A new NASA study finds that warmer than normal waters from rivers draining into the Arctic Ocean each summer are eating away at the sea ice in the Arctic Ocean. Led by Son Nghiem of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., the research team used satellite data to measure the surface temperature of the waters discharging from Canada’s McKenzie River into the Beaufort Sea during the summer of 2012 and noticed surface waters being warmed suddenly due to the sudden influx of warm river water This warmed the surface layers of the ocean, which in turn increased the melting of sea ice.
ADVERTISEMENT
This Arctic process contrasts
starkly with those that occur in Antarctica, a frozen continent without any
large rivers. The sea ice cover in the Southern Ocean surrounding Antarctica
has been relatively stable, while Arctic sea ice has been declining rapidly
over the past decade.
“River discharge is a key
factor contributing to the high sensitivity of Arctic sea ice to climate
change,” said Nghiem. “We found that rivers are effective conveyers
of heat across immense watersheds in the Northern Hemisphere. These watersheds
undergo continental warming in summertime, unleashing an enormous amount of
energy into the Arctic Ocean, and enhancing sea ice melt. You don’t have this
in Antarctica.”
The team said the impacts of
these warm river waters are increasing due to three factors. First, the overall
volume of water discharged from rivers into the Arctic Ocean has increased.
Second, rivers are getting warmer as their watersheds (drainage basins) heat
up. And third, Arctic sea ice cover is becoming thinner and more fragmented, making
it more vulnerable to rapid melt. In addition, as river heating contributes to
earlier and greater loss of the Arctic’s reflective sea ice cover in summer,
the amount of solar heat absorbed into the ocean increases, causing even more
sea ice to melt.
To demonstrate the extensive
intrusion of warm Arctic river waters onto the Arctic sea surface, the team
selected the Mackenzie River in western Canada. They chose the summer of 2012
because that year holds the record for the smallest total extent of sea ice
measured across the Arctic in the more than 30 years that satellites have been
making observations.
The researchers used data from
satellite microwave sensors to examine the extent of sea ice in the study area
from 1979 to 2012 and compared it to reports of Mackenzie River discharge.
“Within this period, we found the record largest extent of open water in
the Beaufort Sea occurred in 1998, which corresponds to the year of record high
discharge from the river,” noted co-author Ignatius Rigor of the University
of Washington in Seattle.
Read more at NASA
Jet Propulsion Laboratory, California Institute of Technology.
Aerial
view of mouth of McKenzie River into Beaufort Sea image via Shutterstock.