Arctic and Subarctic Regions

Arctic ocean

The region encircling the North Pole is called the Arctic Circle, an invisible circle of latitude (imaginary line around the Earth parallel to the equator) at 66°33’ North. The arctic region sits inside the Arctic Circle and the subarctic region lies just below it.

Earth’s arctic and subarctic regions are extremely cold, icy areas of land and sea that receive almost no sunlight during their long, dark winters. Temperatures rarely rise above freezing. This is true even during summer in the “land of the midnight sun.”

The Sun’s rays hit the poles at a very shallow angle and the summer sunlight—while long-lasting—is too weak to provide much heat. Arctic and subarctic regions, however, support diverse groups of land and marine (ocean) plants and animals, including humans that have learned how to survive in their harsh climates.

Ice, Sea-level, and Global Climate

Ice, Sea-level, and Global Climate

The amount of water frozen in Earth’s ice has changed throughout the planet’s history. Earth’s ice budget (total ice volume) grows when the planet’s average temperature falls and shrinks when it rises.

During colder periods called ice ages, ice caps (large dome-shaped glaciers) extend far from the North and South Poles, and mountain glaciers (large masses of moving ice) advance into lowlands. During warmer periods, ice retreats back toward the poles and up mountain valleys. Earth has even been completely ice-free several times during its long history.

Earth’s water budget, the total amount of water on the planet, does not change over time. When more water freezes into ice on land, there is less water in the oceans, so global sea level falls during ice ages.

Glaciers

Glaciers

Glaciers are large masses of moving ice. Glaciers form by the accumulation of snow over tens, hundreds, and even thousands of years. Glaciers grow in cold places where more ice forms than melts each year, namely, close to the north and south poles and at high elevations (near the summits of tall mountains.)

Today, ice covers about one tenth of Earth’s surface. Huge dome-shaped masses of glacial ice, called continental glaciers or ice sheets, cover the arctic island of Greenland and the most of the continent of Antarctica at the South Pole. Mountain (alpine) glaciers flow down valleys in the Himalayas, Andes, Alps and other major mountain ranges.

Glacial ice affects Earth’s climate, drives ocean currents (a moving mass of water that may also differ from surrounding water in properties such as temperature or amount of salt (salinity), and determines global sea level. (When more water is bound up in ice on land, sea level falls. When glaciers melt, sea level rises.)

Polar Ice Caps

Polar Ice Caps

Ice covers Earth’s North and South Poles. Weak sunlight and long, dark winters at high latitudes (imaginary lines on Earth that tell how far north or south a place is from the equator) create frigid conditions that support the formation of year-round glaciers (large masses of moving ice) on land and seasonal ice in the oceans.

An ice cap is a permanent covering of ice over a large area. The arctic ice cap at the North Pole includes sea ice floating in the Arctic Ocean; glaciers in northern Asia, Europe, North America; and sheets of ice on the island of Greenland. The ice cap at the South Pole is made up of the massive Antarctic ice covering and ice in the Southern Ocean.

Polar ice caps play a vital role in regulating global climate, temperature, ocean currents, and sea level. They keep nutrientrich waters of the Arctic and Southern Oceans at a livable temperature for rich communities of biological life. A total of 99.997% of Earth’s fresh water is bound up in polar ice.