Dissertation Biophysical Behavior in Tropical South America

OF DISSERTATION BIOPHYSICAL BEHAVIOR IN TROPICAL SOUTH AMERICA The concentration of CO2 in the atmosphere is rising, in response to human activities such as consumption of fossil fuel, cement production, and land cover change. This increase is mitigated by the fact that currently, approximately one-half of the CO2 of anthropogenic origin does not take up permanent residence in the atmosphere, but is absorbed by the oceans and terrestrial biospherethe ’missing sink’, which is partitioned almost equally between ocean and land. The increasing concentration of CO2 is forecast to alter the radiative forcing at the planet’s surface, resulting in increased global temperatures, although the exact spatiotemporal nature of the warming is uncertain. The missing sink has also eluded a quantitative description. We do not completely understand its spatial patterns, nor can we say with certainty how this sink will evolve under changing climatic conditions in the future. Furthermore, the atmospheric CO2 growth rate is variable with time, and the dominant source of this variability has been traced back to terrestrial processes. The land surface has significant influence over variability in the global atmospheric CO2 growth rate and the tropics, especially tropical South America, has been identified as a region of particular import. The Amazon rainforest is the largest tropical forest in the world, and contains up to 10% of terrestrial biomass. Gross fluxes of CO2 (photosynthesis and respiration) are massive, and slight variability in these large components can impose a net CO2 flux that is felt globally. In the tropics, seasonality in day length and temperature are minimal. The dominant signal is annual wet and dry seasons, caused by the oscillation of the Intertropical Convergence Zone (ITCZ) northward and southward during the year. Interannual variability is imposed by the El Niño-Southern