What is Sea ice?
[[File:Arctic ice.jpg|thumb|upright=1.25|Broken pieces of Arctic sea ice with a snow cover.]] '''Sea ice''' is simply frozen [[ocean]] water. It forms, grows, and melts in the ocean. In contrast, [[iceberg]]s, [[glaciers]], [[ice sheet]]s, and ice shelves all originate on land. Sea ice occurs in both the [[Arctic]] and [[Antarctic]]. == Description of Sea Ice == Because sea ice is made of frozen seawater, it is salty (unlike icebergs). Sea ice generally grows in the winter (when it is often dark all day and night) and melts in the summer (when there is twenty-four hour daylight). Sea ice normally covers more area near in the Antarctic than the Arctic. Because the ice is salty, sea ice is heavier, less transparent and easier to break than ice that isn't salty. === Sea Ice Mechanical Properties === The 'mechanical properties' of sea ice refer to how easy it is to bend, break, squash and stretch the ice. This behaviour is dominated by the fact that sea ice is not entirely solid - instead it contains lots of tiny pockets of salt water. Older ice also often contains many air bubbles. This makes it much easier to squash, break and snap than a normal ice cube in a drink. When two pieces of sea ice squash up against each other, they can crumple up and break to form a 'ridge' at the part where they touch. Before doing this they might bend. It is also relatively easy to pull apart a single piece of sea ice by pulling opposite edges in opposite directions. === Sea Ice Optical Properties === Because sea ice has air bubbles and saltwater pockets inside it, it is much harder to see through than non-salty, clear ice. This is because light can't go through it without hitting the bubbles and pockets. Most sea ice in winter is covered by a layer of snow, which you also can't see through. All this means that when the sun shines on sea ice, not much of its light gets through to the sea below the ice. This limits the amount of algae and tiny plants that can grow in the sea. This is important because when the ice melts, much mo