Role of Megafauna and Frozen Soil in the Atmospheric CH4 Dynamics

TitleRole of Megafauna and Frozen Soil in the Atmospheric CH4 Dynamics
Publication TypeJournal Article
Year of Publication2014
AuthorsZimov S., Zimov N.
JournalPlos OnePlos OnePlos One
Volume9
Date PublishedApr 2
ISBN Number1932-6203
Accession NumberISI:000334103000058
Keywordsabrupt climate-change, carbon storage, greenland, holocene, lakes, last glacial maximum, methane, north-america, permafrost, termination
Abstract

Modern wetlands are the world's strongest methane source. But what was the role of this source in the past? An analysis of global C-14 data for basal peat combined with modelling of wetland succession allowed us to reconstruct the dynamics of global wetland methane emission through time. These data show that the rise of atmospheric methane concentrations during the Pleistocene-Holocene transition was not connected with wetland expansion, but rather started substantially later, only 9 thousand years ago. Additionally, wetland expansion took place against the background of a decline in atmospheric methane concentration. The isotopic composition of methane varies according to source. Owing to ice sheet drilling programs past dynamics of atmospheric methane isotopic composition is now known. For example over the course of Pleistocene-Holocene transition atmospheric methane became depleted in the deuterium isotope, which indicated that the rise in methane concentrations was not connected with activation of the deuterium-rich gas clathrates. Modelling of the budget of the atmospheric methane and its isotopic composition allowed us to reconstruct the dynamics of all main methane sources. For the late Pleistocene, the largest methane source was megaherbivores, whose total biomass is estimated to have exceeded that of present-day humans and domestic animals. This corresponds with our independent estimates of herbivore density on the pastures of the late Pleistocene based on herbivore skeleton density in the permafrost. During deglaciation, the largest methane emissions originated from degrading frozen soils of the mammoth steppe biome. Methane from this source is unique, as it is depleted of all isotopes. We estimated that over the entire course of deglaciation (15,000 to 6,000 year before present), soils of the mammoth steppe released 300-550 Pg (10(15) g) of methane. From current study we conclude that the Late Quaternary Extinction significantly affected the global methane cycle.

Short TitlePlos OnePlos One
Alternate JournalPlos One