Anyway, when the clathrate gun fires it releases large amounts of d13C depleted methane in the air. The methane oxidizes quickly to carbon dioxide in the atmosphere, lowering the overall d13C signature in the CO2 that enters the food chain. So the plant remains in the soil would also have a much more d13C depleted signature when the clathrate gun fired. This takes us back again to the comprehensive study of Schirrmeister et al. about the paleoclimate and paleontology of Northern Siberia during the last 60,000 years. We find this graph (fig 5 - page 7) suggesting clear proof of the clathrate gun. We see the sudden steep negative d13C spike at around 13,000 PB years (or about 15.500 Cal BP years), apparently coinciding with the Bolling Allerod event to be interrupted a little shortly possibly indicating the Younger Dryas when the clathrate gun was silent. This would result into a tendency to normalize the isotope signature again by interactrion with the oceans etc. But then at 11,000 years the steep negative spike continues again, likely indicating the start of the Pre Boreal of the Holocene.
As a side step, note that a temperature rise would cause a tendency for an increased d13C ratio. Instead, the opposite is happening. Consequently this proxy does not support the alleged sudden warming at the end of the Younger Dryas. This may be the reason that Schirrmeister et al do not comment about this result in any way.
Clathrate gun.
Numerical simulation of a clathrate gun sequence have been carried out with the following parameters:
Atmospheric d13C 0 mil PDB.
Clathrate d13C typical-65 mil PDB.
Clathrate delta 14C negligible
1m3 Clathrate expands to 160 m3 methane of 1 hectopascal (hP) pressure.
Straightforward calculations of carbon transport reveals that a total increase of atmospheric CO2 from a typical ice age value of 200 ppm to a typical value of 280 ppm in the Holocene without other factors would require an accumulation of clathrate events with a total volume of 1300 km3. This would also lead to a radiocarbon platform of about 2700 years. This value compares well with the observed total combined radiocarbon platforms between 8000 BP and 15,000 BP (Kitagawa), supporting the clathrate gun hypothesis further. However there are complications. Maslin et al (2004) list 15 clathrate events dated between 8000BP and 17,700 BP with a total discharge of over 10,000 km3 Clathrate. Transport to the atmosphere would lead to a cumulative 820ppm atmospheric CO2. Meanwhile, the observed negative d13C spike of over 5 mil PDB in the proxy of Schirrmeister at the transition from Pleistocene to the Holocene would require only a discharge of about 270km3 clathrate, while the discharge of the required 1300 km for the observed increase in CO2 and radiocarbon platform would have lead to a negative d13C spike of 18,6 mil PDB and the total discharge of 10,000 equals to an d13C drop of -50 mil PDB. Apparently observing this effect, Maslin concluded initially that the Clathrate gun was firing blanks (Maslin 2002).
Obviously, with multiple evidence supporting the events, a better explanation could be that the ocean absorbs most of the excess CO2 gas again. Moreover the constant gas exchange process at the ocean surface, accelerated directly due to clathrate events itself, tends to balance isotope ratios. We assume that this effect shows outstandingly in the comparison of the Dansgaard Oeschger events, including the Bolling Allerod, and the oceanic proxies of ODP hole 893A (Kennett et al 2000) where the termination of the event seem to be almost as abruptly as the onset. This effect would lead to both increasing atmospheric d13C and delta 14C however a residual value would remain due to the fractionation effect. It is believed that these residual value are visible as the noted negative d13C spikes (Schirrmeister et al) and the radiocarbon calibration platforms of the Bolling - Allerod events and the early Holocene (Kitagawa, Van der Plicht).
Furthermore, although Maslin accepts it, the radiocarbon dating of the major clathrate events are not lined up exactly in time with the onset of the Bolling Allerod event and the termination of the Younger Dryas. However, the discussed problems for carbon dating are even exaggerated for ocean floor sediment dating while clathrate guns increase uncertainties by changing ocean currents with variable 14C signatures. The increased outflow of 13C and 14C to the atmosphere during clathrate events would tend to give older indications and decreasing d13C indications. However this effect may be negligible compared to temperature changes due to changing ocean currents as a result of the induced flow of the methane. This would have considerable but unpredictable effect on the fractionation in micro fossils. Consequently d13C and delta 14C and hence age indication could be erratic.
