 300 meters, reeling it in, resetting it, and then redeploying it. All of this is done while the ship is moving at about 8 knots. This will go on for the next day or so, as it takes a few days to traverse an eddy.