Volcanoes: our noble allies in the battle against export productivity

Finally, a blogospheric spat that actually matters. Craig McClain over at Deep Sea News has accused volcanoes of being the implacable enemies of marine life, based on new research linking them to some bouts of extreme ocean anoxia (where the deep oceans become severely depleted in oxygen, to the detriment of much of the life there). Maria jumped to rebut what she views as a vile libel (unsurprisingly, the Volcanism Blog has backed her up), and Craig has now hit back, rebutting her rebuttal.
It’s certainly true that volcanoes can be bad for life, both marine and non. A large-ish volcanic eruption such as the Mount Pinatubo eruption in 1991 has global effects on the atmosphere and climate, and that’s just a small pop compared to those times in the geological past where whole tracts of the Earth’s surface have been resurfaced by flood basalts (over a million square kilometres in the case of the Siberian Traps, which are widely – but not universally – implicated in the end-Permian extinction 250 million years ago).
But what Craig isn’t telling you is that the marine biosphere has it’s own dirty little secret. What do marine organisms do? They take carbon dioxide out of the atmosphere, either directly by photosynthesis, or more indirectly by taking bicarbonate from ocean water to make protective shells. Then they die, and sink to the ocean bottom, where all that organically fixed carbon is incorporated into carbonate- or organic rich sediments. Once buried, it’s pretty hard to remobilise it, and its especially hard to get it back into the atmosphere as carbon dioxide.*
Over geological time, this continual drawdown would leave us with an atmosphere devoid of all CO2, which would severely cool the planet by reducing the greenhouse effect (note: this fact has no bearing on the potentially deleterious effects of anthropogenic global warming. You can have too much of a good thing, and you can certainly have it too fast). In effect, marine export productivity (as it is called) has the potential to freeze all life on the planet to death.
Fortunately, plate tectonics comes to the rescue. When oceanic crust is subducted back into the mantle, the carbon-bearing sediments are heated, degassed, and the CO2 is incorporated into the ascending magma beneath…. volcanic arcs.
So perhaps we shouldn’t be renaming the Ring of Fire the ‘Arc of Evil’ after all. More seriously, life may sometimes be threatened by geology, but it is also intimately shaped by it, and I’m firmly convinced that life, and especially complex life, is dependent on vigorous geological activity to provide – and more importantly, maintain – the thermochemical gradients that drive interesting chemistry. Volcanoes may cause the odd extinction event or two, but they’re also a big part of why there are things to go extinct in the first place.
*This fact is the basis for all of the ideas about stimulating algal blooms in the ocean by seeding them with limiting micronutrients such as iron, to absorb anthropogenic CO2 (see the third item here)..

Categories: climate science, environment, geology, tectonics, volcanoes

Comments (10)

  1. BrianR says:

    “Volcanoes may cause the odd extinction event or two, but they’re also a big part of why there are things to go extinct in the first place.”
    Exactly.

  2. Ole says:

    Well said!
    (Indeed, I agree with both you and Maria)

  3. Kim says:

    I’ve heard it argued that plate tectonics makes Earth a habitable planet*. I don’t remember who argued it, or the basis of the argument, though.
    *Although one could argue that we’re working from a limited perspective: the only life that we know evolved on a wet, tectonically active planet. Evolution on a different planet might result in different life forms.

  4. llewelly says:

    Superbly framed.

  5. Eric G says:

    If there were no geological source of CO2, then we would also lose all our O2 to geological oxidation.

  6. DDeden says:

    Wow Chris. Volcanic CO2 comes from magmatic cooking (gas expansion) of buried carbonate shells, coral, limestone etc. The big picture is a bit clearer now. I’d had no idea where it came from. Now what about the sulfurous gases? From buried green plants, algae?
    AFAICT, Wegener was correct, saying that solunar cycle tides were the cause of tectonic rafting, while the deep underground geothermal plumes are an associated effect but not the primary cause (the solar-lunar orbit being the tidal engine).
    Furthermore, from what I can see, Homo has for 5 million years been strongly associated both with seashore habitat and tectonic margins (rifts, island archipelagos).
    Earth’s orbiting gravitational effect of sun & moon + fluid oceanic thick surface + continental constrictions (+ land bridges) -> tidal action -> tectonic shifting -> vulcanism at active plate peripheries -> subduction -> CO2/SO2/H2S.. gasification of buried sediments and detritus -> Volcanos are earth ‘burps’ during digestion-decomposition-cooking of complex chemical compounds. Wow. This is so trippy! I never saw it like that before. Thanks Chris, Craig, Maria!

  7. James says:

    I must admit that I enjoy being entertained. Particularly when such entertainment is accomplished with a humorous wink and nod to ‘conflicting’ opinions.
    I am adding this intellectual, scientific discussion to my short list of similar ‘conflicts’.
    1. Is World Wrestling Entertainment real or fake?
    2. Is the glass half full or half empty?
    3. Just how many angels can actually stand on the head of a pin?
    Please, continue. I’ll be back shortly with my popcorn and beer.

  8. blf says:

    Is the glass half full or half empty?

    Is the glass too large or are you happily drunk on half of it?

  9. yogi-one says:

    A veritable Journey To The Center of the Earth (and back again)!
    Sorry….somebody had to say it…
    James, make that two popcorns!

  10. YetAnotherKevin says:

    1. Fake
    2. The glass is twice as big as it needs to be.
    3. floor (pi * pr**2 / pi ar**2), where pr is the pin-head radius, and ar is the average radius of an angel, assuming spherical angels.