Caitlin Thompson: Zooplankton, Ocean Currents, and Wave Gliders, August 7, 2011

The Shimada conducts research around the clock, with crew members working twelve-hour shifts. So far, I have worked with the acoustics team studying hake during the day, when the hake school together and are easy to fish. Last night I branched out, staying up with Steve Pierce, the oceanographer studying ocean currents, Jennifer Fisher, a faculty assistant at Oregon State University (OSU) who is studying zooplankton, and her intern, Angie Johnson, a graduate student at OSU. All the different research on this trip complements each other, and I learned more about the acoustic team’s work from the night people.

The map at right shows the transects we follow and the stations that the night team takes samples, which Steve chooses. Just like the acoustics team, he only chooses sites on the east-west transects. The night team usually works one transect ahead of the day team, and must have the ship back where they started by sun-up. Steve is mapping small currents because, he says, surprisingly little is known about ocean currents, even though they have a tremendous impact on ocean life.

He is especially interested in the polar undercurrent that brings nutrient-rich water from the south up along the west coast. A small current, it is nonetheless important because of the nutrients it carries, which come to the surface through upwelling. He uses an acoustic device, the Acoustic Doppler Current Profile (ADCP), to find the velocity of the water at various depths. The data from the ADCP is skewed by many factors, especially the velocity of the ship. Later, Steve will use trigonometry to calculate the true velocity. He also uses the Conductivity, Temperature, Depth (CTD) meter, lowered into the water at every station during the night. The CTD gives much more information than its name would suggest, including salinity, density, and oxygen. It is deployed with a high-speed camera and holds bottles to capture water samples. I was impressed by the amount of work – and math! – that Steve does in between cruises. When he has down time on this cruise, he told me, he is calculating work from two years ago.

Jennifer and Angie are studying plankton, the organisms at the very bottom of the food web. Immediately, I recognized euphausiids, or krill, from the contents of hake stomachs. Actually I recognized their small black eyes, which always reminded me of poppy seeds when I saw them in hake stomachs. Jennifer is conducting this work through her group Northwest Fisheries Science Center, which, as she describes it, gives her a wonderful freedom to research different projects related to ocean conditions, especially salmon returns. In this project, they measuring phytoplankton, tiny, photosynthetic organisms, by measuring chlorophyll and nutrients. They are also looking at zooplankton, like euphausiids, salps, and crab larvae, which we examined other the microscope. To help the acoustics team refine their ability to use sonar to identify zooplankton, Jennifer and Angie record certain species. The acoustics team will match up the acoustics data that is continuously generated on this ship with the samples.

Today, the second catch of the day was aborted because of whales too close to the ship. However, the NOAA’s Pacific Marine Environmental Laboratory (PMEL), had asked the Shimada to investigate its waveglider. A waveglider is type of robot called an autonomous underwater vehicle (AUV). Programmed to travel and record data, it does not need an operator. The PMEL folks were concerned, however, that its AUV might have a problem.The bridge set the course for the AUV, described as a yellow surfboard, and I headed up to the flying deck, the highest deck and an ideal spot for observation, to watch for it. Immediately we saw a humpback whale, just starboard of the ship, spout and roll through the water, its tail raised in the air. Soon the AUV appeared. We saw nothing wrong with it but communicated our observations, photographs, and video tape of it to PMEL. The PMEL’s system of wavegliders monitor carbon dioxide levels and use the kinetic energy of ocean waves to recharge the batteries. The acoustics team hopes to get their own waveglider next year to collect acoustic data in between transects. As I was peering  over the edge of the boat, examining the surfboard-like robot below, I heard a loud splash. A bout ten  Dall’s porpoises were playing around the bow of our boat, rippling in and out of the water. Dall’s porpoises are tremendously playful creatures, and will often play around ships. But our ship was barely moving, and the porpoises soon lost interest and swam away.