[Paddlewise] Freezing Water [was: POST SCRIPT to: Into Winter Mode ...]

In a message dated 12/11/2002 4:35:02 AM Eastern Standard Time, 
mkayaks_at_oz.net writes:

> I think that 40 degrees F and freezing of a waters surface are very close 
> together in nature. If I understand this correctly (and it may be much more 
> complicated than this) the surface of water can't freeze when in contact 
> with freezing air until it reaches 40 degrees F. because water is at its 
> greatest density at 40 degrees. Below that temperature the water expands 
> again until freezing (where it expands a lot more). Therefore, the warmer 
> (less dense water) at the surface no longer floats to the top once the 
> surface temperature reaches 40 degrees. The water "turns" and the colder 
> water, lower than 40 degrees F., that had been below floats to the surface 
> as the denser 40 degree water sank below it. Water colder than 40 degrees 
> that had been lower down now rises to the surface and the icy air can bring 
> down the temperature to freezing at the surface rather quickly since warmer 
> water is sinking rather than rising below 40 degrees F.

Matt, if I understand the above correctly then NO water can freeze until the 
entire body of water has been cooled to 40F, thereby stopping the convection 
process and leaving the increasing less dense (now dropping below 40F) water 
at the surface to cool until it freezes -- fresh water at 32F. 

Now, does the magic 40F mark apply to fresh or salt water? 

At what temperature is the water least dense and would therefore show the 
greatest tendency to rise to the surface? (I'm trying to figure out how close 
the two temperatures are together to see whether surface cooling might under 
certain conditions be rapid enough to proceed faster than the convection 
process can stop actual freezing.)

How does this work in DEEP water? 

For example Crater Lake in Oregon never freezes despite pretty low 
temperatures throughout the year (at the height of summer in July / August 
1982 the ring road was still 2/3 not cleared from the previous winter and 
they expected heavy snow to resume in September). The Park Rangers explained 
that this was due to the lake's enormous depth.

But I seem to remember reading that at a certain depth the ocean temperature 
steadies at about 4C (i.e., in the 40F range) anyway irrespective of surface 
conditions ...

Best regards,
Ralph

Ralph C. Hoehn
Ralph_at_Atlatl-Kayaks.com / Ralph_at_PouchBoats.com
www.Atlatl-Kayaks.com / www.PouchBoats.com
phone: +1-203-324-0901

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