An iceberg is a large mass of freshwater ice that has broken away from a glacier and is freely floating in the ocean. This floating ice is distinct from sea ice, which is frozen ocean water. These structures can extend over 5 meters above the sea surface and are a regular, natural phenomenon in the North Atlantic Ocean. Their presence is a consequence of the planet’s glacial systems interacting with ocean currents.
Glacial Origin and Formation
The vast majority of icebergs in the North Atlantic originate from the glaciers of western Greenland. These glaciers form from centuries of accumulated snowfall that compresses into dense, freshwater ice. This immense weight drives the ice mass slowly toward the coastlines, where it meets the sea.
The process of iceberg creation is known as calving. This occurs when massive chunks of ice break off the glacier’s terminus, or front edge, and crash into the water. The rapidly moving outlet glaciers of the Greenland Ice Sheet are prolific sources, with an estimated 15,000 to 30,000 icebergs calving annually.
Because the freshwater ice is dense, approximately seven-eighths of an iceberg’s total mass remains submerged below the waterline. This submerged portion, known as the “foot” or “keel,” makes icebergs dangerous to navigation. The ice itself can be thousands of years old by the time it begins its journey into the open ocean.
The Role of Ocean Currents
Once an iceberg has calved, its trajectory across the North Atlantic is largely governed by a powerful system of ocean currents. The primary mechanism for southbound transport is the Labrador Current. This cold-water current flows southward from the Arctic, carrying the glacial ice along the coasts of Baffin Island and Labrador.
The Labrador Current acts as a conveyor belt, pushing the ice masses toward lower latitudes. The journey from the calving front to the shipping lanes typically takes between one and three years. The current carries the ice past Newfoundland and into a region known as “Iceberg Alley,” concentrated near the Grand Banks.
This cold flow eventually collides with the warm, northward-moving Gulf Stream. The convergence of these two different water masses determines how far south the icebergs can travel. The meeting point, often near the 48th parallel north, creates a boundary where the ice begins to rapidly deteriorate.
The warm Gulf Stream water dictates the southern and eastern limit for iceberg travel in the Atlantic. Although the Labrador Current can occasionally push icebergs further south, the thermal boundary ensures their destruction. This ocean circulation pattern explains why icebergs appear in the major North Atlantic shipping lanes.
Factors Governing Iceberg Dissipation
The moment an iceberg enters the ocean, forces of dissipation immediately begin to act upon it. The primary factor in an iceberg’s demise is the increasing temperature of the surrounding seawater. Once the icebergs reach the warmer waters influenced by the Gulf Stream, the rate of melting accelerates.
Increased salinity in the ocean water also contributes to the melting process. Salty water has a lower freezing point than freshwater, causing the ice to melt more quickly. The combined effect of warmer water and higher salinity rapidly erodes the submerged portion of the ice mass.
Physical erosion from the surface environment also plays a role in the iceberg’s destruction. Continuous wave action and wind physically batter the exposed ice, causing it to fracture and fragment into smaller pieces. This process, known as ‘tabling’ or fragmentation, reduces the overall size and stability. Most icebergs that calve from Greenland melt long before they reach the major trans-Atlantic shipping routes.