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Ice is rarely a persistent navigation hazard in the Gulf of St. Lawrence and St. Lawrence River until early January, except along the south shore of the river where frequent ice floe interaction occurs.
During the first week of January, new ice begins forming along the north shore of the gulf while that which has formed in the estuary begins to drift through Gaspé Passage.
By the end of January the western half of the gulf is ice-covered. By this time as well, the northern portion of the gulf is ice-covered, as are waters off the west coast of Newfoundland. Ice normally begins to drift eastward around Cape North into the western side of Cabot Strait during this period as well.
Through February, the ice cover continues to grow and gradually spreads eastward to cover most of the remaining areas of the gulf by the end of the month.
Fast ice in the gulf generally does not extend very far seaward. However, a substantial area develops in southern Chaleur Bay, along the north shore islands at Mingan, from Cape Whittle to Blanc-Sablon and in the Bay of Islands.
Break-up usually begins around the middle of March in the leeward and thinner ice areas and proceeds southward and southeastward through the gulf. The main shipping route through the gulf clears first, normally during the early days of April. The last two areas to clear of sea ice are the southern portions of the gulf between Prince Edward Island and Cape Breton Island and the Northeast Arm.
Sea ice begins to form along the coast of southern Labrador normally during the second half of December and spreads southward by the end of the month. It continues to expand seaward and spread southward during January.
In February of most years, the pack ice drifts off to the southeast. This southward penetration of pack ice depends in part on the severity of the winter as well as wind direction. When sea ice is present, the ease of navigation during the winter months along the east coast of Newfoundland depends primarily on wind direction.
Slow retreat of sea ice begins in late March and by the end of April the southern edge of the ice pack has usually retreated only to about the latitude of Cape Freels.
In May the rate of melting increases and the pack usually retreats to the northern end of the Strait of Belle Isle by the end of the month. This retreat of sea ice exposes the icebergs carried south by the Labrador Current; their numbers in Newfoundland waters reach their peak at this time.
Ice formation in the bays and inlets of the Cape Chidley area usually begins during the second half of November with ice formation spreading rapidly southward to the Strait of Belle Isle by the end of December. During December the ice develops seaward and drifts southward in response to temperature, wind and current.
The shore-fast ice which fills the bays and inlets all along the coast during the winter months becomes notably extensive from Cape Harrison to near Saglek.
Melting normally begins in southern Labrador waters at the end of April, reaches mid-Labrador by late May and the Resolution Island area about mid-June. Early in June the southern edge of sea ice has cleared the Strait of Belle Isle and by the end of the month it is north of the approaches to Hamilton Inlet. By mid-July the ice edge is near Nain and at the end of July it is in the Cape Chidley area where patches of ice may linger into the first week of August.
Hudson Strait And Ungava Bay
The ice of Hudson Strait and Ungava Bay is mostly formed locally but winds and currents can carry floes from Foxe Basin or Davis Strait into these areas. Freeze-up usually begins in late October in the western end of Hudson Strait and ice formation progresses eastward to cover the entire area by early December.
Through the winter, shore-fast ice becomes extensive among the islands from Lake Harbour to Cape Dorset and in the bays and inlets of Ungava Bay.
In May, open water leads become more persistent as temperatures rise and the rate of re-freezing is reduced. Ice melt is slow until July but then progresses rapidly. By the second half of July the ice pack is usually confined to Ungava Bay and the south side of Hudson Strait.
Complete clearing of sea ice usually occurs during the second week of August; for the remainder of the shipping season, icebergs from Davis Strait and occasional intrusions of sea ice from Foxe Basin are the only ice hazards.
Freeze-up is a lengthy process because of the great size of Hudson Bay. The first ice formation in the bay is usually in late October in the coastal inlets in the northwestern sector. As the weather grows progressively colder, the ice spreads southward along the shore more rapidly than it extends seaward. Hudson Bay is normally ice covered by mid-December.
During the winter, a 5 to 10 mile wide belt of fast ice develops along most of the coastline. Beyond the shore-fast ice, Hudson Bay is covered with pack ice which moves in response to the wind.
As temperatures rise in May and June, flaw leads in the northwest portion of the bay become persistent. Normal clearing of the pack ice progresses southward from the Chesterfield Inlet - Southampton Island area and westward from the Quebec side of the bay. Associated ice melt is a slow process which accelerates in July with an open water shipping route to Churchill forming by the end of the month. The pack will often separate into a few large patches before melting completely by the middle of August.
James Bay ice is noted for its discoloration. This feature is related to the freezing of muddy water in the fall, a condition caused by the shallowness of the bay and wind conditions in November. Another contributing factor is the spring melting and river run-off which concentrate sediments on the surface of the ice.
Freeze-up in James Bay usually develops during the second half of November; because the bay is shallow, ice spreads quickly to completely cover it by early December.
Melting begins in late April, but it is not until the second half of May that the bay begins to clear. Clearing progresses generally from south to north. Complete clearing normally occurs during the last week of July, but it is not unusual for some ice to persist until early August.
Ice in Foxe Basin is characterized by its extreme roughness and muddy appearance, large areas of land-fast ice and the fact that the pack ice appears to be in constant motion. The roughness of the ice is due to motion and stress produced by currents, winds, thermal expansion, and particularly to the large tidal ranges. Its muddy appearance is due to the freezing of muddy water, large tidal ranges, and winds which keep a large amount of bottom deposits suspended.
New ice forms in northern Foxe Basin normally during the second week of October. It spreads southward more rapidly along the coasts than seaward to completely cover Foxe Basin and Foxe Channel early in November.
The typical ice regime in early March portrays fast ice along most shorelines. It is particularly extensive among the islands to the northeast because of the shallowness of the water.
Melting starts in late May or early June, resulting in puddling and the beginning of the ice weakening. The ice then becomes predominantly composed of small floes but it is August before rapid disintegration occurs. Small patches of loose ice persist during September; they either melt by the end of the month or remain until freeze-up (in October) thus lasting until the following year.
There are major factors controlling the ice regime in this region:
During the winter months, fast ice becomes well established along the Baffin Island and Greenland Coasts partly due to the frequency of winds having an on-shore component. The offshore pack remains mobile throughout the winter and the floes which range from small to vast in size are repeatedly frozen together and broken apart.
Clearing in the spring starts as soon as temperatures begin to rise and melt the thin ice in the "North Water" polynya. This area then expands southward across the approach to Jones Sound about the end of the second week of June, across the approach to Lancaster Sound by the end of June and southeastward to near Cape York around the middle of July.
With some exceptions, the waterways of the Arctic Archipelago are dominated by a consolidated ice sheet during the winter months.
As temperatures rise in May, the open water areas start to expand slowly. During the month of June, clearing of Lancaster Sound progresses from the west. Although the sound itself usually clears of sea ice by early July, subsequent break-up in adjoining waterways can result in ice floes drifting into the area during July and early August.
The consolidated ice cover on many of the waterways is completely broken by the last week of July. The last ice areas to break-up are those in the waterways between the Queen Elizabeth Islands; this usually occurs about the end of August.
During the first week of September, new ice usually begins to form among the old floes in the Queen Elizabeth Islands area. By the middle of September, it begins to spread from the northern and western sections, covering many of the waterways by the end of the month. Lancaster Sound is the last area to become ice covered and this usually occurs by the middle of October. By the end of October, ice in many of the waterways has already consolidated.
During winter, ice coverage is nearly 100%, with ice motion confined to the Beaufort Sea and Arctic Ocean. An extensive belt of shore-fast ice lies along the mainland coast from Point Barrow to Amundsen Gulf.
The first clearing of sea ice occurs in late June in the Mackenzie River-Mackenzie Delta area. A week or two later, the fast ice along the Tuktoyaktuk Peninsula becomes completely fractured and during the fourth week of July an open water route develops from Mackenzie Bay into western Amundsen Gulf. The Arctic Ocean circulation is a delaying factor for break-up of ice along the coast between Point Barrow and Herschel Island. Even though the fast ice becomes completely mobile by early July, open ice conditions do not develop until the first week of August and an open water route not until the first week of September.
The last ice areas to break-up are those from Queen Maud Gulf to St. Roch Basin. Fracturing of the consolidated ice cover usually occurs during the second half of July with much of the area becoming mostly open water around the middle of August.
September is normally normally when the Western Arctic has the most open water. The timing of freeze-up in the Beaufort Sea depends to a very great extent upon the location of the southern limit of the polar pack because initial ice formation occurs among the older floes and spreads southward from there.
In the St. Roch Basin - Rasmussen Basin area new ice begins to form during the first week of October and spreads rapidly. The last area to achieve new ice growth is the central portion of Amundsen Gulf, normally during the fourth week of October.