The Polar Encyclopedia

THE ARCTIC OCEAN AND THE OCEAN CURRENTS
GENESIS OF THE ARCTIC OCEAN
ARCTIC PLANKTON
MARINE BIODIVERSITY AND FOOD WEB
WHALES AND OTHER CETACEANS
SEALS AND WALRUSES

TERRESTRIAL LIFE

POLAR FLORA
POLAR FAUNA
THE POLAR BEAR
ARCTIC BIRDS
SPECIES EVOLUTION AND CLIMATE

HISTORY AND GEOGRAPHY

GEOGRAPHY OF THE ARCTIC REGIONS
GEOGRAPHIC NORTH POLE, MAGNETIC NORTH POLE
WHO OWNS THE ARCTIC?
THE EXPLORERS OF THE FAR NORTH
THE INUIT
OTHER PEOPLES OF THE FAR NORTH
THE ARCTIC TODAY

SEA ICE: MARINE ICE

A LAYER OF ICE ON THE SEA SURFACE

At the end of summer, the polar cold sets in, sometimes abruptly (–40°C); the ocean surface cools. When it reaches –1.8°C, the first ice crystals form. Once the surface is frozen, the seawater is isolated from the cold air and the process slows down. The sea ice then slowly thickens from its underside, reaching approximately 2 meters.

FRESH OR SALTY?

As it freezes, seawater forms an interweaving of freshwater ice crystals and brine droplets. During winter, these salty droplets cluster together, forming wider networks, then pockets, and migrate downwards before being expelled into the sea. Thus, as it ages, the sea ice freshens.

THE LIFE OF SEA ICE

In the heart of winter, sea ice extends over nearly 15 million km², of which almost half will melt during the summer. The remaining portion will persist for 2, 3, 4 years or more, and its thickness will then reach 4 to 5 meters. During this time, this ice crust will traverse the Arctic Ocean, carried by currents: this is the Arctic drift.

A CHAOTIC RAFT

Sea ice is merely a thin eggshell compared to the 4000 meters of water on which it floats! Carried by currents, harassed by winds, it constantly breaks, opens, and overlaps, creating, here, open water channels, and there, ice ridges whose crests can reach ten meters in height.

THE ONSET OF FREEZING

The nature of the first ice depends on the state of the sea. In calm weather, large needle-shaped crystals align parallel to each other and form a 1 to 2 cm thick layer on the surface (an icy ‘soup’). If the sea is rough, small crystals develop in all directions, sometimes up to a meter deep, forming a thick viscous layer: frazil ice. Only then does freezing begin on the surface. This freezing process can last from 9 to 36 days.

WHEN THE ICE THICKENS

As long as the ice is thin, swell and winds fragment it into ‘pancakes,’ which eventually fuse together to form young sea ice, then capable of retaining snow. It takes several weeks for the ice to reach 60 cm in thickness. By slowly expelling air bubbles and brine, the ice compacts, freshens, and becomes blue and translucent.

The Antarctica caught in the ice off Spitsbergen. © F. Latreille/7th Continent

AT THE HEART OF THE ICE

In the Arctic, sea surface salinity varies from 32 to 33 g/L (compared to an average of 35 for the global ocean). The first ice crystals form small lamellae 1 millimeter thick, and tiny brine droplets (about ten micrometers) are trapped within this crystalline network. Young sea ice thus traps up to 22 g/L of salts. Seawater also contains impurities and air bubbles, which are also trapped in the ice.

CONSTANT AGITATION

Under the influence of winds, currents, and tides, sea ice constantly fragments and reforms. Here, open water channels open up, as do sorts of inland lakes (polynyas) due to local upwellings of less cold water. There, fissures close.
Collisions between fragments create compressed ice ridges, whose crests can reach 10 meters and keels can extend up to sixty meters deep!
Near the coasts, sea ice is also shaped by tides, freshwater inputs, coastal currents, and exposure to wind or sun. A grounded ice foot, resting on the seabed, remains attached to the coast. This ‘shore ice’ can be thicker than the sea ice itself and anchor to the seabed; offshore, it extends as a band of ‘fast ice’ (in English fast ice), which can survive for more than 10 years. Sometimes, trapped icebergs are found there.

WHEN MELTING OCCURS

At the end of May, snow and the first centimeters of ice melt, forming melt ponds on the sea ice surface. This water reflects less solar energy than bare ice and warms up faster, locally accelerating the melt. When the sea ice fractures, large sections break free (floes) and then drift with the currents. This is the breakup. In the center of the Arctic Ocean and along sheltered coasts, the sea ice will not thaw.

THE GRAND BALLET OF THE ARCTIC DRIFT

The icy puzzle of the Arctic Ocean follows, over the months, the general movement of the waters that carry it. This is the Arctic drift.Sea ice moves according to two main currents: a large cyclonic loop, centered around 80° N–155° W, and a long drift that crosses the ocean, from the Bering Strait to the Greenland coast. On average, ice can circulate for 5 years in the Arctic loop, while a block will take approximately 3 years to follow the central trans-Arctic current.
The Arctic drift was discovered thanks to the debris from the wreck of La Jeannette (1881), found 3 years later thousands of kilometers from the shipwreck site. Nansen with the Fram in 1893-1896 and Papanin in 1937 utilized this drift.

STUDYING SEA ICE

Channels, compression ridges, ice of varying salinity and age, seasonal pulsation, drift: the entire life of the sea ice is monitored by scientists using drifting stations installed on the ice, beacons, and satellites.

NAVIGATING SEA ICE

Sea ice concentration is subjectively expressed in tenths of occupied sea surface; thus, a pack of 9/10 or 10/10 density is impenetrable – except by powerful icebreakers – while the Antarctica could begin to navigate in 4 or 5/10.

THE PHYSICISTS’ CORNER

The surface water layer of the Arctic Ocean is particularly favorable for freezing, as it is freshened by the influx of relatively low-salinity water from the North Pacific and freshwater from large boreal rivers. ‘Weighted down’ by the winter surface temperature drop, this water should sink to the bottom; however, in the Arctic, a much saltier – and thus denser – water layer blocks this descent and forces the surface water to remain in contact with the cold air for longer.

‘A specific high-latitude phenomenon is ‘smoking sea’, generally produced in winter by the arrival of very cold air over a relatively warm sea: the intense evaporation that results has all the appearances of smoke.’
(Geostrategy of the Arctic – Economica, 1992)

The thicker the ice, the poorer the heat conduction – and thus the freezing rate. ‘In channels, freezing rates are a few centimeters per day, whereas thick ice has a growth rate closer to a millimeter per day (…): a compensatory thermodynamic effect that tends, on one hand, to fill open water areas (…) and, on the other, to limit growth at the base of deformation ridges.’ (The Planetary Ocean – Sciences et avenir 1994)

Since freezing immobilizes liquid water molecules that were previously in motion (thermal agitation), the formation of sea ice releases an amount of energy corresponding to this initial agitation, which warms the ambient air! This energy will again be necessary for melting to occur – that is, to put these water molecules back into motion.

The melting of one gram of ice at 0°C consumes nearly 3.34×10⁵ J·kg⁻¹ calories (latent heat of fusion), which is 8.5 times less energy than the evaporation of one gram of liquid water at around 20°C (latent heat of vaporization).
By definition, 1 calorie is ‘the amount of heat required to raise the temperature of 1 gram of water by 1°C’; it is equivalent to 4.186 joules, and a work of 1 joule per second is equivalent to a power of 1 watt.

The density of sea ice falls within a fairly wide range, depending on the salts and air contained: between 0.857 and 0.920. This ensures comfortable buoyancy in Arctic seawater with a density of 1.024 to 1.026.

The coefficient of thermal expansion of sea ice plays an important role in its evolution. Unlike that of pure ice, it varies considerably with temperature. Furthermore, each dissolved salt – in the chemical sense of the term – reacts differently to freezing. These phenomena result in tensions, sometimes very strong, within blocks where ice of different salinities are juxtaposed.

VOCABULARY

Bourguignons	French name for growlers, small floating ice fragments, undetectable by radar.
Crêpes de glace	Pancakes for the English and blinis for the Russians!
Hummocks	Inuit name for compression ridges.
Frazil	First layer of water and ice mixture; salo, lard, in Russian, and grease, in English, due to its appearance.
Leads	Open water channels, in English.
Floes	Angular, relatively flat sea ice fragments, at least a few meters across, sometimes reaching several tens of kilometers.
Pack	Another name for sea ice; not to be confused with floating ice shelves, which are actual sections of continental glaciers reaching the sea.
Polynyas	‘Lakes’ of open water.
Sorbet	Mixture of seawater and ice, after frazil ice; slush in English.
Stamoukhi	Inuit name for grounded ice formations.
Torros	Russian name for stamoukhi.
Growlers	(see bourguignons)

JEAN-LOUIS ETIENNE ON THE SEA ICE

It was on this sea of icy obstacles that Jean-Louis Etienne walked, alone, pulling his sled, to reach the North Pole in 1986.

‘At times, the sea ice rises before my eyes; the floes collide, pressing against each other with unsettling creaks. They even rise like walls, only to collapse into a dull roar that spreads for kilometers. Sometimes a sudden explosion and the sea ice cracks, the floes separate, revealing a sinister black zigzag: it’s the icy water of the Arctic Ocean! First, it evaporates into a curtain of fog, and then, as soon as the fissure stabilizes, it freezes again.’ (The Poles – Arthaud, 1992)

During the Antarctic Erebus mission in 1994, the Antarctica remained trapped in the sea ice for many days, which was particularly compact in the Ross Sea that year. The crew searched for possible passages by observing the color of the sky, which was locally darker above open water channels. An unexpected solution: to sneak in the wake of an American icebreaker!

DID YOU KNOW?

> One of the seawater desalination processes uses freezing. Indeed, the freezing of saltwater, if slow enough to prevent the inclusion of brine droplets in the ice, yields pure ice.

> The climates of regions covered by glaciers or sea ice are dry climates, because ice emits much less vapor than water in a low-temperature atmosphere.

> During ice formation, the compressive force is so significant that it
can crush a ship’s hull (shipwrecks of the Jeannette in the Arctic, the Endurance in the Antarctic, etc.)… even an oil tanker!

> For English polar explorers, the freshening of sea ice is expressed as follows: ‘one-year-old sea ice is good for nothing, two-year-old ice is good for cooking, and three-year-old ice is good for tea!’

The Pulsations of Sea Ice

Sea Ice	Summer	Winter
Arctic	8 million km²	15 million km²
Antarctic	20 million km²	4 million km²