By the time I started my PhD program, I had decided that field work and chemistry labs weren’t for me. I was content to sit at home in Colorado and study the ocean from afar with my computer. My typical day at home is spent analyzing global-scale data from an Earth system model and satellite remote sensing observations. One morning last fall, I saw an email advertising student positions on the IO9N GO-SHIP cruise. It suddenly hit me—I’m just over a year away from defending my PhD in Atmospheric and Oceanic Sciences, yet there is a whole world of oceanography that I know absolutely nothing about: field observations. I realized that this might be my last opportunity to participate in a research cruise, at least as a graduate student. So, I surprised myself and applied to participate in the cruise as a CTD watchstander! I was thrilled to have the opportunity to dive into the world of observational oceanography.
Photo of Genevieve standing next to the CTD rosette. Photo by Roxanne Mina.
Photo of the CTD instrument resting on the deck. Photo by Allen Smith.
As a watchstander, I help operate the CTD casts that are the beating heart of our cruise … deploy, recover, sample, deploy. The CTD instrument measures conductivity (salinity), temperature, depth (pressure). It is secured on a metal frame, along with 36 10-liter bottles arranged in a ring—the rosette. Our first task is to prepare the rosette for sampling by securing the top and bottom parts of each bottle into the open position. We then return to the computer lab, where the CTD control box and real-time data monitoring screens are located. Crew members on deck deploy the rosette, which is connected to a wire and lowered into the water. It can take nearly 3 hours to reach our target depth—many of our stations are over 5 km deep! On the way down, the CTD is continuously measuring, providing us with vertical profiles from the surface all the way to the seafloor. One of the most important parts of our job as a watchstander is to make sure that the CTD does not hit the bottom of the ocean. As it is lowered, we closely watch the altimeter, which tells us how far away the instrument is from the bottom. Once we reach 10 meters above the seafloor, we radio the winch operator to stop lowering. Then, we start the process of collecting water samples on the way up. We tell the winch operator the depth that we would like to sample, they bring the CTD up to that depth, then we press a button on the computer to close the bottle. Since we have 36 bottles, we sample at 36 depths throughout the water column.
View of the computer lab, where CTD watchstanders see real-time data come in. Photo by Genevieve Clow.
Once the CTD is back on board, lab members hurry out to the deck with empty bottles to retrieve water samples. We use the samples to measure CFCs (Chlorofluorocarbons), dissolved inorganic carbon, dissolved organic matter, pH (acidity), carbon isotopes, alkalinity, nutrients, salts, several biological variables, and other tracers. As CTD watchstanders, part of our job is to assist in the sampling process. While everyone is sampling, the boat transits to the next location, which is approximately 30 miles away. We fill our bottles quickly so that the labs on board can start analyzing the samples before we have a new batch. Once we have collected all of the samples, it’s time to prepare the rosette for the next station and do it all over again. And again, and again… 106 times!
Scientists fill their sampling bottles at the rosette. Photo by Allen Smith.
Well, at least that’s the plan. But I’ve learned that things never go exactly as planned—and that’s to be expected. Issues inevitably arise, but we’re prepared to face them. When something doesn’t work, people troubleshoot the issue, parts are replaced, tests are performed, and we continue on. We’ve already been delayed by multiple instrument failures. On top of that, we’ve experienced adverse weather due to a tropical cyclone that was passing by. When the swells got too high, we were stuck on weather hold until conditions improved. Now that the storm has passed, we’re back to our normal rhythm.
We’re just over a week in, and so far, my main takeaway is just how challenging it is to measure the ocean. Research cruises require so much coordination, teamwork, and perseverance. It’s amazing how much time and effort goes into collecting measurements for one tiny slice of the ocean: something I took for granted as a computer modeler. Throughout my academic studies, my scientific focus has narrowed over time. It’s been nice to take a step back and broaden my perspective as an oceanographer.
~Genevieve Clow
About the Author—Genevieve Clow is a PhD candidate at the University of Colorado Boulder in the Department of Atmospheric and Oceanic Sciences. Job title for the expedition: CTD Watchstander. Duties include: operating the CTD and rosette bottle system both on deck and in the lab, drawing and documenting water samples.