Icebergs are found in many parts of the world’s oceans. Perhaps the best known location is the western North Atlantic Ocean, which is where the RMS Titanic
struck an iceberg and sank in 1912. This is the only place where a large iceberg population intersects major transoceanic shipping lanes.
Numerous and massive icebergs from Antarctic ice shelves populate the Southern Ocean, which surrounds the Antarctic continent. Sometimes these icebergs drift into the South Pacific Ocean near New Zealand and into the South Atlantic near the coast of South America.
The Arctic Ocean has several iceberg sources, including the ice shelves of the Canadian Arctic, the Norwegian Svalbard archipelago, and numerous locations in the Russian Arctic. Finally, there are several glaciers, such as the Columbia Glacier in Alaska, that calve icebergs that do not move very far from their source.
In most years, icebergs enter the North Atlantic shipping lanes (red lines) during the spring and early summer.
Typical distribution of icebergs around the Antarctic continent.
Map from: National Ice Center, September 28, 2011.
Extreme icebergs locations (1881-1993). Icebergs may be found at many locations along the Russian Arctic coast.
Map from: Smolyanitsky, V. and, V. Abramov, 2008. Icebergs climatology in the Russian Arctic, 9th Meeting of the International Ice Charting Working Group, Lulea, Sweden, 20-24 October, 2008.
Icebergs in Newfoundland
Most of the icebergs that enter the North Atlantic shipping lanes come from the tidewater glaciers of the west coast of Greenland. Once an iceberg is calved from one of these glaciers it completes a 1-3 year journey to arrive in the area that the International Ice Patrol (IIP) monitors.
IIP’s data records, which extend to 1900, show that nearly 500 icebergs enter the shipping lanes in an average year. [The 1900-2010 average is 479.] However, the year-to-year variation is wide. In 1984, the busiest iceberg year in IIP’s history, 2202 icebergs entered the shipping lanes. On the other hand, during two years (1966 and 2006) no icebergs reached the shipping lanes.
Researchers have struggled for many decades trying to explain the year-to-year variation in the number of icebergs entering the North Atlantic shipping lanes. It is likely that fluctuation in the number of icebergs produced by the Greenland glaciers plays a role in the variability, but it might not be the dominant factor. The oceanographic and meteorological conditions icebergs encounter during their one to three year journey from the glacier’s calving front to the shipping lanes probably play larger roles.
There seems to be a link between IIP’s iceberg counts and the North Atlantic Oscillation (NAO), the dominant pattern of winter atmospheric variability in the North Atlantic. It fluctuates between negative and positive phases. Conditions associated with the negative phase of the NAO are unfavorable to the movement of icebergs toward the shipping lanes. The characteristic features of this phase include persistent onshore winds along the Labrador coast during the winter. This brings relatively warm maritime air to Labrador. The resulting lack of sea ice exposes icebergs to wave-induced deterioration, and the onshore wind moves them toward the shallower waters near the coast, where they can run aground or become trapped in bays. The positive NAO phase, on the other hand, is characterized by strong and persistent northwest winds along the Labrador coast during the winter. These winds bring cold air and extensive sea ice cover, which protects the icebergs during the last part of their journey south, a journey aided by the long-shore wind.
The inter-annual variability in the western North Atlantic iceberg counts remains impressive and difficult to understand and predict. Although the NAO index offers some help, it is clear that there are other mechanisms at work.