A major, potential stressor of marine ecosystems is the changing water chemistry following the present and simulated future increase in seawater carbon dioxide (CO2), concentration. Increasing CO2 causes a lowering of pH and a re-organisation of the marine carbonate system, commonly termed ocean acidification. Global average long-term ocean acidification projections are intimately linked with future atmospheric CO2 levels, however the local expression of this global ocean acidification is much more heterogeneous, as local oceanic processes alter the average expectations of future ocean acidification. Evidence has mounted over the past years showing the importance of these ‘bottom-up’ local oceanic processes, both natural and anthropogenic, to altering the rate of ocean acidification from the long-term atmospheric top-down perspective. The challenge for Southern Ocean acidification are advancing the observations and constraints at understanding the underlining natural variability and the mechanisms that drive it, which are still poor. Pelagic ecosystems are changing fast, especially in the productive, euphotic zone. Autotrophic production may be changing in the surface Southern Ocean through increased primary productivity and a changing stoichiometry of oceanic primary production. This will have consequences both for energy flow and nutrient transport though Southern ocean ecosystems. Calcifying plankton, such as pteropods, have been shown to be adversely effected by current Southern Ocean acidification. These organisms are prominent players in the Southern Ocean ecosystem both as predator and prey, and control to a significant degree the export of carbon and other elements to the intermediate and deep ocean. There is concern over the future of polar marine organisms that are uniquely adapted towards their extreme and cold surroundings. In an environment where development is ten times slower than that in warmer regions of the world, the ability of these (mostly benthic) organisms to adapt to these changing conditions is questionable. Responses of benthic ecosystems have generally resulted in negative impacts (smaller size, slowed growth and high levels of abnormal development. There is a growing international effort to observe and monitor the marine carbonate system with the emphasis moving away from purely physic-chemical approach to an integrated observing system approach based on ecosystem-carbon-climate coupling. Additionally, coupled biogeochemical-ecosystem modeling efforts are becoming much more unified and assimilated through both a multi-model approach and that regional models are becoming much more to the fore. SCAR has appointed an international ocean acidification Action Group to document the scientific understanding of ocean acidification. This presentation will inform on the latest knowledge of chemical and biological consequences of ocean acidification in the Southern Ocean through an ecosystem and earth system approach. It will also identify important gaps in current research and propose approaches to gain a better understanding of the rates, effects and feedbacks of future ocean acidification. New understanding on Southern Ocean change will also be assessed in light of the recent findings of the AMAP Arctic Ocean Acidification report.