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Introduction

I cebergs are bits of glaciers that have broken off into the sea. An iceberg has over twice as much ice under the water.

L ines of latitude and longitude on the globe.

Under the Ice The great land masses of the northern hemisphere form the edges of the Arctic Ocean, with North America to one side, and Eurasia on the other. The gaps are nearly filled by islands such as Greenland and Spitzbergen. The North Atlantic and Bering Strait are the only way in by ship. Early explorers in small wooden vessels braved these passages. In 1977, a Russian nuclear-powered icebreaker was able to push its way right across the Arctic Ocean, smashing a track through the sea ice and reaching the North Pole. Submarines have traveled beneath the ice, surfacing near the North Pole through cracks in the ice.

Lines on the Earth The globe can be divided up by lines encircling the Earth starting at the Equator, which is exactly around the middle, and going north and south. These are called lines of latitude. And it can be divided by lines running from the North Pole to the South Pole. These are lines of longitude. The point where lines of longitude and latitude cross gives an exact description of a position on the globe. Latitude was known to early Greek and Arab navigators. They made simple devices to measure the angle of the Sun above the horizon at midday. A calculation showed how many degrees they were away from the Equator. The Equator is 0° and if you travel north your latitude gradually increases to 90° at the North Pole. For each degree you travel about 68 miles (110 km). Confusingly, the same thing happens when you travel south from the Equator. Latitude must always have north (N) or south (S) added to show which side of the Equator you are. So, London is 51°N, and the North Pole 90°N. But Sydney, Australia, is 33°S, and the South Pole 90°S. To work out the exact position, degrees are broken down into minutes . Just as there are 60 minutes in an hour, so there are 60 minutes in a degree.

T he Arctic Ocean is covered by sea ice most of the year. This ice is always moving and cracks suddenly open or close.

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