The Washington Monument is embellished by cherry, Dec 14, 2015. [Photo/Xinhua]

This year, over half of the surface of the Greenland ice sheet melted, representing its first significant melting since 2012. In total, "22 of 45 of the widest and fastest flowing glaciers terminating in the ocean had retreated, but the advance of nine relatively wide glaciers resulted in a low annual net loss of 6.4 square miles (16.5 square kilometers)," said the report.

Melting and retreat of sea ice during spring has led to an increase in sunlight reaching the upper layers of the ocean, promoting photosynthesis and stimulating the growth of algae, tiny marine plants which form the base of the food chain.

"Widespread and exceptional phytoplankton blooms were observed in 2015 in Arctic seas along the edge of the continental shelf, including waters to the southwest and east of Greenland, in the Bering Sea between Alaska and Russia, and in the Barents, Kara and Laptev seas north of Russia," the report wrote.

Guest essays included in this year's report showed that the decline in sea ice is dramatically changing the habitat for walruses -- large marine mammals that traditionally use sea ice for mating, giving birth to young, finding food and shelter from storms and predators.

"In recent years, large numbers of walrus have been forced to haul out on land in northwest Alaska," it said. "This behavior, documented through aerial surveys, has created problems such as overcrowding which has led to stampedes that have killed calves, and difficulty finding food."

Scientists from Norway and Russia who drew on annual ecosystem surveys from the Barents Sea from 2004 to 2013 also found "a northward movement of subarctic fish species such as cod, beaked redfish and long rough dab, into Arctic waters."

"These predators may pose potential problems for smaller Arctic fish that must now face these new warmer-water predators," the report noted.

The report included some 70 authors from 11 countries and was guided by an editorial team from the Office of Naval Research, the US Army Corps of Engineers' Cold Regions Research and Engineering Laboratory, and the NOAA.