Obviously all of the ocean is above freezing; but reading about the titanic sub today, I still was surprised to read that it’s still above freezing down 2+ miles down. What keeps it relatively warm? Obviously there is some volcanic activity but it’s not widespread over the entire ocean is it?
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The water pressure is the reason, the normal freezing point we have come to expect is only applying to normal levels of pressure on the surface. in addition heat really can’t get very far to escape down there so the temperature stays rather stable, after all for something to cool down the heat needs to go somewhere. In the vast expanse of the open ocean. Theres few if any objects that heat can be captured.
That being said stuff can “freeze” underwater, for instance we know there is huge “frozen” methane deposits underwater especially around japan.
Which is a problem because we suspect as the oceans warm up all of that pressurised methane is going to come up to the surface.
We also know the oceans of titan have liquid water but 20 kilometers under the ice, the main reason being: the pressure down there is great enough to prevent it from freezing.
>Obviously all of the ocean is above freezing; but reading about the titanic sub today, I still was surprised to read that it’s still above freezing down 2+ miles down. What keeps it relatively warm? Obviously there is some volcanic activity but it’s not widespread over the entire ocean is it?
Water is at its densest at 4°C. Anything above and below that is less dense and will rise above the 4°C water. That means any body of water will always and only ever freeze **from the top to the bottom**. No matter what happens, convection currents will keep the bottom at 4°C *at the very least*, unless the rest of the water has already frozen.
So why is the bottom of the ocean above freezing? Because the top of the ocean is above freezing.
The bottom of the ocean is away from the warm sunlight … but it’s also away from the cold night sky and surface evaporation. So how’s it going to cool down? The earth is very hot in the middle so it’s only near the surface, where the heat can escape, that gets colder.
If anything, it’s surprising that deep water isn’t warmer but water, unlike solid land, it can move around, allowing warm water to naturally rise and cool water to sink. This mobility keeps water temperatures below 1000 metres deep to be very consistent world-wide.
Firstly water is weird, as water freezes and turns solid it is less dense than as a liquid so floats on the liquid water, then water at 4 C is denser than water at cooler or warmer temperatures so it will sink to the bottom of a large body of water. https://youtu.be/J9PPLzUfz9E In addition the Sun isn’t the direct source for all of the heat on Earth the Earth itself is hot.
The better question is if something is covered with a lot of stuff above and below how could it get cold to begin with? For temperature to drop there needs to be a way to remove energy, it spontaneously flows from warm to cold not the other way around. So the water on the bottom of the sea can’t get colder than what is above or below it from just heat transfer to the surrounding. That is if you just have heat transfer and not a moment of any matter.
The surface gets cold because it can radiate heat into space, and the incoming radiation from a dark part of space has a black body temperature of 2.7 kelvin.
Earth’s core is very hot, warmer than the surface of the sun, and heat is transported out all the time. You have a temperature drop from the surface to the area just below it but then if you go down there is a temperature increase that is 25–30 °C/km away from tectonic plate boundaries.
The real question is why it is so cold down not why it is not colder. The same distance below down into the solid part of the earth is a lot warmer. At the same dept on land, you have a temperature around 100C
The explanation is water flows around and is the densest at around 4°C. Ice is also less dense than liquid water. so if you for some reason get water that starts to freeze it will not happen at the bottom and the rise will rise to the surface. Pounds on the ground do not freeze from the bottom but from the surface. The temperature at water freezes depends on salinity, for typical sea water it is -1.8°C so you can have water colder than 0°C and is still liquid, This is why we use salt on roads to keep ice away.
So the reason it is cold deep in the sea is not that there is no sun or volcanic activity there, it is because water gets cooled down on the surface and can then drop because density increases and there iw warm surface currents. Water that gets below the freezing point can sink, it is ice that is less dense and floats. So only water above freezing temperature can move down into the deep part of the ocean.
Lots of wrong answers here. The short answer: things only change their temperature if they are heated or cooled. The deep ocean has nothing to heat it up and nothing to cool it down, so it stays at the same temperature.
Longer answer: the earth’s oceans are slowly overturning. Cold water near the poles is denser than than warm water, so it sinks and spreads out along the bottom. Water near the surface in the rest of the world is warmed and rises. This creates an overturning circulation, a “conveyor belt” in which water cools at the poles, sinks, flows toward the tropics, rises, and returns to the poles.
Thus, the water you find at the sea floor has kept the same cold temperature it had when it was last in contact with the atmosphere, in the Antarctic or Arctic, thousands of years ago.
The bottom water is heated by geothermal heat from the sea floor, but only a little bit.
Other responders have mentioned that water has a maximum density at a temperature of 4 C. This is true for freshwater, but seawater does not behave this way. Seawater just get denser until it freezes.
https://en.m.wikipedia.org/wiki/Thermohaline_circulation
https://en.m.wikipedia.org/wiki/Seawater#/media/File%3AWaterDensitySalinity.png
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