Clim. Past Discuss., 7, 347-379, 2011
© Author(s) 2011. This work is distributed
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This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds
K. B. Rodgers1, S. E. M. Fletcher1,2, D. Bianchi1, C. Beaulieu1, E. D. Galbraith1, A. Gnanadesikan3, A. G. Hogg4, D. Iudicone5, B. Lintner6, T. Naegler7,8, P. J. Reimer9, J. L. Sarmiento1, and R. D. Slater1
1AOS Program, Princeton University, Princeton, NJ, USA
2National Institute for Water and Atmospheric Research, Wellington, New Zealand
3Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
4Carbon Dating Laboratory, University of Waikito, Hamilton, New Zealand
5Stazione Zoologica Anton Dohrn, Naples, Italy
6Rutgers University, New Brunswick, NJ, USA
7Institute for Environmental Physics, University of Heidelberg, Germany
8German Aerospace Center, Institute for Technical Thermodynamics, Department of System Analysis and Technology Assessment, Stuttgart, Germany
9Queens University, Belfast, UK

Abstract. Tree ring Δ14C data (Reimer et al., 2004; McCormac et al., 2004) indicate that atmospheric Δ14C varied on multi-decadal to centennial timescales, in both hemispheres, over the pre-industrial period AD 950–1830. Although the Northern and Southern Hemispheric Δ14C records display similar variability, it is difficult from these data alone to distinguish between variations driven by 14CO2 production in the upper atmosphere (Stuiver, 1980) and exchanges between carbon reservoirs (Siegenthaler, 1980). Here we consider rather the Interhemispheric Gradient in atmospheric Δ14C as revealing of the background pre-bomb air-sea Disequilbrium Flux between 14CO2 and CO2. As the global maximum of the Disequilibrium Flux is squarely centered in the open ocean regions of the Southern Ocean, relatively modest perturbations to the winds over this region drive significant perturbations to the Interhemispheric Gradient. The analysis presented here implies that changes to Southern Ocean windspeeds are likely a main driver of the observed variability in the Interhemispheric Gradient over 950–1830, and further, that this variability may be larger than the Southern Ocean wind trends that have been reported for recent decades (notably 1980–2004). This interpretation also implies a significant weakening of the winds over the Southern Ocean within a few decades of AD 1375, associated with the transition between the Medieval Climate Anomaly and the Little Ice Age. The driving forces that could have produced such a shift in the winds remain unkown.

Citation: Rodgers, K. B., Fletcher, S. E. M., Bianchi, D., Beaulieu, C., Galbraith, E. D., Gnanadesikan, A., Hogg, A. G., Iudicone, D., Lintner, B., Naegler, T., Reimer, P. J., Sarmiento, J. L., and Slater, R. D.: Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds, Clim. Past Discuss., 7, 347-379, doi:10.5194/cpd-7-347-2011, 2011.
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