It's also interesting to note that the CO2 excursion was too big to have come from oxidation of organic matter: "A best fit of the relationship between the total CIE magnitude and paleo-water depth at each site (Fig. 4B<http://www.pnas.org/content/110/40/15908.full#F4>) predicts an atmospheric excursion of −20‰ (R2 = 0.91; SI Text<http://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1309188110/-/DCSupplemental/pnas.201309188SI.pdf?targetid=nameddest=STXT>). Assuming a pre-CIE atmospheric reservoir of 2,000 GtC (with a δ13C of −6‰) (70<http://www.pnas.org/content/110/40/15908.full#ref-70>) and an instantaneous release, a mass balance calculation gives an estimate of the amount of carbon necessary to produce the ∼20‰ atmospheric excursion. No realistic amount of organic carbon (approximately −26‰) can produce a −20‰ atmospheric change (>100,000 GtC is needed). Thermogenic (−40‰) and biogenic methane (−60‰) sources would require 2,900 and 1,200 GtC, respectively, to produce the −20‰ atmospheric excursion. Given the rapidity of the onset, magnitude of the δ13C excursion, and that the observed calcite compensation depth shoaling in deep ocean requires ∼3,000 GtC (3<http://www.pnas.org/content/110/40/15908.full#ref-3>), two mechanisms meet these criteria: large igneous province-produced thermogenic methane (6<http://www.pnas.org/content/110/40/15908.full#ref-6>, 7<http://www.pnas.org/content/110/40/15908.full#ref-7>) and cometary carbon (11<http://www.pnas.org/content/110/40/15908.full#ref-11>, 12<http://www.pnas.org/content/110/40/15908.full#ref-12>). The latter is consistent with the recent discovery of a substantial accumulation of nonbiogenic magnetic nanoparticles in the Marlboro clay, whose origin is best ascribed to impact condensate (71<http://www.pnas.org/content/110/40/15908.full#ref-71>). "
This is quite different from our current fossil organic carbon oxidation event, but nevertheless very interesting and instructive. One concern I have is diffusion of the acidity down into pre-event sediments and thus anomalous depression of the %CaCO3 and possibly d13C from that in the original pre-event deposits. This would tend smear the records and move the anomally back in time, but I'd be surprised if this hasn't been accounted for (or discounted) by someone. Another thought is the effect of increased surface ocean temperature on carbonate saturation state (increased) and hence survival of calcifiers, assuming they are heat tolerant. Relatedly, could the %CaCO3 be used to reconstruct surface ocean pH given the (sometimes) tight relation between calcification rate and pH and assuming sedimentary %CaCO3 is a function of surface ocean production (and not (also) dissolution/preservation effects)? Food for thought. Greg ________________________________ From: geoengineering@googlegroups.com [geoengineering@googlegroups.com] on behalf of Ken Caldeira [kcalde...@carnegiescience.edu] Sent: Monday, October 28, 2013 9:23 PM To: Andrew Lockley Cc: geoengineering Subject: Re: [geo] Offtopic: For instant climate change, just add one large comet if this paper is right it is good news for biodiversity. If 3000 PgC (= 3000 GtC) were released effectively instantaneously and almost nothing went extinct except for some benthic formamifera, and coral reefs etc sailed through unscathed, it suggests that 3000 GtC released over a couple of centuries should not be so big a deal for most biota. It is not clear to me that a single pulse release is consistent with the isotopic data however. If you look at Fig 4 from McInerney and Wing 2011 (attached), you can see that the isotope excursion remained more-or-less constant for more than 100,000 years. I know of no plausible way in which a single pulse release can produce such an isotope curve. Even if the onset of the PETM was sudden as suggested by this paper, there was likely additional release later. In any case, if this paper is right, then most of the biosphere is much more resilient than many believe it to be. For example, most of our work would indicate that coral reefs would be in big trouble with a 3000 PgC CO2 release, but coral reefs sailed across the PETM relatively unscathed (there was loss in the Tethys but not so much globally). _______________ Ken Caldeira Carnegie Institution for Science Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA +1 650 704 7212 kcalde...@carnegiescience.edu<mailto:kcalde...@carnegiescience.edu> http://dge.stanford.edu/labs/caldeiralab https://twitter.com/KenCaldeira On Mon, Oct 28, 2013 at 6:44 PM, Andrew Lockley <andrew.lock...@gmail.com<mailto:andrew.lock...@gmail.com>> wrote: Poster's note - I've agonised for days about posting this, but it's such an important concept in understanding the global climate system that I think it's well worth a read. The paper is at http://www.pnas.org/content/110/40/15908 but the abstract doesn't say as much as the NewScientist article below. I can't see anything which rules out a catastrophic release of clathrates, as an alternative to the impact theory discussed below. I have no idea whether it's conceivable that such a large amount of clathrate could be destabilised and released so fast. Can anyone comment? http://www.newscientist.com/article/mg22029393.000-for-instant-climate-change-just-add-one-large-comet.html#.Um8QnnC-2M4 A COMET may have sent temperatures soaring 55 million years ago. Two geologists claim they have evidence that carbon dioxide levels in Earth's atmosphere more than doubled in a single year at the end of the Palaeocene. The increase helped trigger the most extreme change in surface temperatures since dinosaurs ruled the land. The speed of the change makes an extraterrestrial impact the likely cause, they say. Global temperatures rose by about 5 °C at the end of the Palaeocene – an event known as the Palaeocene-Eocene Thermal Maximum (PETM). Because more CO2 in the atmosphere makes the oceans more acidic, the event can be tracked by looking at the amount of calcium carbonate deposited on the ocean floor by marine organisms. In more acidic waters, less is deposited. Sediment analysis has suggested the increase in CO2 that caused the PETM took between 750 and 30,000 years. But James Wright and Morgan Schaller at Rutgers University in Piscataway, New Jersey, think it happened much more rapidly. They analysed sediments from a shallow Atlantic Ocean shelf where sediment accumulates faster than it does in the deep sea, making it easier to see seasonal fluctuations in the amount deposited. The pair say that within just one annual cycle about 55 million years ago, the amount of calcium carbonate laid down dropped by 5 per cent. This suggests a very sudden addition – within a year – of atmospheric CO2 (PNAS, doi.org/n8t<http://doi.org/n8t>). So what could have caused so rapid a release of such a vast amount of CO2? "A large comet impact meets the criteria," says Wright. If the change to the carbon cycle really was instantaneous, a comet is a good candidate, agrees Dallas Abbott at Columbia University in Palisades, New York – although it would have to have been large to have such a dramatic effect. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to geoengineering+unsubscr...@googlegroups.com<mailto:geoengineering%2bunsubscr...@googlegroups.com>. To post to this group, send email to geoengineering@googlegroups.com<mailto:geoengineering@googlegroups.com>. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/groups/opt_out. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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