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University of Bergen
Geophysical Institute

24 days of kitchen oceanography

Each day a new experiement will be posted here. Reveal what is hidden behind the windows by clicking on the arrows below.

Introduction
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7
Day 8
Day 9
Day 10
Day 11
Day 12
Day 13
Day 14
Day 15
Day 16
Day 17
Day 18
Day 19
Day 20
Day 21
Day 22
Day 23
Day 24

Main content

Double-diffusive mixing in tea

Day 16
16.12.2020

Why are "mushrooms" growing in the tea cup?

Dobbel-diffusiv blanding i svart te
Photo:
Mirjam Glessmer, GFI

Experiment 16:

When we pour a spoon of cream into a cup of tea, we can observe the exciting phenomenon of double-diffusive mixing. The chilled cream at first has a higher density than the hot tea and therefore sinks to the bottom of the cup. However, it heats up quickly and when it has reached the temperature of the tea, has a lower density and therefore rises in "fingers". Mixing of substances is much slower than adjustment of temperature, so you can still recognize the cream finger as such in the tea, rather than just seeing a tea-cream mixture.

Chapter 16: Double-diffusive mixing in tea

Double-diffusive mixing has for example been observed at the lower boundary of the Mediterranean outflow, where warm and salty water is layered above colder and fresher. There, so-called "salt fingers" form, which mix water masses much faster than molecular diffusion could.