4000 robots are listening to the sea to better understand the climate

Oceans cover 71% of the Earth’s surface. It is just over 360 million square kilometers. To monitor the evolution of salinity and the temperature of the ocean’s upper layers, the Argo program was started in 1999, about 25 years ago today. To ensure this surveillance, more than 3,900 floating robots are scattered around the world. They continuously collect data on the physical condition of the ocean, up to a maximum depth of 2,000 meters.

This collection of robots helps the Argo program to continuously send information to scientists and operational agencies around the world to help with research, but also climate and ocean forecasting. A very useful tool for studying climate change and one that resonates even more today, on this first day of the Second United Nations Conference on the Sea (which is being held in Lisbon from 27 June to 1 July).

Global warming: The ocean in the front row

In recent years, a pattern of ocean warming has emerged. The sun’s rays, visible as ultraviolet rays, are slowly warming the ocean. This heat is absorbed especially in the lower latitudes of the earth. As well as in the eastern part of the vast ocean basin. Thanks to wind-driven currents and large-scale conduction types, heat is usually driven west and towards the poles. It is lost by escaping into the atmosphere and space (especially through evaporation).

It is estimated that the oceans absorb about 30% of carbon dioxide emissions from human activity. According to the U.S. Agency for Oceanic and Atmospheric Observations, average annual sea surface temperatures are increasingly detached from the 20th century average. In 2020, the surface temperature of the world’s oceans was 0.76 degrees Celsius higher than the average of the last century. And this upward trend has been growing since the early 1980s. The biggest peak was in 2016. That year, in 2016, the measured sea temperature was 0.79 degrees Celsius higher than average.

Bot data is restored every 10 days

The heat movement of the ocean cools the warmer regions and allows the earth to become habitable by lowering the extreme temperatures. But climate change is changing something. To follow these transformations, the Argo program has deployed its floating robots around the world. The latter, which measures 20 cm in diameter, actually spends most of their time underwater. They go deep into the ocean to measure temperature and salinity. “They spend 90% of their time 1,000 meters below the water’s surface, then sink to 2,000 meters while collecting data.”At IEEE, Susan Wiesfells is a researcher at the Woods Hole Oceanographic Institution in Cape Cod (Massachusetts) and vice chair of the Argo Steering Committee.

Visual interpretation of the circuit created by a robot every ten days. Illustration: Argo program.

Taken away by the current, these robots regenerate about every 10 days to transmit information captured by satellites. There are two collection points: Brest, France, or Monterey, California. The data is then shared with researchers and meteorologists around the world. In total, the Argo program restores more than 100,000 salinity and temperature profiles each year. A real step compared to alternative systems (data held by a boat or anchored boy).

A significant cost but real scientific progress

Always more useful, these floating robots are always more numerous. To date, the Argo program aims to increase the number of robot fleets from 3,900 to 4,700 units. But all this requires a significant budget. “Each robot costs between $ 20 and $ 30,000 [19 à 28 000 euros, ndlr] And a limited duration of 5 to 7 years “.Details Susan Wiesfells at IEEE.

But the information collected is particularly useful for the scientific community. For example, the Argo program has seen the effects of El Ni নিনo. This climatic phenomenon results in an increase in the surface temperature of the water. “We have seen that this increase in temperature is due to an event in the Pacific Ocean. The heat continues to rise 200 to 300 meters below the surface, which is suddenly released into the atmosphere. “Says Susan Wiesfels.

And to further understand the oceans, Argo is currently building a new generation of robots capable of sinking up to 6,000 meters below the surface of the water. In fact, scientists have already noticed water warming at a depth of 6,000 meters in the Southern Ocean. So it is more important than ever to understand deeper currents and understand how they operate.

Leave a Comment