A magnetic compass operates by aligning its magnetized needle with the Earth’s local magnetic field lines. When used in Antarctica, the answer to whether it works is qualified: yes, but with major reservations. While a compass technically responds to the magnetic field, its reliability and directional accuracy diminish significantly near the South Magnetic Pole. This extreme environment renders the standard compass largely impractical for precise navigation.
Geographic vs. Magnetic Poles
The primary complication is the difference between the Geographic South Pole and the South Magnetic Pole. The Geographic South Pole is the fixed point at 90 degrees South latitude, marking the Earth’s axis of rotation. The South Magnetic Pole is the location where the planet’s magnetic field lines are oriented vertically upward from the surface.
These two poles are separated by approximately 2,860 kilometers and are not fixed. The magnetic pole constantly shifts its position due to the churning of molten iron in the Earth’s outer core. Consequently, a magnetic compass points toward this constantly moving Magnetic Pole, not the fixed Geographic Pole, making traditional North-South navigation unreliable.
The South Magnetic Pole has recently been located off the coast of Antarctica and drifts northwestward at a rate of roughly 10 to 15 kilometers annually. This movement causes the “magnetic declination”—the angle between magnetic north and true north—to change rapidly across the landscape. Navigators must constantly consult updated charts to correct for this extreme variation.
The Problem of Magnetic Dip
Even when pointing toward the Magnetic Pole, a compass near Antarctica faces a severe mechanical challenge known as magnetic dip, or inclination. In most parts of the world, the magnetic field lines run parallel to the surface, allowing the needle to swing horizontally. Near the poles, however, these field lines curve sharply to plunge straight into the ground.
At the South Magnetic Pole, the field lines are completely vertical. A freely suspended magnetic needle would attempt to align itself with these lines, pointing straight down at a 90-degree angle. Standard magnetic compasses are manufactured with a weighted needle to maintain horizontal balance in their intended hemisphere.
The overwhelming vertical pull in the Antarctic overcomes this balance, causing the needle to drag against the casing or tilt so severely that it cannot rotate freely. This mechanical interference renders the compass useless for accurate directional readings. Specialized polar compasses must be significantly reweighted to compensate for this extreme dip.
How Navigation is Actually Done in Antarctica
Because magnetic compasses are unreliable in the polar environment, scientists and explorers rely on alternative methods for accurate navigation.
Global Positioning System (GPS)
The most widely used tool today is the Global Positioning System (GPS). It uses a network of satellites to determine a precise location based on a fixed coordinate system tied to the Geographic Pole. GPS provides highly accurate latitude and longitude, eliminating the need to account for magnetic variation. Although reliable, GPS coverage can occasionally be limited at the highest latitudes, or its accuracy diminished due to the low angle of the satellites on the horizon.
Backup Navigation Methods
Navigators employ specialized techniques and instruments as backups:
- Grid North, a simplified coordinate system where all lines run parallel to the Prime Meridian, creating a stable, fixed reference direction.
- Gyrocompasses, which determine direction based on the Earth’s rotation and point to True North, independent of the magnetic field.
- Celestial navigation, using instruments like the astrocompass or sextant to take readings from the sun and stars.