| A high-resolution biogeochemical model is developed to examine the flux of carbon dioxide from the equatorial Pacific Ocean, the major oceanic source of atmospheric carbon. The model is run for the thirty year period from 1965 to 1994 to investigate interannual variability in the carbon dioxide flux and the mechanisms leading to this variability. The model is forced by upper layer velocities and upwelling from a non-linear high-resolution hydrodynamical model of the tropical Pacific Ocean, the Florida State University Wind Stresses, and the Reynolds sea surface temperatures. The two data sets consist of tens of millions of individual real world observations.;The model demonstrates the link between the interannual variations of the carbon dioxide flux and the El Nino/Southern Oscillation (ENSO), and identifies the responsible mechanisms. In particular, ENSO warm events are associated with decreased carbon dioxide flux because of the reduced upwelling of deep, carbon rich water into the surface layer and the weakening of the equatorial trade winds that drive the flux. In contrast, during ENSO cold events enhanced upwelling of deep, carbon rich water and stronger trade winds cause increased carbon dioxide flux from the equatorial Pacific Ocean. Carbon dioxide flux from the biogeochemical model compares well with the limited long-term observational data available. Interannual variations of the flux and proxy ENSO indices of sea surface temperature and thermocline depth also indicate good agreement.;Replacing one input forcing field of either upper layer velocities and upwelling, wind stresses, or sea surface temperatures with six-day climatologies of the respective field indicates that both winds and upper layer physics are essential to reproduce the interannual flux variability. Sea surface temperature is less important in determining the variability. Results from a box model forced by zonally averaged input fields demonstrates that modeling the carbon dioxide flux from the equatorial Pacific requires an accurate representation of the critical horizontal spatial scales in the region. |
