While negotiators were working on agreements to limit greenhouse gas emissions in Cancun, my research group from the British Antarctic Survey were battling the rough seas of the Southern Ocean to further our knowledge of the key physical processes that will determine our future climate.
Of the carbon dioxide emissions human activities generate each year, only about half stay in the atmosphere. The rest are taken up by the land and the oceans, in approximately equal measure. At present the Southern Ocean that encircles Antarctica takes up about 10% of our emissions. Were it not to act in this way as a “carbon sink”, CO2 levels in the atmosphere would increase at a significantly faster rate than we currently observe.
So a key question for scientists to answer is, will climate change invoke changes that alter the Southern Ocean carbon sink? If the answer is yes, then this would change the amount of CO2 in the atmosphere and act as a strong feedback on climate change, with implications for the UN climate negotiations. Concern has been raised recently because some observations have indicated that the Southern Ocean may be taking up less CO2 than we would have historically expected given the current atmospheric CO2 concentrations.
This has prompted a major oceanographic research campaign in the Southern Ocean called DIMES, involving scientists from the UK and the US. The UK side has been funded by the Natural Environment Research Council. The Southern Ocean is a remote and hostile place to do science; the risk of sea-sickness is high and the freezing temperatures make taking water samples an uncomfortable activity as it is almost impossible to do so without getting your hands wet! But this all adds to the sense of adventure.
In this voyage of discovery we were exploring the ocean depths to investigate the ocean circulation. Like a giant global rollercoaster, the world’s oceans are connected by a vast, slow circulation system with water sinking in the North Atlantic, travelling southward, and then rising to the surface in the Southern Ocean. When it reaches the surface, this water is able to exchange CO2 with the atmosphere, before the circulation dips below the surface again, locking the CO2 in the ocean, and returns north. If that circulation were to change, the carbon uptake of the Southern Ocean would change.
So how might climate change be impacting the Southern Ocean overturning circulation? Strong winds blow around Antarctic over the Southern Ocean. These winds have become stronger in recent decades and we think this is due to in part to the increase in greenhouse gases in the atmosphere and in part due to the ozone hole in the stratosphere. We know the winds are responsible for driving the global rollercoaster circulation in the Southern Ocean, in part via their influence on the generation of ocean storms, known as “eddies”. But we still don’t understand all the details, so we are not sure whether the stronger winds will change the circulation and alter the carbon sink.
Therefore, one of the key things we are investigating in our Southern Ocean adventures is the effects of the ocean eddies. To do this we have been tracking a dye and floats deep below the surface as they are taken by the currents from the Pacific to the Atlantic through Drake Passage and we have been sampling the ocean to determine its properties in different locations. It is the first time some of these measurements have been taken in the Southern Ocean.
Weather conditions and technical problems meant we weren’t able to take all the measurement we had hoped in December/January, so in April I am heading South to brave those rough seas again in the name of climate science.