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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

Temperature, salinity and density

Day 4
04.12.2020

Why does the meltwater of pink ice cubes float in one of the glasses, and sink in the other?

Temperatur, saltholdighet og tetthet
Photo:
Mirjam Glessmer, GFI

Experiment 4:

We fill two glasses with water, the left one with fresh water, the right one with salt water, all at room temperature. Two colored ice cubes of similar sizes are placed into the glasses and they start to melt. The melt water has about 0°C.

Due to the different temperatures of the water, as well as the different salinities of the two glasses’ original contents, there are three different densities present in our experiment now. The salt water at room temperature in the right cup has the highest density. The colored, cold melt water forms a layer on top of it. But it has a higher density than the fresh water at room temperature in the left cup, so it sinks to the bottom in that glass.

Chapter 4: Temperature, salinity and density

The density of seawater, and thus the movement of currents, is not only influenced by its temperature, but also by its salinity. Rain brings new freshwater into the ocean, which reduces salinity in areas where it rained. When seawater evaporates, it leaves behind the salt. Salt is also left behind when seawater freezes to ice. Both processes therefore locally increase salinity. Sometimes the influence of temperature dominates density, other times salinity does. Therefore, it is not immediately obvious which water mass is denser or less dense, and therefore what kind of currents will form.

Prepare for day 5:

Put cool pack into freezer.