Atmospheric carbon dioxide and the global carbon cycle: The key uncertainties

The biogeochemical cycling of carbon between its sources and sinks determines the rate of increase in atmospheric CO/sub 2/ concentrations. The observed increase in atmospheric CO/sub 2/ content is less than the estimated release from fossil fuel consumption and deforestation. This discrepancy can be explained by interactions between the atmosphere and other global carbon reservoirs such as the oceans, and the terrestrial biosphere including soils. Undoubtedly, the oceans have been the most important sinks for CO/sub 2/ produced by man. But, the physical, chemical, and biological processes of oceans are complex and, therefore, credible estimates of CO/sub 2/ uptake can probably only come from mathematical models. Unfortunately, one- and two-dimensional ocean models do not allow for enough CO/sub 2/ uptake to accurately account for known releases. Thus, they produce higher concentrations of atmospheric CO/sub 2/ than was historically the case. More complex three-dimensional models, while currently being developed, may make better use of existing tracer data than do one- and two-dimensional models and will also incorporate climate feedback effects to provide a more realistic view of ocean dynamics and CO/sub 2/ fluxes. The instability of current models to estimate accurately oceanic uptake of CO/sub 2/ creates one of the key uncertainties in predictions of atmospheric CO/sub 2/ increases and climate responses over the next 100 to 200 years. 60 refs., 1 fig., 2 tabs

Metagenomic analysis of permafrost microbial community response to thaw

We employed deep metagenomic sequencing to determine the impact of thaw on microbial phylogenetic and functional genes and related this data to measurements of methane emissions. Metagenomics, the direct sequencing of DNA from the environment, allows for the examination of whole biochemical pathways and associated processes, as opposed to individual pieces of the metabolic puzzle. Our metagenome analyses revealed that during transition from a frozen to a thawed state there were rapid shifts in many microbial, phylogenetic and functional gene abundances and pathways. After one week of incubation at 5°C, permafrost metagenomes converged to be more similar to each other than while they were frozen. We found that multiple genes involved in cycling of C and nitrogen shifted rapidly during thaw. We also constructed the first draft genome from a complex soil metagenome, which corresponded to a novel methanogen. Methane previously accumulated in permafrost was released during thaw and subsequently consumed by methanotrophic bacteria. Together these data point towards the importance of rapid cycling of methane and nitrogen in thawing permafrost