The 37 scientists aboard the Research Vessel Roger Revelle left Seattle, WA on September 18 with a plan—a guiding melody for their 67-day GEOTRACES study of ocean chemistry. A few days at sea and three tests of the scientific equipment later, Chief Scientist Greg Cutter and Co-chief Scientists Karen Casciotti and Phoebe Lam changed their tune.
The plan, four years in the making, was to begin at Station 1 off the coast of Alaska. The expedition, code-named GP15, would instead begin with the deep water Station 5—instruments lowering to depths of more than 15,000 feet instead of less than 300 feet on the Alaskan shelf.
“Station 1 is in shallow water, which is more stressful for everyone—nobody wants their gear bouncing off the seafloor,” said Cutter of Old Dominion University in Norfolk, Virginia. A veteran of countless oceanographic expeditions, Cutter helped start the GEOTRACES program in 2001.
The increased risk of impacting the seabed in shallower water is due to the strong currents that often occur near shore. Currents can push expensive equipment into uphill slopes or cause it to take a nerve wracking diagonal route to the bottom. By comparison, the water scarcely moves thousands of feet down.
After a placid first few days at sea, the wind and waves intensified as the Revelle motored northwest to Station 5. The precipitous rise and fall of the ship had some reaching for their seasickness medication.
The Revelle arrived at 11 p.m. Forty mile per hour winds stacked the swells up to 10 feet high—not that anyone could see them in the dark. Walls of water occasionally emerged from the blackness, soaking the deck and everyone on it.
Co-chief Scientist Lam’s group from the University of California, Santa Cruz lowered their carefully calibrated instruments, used to collect and detect particles in the water, at 2 a.m. Deep water or not, Lam was concerned about her delicate sensors impacting the bottom.
“This instrument doesn’t tell you how deep it is in real time,” said Lam. “Instead we have to mostly rely on the winch’s display to tell us how much cable it has let out—it makes me nervous.”
After a tense transit thousands of feet below the surface, Lam’s gear appeared to be around 100 feet off the bottom. The equipment did its job, pumping seawater and filtering out particles for study, for the prescribed four hours.
But the winch had under-reported its unspooled cable, and Lam’s equipment returned with deep sea mud packed into its crevices, mementos from an encounter with the bottom. After years of planning, Lam was terrified she broke her instrument on the first station, less than a week into a 67-day expedition.
“I was feeling so good,” recalled the normally upbeat Lam. “I had just had a birthday at sea, I even saw the green flash for the first time.” GP15 is also Lam’s first as one of the Chief Scientists on board. The potential loss of this instrument would be a blow not just to her own science but to the overall success of an expedition she is partly responsible for managing.
Not one to bog down in dismay, Lam spent the better part of the following afternoon giving her device a bath and then carefully re-calibrating its sensors. To her great relief, the extra TLC paid off and her instrument came back to life.
More than 24 hours after stopping at Station 5 the Revelle moved on to Station 1, which went smoothly despite the shallow water.
Leaving Station 1, near the island of Aghiyuk, the weather again asserted itself. At Station 2, the swell heaved the Revelle up and down, while one of the expedition’s key instruments, called a CTD Rosette or CTD for short, was hundreds of feet underwater.
In the troughs of the slate colored waves the cable went slack, and when the ship rode the next swell back up the cable snapped taught. The cable held, but Chief Scientist Cutter was worried the jags of tension could damage the link between the ship and the instrument he helped design. On GP15, Cutter alone operates the winch controlling the trace metal CTD’s trips to and from the deep. The winch’s roughly 26,000-foot cable not only tethers the CTD to the Roger Revelle but also powers its instruments and allows it to relay information to computers on board.
The CTD measures salinity, temperature and depth, and its rosette holds a ring of bottles that can be remotely triggered to snap shut and collect water from various depths. This particular CTD is used to measure trace metals. These elements, some essential and others toxic to marine life, are exceedingly rare. To measure these scarce materials, the CTD must be kept scrupulously clean, lest the instrument contaminate its own samples. If there is a core to what makes a GEOTRACES expedition, this instrument is part of it.
Inside the computer lab, CTD technician Kyle McQuiggan saw the green, blue, red and yellow lines that chart the CTD’s measurements become scatological abstractions—a beeping, red error message the cherry on top.
Somewhere between the CTD and McQuiggan’s monitor, there was a problem. What if the spikes of tension allowed seawater to sneak past the Kevlar surrounding the power cable? McQuiggan and others removed huge lengths of cable, checked them for weaknesses and then spliced them back together with yards of electrical tape.
Hours later, the refurbished wire was reconnected, but the error message remained. Meanwhile, the Revelle bulldozed through the waves and wind on its way to Station 3. The failure of the previous hours of work to remedy the CTD cable called into question whether the cable was the problem at all.
Cutter and McQuiggan stood in the computer lab around 8 p.m., the portholes painted black by the night, discussing what to do next. Much of the science party was running on only a few stolen hours of sleep after three solid days of work.
Exhaustion sharpened the edge of their frustration at the lost efforts of the afternoon. According to the ship’s captain, even worse weather lay in the path of the Revelle. With one of the expedition’s most crucial instruments offline, charging into swells that might top 15 feet held little allure.
The expedition leaders and the ship’s captain opted to hide out in the lee of an island called Chirikof until the CTD could be repaired. Everything was on hold: the expedition’s 26 research projects frozen and the Revelle stopped in its tracks. Outside the shelter of the island, 50 knot winds whipped the ocean into a range of snow capped peaks.
Cutter and McQuiggan called in technicians Joseph Gum and John Calderwood. Outside of the team assembled to fix the trace metal CTD, most of the science party was on their way to sleep—trying to stock up before the Revelle reached Station 3.
The added expertise winnowed the list of suspects down to the winch’s slip ring. The slip ring is where the ship and the winch’s thousands of feet of cable connect. It’s called a slip ring because it spins in place without tangling the wires leading back to the ship as the winch lets out or takes in cable.
Saltwater must have found a way in and corroded the connections, Gum explained. The corrosion caused volts to spill out across the wires meant to send data back to the ship, producing the rainbow Rorschach on McQuiggan’s monitor.
The faulty slip ring had to be replaced with some stand-in from the limited cast of characters on board the Revelle. After a scavenger hunt through the ship’s machine shop, another slip ring materialized, but it was the wrong size.
On land, a phone call or the click of a mouse could summon the perfect replacement. At sea, “the perfect replacement” is anything that does the job. The new slip ring was too small, but the machine shop had the tools to drill out new holes to make it work—specificity supplanted by ingenuity. “It’s all paperclips and duct tape when you’re at sea,” said Cutter.
After nearly 16 hours of work, McQuiggan, Gum, Calderwood and Shadle installed the new slip ring around 3 a.m. The Roger Revelle left its island refuge and turned south—ready for whatever came next.
GP15 blog posts written by Alex Fox unless otherwise stated.
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GEOTRACES GP15 is supported by the National Science Foundation. Any opinions, findings and conclusions or recommendations expressed in this material do not necessarily reflect the views of the National Science Foundation.
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