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Thread: C-14 in the atmosphere

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    C-14 in the atmosphere

    The proportion of C-14 in the atmosphere should be rising because of nuclear explosions and falling because of fossil fuel burning. Which trend is currently dominant? Is c-14 more common than it was a few centuries ago, or less?
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    Why would fossil fuel be lowering the proportion of C-14?
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    Quote Originally Posted by Noclevername View Post
    Why would fossil fuel be lowering the proportion of C-14?
    Because it's very old carbon, and therefore contains little if any C-14.
    In answer to the OP, the fossil fuels are winning, drawing down the C-14 concentration. This is going to mess up radiocarbon dating.
    Over the next century, fossil fuel emissions will produce a large amount of CO2 with no 14C because fossil fuels have lost all 14C over millions of years of radioactive decay. Atmospheric CO2, and therefore newly produced organic material, will appear as though it has “aged,” or lost 14C by decay. By 2050, fresh organic material could have the same 14C/C ratio as samples from 1050, and thus be indistinguishable by radiocarbon dating. Some current applications for 14C may cease to be viable, and other applications will be strongly affected.
    Grant Hutchison

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    Quote Originally Posted by Tom Mazanec View Post
    The proportion of C-14 in the atmosphere should be rising because of nuclear explosions and falling because of fossil fuel burning. Which trend is currently dominant? Is c-14 more common than it was a few centuries ago, or less?
    The C-14/total C ratio in atmospheric CO2 is currently still slightly above the "natural" ratio. It peaked in the 1960's - 1970's because of the nuclear weapons testing, and has since slowly declined. It is not much above natural now. At work I've got references for this, but I am working from home, and I can't remember what they are called !

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    There is actually a graph on Wikipedia that shows the concentration over time, and as kzb said, it seems still to be above the pre-nuclear testing era level, but is falling since there is no longer any significant atmospheric testing. It is also released to some extent by nuclear power plants.

    https://en.wikipedia.org/wiki/Carbon...bomb_spike.svg
    As above, so below

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    Quote Originally Posted by Tom Mazanec View Post
    The proportion of C-14 in the atmosphere should be rising because of nuclear explosions and falling because of fossil fuel burning. Which trend is currently dominant? Is c-14 more common than it was a few centuries ago, or less?
    Since aboveground nuclear testing has mostly stopped, I would imagine it would be the later.
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    Quote Originally Posted by KaiYeves View Post
    Since aboveground nuclear testing has mostly stopped, I would imagine it would be the later.
    Though actually there are two questions, and I think your answer is to the first one. Fossil fuel burning is currently the dominant trend. And I think the answer to the second question is that it is (still) more common, though it is falling back to "background" levels, as in the graph I linked to.
    As above, so below

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    Quote Originally Posted by Jens View Post
    Though actually there are two questions, and I think your answer is to the first one. Fossil fuel burning is currently the dominant trend. And I think the answer to the second question is that it is (still) more common, though it is falling back to "background" levels, as in the graph I linked to.
    The Wikipedia bomb spike graph stops in 1993, so it doesn't really tell us the current situation. The similar graph in the article I linked to (along with its accompanying text) suggests the current situation is perhaps too close to call.
    From its present value of ∼20‰, which signifies a 2% enrichment in 14C/C of CO2 above preindustrial levels, Δ14CO2 is certain to cross below the preindustrial level of 0‰ by 2030, but potentially as soon as 2019.
    Since the preindustrial level was not constant over millennia, as we know from tree rings, we're presumably in a state at present in which we're higher than some preindustrial levels but lower than others.

    Grant Hutchison

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    Quote Originally Posted by grant hutchison View Post
    The Wikipedia bomb spike graph stops in 1993, so it doesn't really tell us the current situation. The similar graph in the article I linked to (along with its accompanying text) suggests the current situation is perhaps too close to call.
    Thanks for pointing that out. I saw the graph, but the years at the bottom were a bit much for my presbyopic eyes to make out.
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    Carbon-14 concentration variations have also occurred as a consequence of the solar system being bombarded by a few supernovae ejecta clouds of dust from the O and B stars in the Centaurus-Scorpius asscociation over the last millions of years, see:https://www.pnas.org/content/109/16/5967
    I searched many moons ago for evidence of such a cloud during the late Bronze Age, when catastrophic climate saw several civilizations drop population precipitously, ~ 640 AD. Tree ring dendrochronology suggested by Michael Bailley, Queens College, indicated the sudden change worldwide, and Fe-60 deposits in marine sediments suggested supernovae may have contributed, but a firm correlation to a specific supernova (which would have to have been close by), remains elusive in historical records.

    The sun in this image is in the Local Fluff, SEE:https://www.pinterest.com/pin/478648266632026807/

    Fe-60 in Antarctic snow, SEE:https://www.sciencedaily.com/release...0820101623.htm
    Last edited by trinitree88; 2020-Aug-13 at 07:25 PM. Reason: link to image

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    Quote Originally Posted by grant hutchison View Post
    The Wikipedia bomb spike graph stops in 1993, so it doesn't really tell us the current situation. The similar graph in the article I linked to (along with its accompanying text) suggests the current situation is perhaps too close to call.Since the preindustrial level was not constant over millennia, as we know from tree rings, we're presumably in a state at present in which we're higher than some preindustrial levels but lower than others.

    Grant Hutchison
    All carbon dating is referenced to an old archeological wood specimen that has been reliably dated by other means. The calibration line is not straight, because of the natural variations you mention. It has been calibrated via a series of overlapping tree rings in old specimens.

    However, if I have recalled correctly, the current C-14/C ratio would give a date in the future, when calculated using this standard reference wood.

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    "I searched many moons ago for evidence of such a cloud during the late Bronze Age, when catastrophic climate saw several civilizations drop population precipitously, ~ 640 AD."

    640 AD is late Bronze Age, trinitree88???
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    Quote Originally Posted by Tom Mazanec View Post
    "I searched many moons ago for evidence of such a cloud during the late Bronze Age, when catastrophic climate saw several civilizations drop population precipitously, ~ 640 AD."

    640 AD is late Bronze Age, trinitree88???
    The Bronze Age Collapse was roughly ~1200 BCE.
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    Quote Originally Posted by Tom Mazanec View Post
    "I searched many moons ago for evidence of such a cloud during the late Bronze Age, when catastrophic climate saw several civilizations drop population precipitously, ~ 640 AD."

    640 AD is late Bronze Age, trinitree88???
    I stand corrected
    , early Iron age..
    pete

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