Currently we are not sure why the 1999 iceberg season was so mild. In an average year, nearly 500 icebergs pass south of 48º N, the traditional boundary below which icebergs are considered to be a menace to transatlantic shipping. In 1999, 22 icebergs passed south of 48º N. In a typical year, International Ice Patrol issues routine iceberg warnings to mariners from February through July. In 1999, Ice Patrol issued no warnings. Ice Patrol's aerial reconnaissance usually extends well into August. In 1999, routine aerial reconnaissance was suspended at the end of May.

With the hope that history could help us understand what happened in 1999, we reviewed the environmental conditions of twelve previous mild iceberg seasons. We found several features common to most light iceberg seasons:

• mild preceding winters in Newfoundland and Labrador
• persistent winter on-shore winds
• warmer than normal sea surface temperature near Newfoundland
• sea ice arrives late, departs early and is not very extensive
• the offshore branch of the Labrador Current is weaker than normal

Many of these factors were present in 1999. For example, the sea surface temperature (SST) southeast of Newfoundland in spring and early summer was 2 - 3 C warmer than normal. That alone does not explain the lack of icebergs south of 48º N. It takes many days for a large iceberg to disintegrate, and there certainly was an ample supply, had the currents been moving them southward. We examined the links between the iceberg counts and various atmospheric phenomena, such as El Nino-Southern Oscillation (ENSO), La Nina and the North Atlantic Oscillation (NOA). For the most part, these are not correlated very well with the iceberg counts and are not good predictors. For short periods there seems to be a good correlation between the NAO and the iceberg counts. However, the NAO index for 1999 suggested a moderate to severe iceberg season.

 The scarcity of icebergs passing south of 48º N latitude in 1999 was unusual, but not unprecedented. Twelve times in Ice Patrol's history there have been 25 or fewer icebergs reported south of 48º N. In fact, the 1999 season enters into a tie with 1977 for the ninth lowest iceberg count in Ice Patrol's history.

What made the 1999 iceberg season even more remarkable was the fact that there was no lack of icebergs in the western north Atlantic. Indeed, there were several thousand icebergs along the northern Newfoundland and Labrador coasts in the spring and early summer. For example, the chart below shows the Canadian Ice Services iceberg analysis on May 31, 1999, which shows they were tracking hundreds of icebergs between 47º N and 55º N early in the season. Very few of these icebergs moved into southern waters.

Analysis of the 1999 Ice Season provided by Dr. Don Murphy (Int. Ice Patrol Oceanographer)