March 6, 2014
Arctic Sea Ice Melt Fueled By Warm Rivers
Brett Smith for redOrbit.com - Your Universe Online
According to a new study from NASA researchers, warm river waters draining into the Arctic Ocean are adding to the melting of sea ice in the Arctic Ocean each summer.Published in the journal Geophysical Research Letters, researchers reported on an abrupt inflow of warm river water into the Arctic Ocean that swiftly warmed the top layers in the sea, fueling the melting of summer ice.
“River discharge is a key factor contributing to the high sensitivity of Arctic sea ice to climate change,” said study author Son Nghiem of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “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.”
To reach their conclusion, the team looked at the Mackenzie River in western Canada during the summer of 2012 – the smallest overall extent of summer sea ice in the Arctic in over 30 years. The scientists used information from satellite-based observations to examine sea ice patterns and sea surface temperatures in the Beaufort Sea from 1979 to 2012. They compared that data 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 study author Ignatius Rigor of the University of Washington.
The researchers noted that on June 14, 2012, an expanse of sea ice stuck to the coastline established a buffer that held the river discharge near its delta. After the river water melted through the barrier, the average surface temperature of the nearby area of open water rapidly raised by nearly 12 degrees F, the study team reported.
“When the Mackenzie River’s water is held back behind the sea ice barrier, it accumulates and gets warmer later in the summer,” Nghiem said. “So when it breaks through the barrier, it’s like a strong surge, unleashing warmer waters into the Arctic Ocean that are very effective at melting sea ice. Without this ice barrier, the warm river waters would trickle out little by little, and there would be more time for the heat to dissipate to the atmosphere and to the cooler, deeper ocean.”
“If you have an ice cube and drop a few water droplets on it, you’re not going to see rapid melt,” added study author Dorothy Hall of NASA’s Goddard Space Flight Center. “But if you pour a pitcher of warm water on the ice cube, it will appear to get smaller before your eyes. When warm river water surges onto sea ice, the ice melts rapidly.”
The team also projected the heating power transported by the discharge of the 72 rivers in North America, Europe and Asia that empty into the Arctic Ocean. Using statistics on average annual river discharge and supposing an average summer river water temperature of around 41 degrees F, the team found that the rivers are moving as much heat into the Arctic Ocean annually as all of the electric energy utilized by the state of California in five decades at today’s rate.