Huge cap is frozen sea water on the surface of the Arctic ocean and adjacent seas in recent decades has undergone a double blow: its area has decreased, the oldest and thickest ice is either thinned or completely melted, resulting in the ice cover became more vulnerable to the warming of the ocean and atmosphere.
“For many years we have observed how the old ice disappears, says Walt Meier of space flight Center NASA Goddard in Greenbelt, Maryland. Is this the thick coat serves as a protective support for all hats: summer with its warmth can melt the thin ice, but to get rid of old ice beyond him. However, it is becoming less, and the remaining thinner and resistance to zero temperature is not as steady as before.”
Direct measurements of sea-ice thickness in the Arctic are rare and incomplete, so scientists have developed an age model and sea ice evolution from 1984 to the present. A new NASA visualization shows how sea ice has grown and shrunk, melted and drifted over the last three decades. According to scientists, the age of ice is an excellent indicator of its thickness, because when the ice gets older, it becomes thicker. This is because, as a rule, in winter, added more ice than melt in the summer.
In the early 2000-ies scientists from the University of Colorado has developed a way to control the movement of Arctic sea ice and changing its age using data from various sources, mostly based on passive satellite microwave instruments.
These tools evaluate the brightness temperature is a measure of the microwave energy emitted from sea ice, which depends on temperature, salinity, texture of the ice surface and the snow layer on sea ice. Each floe has a characteristic brightness temperature, and scientists have identified and tracked them using the sequential passive microwave images. The system also uses information from the drifting buoys and meteorological data.
“It’s like accounting, we track what’s happening with the sea ice as it moves, grows and recedes, until melted on the spot or released outside of the Arctic,” explains Meyer.
Every year sea ice forms in winter and melts in summer. One that can withstand the melting season, thickens every year. The newly formed ice grows to 1-2 meters in thickness within the first year, while the thickness of perennial ice that has survived several warm seasons is approximately 3-4 meters.
The older and thicker ice, so it is more resistant to melting and are less affected by wind and storm waves.
The movement of sea ice is not restricted to the seasonal expansion and retreat: in addition to coastal areas, the ice cover on the sea is almost in constant motion. The main driving force in this process is the wind.
In the Arctic there are two main air mass circulation: the circulation of Jackboot, where the ice is rotating as the wheel clockwise in the Beaufort sea North of Alaska, and the Transpolar drift current that moves the ice from the shores of Siberia towards FRAM Strait East of Greenland, where it exits the Arctic basin and melts in the warm waters of the Atlantic ocean.
However, about every week on the same trajectory are weather systems that affect these flows. So the velocity of ice is not constant. When spring comes and the ice begins to melt, it will disappear from the peripheral seas. A new video shows the two main loss of thick ice.
The first, which began in 1989 and continued for several years, was associated with changes in the Arctic oscillation, which has weakened the cycle of Treads and strengthened the Transpolar drift current, viewsea from more Arctic sea ice than usual.
The second peak of melting began in mid-2000-ies. “Unlike the 1980s, the years now the old ice is melting within the Arctic ocean in the summer. One of the reasons lies in the fact that multi-year ice has a tendency to unite, and we now see relatively smaller pieces mixed with more fresh ice. These isolated ice floes of thick ice easier to melt,” notes Meyer.
The loss of thick ice, according to scientists, is tremendous. In 1980-e years it was 20% of the sea ice cover. Now — only about 3 %. It is not excluded that very soon the summer, the Arctic will be completely ice-free.
