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December 2010

Amazon freshens up the waters

November 2009

When it comes to studying the ocean, it is important to know the quantity of salts in the water. Either modelled or observed, in-situ or by satellite, salinity varies all over the globe, especially at the mouth of a river as powerful as the Amazon.

Sea water is proverbially known to be salted. But the content in salts (the salinity) of the water is not the same everywhere, as you may note if you have bathed in e.g. the Atlantic Ocean vs. the Mediterranean Sea. And, even in the same sea or ocean, salinity has its geography and dynamics. Currents, rains and evaporation, ice melting or freezing change the salt content of the water. The same applies to rivers that bring fresh water to the ocean, thus decreasing the salinity.

Most pre-eminent among rivers, the Amazon counts for nearly one-fifth of all the river discharges. Amazon discharge changes with the seasons, especially after the annual flood (around May at the river mouth). During that period, the flow of the Amazon is very important and carries hundreds of thousands of cubic meters of water into the ocean. The fresh water plume can be seen hundreds of kilometres from the river mouth. On average, the flow reaches 280.000 m3 per second with bursts up to 400.000 m3 per second, while the average flow of all European rivers is around 40.000 m3/s.

Salinity is one of the parameters that drive ocean dynamics, including the way water can dive into the depths, thus mixing the different water layers. Monitoring ocean salinity is thus important to better know – and forecast – the ocean, its composition and movements.

Knowledge of salinity can be used to improve both ocean and climate forecasts (to plan for such events as El Niño Southern Oscillation, or for next seasons’ trends), to estimate rains and evaporation over the ocean, ice melting, etc.

MyOcean is a European project dedicated to operational oceanography. MyOcean Service provides the best information available on the ocean, on both large and regional scales (European seas), based on the combination of satellite and in situ observations and their use in models: temperature, salinity, currents, ice extent, sea level, primary ecosystems, ...

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Source: MyOcean