THE CLATHRATE GUN IS FIRING BLANKS: EVIDENCE FROM BALANCING THE DEGLACIAL GLOBAL CARBON BUDGET

Kennett et al. (2003) have suggested that the large changes seen in the ice core atmospheric methane record are due to gas hydrate dissociation rather than changes in tropical wetlands. We use the global carbon isotope budgeting method to calculate the amount of gas hydrate release which would be required to balance the deglacial carbon isotope shift. A release of only ~120 GtC methane, is required to make a biospheric carbon transfer of ~1000 GtC compatible with the marine carbon isotope data. This represents less than 20 percent of the atmospheric methane increase between 18 and 8 ka observed in ice cores. This supports the theory that glacial-interglacial variations in atmospheric methane were driven primarily by changes in the extent of tropical and temperate wetlands and not by methane release from clathrates. Hence the Clathrate Gun Hypothesis is firing blanks. This method also invalidates the carbon isotope budget method as a means of estimating glacial-interglacial land carbon, as the release of very light gas hydrate carbon must be taken into account. This resolves the long running discrepancy between isotope and paleovegetation estimates of carbon transfer. Therefore we suggest global carbon models will have to incorporate glacial-interglacial vegetation shifts of at least 1000 GtC. Modelled time-series of gas hydrate release and the carbon budget; indicates that 1. Gas hydrate release is controlled by N. Hemisphere deglaciation while 2. most of the increase in atmospheric carbon dioxide is very rapid and occurs synchronous with warming in Antarctica