The findings are the result of a collaboration among geoscientists and biologists from several institutions: Song-Miao Fan and Emanuel Gloor, Princeton research scientists; Jerry Mahlman, director of the Geophysical Fluid Dynamics Laboratory (GFDL), a NOAA facility on the Princeton campus; Stephen Pacala, professor of ecology and evolutionary biology at Princeton; Jorge Sarmiento, professor of geosciences at Princeton; Pieter Tans, of the Climate Modeling and Diagnostics Laboratory, a NOAA facility in Boulder, Colo., and Dr. Takahashi.
The researchers used atmospheric data provided by Dr. Tans, observations of ocean-based sinks contributed by Dr. Takahashi, and one ocean and two separate atmospheric models developed at Princeton's Geophysical Fluid Dynamics Laboratory. The team created a three-dimensional grid of the earth to model the worldwide flow of carbon dioxide. Researchers anticipated that as they moved from point to point on the grid across North America, atmospheric carbon levels would rise, based on the fact that North America is a major producer of carbon dioxide from the burning of fossil fuels. Instead, carbon levels actually dropped between the North Pacific and the North Atlantic.
The results suggest the presence of a carbon sink, which occurs when carbon dioxide absorbed by plants as they grow exceeds carbon dioxide released by dead material as it decays. Although the method does not identify the causes, there are a number of possible mechanisms that could be responsible for the sink. Forest regrowth in areas where generations of pioneers leveled trees to create farmland almost certainly plays an important role. Millions of acres east of the Mississippi have returned to forest.