Arctic climate and ice sheet

The climate in the Arctic is cold all the year round, and most of the ocean surface in the Arctic Ocean is frozen all the year round.

Winter in the Arctic lasts for six months from June 1 1 to April of the following year. May, June, September and 65438+ October belong to spring and autumn. In summer, it only lasts for seven or eight months. The average temperature in June+10/October in 5438 was between-20 and-40℃. The average temperature in the warmest August is only MINUS 8 degrees. The lowest temperature measured at the drifting station near the pole of the Arctic Ocean is -59℃. Due to the influence of ocean currents and Arctic anticyclones, the coldest place in the Arctic is not in the center of the Arctic Ocean. The lowest temperature was recorded at -70℃ in Jansk, Vilho, Siberia, and at -62℃ in Alaska.

Winter in the Arctic is long, cold and dark. From the end of June 165438+ 10 every year, the sun will not be seen at all for nearly half a year. The temperature will drop below MINUS 50 degrees. At this time, all the waves and tides disappeared because the coast was frozen.

In April, the weather gradually warmed up, the ice and snow gradually melted, and large pieces of ice began to melt and break; The sky becomes bright. In May and June, plants turn green and animals become active. In summer, animals need to get enough food and accumulate enough nutrition and fat to spend the long winter.

Autumn in the Arctic is very short, and the first snowstorm will come in early September. The arctic soon returned to the cold and dark winter.

The North Pole and the South Pole have extreme day and night phenomena, and the closer to the North Pole, the more obvious it is. There seems to be only one day and one night in a year. Even in midsummer, the sun just hangs on the distant southern horizon, with a bleak white light. The height angle of the sun never exceeds 23.5, and it moves slowly around this endless white world quietly. A few months later, the sun's trajectory gradually approached the horizon, so the evening season in the Arctic began. Near the North Pole, there are nearly six months of night without day (June 10 to March of the following year), and the remaining six months are days without night.

The average annual precipitation in the Arctic is only 75 ~ 200mm, mainly snowfall, and the Greenland Sea can reach 500mm. There are often violent storms in winter. Affected by the North Atlantic warm current, the water temperature and air temperature in the Nordic sea area are higher, with more precipitation and lighter ice conditions. There is a lot of sea fog in warm seasons, and it is foggy every day in some months, even for a few days and nights. In the Arctic sea area, the water temperature from the water surface to the water depth of 100 ~ 225m is 1 ~ 1.7℃, and the water temperature along the coast varies greatly throughout the year, which is 1.5 ~ 8℃. In the northern European waters, the water surface temperature is between 2 ~ 12℃ all the year round. The water depth of the Arctic Ocean is 100 ~ 250 m to 600~900 m, and there is a warm water layer in the middle from the North Atlantic warm current, with the water temperature of 0 ~ 1℃.

2. Arctic sea ice and Greenland ice sheet

(1) Arctic sea ice

Located in the Arctic Circle, the Arctic Ocean receives little solar radiation heat all the year round, with low temperature and frequent snowstorms. Most of the surface of the Arctic Ocean is covered with sea ice all year round, and it is the only white ocean on the earth. The average thickness of Arctic sea ice is 3m, covering 73% of the whole ocean area in winter, about (1000 ~100 )×104km2, and covering 53% in summer, about (750 ~ 800) × 104km2. The sea ice in the center of the Arctic Ocean has existed for 3Ma, which belongs to permanent sea ice. There are drifting icebergs and floating ice on the sea; Only the Barents Sea area is affected by the North Atlantic warm current, and it is not frozen all year round. Most of the islands in the Arctic Ocean are covered with glaciers and ice sheets, while the coastal areas of the Arctic Ocean are mostly frozen soil, and the frozen soil layer is hundreds of meters thick.

The area of Arctic Ocean ice sheet is the largest in March and the smallest in September. However, it is not a contiguous ice sheet, but an ice cluster composed of large and small ice blocks, with an area of one to dozens of square kilometers and a thickness of 2.5 to 4 to 5 meters. The surface is flat or undulating and relatively firm. In addition to the ice sheet, there are Iceland or icebergs in the Arctic Ocean, which are formed by the ice on the continental shelf of polar islands entering the sea. Iceland has slow water flow, flat surface, large area (up to 600~700km2) and thickness of 30 ~ 35m. Icebergs are distributed around Iceland, and the area is very small.

Due to the movement of ocean currents, the sea ice on the surface of the Arctic Ocean has been drifting, cracking and melting, so it is impossible to accumulate thousands of meters of ice and snow like the Antarctic continent over millions of years. Therefore, the total amount of ice and snow in the Arctic is only close to110 in the Antarctic, and most of it is concentrated in the continental ice sheet of Greenland, while the permanent ice and snow in the Arctic Ocean, other islands and surrounding land only accounts for a small part.

The sea ice boundary is not fixed, and it can often change by hundreds of kilometers with the change of hydrometeorological conditions. Under the action of wind and current, ice floes can pile up and form huge floating icebergs. Most icebergs usually refer to those huge ice bodies with a diameter of more than 5 meters that have collapsed from the continental shelf or continental ice sheet. Generally, the thickness of large table icebergs can reach 200 ~ 300 m, and the average life span is as long as 4 years. Floating icebergs formed by sea ice in the Arctic Ocean, together with icebergs formed by glaciers and ice shelves from Greenland and other islands, enter the Atlantic Ocean or Alaska with the current, and some icebergs can drift south to 40 north latitude.

Because of the low temperature and weak evaporation in the Arctic Ocean, the salinity is very low, with an average salinity of 30 ‰ ~ 32 ‰, which is the lowest among the four oceans. The western part of northern Europe (Barents Sea and Greenland Sea) is slightly higher, ranging from 34.5 ‰ to 35 ‰, and the coastal area is 33 ‰. The eastern Arctic waters are low, with an average of 28 ‰ ~ 32 ‰, and the coastal waters are the lowest, with only 25‰.

(2) Greenland ice sheet

Continental ice sheet refers to the ice body that covers the land area of more than 5× 104km2 for a long time, also known as continental glacier. The central part of the continental ice sheet is an accumulation area, and the edge is an ablation area. The ice in the ice sheet is almost unaffected by the underlying topography, and flows out from the center to the surrounding areas; The edge part extends from the land to the sea, and some ice bodies floating on the sea are called ice shelves (continental ice), ice sheds or ice barriers. The ice on the ice shelf broke apart and entered the sea to form icebergs.

The existing continental ice sheets on the earth include Antarctic ice sheet and Greenland ice sheet. These two ice sheets account for about 97% of the global glacier area and 99% of the total ice.

Greenland ice sheet was formed in Quaternary. The peak of the last ice age is about 18000 aB. P, the ice sheet area is much larger than today, which is connected with the North American ice sheet. Lan Bing, covered with white snow, granular snow and new ice, constitutes the main body of the continental ice sheet. Moreover, the deeper the ice, the longer it takes to form. It is estimated that the age of the deepest ice layer in Greenland ice sheet can reach hundreds of thousands of years or even more than 1 Ma.

Most of Greenland is located in the Arctic Circle, with an ice sheet area of about 180× 104km2, accounting for 84% of the total island area, with an average thickness of about 1500m and a maximum thickness of 3200m, accounting for 7% ~ 9% of the world ice volume, and the total amount of ice and snow contained is 300×/kloc-. It consists of two dome-shaped ice sheets in the north and south. The edge of the ice sheet is covered with the sea, and the glacier tongues of many glaciers extend into the sea, forming many icebergs in several fjords. Some glaciers in West Greenland, such as Jakoban Isboyi Glacier, flow at a speed of 7,000 meters per year, making them the fastest glaciers in the world. The ice surface on the west side of the central ice sheet thickens at the rate of 0. 1 m per year, while it is slightly thinner on the east side. The ice surface in the ablation zone on the west coast of the ice sheet becomes thinner by about 0.2 meters every year.

Greenland ice sheet shows strong characteristics of polar ocean glaciers. The annual average temperature in the southwest coast of the ice sheet is 1℃, and the average temperatures in June and July are -7.8℃ and 9.7℃ respectively. The annual precipitation reaches 1000 mm, and a large number of ice and snow are accumulated and melted. The situation inside the ice sheet is obviously different. The average annual temperature is around -30℃, and the average temperatures in February and July are -47.2℃ and-12.2℃ respectively. The annual precipitation is only 200mm, which is low in temperature, less in precipitation, less in accumulation and melting of ice and snow, and the process of ice formation is slow.

The main body of the Greenland ice sheet moves at a speed of 20m/a, while the speed of the glacier tongue reaches1000 ~ 7000m/a. The Greenland ice sheet consists of three active centers, one of which is near 65 north latitude and 2700m； above sea level; ; The other is near 70 north latitude, with an altitude of 2800 m; ; There is another one near 76 north latitude, with an altitude of 3000 m. The snow line in Greenland varies between 300 ~ 1500m, decreasing from south to north, and dropping to sea level in some places.

Most icebergs in the Arctic Ocean come from the Greenland ice sheet. In the western part of Greenland alone, there are more than 65,438+000 icebergs formed when glacier tongues break into the sea. The Jakobshavin Glacier provides 1400 icebergs for the Arctic Ocean every year. Because of the high water temperature and air temperature in the Arctic Ocean, icebergs melt quickly, and most of them are pyramid-shaped, and the height is often between 10 ~ 12m, and some of them can reach 30 ~ 170 m. Icebergs can float to the sea surface at 40 north latitude.

Third, Arctic and global climate change.

It is an indisputable fact that global warming has caused more and more serious consequences on a global scale. Global warming will redistribute global precipitation, melt glaciers and frozen soil and raise sea level, which will not only endanger the balance of natural ecosystems, but also threaten human food supply and living environment. The change in the Arctic is more obvious.

In 2004, a group of scientists from eight countries, including the United States, Canada, Denmark, Finland, Iceland, Norway, Russia and Sweden, specially studied the climate change in the Arctic, and concluded that climate warming had a significant impact on the climate in the Arctic region. The survey results (/info/2004/1119115.htm) show that the Arctic region is more seriously affected by global warming than other regions, and its warming rate is twice the global average. The report predicts that by 2 100, the temperature in the Arctic will rise by 4 ~ 7℃ compared with the present, which is about twice the global warming predicted by the United Nations. Since 1950s, the temperature in Siberia, Russia and Alaska, USA has increased by 2 ~ 3℃.

The report (/info/2004/1119115.htm) also said that by the end of February1,the ice sheet near the North Pole will be almost in summer. From 1979 to 200 1, the ice-covered area of the Arctic has been shrinking at a rate of 6.5% in September. In the middle and late 1980s, the Arctic sea ice showed an obvious decreasing trend, and suddenly decreased after 1997. In the past 30 years, the Arctic ice sheet has shrunk by 15% ~ 20%. According to the data in September 2007, the area of the Arctic ice sheet was 4 13× 104 km2, while in 2005 it was 530× 104km2. At least part of the disappearing Arctic ice sheet is irreparable.

As a result of the shrinking ice sheet, the sea level rises. In the past 20 years, the melting of Arctic ice has caused the global sea level to rise by about 7.6cm on average. It is predicted in the report that the global sea level will rise by about 1m at the end of 2 1 century, of which 15% is caused by Arctic warming.

The ice and snow in the Arctic can reflect the solar thermal radiation and play an important role in maintaining the global thermal balance. Another reason why the Arctic region is warming faster than other parts of the world is that after the white ice and snow melt, dark land and sea water are exposed, absorbing more heat, and the ice and snow melt faster, thus aggravating the climate warming. This forms a vicious circle. At the same time, the consequences of climate change in the Arctic will also react on the climate system, causing greater global changes.