- #1
Outrageous
- 373
- 0
During winter why not all the water molecules on the water surface that have 4°C go deep under the water?
Water at 4 degree Celcius has maximum density
Click For Summary
Discussion Overview
The discussion revolves around the behavior of water at 4°C, particularly in the context of its maximum density and implications for bodies of water during winter. Participants explore the conditions under which water at this temperature behaves in frozen-over ponds and oceans, addressing both theoretical and practical aspects.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
Main Points Raised
- Some participants suggest that water at the bottom of a frozen-over pond is typically at about 4°C, which is why lakes freeze from the top down.
- One participant questions whether the highest temperature of water in a frozen-over pond can be stated as 4°C, noting that while this is usually true, it may not hold under all conditions.
- Another participant explains that while the warmest water can be at 4°C, it is possible for the rest of the water to be colder, especially as freezing progresses.
- Some participants note that in the ocean, deep water is generally colder than 4°C, typically between 0 and 3°C, and inquire about the reasons for this phenomenon.
- One participant proposes that salinity and high pressure may affect the properties of water, contributing to the lower temperatures observed in ocean depths.
- Another participant emphasizes that the density behavior of seawater differs from that of pure water, stating that seawater's density increases with decreasing temperature down to below zero degrees Celsius, without exhibiting the same anomalous maximum density behavior.
- It is mentioned that the freezing point of seawater depends on its salinity, which is a factor in its density characteristics.
- One participant adds that icebergs float due to the air they contain, which is relevant to the discussion of density.
Areas of Agreement / Disagreement
Participants express a mix of agreement and disagreement regarding the behavior of water at different temperatures and conditions. While there is some consensus on the behavior of freshwater, the discussion highlights competing views on the properties of seawater and the effects of salinity and pressure.
Contextual Notes
Participants acknowledge that the behavior of water can vary under different conditions, such as salinity and pressure, which may not be fully explored in the discussion. There are also indications of missing assumptions regarding the specific conditions under which the discussed phenomena occur.
- #2
K^2
Science Advisor
- 2,470
- 33
They basically do. Water at the bottom of the frozen-over pond will be at about 4°C. That's also why lakes freeze starting from the top.
- #3
Outrageous
- 373
- 0
K^2 said:
Can I say in a frozen-over pond, the highest temperature of the water will be 4 °C which is at the bottom?
- #4
K^2
Science Advisor
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In practice, almost always, but it isn't necessarily true under all conditions. Certainly, there cannot be any water warmer than that. If there is, it will rise to the top, until it either meets colder water and cools, or until it gets to the very top and meets ice, in which case it will melt some ice and cool down. So in equilibrium, the warmest water you can have is 4°C.
However, all water in the pond could be colder than 4°C. That really should only happen right before the entire thickness of water freezes through, because while there is still a lot of water, the heat is lost only from the surface, and whatever little heat there is coming from the ground will keep the bottom at these 4°C. But if for whatever reason there is no heat from bellow, it could, in principle, be colder.
But certainly, you could say that there is no water warmer than 4°C, and whatever temperature the warmest water is, it is at the bottom.
However, all water in the pond could be colder than 4°C. That really should only happen right before the entire thickness of water freezes through, because while there is still a lot of water, the heat is lost only from the surface, and whatever little heat there is coming from the ground will keep the bottom at these 4°C. But if for whatever reason there is no heat from bellow, it could, in principle, be colder.
But certainly, you could say that there is no water warmer than 4°C, and whatever temperature the warmest water is, it is at the bottom.
- #5
Outrageous
- 373
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Thank you very much
- #6
Borek
Mentor
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Note in the ocean things get slightly different - deep ocean water is colder, usually between 0 and 3°C.
- #7
Outrageous
- 373
- 0
Borek said:
Is that because there is high concentration of salt? Since 3°C is lower than 4°C , why not lower than 0 ?
- #8
Borek
Mentor
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I believe it is a combination of salinity and high pressure that changes water properties. Perhaps there is more to it, I don't know details. Sorry.
- #9
K^2
Science Advisor
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At high pressure, the maximum density will certainly be at a lower temperature, so it's probably a factor. But I don't know how significant that would be or how the salt will play into it.
- #10
Outrageous
- 373
- 0
Thank you guys
- #11
Studiot
- 5,440
- 11
Do not try to apply the 'anomalous' density curve for pure (fresh) water to sea water.
For sea water the density continues to increase as temperature decreases all the way below zero (C) to the freezing point. There is no anomalous maximum.
Of course the actual value of freezing point depends on the salinity, as Borek said.
The reason icebergs float is tha they contain a large quantity of entrained air.
For sea water the density continues to increase as temperature decreases all the way below zero (C) to the freezing point. There is no anomalous maximum.
Of course the actual value of freezing point depends on the salinity, as Borek said.
The reason icebergs float is tha they contain a large quantity of entrained air.
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