Glaciers don’t just melt from the top, where they’re exposed to air – some are melting from the bottom, where seawater is lapping away at them. This type of melting can be hard to study, since scientists can’t exactly get down there. But now, researchers have used robotic kayaks to monitor plumes of freshwater coming from beneath glaciers, and found that they’re melting much faster than we thought.
LeConte Glacier in Alaska is what’s known as a tidewater glacier – essentially, it’s a 20-mile-long (32-km) river of ice that ends in the ocean. For the new study, the researchers were interested in how and to what extent the ice was melting where it meets the sea, but it’s dangerous to get too close because of chunks regularly falling off. So the team sent robotic kayaks in instead. These were programmed to swim up near the icy cliffs and measure the “ambient meltwater intrusions” – basically, how much fresh water is flowing into the ocean from underneath the glacier. This particular type of melting hasn’t been studied very closely in the past due to the hazards involved, so has only been estimated in models.
Traditionally, these models have suggested that this ambient melting would be relatively minor compared to discharge-driven melting, which occurs from the glacier’s surface where ice meets air and includes chunks calving off. But the new study found ambient melting to be much higher than the models anticipated – up to 100 times higher, in fact.
“With the kayaks, we found a surprising signal of melting: Layers of concentrated meltwater intruding into the ocean that reveal the critical importance of a process typically neglected when modeling or estimating melt rates,” says Rebecca Jackson, lead author of the study.
The new study isn’t the only one to try to peer beneath the waves to see what’s going on underneath glaciers. Last year a NASA satellite used radar to reveal a huge cavity beneath Thwaites Glacier in Antarctica, which would have previously contained 14 billion tons of ice. Another study found that melted glacier water alters the chemistry of surface seawater, which can accelerate sea level rise even further.