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Temperature of water

  1. Oct 19, 2011 #1
    hi,

    The temperature of the top of a frozen lake is – 15°C .
    What is the temperature of the water in the lake in contact with ice layer ?
    0 or 4 °C

    Sam
     
  2. jcsd
  3. Oct 19, 2011 #2
    Ack, I lost my post (I think.)
    Several questions:
    q1: the ice temp at the top or the air temp at the top?
    q2: what is the temp gradient of the ice?
    q3: Fresh water or salt water?
    q4: Is there permafrost under the lake? If there is then the water is under pressure and it throws off the calculation. (Look up pingos)
    q5: what grade level are you in? the answer for 10th grade chem is different from the answer for post doc physics.
     
  4. Oct 19, 2011 #3
    hi,
    1.The temp of the water in contact with the ice layer.
    2.Sorry,i dont know
    3. fresh water.
    4.Sorry, I dont know.
    5. I am doing phd in lifesciences.

    Sam
     
  5. Oct 19, 2011 #4
    I don't think there is enough information to answer your question. Where does the question come from? That might help make it answerable.
     
  6. Oct 19, 2011 #5
    If you assume the conditions are in equilibrium, then the temp difference through the ice
    layer should be linear....so if the surface is -15 degrees and the temperature of the water in contact with the ice undeneath is zero degrees (unfrozen) that temperature differential
    will remeain...but over time if the surface temperature remains at -15 degrees, heat will be
    lost and the ice layer will get thicker, right.

    Also the water under the ice circulates very slowly as it is most dense just above freezing.....so in general water down deep will be a bit warmer than the frozen surface layer.
     
  7. Oct 19, 2011 #6
    Water is most dense at about 4 degrees C.

    Assuming no snow, wind,
    As the air temperature drops, the water temperature at the surface drops and becomes more dense and sinks and warmer water takes its place. This circulation of lake water continues until the lake is at a relatively uniform temperature of 4 degrees C. As the surface temperature of the water drops below 4 deg C, this less dense water will stay at the top, cool to 0 deg C, and finally freeze forming a layer of ice and grow in thickness as heat is lost. As Naty stated the temperature through the ice layer can be assumed to be linear.
     
  8. Oct 19, 2011 #7
    Unless there is permafrost, at which point it becomes a closed hydrostatic system. It's not what hes getting at, but it's a valid point.
     
  9. Oct 19, 2011 #8
    Really? A Ph.D. in life sciences? And you have absolutely no idea how to think about this problem?
     
  10. Oct 19, 2011 #9
    I also have never figured out why people feel they need to disseminate in an anonymous environment either. Me, I'm a science hack. Love it, but spent my youth being afraid of math. Trying to fix that now. Anyway, I'm out. Seriously though Sam, go look up pingos.
     
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