Air bubbles trapped in ice can store messages in cold places

For as long as humans have lived, they’ve found ways to store information for others to find. Cave paintings were perhaps the first examples, followed later by messages in bottles, semaphore, books, persistent URLs, and so on.

Now, a research team from China and Czechia has reported in Cell Reports Physical Science a way to store messages by freezing air bubbles into ice. The researchers were inspired by bubbles in glaciers that preserve ancient air. They developed a method that could be useful in cold places like the Arctic, the moon or Mars, where traditional storage like paper or electronics is hard to maintain.

The idea is based on the fact that when water freezes, it traps air bubbles. The shape and arrangement of bubbles depend on how fast the water freezes. By carefully changing the freezing speed, the scientists could create layers of bubbles at specific spots in ice. These layers can be used to represent information just like the dots and dashes in Morse code or the 1s and 0s in binary code.

The scientists found that a bubble started smaller, grew, and shrank just a little before finally freezing. The bubble’s final shape depended on how fast the freezing front, the part of water turning to ice, moved.

The team discerned two main bubble shapes: egg-shaped and needle-shaped. By measuring the height and width of the bubbles, team members classified regions as containing egg-shaped only, both eggs and needles, needle-shaped only, and no bubbles.

Next, the team created bubble layers by rapidly changing the freezing speed. This was done by suddenly lowering the temperature of the plate the water sat on. Each sudden change formed a new layer of bubbles. The scientists could form multiple layers in one ice slice by repeating this trick.

Finally, they developed a seven-step process where a message, like letters, is turned into a temperature-control pattern. The pattern guided the freezing process to make bubble layers at the right positions. A camera then scanned the ice and a computer ‘read’ the layers using light and dark bands in the image. These bands encoded messages the way Morse code can.

In fact binary code turned out to be most efficient to deliver messages while Morse was easier to control. The team managed to record the letters “FL,” “CN,” and “BJ” using this technique.