Creating saltfingers in the Lab

16 August 2025, by Till Moritz

Photo: Till Moritz

As part of the course " Oceanic Processes and Observations" in our master's program Ocean and Climate Physics, we had the opportunity to investigate a fascinating little process in oceanography through a laboratory experiment. The concept of the experiment is to simulate processes in the ocean and thus improve our understanding of various physical phenomena.

In this particular set up, we are investigating what happens when warm, salty water lies on top of cooler, fresh water – a situation that leads to the formation of so-called salt fingers. These are narrow, finger-like patterns that arise due to differences in the diffusion of heat and salt through the water. Although they are tiny and seemingly insignificant, such processes can influence the movement of heat and nutrients in the ocean on a large scale.

What makes this topic particularly interesting is that such small-scale processes are not yet well understood on a global level. Due to their size, they are too small to be directly captured by climate models – but that does not mean they have no influence. A better understanding of these processes can help to find good parameterization for climate models and thus ensure that the influence of small-scale processes is not neglected. Laboratory experiments can be a valuable tool in this regard, as they allow a single process to be studied in isolation from confounding factors.

In a video, we explain the basic concept of salt fingers and show how we created the phenomenon in a controlled laboratory environment using simple tools. We used only two water masses with different temperatures and salt contents, one of which was dyed, a laser sheet and temperature sensors. The goal was to generate salt fingers in the laboratory and use camera recordings to calculate the transport dynamics within the tank.

Whether you are interested in marine science and climate studies or simply enjoy observing fluid dynamics in action, we invite you to dive into our video and discover the fascinating world of salt fingers.