Physical Oceanography Density. Measured in mass/volume (g/mL) Is the major factor in water...
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Transcript of Physical Oceanography Density. Measured in mass/volume (g/mL) Is the major factor in water...
Physical OceanographyDensity
Density• Measured in mass/volume (g/mL)• Is the major factor in water
circulation and distribution of plankton
• Controlled by temperature and salinity
• Measured with a hydrometer
Why Does Ice Float?• Water molecules push apart during
freezing, increasing the volume.
• Since the mass is unchanged, but the volume is larger the ice has a lower density than the surrounding water and it floats.
• Ex) water: 1.00 g/1.00 mL = 1.00 g/mL densityice: 1.00 g/1.10 mL = 0.90 g/mL density
Liquid Water Frozen Water
• If sea water has a salinity of 35 ‰, then it will freeze at -1.94 °C.
• If ice freezes rapidly, salt pockets are trapped in it – this makes it very brittle and is called ‘first-year ice.’
• Salt pockets migrate downward and out, making ice ‘fresher’ as it gets older; this also makes the ice much stronger.
Generalities about Density
1. Normal salt water has a density between 1.01 and 1.03 g/mL
2. Density increases with depth3. Density increases as temperature
decreases4. Density increases as salinity
increases
5. Water is normally stratified (in layers) based on density
Q: Is it possible to have a layer of warm ocean water below a layer of cold ocean water?
A: Yes. If the warm water has a greater salinity than the cold water, this makes it more dense. Also, if two water masses have the same density but have different temperatures, then one must have a higher salinity than the other.