On the timescale of decades, the Southern Ocean absorbs less CO2 due to changes in atmospheric forcing such as wind intensification.
By assimilating atmospheric data into an OGCM coupled to the PISCES-T biogeochemical model, as well as using the inverse method, Le Quere et al. show that wind-induced physical mixing of surface waters on timescales of decades reduces the Southern Ocean capacity to absorb atmospheric CO2. CO2 flux variability is positively correlated to the Southern Annular Mode (SAM - index of the dominant atmospheric variability mode) and the decrease of 0.08 PgC/y per decade, is statistically different (99.5% level) from the saturation trend of 0.051 PgC/y per decade expected from atmospheric CO2 increase alone. In addition, the enhanced mixing accelerates surface waters acidification.
The authors conclude that “(i) the fraction of the CO2 emissions that the ocean is able to absorb may decrease if the observed intensification of the Southern Ocean winds continues in the future, and (ii) the level at which atmospheric CO2 will stabilize on a multicentury time scale may be higher if natural CO2 is outgassed from the Southern Ocean.”
Corinne Le Quere*, Christian Rodenbeck, Erik T. Buitenhuis*, Thomas J. Conway, Ray Langenfelds, Antony Gomez, Casper Labuschagne, Michel Ramonet, Takakiyo Nakazawa, Nicolas Metzl, Nathan Gillett, Martin Heimann, 2007. Saturation of the Southern Ocean CO2 Sink Due to Recent Climate Change, Science 17 May 2007, DOI:10.1126/science.1136188
- NATURENEWS - Polar ocean is sucking up less carbon dioxide;