Icebergs in the North Atlantic and the International Ice Patrol

The International Ice Patrol was set up in 1914, two years after the Titanic sank, to track icebergs in the North Atlantic and warn ships about them. Operated by the U.S. Coast Guard, it surveys the Grand Banks region during the ice season and publishes the limit of all known ice, which reaches ships as NAVAREA IV warnings.

Because those bulletins are broadcast every day of the season, iceberg messages rise sharply each spring in this archive and almost vanish in autumn.

The bulletins are issued under the name of the North American Ice Service, a partnership that includes the Ice Patrol and the Canadian Ice Service, which is why "NAIS" appears as the originator of so many NAVAREA IV messages. The limit of all known ice is a line: outside it the ice services have no report of ice, inside it ships are expected to take extra care. It moves through the season as ice drifts south and melts, so each bulletin replaces the last rather than adding to it.

The largest icebergs are easy to see and to detect on radar. The harder hazard is the small ice that breaks off them: a bergy bit stands roughly one to five metres above the sea, a growler less than one — low enough to hide in waves and return a weak radar echo. Ice warnings describe the area where such ice may be found, not every piece in it.

Further north, five Arctic NAVAREAs coordinated by Canada, Norway and Russia broadcast warnings through the summer navigation season: survey work, scientific moorings and ice-related notices along the Northwest Passage and the Northern Sea Route.

Icebergs also appear in warnings from the southern oceans, where ships on routes round the southern capes or to Antarctica report bergs, and where very large icebergs tracked by satellite occasionally drift toward shipping lanes. Those reports are far fewer than the North Atlantic bulletins, and in this archive they are mostly NGA relays of the southern NAVAREAs' warnings.