Thursday, August 17, 2017

The Patagonian Sea climate ranges from temperate to cold, depending on the latitude, and strong west winds prevail, especially to the south. In the South Atlantic, east of the South American continent, a prominent feature is the vast continental shelf or submarine plain, the shape of which is irregular, being widest at 52 degrees latitude and narrowing gradually towards the north.  The shelf slopes very gently from the coast to 200 m depth and then drops abruptly at the continental slope down to the deep basin.  On the South Pacific side, the shallow area near the coast is very narrow as the deep areas are near the continent. On the Atlantic side the coastline is fairly regular but there are some geographical physical features such as gulfs, peninsulas and estuaries of a considerable size. The coast of the Patagonian region is full of cliffs but to the north there are long sandy beaches with salt marshes, coastal lagoons and a few rocky protuberances jutting out here and there. The Pacific coast has many fjords and channels together with intricate archipelagos of small coastal islands.


Three-dimensional graph of marine currents and the seabed – © Sea and Sky Project (WCS)

Water masses are constantly moving. South of the Patagonian Sea, the Antarctic Circumpolar Current, the strongest of all currents, circulates around Antarctica , from west to east, pushing in its stride the water masses which are further north.  On the Pacific side, the cold Cape Horn current flows southwards, parallel to the coast, carrying low salinity waters towards the Atlantic, as a result of the discharge of fresh water from glaciers and rivers in southern Chile.  On the other side of the continent an arm of the Antarctic Circumpolar Current breaks off flowing in a northerly direction bordering the Falklands (Malvinas) Archipelago and later over the continental slope.  It is known by the name of Falklands (Malvinas) cold current and and its main characteristics are its nutrient-rich waters and high salinity. The Brazil current of warm, nutrient-poor, low salinity waters, descends from the north flowing in the opposite direction.  Both currents come into contact in a broad Confluence zone where mixing takes place at temperate latitudes.

Tides in the Patagonian Sea are strong.  On the Patagonian shores the difference between daily high tide and low tide are usually various metres.  This gives rise to short currents which can be very strong near geographical coastal features such as the Valdes Peninsula or the Le Maire Sound between Tierra del Fuego and Isla de los Estados.  Tidal currents help to mix layers of deep waters with other superficial layers.

Fronts and productive areas

Primary productivity of the Southern Atlantic – © Seawifs

Primary biological productivity of the sea is the concentration of small living organisms which perform photosynthesis. These living organisms can be found suspended in sea water at the mercy of currents and are known by the collective name phytoplankton.  Scientists can estimate biological productivity of the sea by studying satellite images which show the concentration of the main pigment used in photosynthesis (chlorophyll-a).  Primary production at sea is limited by two factors: sunlight and the concentration of mineral nutrients.  On average, sea water is poor in so far as nutrients necessary to sustain life whereas the seabed is full of them.  Oceanographic fronts are the areas at sea where deep, nutrient-rich layers of the sea mix with superficial well illuminated waters.  Different mechanisms give rise to fronts: winds, tides, currents or the contact of water masses of different density.  Around fronts there tend to be areas of high primary biological productivity. The abundance of phytoplankton during long periods throughout the year sustains a food chain there involving zooplankton, small and large swimming organisms, superior vertebrates and a rich benthic community which feeds on discards that fall from the illuminated area.

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