Science Buddies: "Ask an Expert"

I am wondering how does how salty does the ocean need to be for a egg to float help people or the world

Well, floating eggs on the ocean may be fun but it isn't going to benefit many people. Salinity, on the other hand is very important. Why does the egg float in salt water but not in fresh? Because salt water (above a certain concentration of sodium chloride) is denser than the egg.

Salt water is also denser than fresh water and the saltier the water the denser it is. Why is this important to people? This fact can make the difference between a warm climate and an ice age. The oceans are always on the move. Wind makes wave and currents like the Gulf Stream that move warmer water from the equator north to keep New England and Europe from freezing.

But wind is not the only mover. There is a vertical movement of water in the ocean that is of immense importance. I said that saltier water will sink through water that is less salty, but cold water is also more dense and will slowly descend through warmer surface waters. So, as the Gulf Stream current makes its way north, the surface water cools off until eventually it sinks down through the water column. At the same time, warm water around the equator rises.

This is all well and good as long as the cold, salty water is denser than the surface water, but sometimes the climate warms up so much that the glaciers and ice caps melt pouring billions of gallons of fresh water into the north Atlantic. This mixes with the saltwater and makes it less salty so it can no longer sink. The conveyor that was bringing warm water north stops working and the northern regions get colder and colder.

The scientific name for this flow of warm water north and cold water back south is the thermohaline circulation--'thermo' for temperature and 'haline' meaning salt. Here's some references so you can read more about it:

https://en.wikipedia.org/wiki/Thermohaline_circulation
http://www.pik-potsdam.de/~stefan/thc_fact_sheet.html
http://pmm.nasa.gov/education/videos/th ... veyor-belt

I'm sure you can think of other ways that salinity can be important in nature. If you have more questions let us know.

Sybee