Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds

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,...

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Bibliographic Details
Main Authors: Rodgers, K.B., Fletcher, S.E.M., Bianchi, D., Beaulieu, C., Galbraith, E.D., Gnanadesikan, A., Hogg, Alan G., Iudicone, D., Litner, B., Naegler, T., Reimer, Paula J., Sarmiento, J.L., Slater, R.D.
Format: Article in Journal/Newspaper
Language:English
Published: Copernicus Publications 2011
Subjects:
Δ¹⁴C
Southern Ocean
Reimer
Online Access:https://hdl.handle.net/10289/5134
https://doi.org/10.5194/cpd-7-347-2011
Description
Summary: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.

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