Experimental Splashing
When we think about splashing around, we think of sunscreen and swimming trunks. Environmental physicists, however, are not only interested in the beneficial refreshment but also in the physical processes that take place in the cool water. Because they help determine how the oceans and groundwater affect the climate and living environment. Even water still has secrets. For example, how does the gas exchange between the ocean and the atmosphere actually work? Do methane bubbles make their way from the sea floor to the air? And how "Image" is our groundwater actually? At the conference of the German Physical Society (DPG) in Heidelberg, researchers presented how they use laser beams, noble gases and natural radioactive decay to lift the curtain and look behind the scenes. alt="
Uwe Schimpf from the University of Heidelberg and his team ask themselves, for example, how the oceans and the atmosphere exchange heat and gases that are important for the global climate. The scientists knew that turbulence, which is caused by wind or tides on the water surface, is mainly responsible for this. But how exactly do heat and gases get into the body of water?
Turbulent hustle and bustle: Infrared light as a tracker for substance transport
The researchers use infrared measurements to track down the transport mechanisms. They call their method "active thermography" - "thermography" because they take heat measurements. They take a lot less time than experiments with gases, and after all, the same principles apply to both.
In their process, a CO2 laser shoots an infrared beam perpendicularly onto the water surface at regular intervals, an infrared measuring device records exactly how much the water heats up, and an integrated Infrared camera visualizes the heat transport into the next deeper water layers.
Water channel tests show that the faster the water flows, the faster the heat transport. In addition, heat and gases appear to enter the water in bursts rather than uniformly, with bursts becoming increasingly periodic at higher velocities.
Rolf Kipfert from the Swiss water research institute eawag and his colleagues, on the other hand, pursue completely different transports. They want to know what happens to the free methane that bubbles out of the ground in the Black Sea – near Crimea, for example. Could the greenhouse gas reach the surface of the water and then directly into the atmosphere? And above all: How can this be checked?
The greenhouse gas gun fires: noble gases as methane detectives
With his lecture, Kipfer broke a lance for noble gas measurements - for the sake of simplicity. With the exception of helium, all noble gases are only produced in the atmosphere and only get into the water body via exchange processes on the water surface. If their concentrations deviate from atmospheric equilibrium, this can only happen through secondary gas exchange in the water column.
The bubble gun did shoot – but not too far
(Rolf Kipfert) And indeed: the researchers measured lower inert gas values than expected for all the methane emissions examined. The physicists discovered that a mass exchange takes place at the interfaces between the methane bubbles and the surrounding seawater: the seawater gives off noble gases to the gas bubble and receives methane in return, which immediately dissolves.
So no free methane reaches the surface of the water from undersea gas wells: "The bubble gun did shoot – but not too far," says Kipfert. The natural exchange of methane between the ocean and the atmosphere seems to take place almost exclusively via dissolved methane, not via free methane.
Like Kipfer, Jürgen Sültenfuss from the University of Bremen is also fascinated by noble gases. Because they can not only be used to track bubbles in seawater, but also to determine the age of groundwater.
Face wrinkles from groundwater: helium-4 as an indicator of age
Public utilities in particular need to know how "Image" the water in their catchment area is. After all, the time spent in the soil is also related to age. And it determines how long the water can absorb pollutants and whether expensive cleaning measures are necessary or superfluous. alt="
The Bremen researcher is currently pursuing an initial approach to dating groundwater using helium-4 nuclei.
He had measured helium-4 concentrations in various groundwaters in northern Germany that were well above the solution equilibrium and could not be explained by additional air intake from the atmosphere. Sultenfuss attributes these high concentrations to the natural decay of uranium in rock. The researcher speculates that the glaciers of the last ice age had worn down the subsoil so severely that these sediments are therefore increasingly releasing helium-4 nuclei today.
So if you subtract the value of the solution equilibrium from the measurement data, only the helium-4 concentration from the decay series remains. And from this it can then be calculated how long the groundwater was exposed to the outgassing rock. The first age estimates at least agree with those from radiocarbon determinations.
For Sültenfuss it is now a matter of checking his assumption about the higher helium4 concentrations in formerly glacier-covered areas. If it is confirmed, water suppliers from all over Northern Europe may soon be using his method.
And Kipfer and Schimpf also have a lot to do. Schimpf, for example, now wants to leave the water channel from his doctoral thesis behind and test "active thermography" on open water together with his colleagues.
