Why Does Sea Ice Matter?
Updated: Oct 2
Sea ice can change an Arctic expedition completely.
When there is too much ice for a vessel to safely pass, the itinerary has to change. Modern ships operating in polar waters are subject to specific requirements covering vessel capability, navigation, training, safety and environmental protection. The IMO Polar Code also requires ships covered by the Code to operate within assessed capabilities and limitations for the conditions they may encounter.¹
That may sound technical, but for a traveler it comes down to something quite simple. The Arctic is not a fixed landscape. The ice moves, and the expedition has to move with it, with safety always taking priority.
Sea ice is also different from the icebergs and glaciers we see in the Arctic. Sea ice is frozen seawater that floats on the ocean. Glaciers form from accumulated snow on land, and icebergs are pieces of glacier ice that have broken away and entered the ocean. Sea ice also plays an important role in the polar climate and ecosystem.
For the people who explored the polar regions before modern navigation, however, moving sea ice was not something to be monitored from a bridge. It was the surface they were standing on.
When the Ice Moves South
One of the most difficult things to understand about travelling across Arctic sea ice is that walking north does not necessarily mean that you are getting north at the same rate.
Robert Peary recorded this problem during his attempt to reach the North Pole.² Bartlett could march five miles north in a morning and still find that his position had barely advanced. The reason was that the ice itself was moving south beneath them.
Peary wrote that the northerly wind had “crowded the ice southward as we traveled over it northward.” During five marches, they had travelled fully twelve miles more than their observations showed, but the movement and compression of the ice had taken those miles away again.²
The numbers give some idea of the scale of the problem. One account records an expedition having spent six months on the floe while drifting more than 1,600 miles.³
This is why polar exploration could involve extraordinary distances without the explorers actually covering the geographical distance they intended. They were walking across a moving surface.
The same principle explains why sea ice has to be treated as part of the navigation system on a modern expedition. The vessel is not simply moving through a static map. The conditions are changing around it.
When the Ice Cracks Beneath You
For early explorers, the movement of the ice could become an immediate physical danger. One account describes an explorer settling down to sleep after hearing the ice creaking and groaning around his igloo. He checked that his mittens were within reach, lay down again and tried to sleep.
Then someone shouted outside.
When he looked through the opening of the igloo, there was suddenly a broad lead of black water between the camps. The ice had broken within a foot of one of the dog teams. Another team narrowly escaped being buried beneath a pressure ridge. A section of the floe carrying another group had separated and was drifting away.⁴
The expedition had been divided by the movement of the ice while everyone was asleep.
The men had to pack their equipment, cross the crack and wait for the detached floe to drift close enough for the separated party to make the crossing. They eventually managed to recover the men, sledges and boats. But there was no certainty that the ice would remain stable. They went to sleep again wearing their mittens, ready to move at a moment's notice.⁴
The explorer's description of the ice as a “treacherous antagonist” is unusually effective because it captures the reality of travelling on a surface that looks solid while remaining in constant motion.
There was even a biblical phrase that Peary used to describe this kind of existence:
“Sufficient unto the day is the evil thereof.”
It comes from Matthew 6:34, but Peary used the phrase as a fitting motto for life on the ice. Each day could bring its own problem, and there was little value in assuming that tomorrow's conditions would resemble today's.⁵
The historical examples also show why expedition travel cannot be understood simply through distance. An explorer might spend weeks travelling north, only to discover that the ice had carried the entire party in another direction.
The Ice Can Take You With It
This relationship between people and moving ice becomes even more striking in the Antarctic. Ernest Shackleton's Endurance entered the Weddell Sea during his 1914–1917 expedition and became trapped in the pack ice, which was not an uncommon occurance during the winters. The ship could no longer control its own movement. The ice carried it through the Weddell Sea while pressure gradually increased around the hull.
Shackleton described the situation in stark terms:
“Millions of tons of ice pressed inexorably upon the little ship that had dared the challenge of the Antarctic.”⁶
The pressure was not simply a slow squeeze. Shackleton described new pressure ridges rising around the ship, timbers creaking and groaning, and the vessel bending under the strain. Eventually the Endurance could no longer survive the forces around it.⁶
The photographs from the expedition make this history particularly tangible. They show the Endurance surrounded by the pack, with enormous pressure ridges building around the ship as the ice closed in.⁷
When Shackleton finally recorded the loss of the Endurance, he described the ship as crushed after 281 days in the ice. It had drifted more than 570 miles northwest, while the total drift through its recorded positions was 1,186 miles. Shackleton estimated that the actual distance travelled may have exceeded 1,500 miles.⁸
That is one of the most useful historical connections for understanding polar travel today. The explorers experienced sea ice as a physical system that could carry them, trap them, separate them and destroy their vessel. Modern expedition teams have vastly better information and equipment, but the underlying environment has not become predictable.
The Ice Still Decides Where You Go
Today, the bridge and expedition team can work with satellite information, weather forecasts, ice charts, local observations and information about the vessel's capabilities. Ships operating under the Polar Code have documented operational limitations and a Polar Water Operational Manual to support decisions about where and how they can operate. The Code also requires voyage planning to take account of conditions such as ice, icebergs, darkness, fog and pressure ice.¹
The technology has changed enormously. The principle has not.
A modern expedition may approach an area expecting to follow a particular route and discover that the ice has closed the passage. The team may then have to wait, find another route or change the day's plans. This is not simply a logistical inconvenience. It is part of what makes an expedition different from a conventional cruise.
The history makes that easier to understand. When Peary's party marched north while the ice moved south, they were experiencing the same fundamental relationship between human movement and sea ice. When Shackleton watched the Endurance being carried hundreds of miles by the pack, he was experiencing it on an even larger scale.
For today's traveler, sea ice may be something we watch from a ship, observe from a Zodiac or see stretching toward the horizon. But it is still an active part of the environment around us.
It also matters because of what lives there. Sea ice forms habitat for species including seals and polar bears and influences the wider Arctic marine ecosystem. Its seasonal formation and retreat affect animals as well as navigation and human activity.
That is why understanding the ice changes the way we look at the Arctic.
You are not simply looking at white, frozen water.
You are looking at something that moves, changes shape, carries heat and salt, creates habitat, affects wildlife and can determine where a ship is able to go.
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Choosing an Expedition That Works With the Ice
When comparing Arctic expeditions, we look closely at how the vessel and expedition team respond to changing conditions. Ice capability, safety procedures, the experience of the bridge and expedition team, and the operating environment all matter.
The best preparation is understanding before departure that the ice is part of the journey itself.
The explorers who travelled across it had no choice but to accept that reality. Modern travelers have the advantage of seeing it with considerably more information, technology and comfort.
The Arctic is about far more than reaching a remote destination. Explore our broader approach to Expedition Travel.
International Maritime Organization, International Code for Ships Operating in Polar Waters (Polar Code). The Code covers ship design, construction, equipment, operations, training, navigation, search and rescue, and environmental protection in polar waters. It also requires Polar Ship Certificates and Polar Water Operational Manuals for applicable vessels.IMO Polar Code
T. McCarthy (Ed.), The Greatest Polar Exploration Stories Ever Told (Lyons Press, 2004), “In Search for Franklin,” p. 96. Account of Peary and Bartlett's northward progress being offset by the southward movement and compression of the sea ice.
Ibid., p. 96. Account of the expedition having spent six months on the floe and drifting more than 1,600 miles.
Ibid., pp. 102–103. Account of the ice cracking beside the igloos, a dog team nearly being pulled into the water, Bartlett's party becoming separated on a drifting ice raft, and the expedition moving camp.
Ibid., p. 105. Passage using “Sufficient unto the day is the evil thereof” as a motto for life on the Arctic ice.
Ibid., p. 228. Ernest Shackleton's account of the Endurance being subjected to increasing pressure from the Antarctic pack ice.
Shackleton's Expedition to the Antarctic: Terrors of the Weddell Sea. Historical photographs of Shackleton's expedition and the Endurance in the Weddell Sea.Shackleton's Expedition to the Antarctic: Terrors of the Weddell Sea
Ibid., pp. 229–230. Ernest Shackleton's account of the final destruction and abandonment of the Endurance after 281 days trapped in the ice, including the ship's recorded drift and his estimate of the total distance travelled.
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