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Thermohaline circulation

  1. Aug 17, 2004 #1
    When the flow of deep cold water in the atlantic speeds up what causes
    the amount of water vapour in the tropics to increase too.Could
    magma in the Earth be heating the sea water or hydrothermal vents - presumably sea currents would have to move to a hot spot or somehow
    encourage vents to release more energy.
     
  2. jcsd
  3. Aug 18, 2004 #2
    hmm, i'd say thermal vent won't have a big effect.
    Its like trying to boil a swimming pool wit 20 guys holding a blowtorch.

    Ocean currents are maily controlled by the sun and the balance of salt and fresh water.
     
  4. Aug 18, 2004 #3
    Maijn:
    Ocean currents are maily controlled by the sun and the balance of salt and fresh water.

    Kurious:
    I agree with what you say but is it not the case that even phenomena like the Milankovitch cycles cannot fully account for the energy changes involved in the thermohaline circulation?
     
  5. Aug 18, 2004 #4
    Your right on that one.
    But without calculating it, you can fairly easilly rule out thermal vents.
    Consider the amount of water coming from themal vents, in relation to the watermass it vents into, it's peanuts.

    Vulcano's are fairly save to rule out as well.
    Being that their activity is very local, and not prolonged (could be rong on the duration).
    I think their effect is relatively small compared to the Milankovitch cycles.
    The Milankovitch cycles are an influence quite bigger than vulcano's and thermal vents, afteral the Milankovitch cycles are being held responsible for finishing the last ice-age (Berger (1991), and Laskar (1993)).

    What does cause the changes i can't say, and i don't know if anyone does.
    There are just to many influences to pick one (or a combination) to say, "yeah, thats causing it!".

    Maybe Andre has some more info on this, afteral its related to his hobby: ice-ages.
     
  6. Sep 13, 2004 #5
    Sorry missed this one. I have not really additional information on the variation in the THC. But something has been puzzling me. We consider de engine motoring the THC to be Atlantic surface water that cools due to prolongued evaporation. Hence it gets saltier but also enriched in heavy 18O oxygen because the lighter 16O oxygen evaporates more easily. Now the sinking heavy and salty water starts a journey of several thousand years close to the ocean bottom, whilst the surface water is refreshed mainly by light fresh precipitation water -hence heavy oxygen depleted - Consequently, after hundreds and thousands of years you would expect a distinct isotope differentiation between ocean bottom water and surface water. But this is not true. Have to find the link back but most of the ocean water is pretty much within less than a mil difference in isotope ratios.

    My idea is that this is odd. Somebody agree, disagree?
     
  7. Sep 13, 2004 #6
    "Now the sinking heavy and salty water starts a journey of several thousand years close to the ocean bottom,"

    How do we know this? We have seen how the tanker spill of yellow rubber ducks migrated, but what about movements deep under the ocean?

    "Consequently, after hundreds and thousands of years you would expect a distinct isotope differentiation between ocean bottom water and surface water."

    Would you? The bottom of the ocean is not a desert. There is a lot of biological activity going on. And is saltwater a static thing? Does the salt affect isotopic behavior?
     
    Last edited: Sep 13, 2004
  8. Sep 15, 2004 #7
    Andre you're now talking about the "conveyor-belt" right?

    Does it take several thousands of years to travel that distance?
    Thats a bit hard to believe.
    The route it would take surely has some more elevated parts in it.
    Thus the water would release some Co2 because of lowered pressure.

    This appart from what the effects of life would be on the Co2 level.

    Could you explain a bit more what you meant?
     
  9. Sep 15, 2004 #8
    Right, well looking at this figure it appears that speeding up the conveyor belt would indeed bring more warm surface water to the Atlantic.

    "Conveyor circulation takes about 1500 yrs" I wasn't that far off. :tongue2:

    Again, my area of interest is the d18O and dD isotope ratios thoughtout the whole ocean. I used to have an excellent link showing the ratio / salinity properties throughout the Atlantic but can't find it back right now. Files too thick and no luck with google. Anyway it showed that the variation in isotopes is very small.

    If the downdraft in the North Atlantic pushes heavy isotope enriched water down, then why isn't oceanic bottom water enriched in heavy isotopes?

    The fact that it isn't, may be a very important piece of evidence for a few ideas.
     
  10. Sep 15, 2004 #9
  11. Sep 15, 2004 #10
  12. Sep 15, 2004 #11
    Thanx, Nilequeen, excellent study material.
     
  13. Sep 15, 2004 #12
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