MISSION: WATER 26 FEATURE STORY NEW FRONTIER Overstreet and Pitcher were no strangers to the Greenland Ice Sheet, 2.8 million cubic kilometers (684,000 cubic miles) of ice blanketing Greenland in a bluish-white mass 2,400 km (1,500 miles) long. In 2012, they were part of an expedition led by UCLA professor Laurence C. Smith and Rutgers professor Asa Rennermalm that provided rare direct discharge measurements of supraglacial rivers, the streams of meltwater that race across the top of the ice sheet before disappearing into deep shafts called moulins. Most meltwater research in the area has been done on proglacial rivers at the edges of the ice sheet, within walking distance of the tundra. The team's 2012 fieldwork was revolutionary, proving that the latest tools and techniques from the temperate world could be used successfully in the Arctic. (In fact, the veteran meltwater researchers use the term "terrestrial rivers" when they talk about their training back home, contrasting more conventional research environments with the otherworldly nature of glacial hydrology.) In 2015, Smith, Rennermalm and their team—including UCLA graduate student Matt Cooper—returned to southwestern Greenland to study meltwater runoff over three solid days of uninterrupted monitoring. If the 2012 expedition provided snapshots of the movement of meltwater, the 2015 research—and their follow-up 2016 study that measured the same stream hourly for seven days straight—delivered a movie. "In 2012, supraglacial stream flow data—especially in large streams in the interior of the Greenland Ice Sheet—remained sparsely studied, so our strategy was just 'capture data from as many rivers as possible,'" Overstreet explains. "But if you capture that discharge at just one point in time, you're missing a big part of the picture. In 2015, we went back to focus on one river and see how discharge changes diurnally." The team set up camp (lower right) beside a supraglacial river that dropped into a deep moulin. Photo Courtesy: Johnny Ryan "...if you capture that discharge at just one point in time, you're missing a big part of the picture."