Deep-sea mixing (ventilation) rates depend on how fast deep sea water is formed. The deep sea contains more than 95% of the carbon in the ocean-atmosphere system, so the ventilation rate directly affects atmospheric composition and radiative forcing. Goldstein et al. present a suite of radiocarbon and uranium-series dates of deep-sea corals from the Southern Ocean and derived rates of deep-sea ventilation for the present and the last glacial period (about 16,500 years ago). They calculate that the ventilation age then was 20 to 40% greater than at present. This result is consistent with reported findings from the Atlantic and Pacific Oceans and suggests that glacial oceans mixed more slowly than today's oceans. Thus, glacial-age, carbon-rich deep water may have mixed less quickly with surface water and exchanged CO2 less rapidly with the atmosphere. Slower mixing would have significantly lowered the partial pressure of atmospheric CO2 during that period. -- HJS
Earth Planet. Sci. Lett. 193, 167 (2001).
