Warm River Waters Contribute to Melting of the Arctic Sea Ice: NASA

First Posted: Mar 07, 2014 11:23 AM EST
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The heat from warm water discharged from rivers into the Arctic Ocean contributes to the melting of the Arctic sea ice every summer, according to NASA findings.

The finding was made using satellite data that measured the surface temperature of the water that is being released from Canadian rivers into the icy Beaufort Sea during the 2012 summer.  The research team led by Son Nghiem of NASA's Jet Propulsion Laboratory noticed a sudden influx of warm waters into the sea that quickly warmed the ocean's surface layer, thereby enhancing the melting of sea ice.

"River discharge is a key factor contributing to the high sensitivity of Arctic sea ice to climate change," said Nghiem, in a news release. "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."

This event in the Arctic does not occur in the Antarctica, continent where large rivers are absent.  The sea ice cover in Antarctica's southern ocean has been stable while in the Arctic a rapid decline in the sea ice has been observed over the past decades.

The researchers highlight three major factors that cause a rise in the flow of warm river waters. First, an overall increase in the volume of the water released from rivers into the Arctic Ocean. Second, as the watersheds heat up, the rivers get warmer making the ocean more susceptible to rapid melting. Third, due to thinning ice cover large amount of solar heat is sucked into the ocean causing more and more sea ice to melt.

In order to demonstrate the effect of warm Arctic rivers on the sea ice surface, the team focused on the Mackenzie River in western Canada. They zeroed in on the 2012 satellite data as that year made a record for the smallest total extent of sea ice measured in over 30 years of observations.

The extent of sea ice in the study area right from 1979 to 2012 was examined using data from satellite microwave sensors. They compared this result to the 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.

On examination of the data, they noticed that on June 14, 2012 a stretch of the sea ice that is glued to the coastline stood as a barrier and held the river discharge close its delta. During  June 14-July 5, the river water broke the ice barrier and there was a noticeable rise in the average surface temperature of the area of open water. The temperature soared to 11.7 degrees Fahrenheit.

"When the Mackenzie River's water is held back behind the sea ice barrier, it accumulates and gets warmer later in the summer," said Nghiem. "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."

Data suggests that waters from 72 rivers in North America, Europe and Asia flow into the Arctic Ocean. Assuming the average summer river water temperature to be 5 degree Celsius, the researchers calculated that the heat from the rivers discharged into the Arctic Ocean every year can be compared to all of the electric energy the State of California used in the last 50 years at present consumption rate.

The researchers suggest that further studies need to be done in order to establish the readings of water temperature in the Arctic river in order to known more on their contribution to sea ice melt.

The study was publsihed in journal Geophysical Research Letters.

 

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