To learn how these waters work, University of Washington oceanographers are sending robots to monitor conditions too dangerous or expensive for research ships to visit regularly.
“The Southern Ocean is taking up a sizable fraction of all the atmospheric CO2 that goes into the ocean. But we know very little about the Southern Ocean, especially under the ice,” said Stephen Riser, a UW professor of oceanography.
His group has built Argo ocean-monitoring floats since 1999, and still builds about 120 per year for several international efforts. The hardy, low-power robots cruise through the world’s oceans collecting observations, what The New York Times a few years ago called “one of the scientific triumphs of the age.” The Seattle group is now in the middle of its toughest mission yet.
In 2014 the UW joined a $21 million, six-year National Science Foundation-funded project to build more robots specifically to study the Southern Ocean. The Southern Ocean SOCCOM floats are broader and longer, and include biogeochemical sensors to measure oxygen, pH, chlorophyll and nitrate to track ocean acidification, carbon uptake and the massive subsurface plankton blooms that are key to marine ecosystems.
The SOCCOM robots have novel algorithms to avoid ice floes. When conditions allow they will pop up, every 10 days or more, and transmit data back to shore.
“It takes about one day to build a standard Argo float. A SOCCOM float takes more like one week,” Riser said. This also quadruples the construction costs. But even if it were smooth sailing to do research near Antarctica, these floats would be a bargain.
“We can put these things out in the hundreds and it still doesn’t cost as much as doing the work from ships,” Riser said.
He was aboard a research cruise in January to deploy a dozen UW-built SOCCOM floats off Antarctica. These are new-generation floats that use lithium batteries and are expected to collect data 24/7 for about six years. When they are able to bob to the surface and transmit, their data will be available on public servers within a day.
“Many of the floats have now disappeared under the seasonal Antarctic ice, and we likely won’t hear from them until mid-January,” Riser said.
So far the UW team has built 90 SOCCOM floats, roughly halfway to the 185 to 200 total that are expected to be in the water by 2020. Almost all the floats for the SOCCOM project, which is based at Princeton University, are being built at the UW. The next batch will be deployed in September, during the Southern Hemisphere spring, from a ship that will sail from South Africa.
The floats will monitor a region that is poorly understood even as it’s changing rapidly. For example, the Larsen-C ice shelf recently collapsed into the sea off West Antarctica. While this won’t affect sea level, since the shelf was already floating, its absence changes the geography of the region and alters forces on the surrounding ice sheet.
SOCCOM floats are designed to spend long stretches operating under sea ice, but instructions command them to stick to deeper water, not the hazardous shallow areas near an ice shelf. As a result, no SOCCOM floats were near the Larsen-C ice shelf when it cracked. But as the ice shelf drifts and melts, the floats may detect the freshwater melting signal in summer months, Riser said.
On a recent trip to the lab in the UW Ocean Sciences Building, dozens of floats were in various stages of construction. The team was preparing for its largest shipment of the year, a 47-float delivery to New Zealand, where an annual cruise has been dropping UW-built floats since 2003. Two of those will be the more expensive SOCCOM floats. The team’s second-largest shipment of the year, of 28 floats, will be to Sydney, Australia, in early September.
Most of the Argo floats built at the UW and the other leading U.S. lab, at Scripps Institution of Oceanography, are destined for the Southern Hemisphere. That’s where the biggest data gap exists, Riser said, and where there is the most opportunity to learn.
But while many Southern Hemisphere instruments fill a scientific hole, the Antarctic oceanography is truly at the frontier. When his students and other researchers publish papers that use data collected in the Southern Ocean, Riser said: “You really can’t miss — it’s all new.”