Southern Ocean – Buoyancy Forcing of Ocean Ventilation and Glacial Atmospheric CO2

Australia: The Land Where Time Began

Southern Ocean – Buoyancy Forcing of Ocean Ventilation and Glacial Atmospheric CO₂

According to Watson et al., concentrations of atmospheric CO₂ over cycles of glacial and interglacial phases correspond to temperature patterns in the Antarctic (Siegenthaler et al., 2005). As these are distinct from variations of temperature in the mid- to northern latitudes (Shakun et al., 2012) this suggests the Southern Ocean is pivotal in controlling concentrations of natural CO₂ (Sigman, Hain & Haug, 2010). In this study Watson et al. assessed the sensitivity of atmospheric concentrations of CO₂ to glacial-interglacial changes in the meridional overturning circulation by using a circulation model (Nikurashin & Vallis, 2011; Nikurashin & Vallis, 2012) for upwelling and eddy transport in the Southern Ocean coupled with a simple biogeochemical description. A broader region of surface buoyancy loss results in upwelling farther north under glacial conditions. Outgassing of CO₂, and stronger carbon sequestration in the deep ocean, results from the northern location of upwelling: Watson et al. calculating that the shift to this glacial style of circulation can draw down 30-60 ppm of atmospheric CO₂. Therefore they suggest much of the strong correlation between temperature variations in the Antarctic and concentrations of CO₂ over glacial-interglacial cycles explains the direct effect of temperature on buoyancy forcing in the Southern Ocean, and hence the residual overturning circulation.