© Parks Canada / C. Kavanagh / N 15 02, 1984
From the point to the east of Pointe-des-Monts where it widens, the Gulf of St. Lawrence becomes a true inland sea, covering more than 195,000 km 2 . The Mingan Islands lie at the heart of this huge basin. Fresh water coming from the river constitutes in fact only one-twelfth of the water in the Gulf, most of which comes from the Atlantic Ocean and Labrador via two major sea routes: the straits of Cabot and Belle-Isle.
Due to the way currents work plus a rather special undersea topography, this water from various sources mixes together and creates a great deal of biological activity. An entire living world benefits from the abundance of food that results.
Around the islands, the Gulf orchestrates the ups and downs of the weather: fog, wind, waves and tides.
A frequently-observed phenomenon in the Mingan Archipelago is the presence of a surface layer of cold water. This is in contrast to the surrounding waters, which regularly warm up during the summer months. Two separate causes broadly account for the presence of this phenomenon.
The first cause is the shallow plateau which exists between the Mingan Islands and the isle of Anticosti. Swept over the plateau by the tides, the waters undergo intense commingling in a vertical direction. Thus the warmer surface waters, forever combining with the underlying colder waters, rarely get a chance to warm up.
The second reason for the existence of cold water on the surface applies equally to the entire north shore of the Gulf of St. Lawrence. At this latitude, prevailing winds from the west impel the surface water to the east. Lower layers of colder water then emerge to replace the surface water that is displaced by the wind. This phenomenon is known as "upwelling", and is common on coastlines the world over.
Different factors favour the Mingan region's biodiversity and the richness of the waters surrounding the archipelago.
Cold water physically contains more oxygen than warm water. The surface layer of cold water, occasioned by the tidal currents, prevailing winds and a particular undersea topography, thus contains a larger quantity of oxygen, which in turn allows for the proliferation of more animal and vegetal life forms.
In addition, the upwelling of subjacent colder waters brings vast amounts of nutritious elements to the surface. These nutrients favour the propagation of phytoplankton (vegetable plankton), which are the foundation of the marine food chain. The proliferation of phytoplankton in turn engenders the abundant growth of zooplankton. Whales, fish and seabirds all benefit from the immense biological richness in the waters surrounding the Mingan Archipelago National Park Reserve.