W1-M3A station

Location of W1-M3A station
Location of W1-M3A station

Why observing here?

Characteristics of the oceanic region:

The Mediterranean Sea is almost completely enclosed by land. With an average depth of 1500 m it covers approximately 2.5 million km2 and its connexion to the Atlantic Ocean, the Strait of Gibraltar, is only 14 km wide.

Its major source of replenishment and water renewal is the continuous inflow of surface water from the Atlantic, while another deep current takes water from the Mediterranean back to the Atlantic. The volume of the Mediterranean basin takes over a century to be completely renewed through the Strait of Gibraltar, which is only 300 m deep. Due to the scarce inflow and the high evaporation, the Mediterranean Sea is much saltier than the Atlantic. In the absence of strong currents and low amplitude tides, the marine environment shows relatively few variations in seawater temperature, salinity and light.

The Mediterranean basin is divided in two parts by a shallow submarine ridge (the Strait of Sicily) between the island of Sicily and the coast of Tunisia. The two main subregions are the Western Mediterranean and the Eastern Mediterranean.

Located in the Western Mediterranean basin, the Ligurian Sea is one of the most dynamically active and productive areas. It gathers a great variety of pelagic fishes and cetaceans. We can also find the same species of krill that is present in the North-Atlantic (Meganyctyphanes norvegica) which plays a key role in the trophic chain of large pelagics, directly (young tuna, fin whales) or indirectly (swordfish, sperm whales).

During the winter, dense water formation is often observed.

The Ligurian Sea is characterised by a permanent cyclonic circulation involving both the surface and intermediate waters. More specifically, the waters flowing northwards either side of Corsica, the Western Corsica Current (WCC) and the Tyrrhenian Current (TC), join along the eastern periphery of the basin and form the Ligurian-Provençal Current (LPC), which flows westward along the coast of Provence, completing the cyclonic loop.

Ocean circulation : The main surface current comes from Gibraltar (superficial Modified Atlantic Water), flows along the African coast, goes up in the Thryrrenian Sea, reaches the basin trough the Tuscan Archipelago and forms a cyclonic circulation.

A deeper current with warmer and more saline waters (Levantine Intermediate Water) follows the same path. Vertical currents of the surface waters are mainly driven by local climatic and atmospheric conditions. Northern winds push coastal waters off-shore pumping deep nutrient-rich waters to the surface.

Data collected in the past have shown that both the Tyrrhenian Current and the Western Corsica Current undergo seasonal changes. In particular, the Tyrrhenian Current is stronger in winter than in summer, when it can even reverse its direction. The Western Corsica Current intensifies in spring and weakens in late summer/autumn. Being the sum of the above currents, the Ligurian-Provençal Current also shows a seasonal variability modulated by the Tyrrhenian Current changes.

Over the last few years, the continuous acquisition of open-sea measurements has been particularly useful in the study of certain phenomena such as the anomalous warming of the sea waters and the presence of certain tropical species which have colonised the area around the buoy.

Particular characteristics of the site

The buoy is moored in the middle of the Ligurian Sea between Genoa and Cape Corse where the water depth is 1300m. The buoy is positioned about 75 km off the coast of Liguria. The sight upon reaching the buoy is amazing: just the sea and not a single human activity in sight…

The buoy gathers essential measurements for weather forecasts and allows researchers to study and compare the data collected from space satellites and directly at sea. New experimental techniques for gathering of measurements at sea and transmitting them to the lab, make the bouy a great prototype of an autonomous remote unit for the study of the marine environment.

Thanks to the satellite connection, the data is available on the web in real time .

The W1-M3A system is a spar buoy made up of a 51 meter-long tubular steel structure divided into five parts. It is maintained in position thanks to a 2 km-long mooring line attached to an old ship anchor at the bottom. The bottom part of the buoy is filled with water and ends with a large stabilizing disk to dampen the vertical motion caused by waves. A 1300 kg ballast hangs below the buoy.

The electronic laboratory and the instruments themselves are placed on the top of the buoy. The laboratory is not very big, but it can accommodate up to two people. On top of the laboratory is the trellis on which the meteorological sensors and the signal lights are rigged. Most of the instruments are in fact about 14 meters above sea-level.

The buoy is completely energy independent, generating its own energy from the sun and the wind and it communicates with the outside world via a satellite connection. To climb aboard the buoy, which is almost 15 meters high above sea-level, one must climb two ladders which lead to the laboratory roof and enter it through a hatch. Apart from the researchers, professional divers are often needed to carry out maintenance work on the underwater sensors and to analyse and photograph everything that happens under the surface of the water.

Scientists or technicians in charge of the observatory

8
Roberto Bozzano
9
Sara Pensieri

Name of their institution

National Research Council (CNR), Institute of Intelligent Systems for Automation (ISSIA) CNR-ISSIA, Genoa, Italy.

Distance from shore

38 nautical miles from the coasts of Liguria (4 hours of sailing from Genoa)

Max depth

1300 m