Hot water may be a foreign concept on the West Antarctic Ice Sheet, but it’s highly useful: In 2013, researchers used tens of thousands of liters of the stuff to bore deep into the ice, reaching a hitherto hidden world—a subglacial lake. They sampled the lake’s waters, a scientific first, and now they’ve analyzed its biogeochemistry. The team found that subglacial Lake Whillans contains roughly 5,400% of the organic carbon needed by microbes at the lake’s drainage outlet. This lake may therefore provide an important source of nutrients for the Southern Ocean’s vast food chain, the researchers suggest.
Bringing Europa to Earth
Subglacial lakes lurk in the darkness below glaciers, capped by hundreds or even thousands of meters of ice. Created by melting triggered by the pressure of the thick ice sheet above, roughly 400 such lakes are scattered across Antarctica, researchers believe. Subglacial lakes represent more than just an extreme environment, however—they’re also a tantalizing analog for ice-covered oceans elsewhere in the solar system, such as the one on Jupiter’s moon Europa.
In late January 2013, a team of researchers working with the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project bored through the ice of West Antarctica using a hot-water drilling system. They melted a hole roughly 60 centimeters in diameter and nearly 800 meters deep to reach Lake Whillans. This body of water is about the size of Oregon’s Crater Lake but only as deep as a backyard swimming pool.
The WISSARD team collected water and sediment from the lake using sterile vessels. Cleanliness was paramount during the fieldwork because contaminating the lake would bias analyses of its biogeochemistry. “It’s not a simple operation,” said Jemma Wadham, a glaciologist at the University of Bristol in the United Kingdom who was not involved in the research. “You have to put in place a whole series of environmental protection protocols. Everything that goes down that hole has to be clean and sterile.”
Other subglacial lakes have been breached before, like Antarctica’s Lake Vostok, but water and sediment samples have never been retrieved, said WISSARD team member Trista Vick-Majors, a microbial ecologist at Michigan Technological University in Houghton. “Whillans is really the first lake that has been directly sampled.”
Powering a Food Chain
Subglacial Lake Whillans is part of an interconnected network of lakes that drains into the ocean at the grounding zone of the Ross Sea Shelf. It’s the last stop for water on its way off the Antarctic continent, said Vick-Majors, so its waters directly reflect what’s entering the Southern Ocean. The Antarctic food chain—crowned by megafauna such as penguins, whales, and seals—is anchored by phytoplankton, bacteria, and zooplankton, which are sustained by waterborne nutrients that lakes like Whillans could provide.
When the WISSARD team analyzed water pulled up from Lake Whillans, they surprisingly found that it was rich in microbial life, researchers reported in 2016. “We expected a very dilute, low-activity environment,” said Vick-Majors. “That’s not what we found.”
Have Time, Make Molecules
Now Vick-Majors and her colleagues have analyzed the biogeochemical effects of those microbes on Lake Whillans’s water. By studying the fluorescent properties of organic matter in the water, the researchers determined that carbon-containing molecules—sources of food and energy—are largely microbially produced. Thanks to microbes, Lake Whillans is acting like a nutrient concentrator, said Vick-Majors. “When the water slows down in these lakes, it sits there for long enough that microbes can chew on it,” she said. “It’s like a little biological reactor.”
Vick-Majors and her collaborators next calculated, on the basis of the rate at which Lake Whillans empties, how much water and therefore carbon flowed into the Ross Sea each year. They compared those data with laboratory experiment–based estimates of the carbon needs of bacteria living at the grounding zone of the Ross Ice Shelf. Vick-Majors and her colleagues found that carbon levels in Lake Whillans were 5,400% higher. “The calculated carbon coming from subglacial outflow far exceeds the demand,” said Vick-Majors. Subglacial Lake Whillans could therefore be an important contributor of nutrients to the region, the researchers concluded.
“That’s a fascinating discovery and matches nicely with what we see elsewhere on glaciers and ice sheets,” said the University of Bristol’s Wadham. It also makes sense, Wadham said, because the undersides of ice shelves are dark and microbes there can’t produce their own carbon via photosynthesis. “They need a subsidy.”
These results were published in Global Biogeochemical Cycles in February.
—Katherine Kornei (@KatherineKornei), Science Writer