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All About Sea Ice

Credit: Jaclyn McPhadden

Sea Ice, Icebergs And Glaciers

Sea ice is frozen ocean water. It forms, grows and melts on the ocean. An iceberg is not sea ice but pieces of glaciers that break off from the land into the sea. A glacier is formed from compacted snow and rests as a thick mass of ice on land, built up from many seasons of snowfall.

Sea ice moves constantly with the dynamic ocean. Forces such as wind and ocean currents push sea ice around, causing ice sheets to collide or break apart. This creates channels of open water called leads.

Creating Underwater Castles

Although sea ice is always present on the Arctic Ocean, it’s not a stable surface. It freezes, grows, melts or can completely disappear with the seasons. Sheets of sea ice collide, break apart, or pile on top of each other.

Pieces of ice pile up and down when they push into each other, forming ridges and keels. These broken ice pieces refreeze to form large three-dimensional structures that look like underwater ice castles. Like trees in a forest, these underwater sea ice habitats provide homes and structure for life living in, on and around them.

Age Matters

Because some sea ice melts every summer, not all sea ice on the Arctic Ocean is the same age or thickness. First-year ice forms during winter. It can grow to over two meters thick in a single season, but that’s still relatively thin, and it is likely to melt by the following summer. Multiyear ice has survived a summer season. It is typically 2-4 meters thick. Older, thicker sea ice is disappearing from the Arctic and being replaced by thinner first year ice that melts away in the summer and refreezes in the winter. In 1985, multiyear ice made up 45 per cent of the sea ice cover; in March of 2016, it made up only 22 per cent of the ice cover. Ice over 5 years old makes up only 3 per cent of the total sea ice extent and there is no ice over 9 years old anymore. Central Arctic Ocean sea ice thickness decreased by 65 per cent from 1975 to 2012 (3.6 meters to 1.25 meters).


The Smallest Creatures
Who Live Here

Sea ice plays an important role for people, marine mammals and birds, and also serves as an amazing habitat for a highly specialized community of very small algae and animals. When sea ice forms, growing ice crystals push salt into pockets and channels that are surrounded by ice. This network of pores and channels shelter and anchor tiny ice algae and provide homes to microscopic animals, as well as ice amphipods. We’re unsure how the disappearing sea ice will affect this unique community of sea ice organisms.

The Critical Impacts
Of Melting Ice

Most months of the year, sea ice is a resting spot for walruses, who rest on these ice platforms between periods of clam feeding. Sea ice is also a hunting platform for the people living in Arctic communities and a highway for travel. Inuit hunters travel to the ice (floe) edge to hunt whales, seals or walruses. Polar bears, the Arctic’s top predators, also use sea ice as hunting platforms.Research shows that the sea ice is forming later each year, breaking up earlier and melting more in the summer. This results in more hungry and skinny polar bears and fewer resting areas for walruses. 

Polar Bear on Sea Ice Credit: Getty Images

Sea Ice Is A Banquet Table

Sea ice is like a banquet table, offering an abundance of organisms that live in its pores, cracks and crevices. Ice algae are an important food source for ice amphipods and Arctic copepods, which are crustaceans, like crabs and shrimps. They in turn are food to carnivorous ice amphipods, Arctic cod and seabirds. Ice amphipods can grow so big, Arctic cod, seabirds and even ringed seals feast on them. Whales, such as narwhals and belugas, gorge on Arctic cod. Researchers are investigating the potential impacts of lost summer ice on Arctic cod populations, and therefore whales and seabirds.

Sea Ice Gives And Takes Life

Ringed seals, which are found only in the Arctic, use sea ice as a pupping platform by creating snow caves called lairs. They also hunt, molt and rest on the ice, rarely moving onto the land. Consequently, they’re particularly vulnerable to the estimated increases in sea ice melting rates.

Whales periodically get trapped in drifting sea ice that in certain conditions can solidify very quickly. This unique Arctic phenomenon, called a sassat, means death for the trapped whales but life for polar bears, Greenland sharks, other scavengers and Inuit that prey on them.

The Earth’s Air Conditioner

Sea ice regulates the planet’s temperature by reflecting the sun’s radiation and heat. It also affects ocean currents. Cold, salty and dense polar water sinks and moves along the ocean bottom toward the equator, while the upper layer of warm water from the equator moves toward the poles where it cools and sinks to begin the journey again. The presence of the Arctic’s sea ice may be critical to maintaining this global ocean circulation. Even a 1°C - 2°C warming of the Arctic can greatly affect sea ice formation, making the Arctic one of the most sensitive regions to climate change in the world.

In The Grip Of Change

In March 2009, the melt season began with less of the thick multiyear ice and more of the thin first-year ice, which is vulnerable to melting in the summer. Arctic researchers are in a race against time and melting ice to document the diversity of life in and under the sea ice. The organisms that form the sea ice (sympagic) community are still little known, yet their home is melting away. Scientists also study sea ice to understand its role in the Arctic food web. This research will help us understand the impact of declining ice cover on Arctic life.


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