This graph shows a vertical section of DIC through the Atlantic Ocean. Superimposed on the DIC section are contour lines (in white) showing the depth of the 0.1 and 0.4 pmol/kg CFC-11 concentrations. CFC-11 is a man-made gas and its presence indicates water that has been in contact with the atmosphere during the last 50 years. The CFC-11 penetrates to over 4000 m in the North Atlantic, indicating that this area is a source of deep water during winter. This brings water with relatively low DIC into the deep-sea. Deep water flows away from the North Atlantic source to the south and its age increases. DIC concentrations also increase in the older water as more POC falls into it and bacteria convert the POC to DIC during respiration. Figure source http://www.pmel.noaa.gov/co2/co2-home.html