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Habitats - Environment - Saguenay : An exceptional fjord!

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Musée du Fjord

Climate | Ice | Water circulation

Saguenay River water circulation

Graphic of the Saguenay River water circulation
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Salt water (Cold)

Briny water (Hot)

The Saguenay is a dynamic and complex ecosystem. Water circulation obeys to specific and even spectacular physical laws. We can find two very distinct bodies of water, their differences being in temperature and in the degree of salinity whose layer of separation is called thermo halocline. This phenomenon results in two layers of very different density. Fed by the fresh water tributaries of the fjord, the first layer is slightly salted and found on the surface. The second is a very cold and deep layer whose salinity level is as high as ocean water. As a matter of fact, the Saguenay fjord could be compared to a sound onto which a fresh water mass glides on it from inland.

The surface layer isn't as dense as the cold and salted waters of the deeper layer. It flows towards the estuary while the Coriolis force is literally expelling the Saguenay's waters into the St. Lawrence. The latter is created by the earth's rotation thus evacuating the St. Lawrence's waters towards the south shore of the estuary. So, the St. Lawrence fresh waters coming in from upriver flow along the southern shoreline. All the surface water of the Saguenay region is added to this flow and contributes to the formation of the Gaspé current at the mouth of the St. Lawrence.

Most fjords are natural environments were all formation of aquatic life is limited by the rarity of the oxygen. Yet, the Saguenay fjord is a radical exception to this rule because it is very well oxygenated down to its greater depths. The physical phenomenon permitting this oxygenation is related to the geography of the seabed of the St. Lawrence estuary . As a matter of fact, their depth gradually diminishes and the estuary is narrower at the mouth of the Saguenay. Coming in from the gulf of the St. Lawrence, the amplitude of the tides is increased when reaching the area. The consequence of this phenomenon being those great quantities of very cold sea waters on top the 20-meter threshold near Tadoussac, at the mouth of the Saguenay. These cold and well-oxygenated waters then slide under the surface layer coming from the fjord and their strong density leads them to its depths. This then feeds its deep water current. While the surface current drains the continental waters towards the gulf, these salted waters circulate in the opposite direction going up the Saguenay, thus feeding the fjord's ecosystem to its deepest trenches, which, for one, reaches down to 275 meters in depth.

© Copyright Musée du Fjord 2002.