This report is the first in a series of monographs put together by Enfotec Technical Services to describe environmental conditions of interest to mariners. This report provides a description of the ice conditions that form in the Gulf of St. Lawrence each winter, one of the busiest shipping channels on earth where sea ice occurs. This report is intended to serve as a guide to ice conditions for users of Enfotec’s IceNav^TM shipboard ice navigation service in the region.

Ocean currents play a critical role in determining the pattern of formation and distribution of sea ice in the Gulf of St. Lawrence. In fact, the preferred shipping channels that avoid most of the sea ice in the Gulf are created in large part by the currents in the water body.

The major feature of the oceanography of the Gulf of St. Lawrence is the outflow of fresh water from the St. Lawrence River into the estuary. The majority of the flow occurs along the north coast of the Gaspe Peninsula and is called the Gaspe Current. This current flows eastward at a rate varying from 10 to 20 nautical miles per day, increasing during the ebb tide and decreasing during the flood tide. The total volume of flow involved with the Gaspe Current is more than 20 times that of the volume of outflow from the St. Lawrence River, indicating that subsurface upwelling of ocean water plays a major roll in sustaining the current (we can see the effect of this on the ice but more about that later). Once past the Gaspe Peninsula, the currents follow a general counter clockwise flow in the Gulf of St. Lawrence with majority of the water exiting the Gulf in Cabot Strait along the Cape Breton coastline.

The tidal pulse from the Atlantic Ocean enters the Gulf of St. Lawrence from both the Cabot Strait and the Strait of Belle Isle. Tidal energies flow in a counter clockwise fashion around the Gulf increasing in height from .6 metres at the Magdalen Islands to nearly 5 metres at Quebec City.

Freeze-up

The first ice forms in the St. Lawrence River and along the north coast of the Gulf in mid to late November. Sea ice growth continues eastward past the Gaspe Peninsula to Anticosti Island as well as south of the north shore covering the Strait of Belle Isle to western Newfoundland by mid-January. Simultaneously, ice growth extends eastward from the coast of New Brunswick and Prince Edward Island to the Magdalen Islands and the west coast of Cape Breton Island by the end of January. Ice thickness rarely exceeds the grey and grey-white stage in the Gulf during January with new ice predominating along the lee side of landmasses, particularly the north shore of the Gulf of St. Lawrence.

Scattered floes of fresh water river ice and batture floes drift out of the St. Lawrence River into the Gulf of St. Lawrence throughout the ice season. Batture floes are large thick floes of mostly river ice that form on the upstream side of shoals in the St. Lawrence River when cold weather precedes the neap tide. These floes often break off during the spring tides and form formidable floes that should be avoided by mariners. Batture and river ice floes drift eastward into the Gulf of St. Lawrence primarily along the north coast of the Gaspe Peninsula then southward across the Bay of Chaleur. These floes are particularly dangerous, as fresh water ice is much harder and stronger than corresponding sea ice of the same thickness.

Ice development has usually reached its maximum extents in the Gulf of St. Lawrence by mid to late February, covering the entire Gulf to the Cabot Strait. In a colder than average winter, the sea ice edge will extend through the Cabot Strait to as far south as 43⁰N and west along the Nova Scotia coastline to as far as Halifax. In a warmer than average winter, ice development may not extend beyond the Magdalen Islands.

The existence of persistent leads and thin ice areas along the north coast of the Gulf of St. Lawrence as well as along the west coast of Newfoundland opposite Corner Brook are distinctive features of the early winter ice regime of the Gulf. The lead along the north shore is the result of the predominate north-west wind flow while the west Newfoundland lead is due to the inflow of warmer water currents from the Atlantic Ocean from the Cabot Strait in this area.

February 4, 1997 / February 20, 1997

Mid-Winter

There isn’t much of a mid-winter ice regime for the Gulf of St. Lawrence, usually only lasting from late February when the maximum ice extents are achieved until mid March when break-up and clearing begins. This mid-winter period is characterized by a thickening of the ice cover from young ice to thin first year ice over much of the central portion of the Gulf. The thickest ice in the Gulf of St. Lawrence is found in a triangle between the Magdalen Islands, P.E.I and Cape Breton Island, where pressure and ridging are also common. The thinner ice in the Gulf is usually found along the south facing shorelines of the north coast of the Gulf and along the south coast of Anticosti Island. These thinner ice areas form an important link in the shipping channel into the St. Lawrence River in winter. If you refer back to the current map of the first page, you will notice that the currents push the ice down toward P.E.I and diverge away from the area of the Gulf between Anticosti Island and the southwest tip of Newfoundland. This current pattern creates the lighter ice conditions that form the shipping channel through the centre of the Gulf.

February 28, 1997

Spring Break-up and Clearing

The start of the spring break-up usually begins in early to mid March when daylight hours increase and temperatures begin to rise to above the freezing point. The start of break-up is first evident in the estuary of the St. Lawrence River where loose pack and open water conditions expand from the Saguenay River eastward to the Gulf opposite Anticosti Island. The cause of this early expansion in the river is thought to be the result of the upwelling of warmer ocean water currents at the head of the Gulf leading into the St. Lawrence River, where thinner ice persists during the winter (I told you I was going to mention this again).

March 14, 1997

The pace of ice clearing is rapid during the month of March following the pattern of first clearing from the River eastward through the Gulf. Large expanses of open water occur in the western and central portions of the Gulf by the end of March with heavier ice conditions persisting in the area bordered by the Cabot Strait, Cape Breton Island, the Magdalen Islands to Prince Edward Island. High ice concentrations also occur in the Strait of Belle Island area west of the Island of Newfoundland. The higher concentrations of ice found off Cape Breton Island and the west coast of Newfoundland become separated by an open pack/open water route by early April.

Sea ice persists in the area north of Cape Breton Island well into May and in the Strait of Belle Isle until early June in most years.

During the late winter and early spring, icebergs can occasionally enter the Gulf of St. Lawrence from the Labrador Sea via the Strait of Belle Isle and can, on rare occasion, penetrate as far westward as Anticosti Island. Old ice does not occur in the Gulf of St. Lawrence and there are no known records of old ice floes from the Labrador Sea penetrating westward through the Strait of Belle Isle to reach the Gulf.

March 20, 1997

April 5, 1997

The general pattern described above usually always develops every year but the timing of the development and how much ice eventually develops can vary quite a lot. In some winters, the ice may not grow any further south and east than the Magdalen Islands and in other years it may extend well south of the Cabot Strait to south of Halifax. Trying to predict what will develop can be quite difficult since light ice years can sometimes start with a very cold November and December (like the winter of 1997/98) with mild temperatures after the New Year. Conversely, heavy ice years may start mild enough but develop quickly after a mid winter cold spell. Below are ranked the winters of the past two decades as above, normal or below normal winters for ice development in the Gulf of St. Lawrence:

Better than average ice conditions occur when the ice growth doesn’t extend south and east of the Magdalen Islands. Average ice conditions occur when the ice extends to the entrance to the Cabot Strait and worst than average conditions occur when the ice growth extends south beyond the Cabot Strait. Despite what everyone is saying about global warming, of the nine winters of this decade, five have been below average for the Gulf of the St. Lawrence!

Another important factor to consider for shipping into the Gulf of St. Lawrence is the timing of the closing an opening of the Strait of Belle Isle, the use of which can save more than a day’s sailing from Europe compared to Cabot Strait. The historical dates for ice formation and melt for the Strait of Belle Isle is listed below:

Enfotec provides a wide range of environmental information services to the marine and resource industry, particularly relating to information on sea ice and marine shipping. Our services include the IceNav shipboard ice navigation system as well as a comprehensive consulting service. Should your company require any information, support or consulting service relating to sea ice, please give us a call. Are you discounting new resource developments or shipping opportunities anywhere in the world because you think sea ice prevents ships from getting there? Well don’t! We have the information and know the shipping technology that can handle just about any sea ice problem! So give us a call! We are a world leader in private ice information services.

Enfotec Technical Services

25 Tapiola Crescent, Suite 206

Ottawa, Ontario

K1T 2J7  Canada

Telephone: 613-248-0189 Fax: 613-248-0191 Email: gorman@enfotec.ca