A volunteer collects seawater from the deep on the Seward Line, Part 1 of 4
Editor’s note: Terry Johnson, Alaska Sea Grant Marine Advisory faculty member, spent a week aboard a research vessel in the Gulf of Alaska. He tells about the adventure in four parts.
Weather with 10–12 foot seas is suitable for working. Terry Johnson photo.
Monday, our third day at sea, I step out on deck shortly after 0700 to see the sun poking through the clouds on the southeast horizon. We’ve been working in 10-12 foot seas; the 108 foot, 400 ton Tiglax (pronounced “Tekla”) rolls enough that we on the scientific crew careen off the walls in the hallways if we don’t maintain a grip. I don’t get seasick, but shortage of sleep and the effort needed to stay upright as the boat lurches side to side contributes to a vague sense of unease.
The boat works round the clock so although I’m fortunate to have day shift, sleep is fitful as I wake to every roll, plunge and shudder of the steel hull, each change of engine speed and shift of transmissions, and the whine of the hydraulics. Decades of running my own boats makes me sensitive to every sound while at sea.
The multinet, ready for deployment. Terry Johnson photo.
We’re on the Seward Line, at this point about 150 nautical miles offshore. The line is a series of points, latitude and longitude, in an otherwise featureless ocean. The first is just a few miles outside Resurrection Bay, and the others, each separated from the next by 10 nautical miles, extend roughly south, across the continental shelf and slope.
At the 15th station the water is a thousand meters or almost two-thirds of a mile deep. We’re out for a week, on the Seward Line and at some stations in Prince William Sound and Resurrection Bay. Since we have a period of moderate fall weather we’re doing the open-ocean work first.
Scientists from the University of Alaska Fairbanks have been taking samples on the Seward Line for 21 years now, providing an important time series of data on ocean chemistry and biological productivity.
Our cruise leader is Russ Hopcroft, a plankton specialist at the University of Alaska Fairbanks College of Fisheries and Ocean Sciences. We are 13 in the scientific crew, about half PhD chemists and marine biologists and half techs, including graduate students and volunteers like myself. That’s in addition to the six professional vessel crew members.
The scientific crew has several objectives, mostly variations of taking water samples for chemical analysis back in a lab ashore, and collecting plankton specimens. To get these samples we use three devices that, separately, we send overboard.
The CalVET, up from the depths. Terry Johnson photo.
A CalVET is a four net plankton catching device that is lowered and retrieved by cable over the starboard side and samples the water column vertically. The multinet is a more sophisticated, electronically controlled device, also consisting of four nets that can be opened or closed remotely and is towed behind the boat. The multinet is towed only at night, near the surface where certain key zooplankton species come to feed during the hours of darkness.
The device with which I am most directly concerned is the CTD (conductivity-temperature-depth), a 500-pound stainless steel cage containing electronic control units and an array of 15 five-liter bottles that can be opened and closed remotely so that water samples can be captured at discrete predetermined depths. My main job is assisting Ana Aguilar Islas (also UAF CFOS) in meticulously taking water samples from each bottle and conveying them to small, correctly labeled and cataloged sample bottles and storing them in a freezer in the ship’s cargo hold.
— By Terry Johnson