Why is deep ocean cold

The first problem is solved by increasing density. The more nuclei you have in the same volume, the higher the likelihood of close contact.

This is where pressure comes in - that's how you get a higher density. Stars are made of plasma, and plasma is easily compressible, similar to a gas, so as pressure increases, so does density. How compressed is it? In the centre, the density is around times the density of liquid water. The pressure is about times the pressure in the Earth's core, and about times the pressure of the water on the bottom of the Mariana trench.

The second problem is solved by increasing the kinetic energy of the individual nuclei. In other words, increasing the temperature. Just like with compressing air, pressure is only a one-off deal in increasing temperature; the fusion reaction in the Sun was started using the residual heat of the collapse of matter forming the star the gravitational potential energy - I'm not sure how much of a factor was compression in particular.

But again, this was only responsible for the initial ignition - today, the reaction is running entirely on the heat produced by fusion and the pressure supplied by gravity which is actually lowered by the outward pressure of the energy released in the core - the two pressures form a stable equilibrium.

As a side note, despite the high temperatures and pressures, the fusion reaction powering the Sun is incredibly weak. If we could magically reproduce the same conditions on the Earth, it wouldn't really be usable for power generation at all - the energy produced is about Watts per cubic metre at the very centre. To have a comparison, this is comparable to power density of a compost heap, and less than the power density of human metabolism.

Yes, your own body is producing more power than the same volume of the centre of the Sun. I unsuccessfully tried to find data on power density of fission reactors, but a single CANDU reactor produces about MW that's "million watts" , and it sure isn't three million times as big.

It's not so much the pressure, but rather compression that creates heat. Heat is a measure of increased kinetic energy as molecules are forced into a smaller space.

Water is not very compressible, and water at the bottom of the ocean is not confined to a significantly smaller space under pressure. The kinetic energy of water molecules at the bottom of the ocean does not increase significantly under pressure, as there is little compression of the liquid.

A mole of water 4, meters beneath the ocean occupies only about 1. The bulk modulus of water indicates that water requires a great deal of pressure for a small change in volume. Colder water is denser until it reaches a temperature a couple degrees above freezing, then it gets lighter again. So the water at the bottom is at the specific temperature where it is densest: any heating makes it rise. Any further cooling makes it rise. See Why does the ocean get colder at depth?

This further points out that without ocean circulation it would take a year for the Earth's heat at the ocean floor to heat up the water at the bottom by one degree C. It has been covered above that there is little scope for water to be heated by compression to begin with. Another aspect is that the water at the bottom of the ocean has been there for a considerable length of time.

Hence, if it had heated up to any large extent when the oceans were formed, there has been ample time for the heat of compression to have dispersed, even if it were several degrees Centigrade. Btw, the notion of a gas being heated by compression, and the heat being lost easily, is crucial to refrigeration, as if one pressurises a gas, then allows it to cool before depressurising it again, the final temperature will be lower than ambient reverse Carnot cycle.

There is another factor that I feel the other answers have overlooked, because there is a similar analogy with air, and air is compressible. Specifically, why is air in valleys often colder than at the top of the hill when pressure heats things? In reality, there are two different dynamics at work. One is adiabatic compression, which as has been mentioned isn't significant for water, because water isn't very compressible. The other dynamic is convection, or in water, currents, which redistribute bulk matter.

Cold water or air is heavier than warm water or air and thus will sink to the bottom. In the atmosphere this is at odds with adiabatic compression, as well as wind cycles generated by the sun. In water those effects are less, and thus cold water sinking becomes a more dominant factor.

Sign up to join this community. The best answers are voted up and rise to the top. The candidate with sulfur would be, I guess, H2S. As I recall it, though, the bacteria that produce that need anoxic conditions, and the polar oceans are well-oxygenated. I tend to think that meltwater, at least from melting sea ice, is unlikely to drive any major change in the North Atlantic branch of the ocean circulation.

A sufficiently large, rapid, melt of Greenland -- that managed to send its meltwater far off the coast of Greenland -- might do it. Moving the main sinking region south of the Greenland-Iceland-Faroes ridge might mean that the water there didn't sink to great depths, and instead the source became the Labrador Sea. Labrador water already sinks fairly deep. Without the densest North Atlantic water, it could sink deeper. At least if nothing changed over the Labrador Sea.

Since that area also is experiencing changes In general, if something gets to be hard to predict, I figure it's unlikely to work out in my favor. Hank: Oops. Stopped too soon. If historical observations will do for you, then the polar observations from the Soviet Union, and then Russia, and the US were made available as part of the s 'Gore-Chernomyrdin' accord.

I don't know of any oil company data being released, but I'm sure they the companies, that is have some. Lots of publications have come out referencing those data, e. Also interesting that the N. Fide Wikipedia , CO2 is one of the gases that forms clathrate hydrates. One would have to dig deeper to find out under what conditions it does so. I do wonder whether this can be exploited for CO2 sequestration.

Robert, a couple more questions about the meridional overturning circulation. First, what fraction of the ocean is participating in the flows that we call the MOC at any given time? That question is motivated by thinking of the atmospheric jet streams which only contain a small fraction of the air at any given time.

Second, if the cycling time is years, then a good fraction of the deep water currently in the MOC was formed during the little ice age. Would that deep water be any colder than deep water formed today or during the MWP for that matter? If so, that could create a mechanism for multi-centenary internal variability.

Is that reasonable? Already well known? Already considered and dismissed? A third - is there a difference in definition, opinion, or otherwise between your statement of years for the cycling time and this from Wikipedia: "While the bulk of it upwells in the Southern Ocean, the oldest waters with a transit time of around years upwell in the North Pacific Primeau, I thought of his Medea Hypothesis when I read this: " But they are all too scared of being ostracized in the scientific community if they speak of it.

Hank: I'll have to follow up your article. Before I shifted to my current line of work, I was looking at deep ocean circulation. Temperature was one part. But the other was to consider the carbon budget in the deep ocean. A warming deep ocean is going to be carrying less carbon out of the atmosphere. The Medea Hypothesis is not exactly new. The name, perhaps, and particular examples. But ages back, when I was in graduate school, we raised some of these same examples to James Lovelock when he visited our department.

I think it's probably going too far to assign 'suicidal' to the planetary system, for much the same reasons as I think it's too far to assign 'stable' to it. But I'll have to look up Ward's work and see what he had to say in detail. GFW: Darn. Sorry I hadn't gotten back to your questions.

They're good, and I'll probably take them up in their own post, with link from here. Post a Comment. Thoughts and notes on science from another blogging Grumbine. Pages Home What is Climate? The Simplest Climate Model Old locations and retired blogs. Folks reading headlines about record warm oceans might be surprised by this question. But it's a real question, if perhaps from a different viewpoint than you might think.

If we look at the surface of the ocean , we see that most of the ocean is warm. The presentation at the link over-emphasizes the polar regions -- they're actually much less of the earth's area.

Even so, over half the ocean -- surface -- is warmer than 20 C. So you might figure that the volume of the ocean would also be some moderately warm figure, maybe a bit colder since cold water sinks, but still fairly warm. Surely over 10? In fact, the volume of the ocean -- average up every blob of water there is -- averages 3. Go back to the surface map and take a look at how much of the ocean is that cold.

Answer: Not much. The importance of those small areas of cold water is that there is no refrigerator in the ocean. Once water leaves the surface of the ocean except for one even smaller exception I'll get to , there's no way to make the water any colder. So if you see water that's It could have been even colder -- the original cold blob might have mixed with a warmer blob of water.

Some of you might have objected up there when I mentioned that the average ocean temperature is 3. There's a fairly popular error that says the deep ocean has to be 4 C. It runs this way: Water is densest at 4 C, so as you cool a body of water, once it reaches 4 C all this cold water sinks to the deeps.

As you cool the surface further, the water is less dense, so it quits sinking. That leaves you with 4 C water in the deep. The thing that is wrong with that, and it's only one error, is that the statements are only true for fresh water. If you're looking at ocean water -- where the density and freezing point also depend on how much salt you have, things are different.

For saltwater with salinity greater than 22, the water gets denser all the way down to the freezing point. Typical ocean water has a salinity of about 35, and extremely little of the ocean is as fresh as So you can get as cold as about Or at least it tries. One part of our story, then, is that the deep ocean is cold, very cold, because cold water is denser than warm water and salt water gets denser all the way to its freezing point.

We can look at the maps of surface temperature and see that the only areas that get cold enough to supply most of the volume of the ocean are the Antarctic, the North Pacific and Sea of Okhotsk, the Labrador Sea east coast of Canada , and the Nordic Seas between Greenland, Iceland, and Norway.

If we look at the bottom of the ocean, we see even colder temperatures than the 3. Makes sense -- the bottom would have the coldest, densest water of all. This may be owing to the defective instruments, but if go, a consistency of error was preserved almost beyond the possibility of chance.

The hams at. Secondly: My establishment ia on the banks of the Ohio river ; the lower story is subject to be overflowed or submerged in OHr greatest floods in the winter or spring. On one occasion of a flood we had several open tubs of pickle on the lower floor, which we found impossible to move before the water came upon us.

The river rose at least eight feet above the tops of the tubs of pickle. We supposed that the pickle—from the motion and agitation of the waves and water—would all be destroyed, and the tubs displaced. These facts demonstrate two things : first, that pickle will not freeze or become solid at 20 below the freezing point; and second, that its specific gravity and density is such that it will not mingle with water without a considerable degree of agitation.

I would, therefore, suggest the query to Lieut. Berryman, whether or not the peculiar thermometrical phenomena he discovered in the deep sea soundings were not owing to the increased density and saltness of the water at the bottom of the ocean.

Louisville, Ky. Berryman have done much to confirm a theory found in Lieut.