McKinley¹, Galen A., Michael Follows² and John Marshall²

¹Instituto Nacional de Ecologia, Periferico 5000 piso 4, Mexico DF, CP 04530 Mexico, Tel: 5255 5665 9750, Fax: 5255 5424 5404, E-mail: galen@alum.mit.edu and ²Department of Earth, Atmospheric and Planetary Sciences, MIT 54-1514, Cambridge MA 02139

Mechanisms of CO₂ air-sea flux variability in the North Atlantic and equatorial Pacific

Using a global version of the MIT ocean general circulation model driven by analyzed winds and fluxes, we consider global air-sea CO₂ flux variability. The mean air-sea CO₂ flux is consistent with the study of Takahashi et al. (Proc. CO₂ in the Oceans, 1999), and the interannual variability from1980-1998 is ± 0.5 PgC/yr. The equatorial Pacific, North Atlantic, and North Pacific, and to a lesser extent, the Southern Ocean exhibit a large root mean square interannual variability over this period. Nonetheless, consistent with previous ocean modeling studies (LeQuere et al, 2000; Winguth et al. 1994), we find that the equatorial Pacific is the primary driver of global interannual air-sea flux variability, and that higher latitudes play a minor role. Variability in the equatorial Pacific is driven by large-scale coordinated physical changes associated with ENSO. In the high latitude North Atlantic, by contrast, flux variability is driven by small-scale convective variability which is associated with the North Atlantic Oscillation. Here, a pronounced intra-regional cancellation of air-sea flux anomalies, the slow air-sea exchange timescale of CO₂, and a rapid biological response to convective nutrient supply combine to minimize the net regional interannual variability. Our finding of small high latitude flux variability contrasts with recent atmospheric inversion results (Bousquet et al. 2000) and estimates based on BATS observations (Gruber et al. 2002). Possible explanations for this discrepancy are discussed.