US: A new study led by NASA researchers demonstrates that fresh water flowing from rivers into the Arctic Ocean can have a significant effect on the extent of sea ice cover. Warm water discharges can accelerate the melting of sea ice near the coast. It also can have a wider climate impact by creating more open water, which is darker than ice and absorbs more heat from sunlight. The scientists used satellite data to examine Canada’s Mackenzie River Delta and the Beaufort Sea in 2012—the year of the lowest Arctic sea ice extent in 35 years of satellite records. They found that a massive pulse of river water in early summer raised offshore water temperatures across hundreds of kilometers and seemed to contribute to the melting and dispersal of nearby sea ice.
Ground- and satellite-based observations showed that Mackenzie River water accumulated behind a barrier of sea ice along the coast (visible in the top image above) and warmed up in the summer sunlight. The ice barrier then broke free and released a massive pulse of warm, fresh water across the sea surface. “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,” said Son Nghiem, the lead author of the study and a cryospheric scientist at NASA’s Jet Propulsion Laboratory. River discharge is becoming more important as a contributor to melting sea ice in the Arctic Ocean, according to Nghiem and colleagues. That’s because the volume and temperature of fresh water discharge is increasing as inland Arctic areas warm more each summer. In the ocean itself, the sea ice is much thinner and fragmented than in years past, so it is much more vulnerable to pulses of warm meltwater.
Source: Earth observation