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View Diary: Profile of A "Dangerous Nuclear Waste:"  Cesium, Part 3. (26 comments)

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  •  yes, but some K stays in seawater (1+ / 0-)
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    NNadir

    The concentration of K in seawater is not constant in the geological record.

    "It's the planet, stupid."

    by FishOutofWater on Fri Feb 02, 2007 at 03:58:20 PM PST

    [ Parent ]

    •  True (1+ / 0-)
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      NNadir

      but with the current level of 5x10^17 Kg of potassium in seawater, 5x10^14 Kg of K-40, even fluctuations of two orders of magnitude aren't going to make human contributions that important - to change the amount of K-40 in current seawater by 1% you'd need to add 5 billion tons of K-40.

      I'm not sure what the long term amount of potassium in seawater has to do with this- the equilibrium with clays is fairly slow, climatic shifts can change weather enough and fast enough to upset the equilibrium. As you said, difficult to know the exact amount of potassium in seawater, but I doubt it fluctuates over an order of magnitude. The amounts of manmade K and Cs are way below the noise floor.

      •  This is quite the tangent (0+ / 0-)

        I was merely commenting on the unsupported conclusion that K-40 was at its lowest level ever in the ocean. Thanks for the interesting details.

        "It's the planet, stupid."

        by FishOutofWater on Fri Feb 02, 2007 at 06:31:35 PM PST

        [ Parent ]

        •  Ah (1+ / 0-)
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          NNadir

          Yes, it is. I got it conflated with a disscussion somewhere else entirly, and which included arguements on the impact of manmade isotopes on the natural concentration.

          OK, if constant concentration of potassium in the ocean is assumed, then there should be about 1/16 (mind the waving hands) as much potassium today as there was at Earth's formation. This amount is affected by orogenic intervals, which result in increased erosion of rock and increasing amounts of potassium in the sea, and periods of low erosion where potassium is removed from the oceans. What's not clear is how much 'wiggle' is caused by those events.

          I remember reading in a geology book decades ago that the reactions and rates of exchange between sea water and sediments were difficult to stuff, in part because "equilibrium times are on the order of X thounds of years, and few grad students stay around for that long"

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