Polar ice cap in the context of "Sympagic ecology"

The salinity of water bodies varies widely, being lower near the surface and the mouths of large rivers and higher in the depths of the ocean; however, the relative proportions of dissolved salts vary little across the oceans. The most abundant solid dissolved in seawater is sodium chloride. The water also contains salts of magnesium, calcium, potassium, and mercury, among other elements, some in minute concentrations. A wide variety of organisms, including bacteria, protists, algae, plants, fungi, and animals live in various marine habitats and ecosystems throughout the seas. These range vertically from the sunlit surface and shoreline to the great depths and pressures of the cold, dark abyssal zone, and in latitude from the cold waters under polar ice caps to the warm waters of coral reefs in tropical regions. Many of the major groups of organisms evolved in the sea and life may have started there.

The polar regions, also called the frigid zones or polar zones, of Earth are Earth's polar ice caps, the regions of the planet that surround its geographical poles (the North Pole and the South Pole), lying within the polar circles. These high latitudes are dominated by floating sea ice covering much of the Arctic Ocean in the north, and by the Antarctic ice sheet on the continent of Antarctica and the Southern Ocean in the south.

The Blue Marble is a photograph of Earth taken on December 7, 1972, by Harrison Schmitt aboard the Apollo 17 spacecraft on its way to the Moon. Viewed from around 29,400 km (18,300 mi) from Earth's surface, a cropped and rotated version has become one of the most reproduced images in history.

In the original NASA image, named AS17-148-22727 and centered at about 26°19′49″S 37°25′13″E / 26.33028°S 37.42028°E / -26.33028; 37.42028 with the South Pole facing upwards, The Blue Marble shows Earth from the Mediterranean Sea to Antarctica. This was the first time the Apollo trajectory made it possible to photograph the south polar ice cap, despite the Southern Hemisphere being heavily covered in clouds. In addition to the Arabian Peninsula and Madagascar, almost the entire coastline of Africa and most of the Indian Ocean are clearly visible, a cyclone in the Indian Ocean is also visible, the South Asian mainland and Australia is on the eastern limb, and the eastern part of South America lies on the western limb.

The planet Mars has two permanent polar ice caps of water ice and some dry ice (frozen carbon dioxide, CO₂). Above kilometer-thick layers of water ice permafrost, slabs of dry ice are deposited during a pole's winter, lying in continuous darkness, causing 25–30% of the atmosphere being deposited annually at either of the poles. When the poles are again exposed to sunlight, the frozen CO₂ sublimes. These seasonal actions transport large amounts of dust and water vapor, giving rise to Earth-like frost and large cirrus clouds.

The caps at both poles consist primarily of water ice. Frozen carbon dioxide accumulates as a comparatively thin layer about one meter thick on the north cap in the northern winter, while the south cap has a permanent dry ice cover about 8 m thick. The northern polar cap has a diameter of about 1000 km during the northern Mars summer, and contains about 1.6 million cubic km of ice, which if spread evenly on the cap would be 2 km thick. (This compares to a volume of 2.85 million cubic km (km) for the Greenland ice sheet.) The southern polar cap has a diameter of 350 km and a thickness of 3 km. The total volume of ice in the south polar cap plus the adjacent layered deposits has also been estimated at 1.6 million cubic km. Both polar caps show spiral troughs, which analysis of SHARAD ice penetrating radar has shown are a result of roughly perpendicular katabatic winds that spiral due to the Coriolis Effect.

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The history of Sweden can be traced back to the melting of the Northern polar ice cap. From as early as 12000 BC, humans have inhabited this area. Throughout the Stone Age, between 8000 BC and 6000 BC, early inhabitants used stone-crafting methods to make tools and weapons for hunting, gathering and fishing as means of survival. Written sources about Sweden before AD 1000 are rare and short, usually written by outsiders. It is usually accepted that Swedish recorded history, in contrast with pre-history, starts around the late 10th century, when sources are common enough that they can be contrasted with each other.