【気候科学】南極の融解水による湖と河川の全体像を描く

Extensive networks of lakes and streams have persisted for decades on Antarctica’s ice shelves, making them vulnerable to instability and possible collapse, reports a paper in this week’s Nature. However, evidence from Antarctica’s Nansen Ice Shelf, analysed in a second paper, suggests that large rivers can, in some cases, mitigate this effect by transporting meltwater into the ocean.

Surface meltwater is thought to contribute to the collapse of ice shelves by seeping into crevasses, refreezing and generating hydraulic fracturing. However, the full extent and duration of meltwater ponds, streams and rivers that form on Antarctica has remained unknown.

Jonathan Kingslake and colleagues use satellite imagery from 1973 onwards and aerial photography from 1947 onwards to analyse meltwater drainage across Antarctica. They show that surface drainage has occurred for decades, transporting meltwater up to 120 kilometres from grounded ice, across ice shelves and feeding vast networks of ponds. These findings suggest that surface water drainage in Antarctica is more extensive than previously thought and, as the climate warms, could potentially accelerate future ice-mass loss from the region.

In a separate study, Robin Bell and colleagues describe a surface river network that has, for more than a century, exported a significant proportion of meltwater from the Nansen Ice Shelf in Antarctica into the ocean. The river terminates in a 130-metre-wide waterfall that can drain the ice shelf’s entire annual meltwater production in just seven days. This surface drainage system seems to prevent meltwater from destabilizing the Nansen Ice Shelf. Further research is needed to understand why meltwater is retained in some systems and drained in others, but these results indicate that meltwater movement may not always be an ice-destroying mechanism.