In November 2000, a second iron enrichment experiment (EisenEx) was carried out in the Southern Ocean. Iron was added on the 8th of November in the centre of an eddy at 218E, 488S. During the cruise, the carbonate parameters dissolved inorganic carbon (DIC), fugacity of CO 2 ( f CO 2 ) and pH on the hydrogen ion scale (pH T ) were determined from water samples from both inside and outside the iron fertilized patch. Before the start of the experiment, the surface properties of the eddy were quite uniform with respect to the carbonate system and representative of the High Nutrient Low Chlorophyll (HNLC) regions in the Southern Ocean. The response of the carbon dioxide system to the initial c4 nM iron (Fe) infusion and to two subsequent reinfusions at 15 m depth was measured every day during the study. The changes in the carbon dioxide system and major nutrients were strongly influenced by the meteorological conditions with a rapid succession of calm, often sunny spells and storm force winds during the 21 days of experiment. Twenty days after the first Fe-infusion, the maximum changes of the carbonate parameters in surface waters of the patch relative to outside patch were ร15 Amol kg ร1 in DIC, ร23 Aatm in f CO 2 , +0.033 units in pH T , ร1.61 AM in nitrate and ร0.16 AM in phosphate in a mixed layer of 80 m depth. In addition to the daily measurements, several transects were made across the patch that showed a response of the carbonate system to the influence of iron, concomitant with a response in nutrients and chlorophyll. The relative changes in dissolved inorganic carbon to nutrient concentrations inside the patch during the experiment give N/P=12, C/P=82, C/N=5.9, C/Si=2.9 and N/Si=0.5. The effect of the influx of atmospheric CO 2 on the DIC inventory was small with values between 0.05 and 0.10 Amol kg ร1 day ร1 , and did not significantly affect these ratios. Although the observed change in DIC in the Fe-enriched surface waters was lower than in the