Expedition Guide: Sea ice

Sea ice is a critical component of the polar regions and plays a significant part in global ocean circulation, atmospheric patterns, and marine life. Studying sea ice provides valuable insights into climate change, as its dynamics are sensitive to fluctuations in temperature and environmental conditions.
Sea ice formation influences the global ocean circulation through thermohaline circulation. When sea ice forms, the salt rejected during the freezing process increases the salinity of the surrounding water, making it denser. This dense water sinks and contributes to deep ocean currents that help regulate global heat and nutrient distribution.

Scientists monitor sea ice using satellites, which provide data on ice extent, thickness, and movement. Instruments like passive microwave sensors have been crucial for tracking changes in sea ice since the late 1970s.

Researchers also conduct field studies, drilling ice cores to analyse salinity, temperature, and the chemical composition of sea ice. These studies help scientists understand the physical processes that govern ice formation, melting, and interaction with the atmosphere and ocean.

Sea ice takes various shapes and forms depending on its stage of development and several environmental and meteorological conditions.

Pack ice is a large area of floating sea ice driven together into a nearly continuous mass, typically by wind and ocean currents. It is composed of individual pieces of ice, known as floes, which can vary in size from small chunks to vast fields that cover many square kilometres. Pack ice is commonly found in polar regions, particularly in the Arctic and Antarctic, where temperatures are low enough to freeze seawater.

Pack ice forms when seawater freezes. It consists of numerous pieces of floating sea ice, known as ice floes, that are driven together by wind and currents. The ice can range from small chunks to large expanses covering many square kilometres. It constantly shifts due to winds, tides, and ocean currents. This movement can cause the ice to crack, compress, and pile into pressure ridges.

Pack ice is crucial for polar ecosystems, providing habitat for seals, penguins, and polar bears. It also reflects sunlight, helping to regulate global temperatures.

An iceberg is a large piece of freshwater ice that has broken off (or "calved") from a glacier or an ice shelf and floats freely in the ocean. While icebergs can be found in the Arctic and Antarctic regions, they are most associated with the North Atlantic and Southern oceans around Antarctica.

Unlike pack ice, icebergs originate from land-based ice and can be found drifting in the ocean, primarily in the North Atlantic and around Antarctica. They often float far from their point of origin, sometimes reaching more temperate regions. Typically, they are white or blue. Their blue colour is caused by the compression of ice, which forces out air bubbles and allows the ice to absorb red wavelengths of light while reflecting only blue.

They can be massive, with some towering above the water, but most of their mass (about 90%) is submerged underwater. They vary in size from small bergy bits to colossal icebergs that can be as large as small islands.

Arctic Icebergs originate from glaciers in Greenland and the Arctic Archipelago. They are often irregular in shape and can be found drifting in the North Atlantic Ocean.

Antarctic Icebergs are primarily tabular icebergs that break off from the vast ice shelves surrounding Antarctica. They can be massive and tend to be more uniform in shape compared to Arctic icebergs.

Types of Icebergs:

Tabular Icebergs: These are large, flat, and often rectangular, resembling a table. They are common in Antarctica, where they break off from ice shelves.

Pinnacled or Non-Tabular Icebergs: These have irregular shapes with peaks and ridges. They are more commonly found in the Arctic and result from glacier calving.

Sea ice is frozen ocean water that forms, grows, and melts in the ocean. It occurs in polar regions and can cover vast areas of the Arctic and Southern Oceans, particularly during winter. Unlike icebergs, which are chunks of ice that break off from glaciers and float in the sea, sea ice forms directly from seawater.

Sea ice plays a critical role in regulating the Earth's climate by reflecting sunlight, influencing ocean circulation, and providing habitat for various polar species. The extent and thickness of sea ice are sensitive indicators of climate change, with significant declines observed in recent decades, especially in the Arctic.

Main types of sea ice:

Pack Ice (Drift Ice): This type of sea ice is not anchored to the coastline or sea floor. It moves and shifts with winds and currents. Pack ice can vary in thickness and may cover large ocean surface areas.

Fast Ice: As mentioned earlier, fast ice is sea ice that is attached to the coast, islands, or other fixed objects. It is stationary compared to pack ice.

Old ice, also known as multi-year ice, is sea ice that has survived at least one summer melt season. Unlike newly formed sea ice, which is relatively thin and more prone to melting, old ice has been through several freeze-thaw cycles, making it thicker, more compact, and less saline. This process makes old ice more durable and less likely to melt in the summer.

Old ice is significant in the Arctic, providing a more stable platform for wildlife and a vital component of the region's ice cover. However, due to climate change and rising temperatures, the extent of old ice has been decreasing, making the Arctic more vulnerable to warming and further ice loss.

Categories of old ice:

Second-Year Ice: This ice has survived one summer and is in its second year of growth. It tends to be thicker and more robust than first-year ice.

Multi-Year Ice: This ice has survived two or more summers. It can be several meters thick and is the most stable and long-lasting sea ice type.

Growlers are small chunks of ice that have broken off from more enormous icebergs or glaciers. They are typically less than 1 metre above the waterline and can extend 5 metres below the surface. Despite their relatively small size, growlers can still pose significant hazards to ships, as they are difficult to spot and can cause damage if they collide.

Growlers get their name from the noise they often make as they bob in the water and melt, creating a "growling" sound. Their small size and low profile make them hard to detect visually or by radar, particularly in rough seas. This makes them a concern for navigation in polar and cold-water regions.

Bergy bits are medium-sized chunks of ice that have broken off from glaciers or icebergs, larger than growlers but smaller than full-sized icebergs. They typically rise 1 to 5 metres above the waterline and can be up to 10 metres long. Bergy bits often result from the fragmentation of larger icebergs as they melt or break apart.

Like growlers, bergy bits can be hazardous to ships because they are difficult to spot and can cause significant damage if hit. Their size makes them more visible than growlers, but they still pose risks, especially in foggy or rough conditions where they might not be easily seen or detected by radar.

Pancake ice is a type of sea ice that forms in circular, disk-shaped pieces with raised edges. These "pancakes" typically range from 30 centimetres to 3 metres in diameter. The raised edges are created as the ice floes collide, causing their edges to thicken and round off.

Pancake ice forms in turbulent waters, such as in the early stages of sea ice formation, when wave action is present. It can also develop when existing ice floes break up and are reshaped by wave motion. Pancake ice can eventually consolidate into larger ice floes as the pieces freeze together, forming more extensive sea ice coverage.

This type of ice is expected in the polar regions and indicates early ice formation, often seen during the transitional periods of freeze-up or melt seasons.

Nilas ice is a thin, elastic layer of sea ice that forms in the early stages of ice formation. It is typically less than 10 centimetres thick and can be easily bent by waves and currents. Nilas ice has a smooth, dark surface, appearing almost black due to its thinness, which allows more of the underlying water to show through.

Nilas ice can grow into thicker ice forms as it continues to freeze, often transitioning into young ice as it consolidates. In calm conditions, nilas can spread over large areas, gradually thickening into more stable ice. Its formation is an early indicator of seasonal ice development, especially in polar regions.

There are two main types of nilas:

Dark Nilas: This is the thinnest form, generally less than 5 centimetres thick. It has a darker appearance due to its thinness.

Light Nilas: As the ice thickens slightly (up to 10 centimetres, it takes on a lighter colour because it reflects more light.

Brash ice refers to a collection of small, broken pieces of sea ice, icebergs, or ice floes that typically form a loose, floating layer on the ocean surface. These ice fragments are often no more than 2 metres in size and can be created from the breakup of more giant ice formations due to winds, currents, or the movement of ships through ice-covered waters.

It can appear as a chaotic, jumbled mass of ice pieces floating on the water's surface. It is typically found in narrow channels, near the edges of ice fields, or along coastlines where ice has broken up.

The individual pieces of brash ice are generally less than 2 metres, and the layer of brash ice is usually thin, making it different from larger, more consolidated ice floes or icebergs.

Floe ice (or ice floe) refers to a large, flat, free-floating sheet of sea ice or freshwater ice that has broken off from a larger ice mass, such as an ice pack. These floating ice sheets can vary significantly in size, from a few meters across to several kilometres wide, and they drift with ocean currents and winds.

Ice floes provide crucial habitats for polar species, including seals, penguins, and polar bears. The underside of the ice also supports algae growth, which is vital to the polar food chain.

In winter, ice floes grow more extensive and merge with other floes, contributing to the overall expansion of sea ice. Meanwhile, warmer temperatures cause ice floes to shrink or break apart in summer. These smaller floes drift farther, sometimes reaching subpolar regions before melting completely.