The air temperature on this mid-December morning was 31 degrees Fahrenheit, but felt more like 40. Winds were blowing lightly at about 10 miles per hour. In other words, it seemed like a perfect day for launching RU25, a shiny, yellow, missile-shaped autonomous underwater glider, into the Southern Ocean. So a team of Rutgers University researchers checked out two Zodiacs from Palmer Station, and set off to deploy RU25 into the undersurface world.
Each time people at Palmer check out a Zodiac, they make up a new name for it. The crew in Apollo 25 would deploy the deep-water glider, which is about 1.5 meters long and weighs roughly 50 kilograms.
I rode out in the other Zodiac, named Houston, with oceanographer Travis Miles. A Rutgers doctoral student, Miles was on this day in charge of the technical aspects of the mission, such as conferring with the technicians at Rutgers who had pre-programmed the glider, and could control most of its moves even when submerged underwater at the bottom of the world.
As we cruised out to the launch point, not far offshore from Palmer Station, Houston and Apollo 25 passed a two-story-tall iceberg. A handful of Adelie penguins stood erect on the floating ice, a few gently flapping their paddle-like wings as though ushering us to our deployment spot. Despite the calm day, Miles and Rutgers graduate student Mike Garzio were business-like, purposeful. They'd been preparing the glider for weeks, testing its vacuum seals and checking for any water or oil leakages.
RU25's mission was to cruise underwater to depths of 180 meters for three weeks, amid the Antarctic Circumpolar Current, which swirls clockwise around Antarctica. RU25 is equipped with sensors that can gather data on depth, temperature, salinity, and other properties of the water, as well as detecting how much heat is transported by this massive current. These data would held reasearchers determine how the current influences the sea ice and ecosystems along the peninsula.
"There's some kind of heat storage in the ocean," Miles told me. And the heat content is actually rising in the ocean along the western shore of the Antarctic Peninsula, largely due to an upwelling of the warm deep water of the circumpolar current. Further, the circumpolar deep water has been getting warmer over the last 50 years. Data show that the average annual heat flux from the ocean to the atmosphere has been decreasing, which means that heat is building up in the ocean rather than being exchanged with the atmosphere.
Gliders like RU25 can access deep-water canyons that are considered "hot spots" for their high concentration of nutrients that are delivered there by the upwelling of warm, deep waters in the Antarctica Circumpolar Current. The gliders can also reach other places where research vessels and divers can't go, and they can collect data points from a broad geographic area. The longest mission one glider swam was roughly 7,000 kilometers, Miles said.
When we reached the drop-off spot, Garzio and team member Kaycee Coleman prepared to put RU25 overboard, while Miles talked with a technician who was also communicating with RU25 from the Rutgers Coastal Ocean Observation Lab (known as RU COOL), in far-away central New Jersey. The plan was that once released, RU25 would sink deep and steadily undulate through the water, frequently sending data to the Rutgers lab whenever it poked its tail above water before diving again.