1. What is the difference between in situ and potential temperature?

In situ is a Latin phrase meaning: in the place. This means that in situ temperature is the temperature that is measured in place. For example, if you were to put a thermometer in the water and measure the temperature at 10 meters. That is the in-situ temperature. The potential temperature of a parcel of fluid at pressure P is the temperature that the parcel would acquire if adiabatically brought to a standard reference pressure P0, usually 1000 millibars.

2. Compare the central water masses for the North Atlantic, South Atlantic, North Pacific, and South Pacific.
3. Compare the central water masses for the Arctic Ocean and Circumpolar Current.
4. Where is deep water formed?

Deep water is formed in the North Atlantic Ocean where the Gulf Stream makes contact with cold Arctic waters. Gulf Stream water is cooled and has its salinity increased, both of which make it more dense and therefore causes it to sink. Following the 'conveyor belt' circulation, this cold, salty water travels south to the Southern Ocean, and either east into the Indian ocean or past Australia into the Pacific. Whatever it's course, once it reaches the continental shelf it is directed upwards and becomes surface water once again.

5. What are the distinguishing salinity – potential temperature characteristics of Mediterranean and Antarctic Intermediate Water?

Mediterranean water is the saltiest water source, due mostly in part to the Mediterranean's shape: a large sill keeps the majority of water inside its basin where it can stagnate and become highly saline. There is little transfer of water between the Atlantic and Mediterranean compared to other ocean basins. The Antarctic is the coldest water in the world's oceans and as a result is the dominant bottom water in the oceans. Despite being warm, the Mediterranean waters are dense enough to sit below colder Atlantic waters, but the Antarctic water is more dense than both and rests deeper in the water column.

6. Why is there a mixed layer?

There can be both surface and bottom mixed layers. The Strong winds at the sureface can mix a stratified surface layer, resulting in a mixed layer. Bottom mixed layers occur due to currents interacting with the bottom. This causes bottom friction and turbulence which causes a mixed layer.

7. Compare typical mixed layer depths for the North Atlantic, Arctic, and Lake Michigan.

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