An iceberg is a substantial piece of freshwater ice, typically more than 15 meters long, that has detached from a glacier or ice shelf and floats freely in open water. While their appearance above the water can be striking, about 90% of an iceberg remains hidden beneath the ocean’s surface. Various natural forces influence their journey across the oceans, determining how far they travel from their polar origins.
From Glaciers to Open Ocean
Icebergs begin as part of vast ice sheets and glaciers, primarily in regions like Greenland and Antarctica, where snow compacts into dense ice over centuries. These formations slowly flow towards the ocean. The process where chunks of ice break off from a glacier or ice shelf and fall into the water is known as calving.
The detached ice varies greatly in size, from small pieces called “growlers” to massive icebergs. Once calved, icebergs embark on journeys that can span thousands of miles across the global oceans. This detachment is a regular occurrence, with some Greenland glaciers producing thousands of new icebergs annually.
Forces Shaping Their Path
Ocean currents play a primary role in determining an iceberg’s trajectory, carrying these ice masses across vast distances. For instance, the Labrador Current transports icebergs southward from the Arctic into the North Atlantic, while the Antarctic Circumpolar Current drives icebergs eastward around Antarctica. The deep draft of icebergs means they are predominantly steered by underlying water currents, which can make their paths unpredictable.
Water temperature is a significant factor in an iceberg’s melting. As icebergs encounter warmer ocean waters, the rate of melting accelerates, with the sides melting faster than their bases. Air temperature also contributes to surface melting and can weaken the iceberg.
Wave action further contributes to iceberg deterioration through erosion and fracturing. Waves can eat away at existing cracks, leading to the collapse of sections and the formation of smaller pieces. The size and shape of an iceberg also influence its longevity; narrower icebergs that extend deeper underwater may melt faster than wider, less submerged ones.
The Southernmost Reaches
An iceberg’s journey is limited by warming ocean waters and the forces that cause them to melt and break apart. In the North Atlantic, icebergs typically travel as far south as the Grand Banks off Newfoundland, usually reaching latitudes around 48°N. Larger icebergs can occasionally drift further south, such as one sighted near Bermuda in 1926, approximately 30°N.
In the Southern Hemisphere, icebergs from Antarctica populate the Southern Ocean, often drifting into the South Pacific near New Zealand and the South Atlantic near South America. The Antarctic Circumpolar Current generally keeps southern icebergs between 50°S and 70°S. However, under specific conditions, they can reach lower latitudes. For example, in November 2006, a chain of icebergs was observed off Dunedin, New Zealand, at about 46°S. Large icebergs, like A23a from Antarctica’s Filchner Ice Shelf, have drifted towards the sub-Antarctic island of South Georgia. These icebergs inevitably break up and melt as they encounter warmer waters.