At the poles, unlike elsewhere on Earth, the day–night cycle lasts a full year rather than 24 hours. Annually, each pole has a single sunrise and a single sunset. Such a year of extremes guarantees long winters and summers intense enough to melt some, but not all, of the snowfall. The cycle gives rise to the planet’s ice sheets.
The Greenland Ice Sheet holds an amount of water equivalent to 7 m of global sea-level rise, while the East and West Antarctic Ice Sheets lock away 60 m. Summertime meltwater is plentiful in Greenland, but in Antarctica, it is found only around the fringes.
On the ice sheets, natural surface depressions collect meltwater into lakes—a few kilometers wide and a few meters deep—as shown in figure 1. Without the depressions, meltwater would run off the ice into the ocean. But instead, the water in the lakes can short-circuit that...
