Analysis of the Seasonal and Geographical Patterns of Atmospheric CO2 Distributions with a Three-Dimensional Tracer Model

Abstract

The measured concentrations of CO2 at several locations illustrate large variations in the amplitude and phase of the seasonal cycle; amplitude may be increasing with time. Fung discusses a model developed to assess the sources and sinks of CO2; the approach is to use a 3-D global transport model, based on winds from a 3-D general circulation model (GCM), to advect CO2 as a tracer, with specified sources and sinks. The model estimates the effects of terrestrial biota (The chief contributor to the seasonal cycle), the seaa surface temperature (SST), and atmospheric perturbations such as those caused by ENSO. Simple curves of CO2 uptake and release constructed by Azevedo are combined with an NPP map constructed by Matthews to form a monthly flux of carbon atmosphere. The model produces large contrasts in CO2 concentration between land and sea created by the highly productive and seasonal land vegetation; amplitudes increase with latitude and are greater than 20ppm in the boreal forests of N. America and Siberia. Except in the tropics of the Northern Hemisphere, the isopleths closely parallel the coastlines. However, differences in the growing season net flux (GSNF) point to the need for an ecological model rather than one based on transport model requirements. In the ocean, the seasonal peak-to-peak amplitudes produced by SST oscillations vary inversely with and are lower than those produced by terrestrial biota exchanges. Atmospheric perturbations may affect the amplitude of the seasonal cycle.