Meter, cylindrical, with a protruding antenna – Argo oceanographic works collect data about the Baltic. It happened that they were accidentally fished out, arousing anxiety because they resemble the shape of a torpedo. That is why the Institute of Oceanology of the Polish Academy of Sciences places clear markings on them – notes the oceanographer Dr. Daniel Rak.
Argo autonomous floats provide information that was previously missing, helping scientists to track climate change, detect dead zones and analyze all processes under the water surface.
The global Argo system was created at the beginning of the 21st century as a support for scientists in conducting permanent, global ocean monitoring, without the need to organize expensive research expeditions. Currently covers over 4,000 Autonomous swimmers, which, drifting with sea currents, measure key physical parameters of water, and above all its salinity, temperature and pressure.
“Although they were created primarily with the examination of oceans, not shallow seas, a dozen or so years ago Poland joined the Argo network and swimmers also began to appear in the Baltic Sea,” Dr. Daniel Rak from the Institute of Oceanology of the Polish Academy of Sciences (IO PAN) in Sopot told the PAP.
He added that it was associated with some challenges, because the robots were not adapted to act in waters with large, vertical gradients of salinity that prevail in the Baltic Sea. However, in time they were also adapted to such conditions.
ARGO swimmers operate in continuous mode – they monitor the sea throughout the year, regardless of the weather or season. They do not have their own drive, so they drift with sea currents, controlling only immersion. They can change their buoyancy thanks to a special pump and oil bladder, which acts as a swim bladder in fish.
Polish robots are launched from the deck of the “Oceania” research ship. After starting work, they fall to the depth of “parking” determined by scientists, and once in a while they emerge and send data through the satellite to scientific centers.
There are eight active swimmers in the Baltic Sea region. The simplest ones measure water temperature, salinity and pressure. However, there are more complicated models, extended with a number of other sensors, which can measure e.g. pH, nitrate concentration or oxygen dissolved in water. Thanks to this, they help, among others detect the so -called Dead zones, i.e. oxygen -free areas in which sea animals cannot live.
“This is a very important skill, because the recently dead zones in the Baltic Sea are coming. They once occurred mainly on the depths of Gotland, but recent studies show that they begin to appear even at the depths of Gdańsk. In such areas, due to the lack of oxygen, anaerobic bacteria distribute organic matter, as a result of which a toxic hydrogen sulfide is formed. – explained Dr. Rak.
Data from swimmers also allow you to follow global climate change and local processes regarding a given basin. They are used to monitor ecological conditions and analysis of many processes, including water exchange or changes in water conditioning.
“In January 2024, one of the Polish swimmers operating in the area of the Bornholm pool recorded a sudden increase in salinity and oxygen content at the bottom. It was a clear signal of the influx of salt water from the North Sea, which was almost immediately confirmed by foreign institutions monitoring the Baltic” – emphasized the interlocutor of PAP.
Flawners can also be used in numerics forecasting weather and sea condition. They indirectly help to determine the direction and speed of sea currents (based on the position of the device), and also support the calibration of sonars and echosondes – important for both the army and fishing.
As Dr. Rak explained, the spread of sound in water depends on its physical properties. Sonars of submarines or fishing boat cutters assume a certain average speed of sound in water, which can actually differ. For example, an increase in temperature by 1 degree C increases the speed of sound by about 4.5 m/s, and the increase in salinity by 1 dog (unit of practical salinity) – by about 1.3 m/s. Seemingly these are small values, but in the situation of large gradients between warm and less salt surface water and cooler and more salty water at the bottom can arise a clear difference in the speed of sound. In such a situation, the sound bends (refraction) on the border of layers, which for sonars means “acoustic shadows” – areas where they may not detect underwater objects correctly.
“For the devices to work effectively, it is therefore necessary to know the current speed of sound speed in water and take into account it in calibration. And this is where data from Argo swimmers is useful. This is of particular importance in the Baltic Sea, where hydrodynamic conditions can be significantly different even in a small area” – noted Dr. Rak.
He explained that modern floats are relatively inexpensive, but very effective. In the oceans, their work time determines battery life. On such extensive waters, recovering once released devices is usually not profitable. However, this is possible in the Baltic Sea. Scientists from IO PAN often locate discharged floats, catch them, then service and use them again.
“Such a time and spatial resolution, as thanks to them, we are not to be obtained with any other research platform. Research cruises allow observation only at a given moment and a given area. So they show a slice of the entire hydrodynamic situation. Floating floats give us information constantly, on a regular basis, in large areas,” said the scientist from the Institute of Oceanology of the Polish Academy of Sciences.
He emphasized that due to the size and shape of the Argo device you can be mistaken with … torpedoes. It happened that they were accidentally caught by fishermen or tourists, arousing their anxiety. That is why the Institute places clear markings on them. “So if during a walk by the sea or cruise we notice something like a torpedo in the water, let's not panic. It is worth watching the device and contact the Institute of Oceanology of the Polish Academy of Sciences in Sopot” – he noted.
Katarzyna Czechowicz (PAP)
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