In March and April 2010, we investigated the development of young landfast sea ice in Kongsfjorden, Spitsbergen, Svalbard. We sampled the vertical column, including sea ice, brine, frost flowers and sea water, to determine the CO2 system, nutrients, salinity and bacterial and ice algae production during a 13 day interval of ice growth. Apart from the changes due to salinity and brine rejection, the sea-ice concentrations of total inorganic carbon (C
T), total alkalinity (A
T), CO2 and carbonate ions (CO3
2–) in melted ice were influenced by dissolution of calcium carbonate (CaCO3) precipitates (25–55 μmol kg-1) and played the largest role in the changes to the CO2 system. The C
T values were also influenced by CO2 gas flux, bacterial carbon production and primary production, which had a small impact on the C
T. The only exception was the uppermost ice layer. In the top 0.05 m of the ice, there was a CO2 loss of ∼20 μmol kg-1 melted ice (1 mmol m-2) from the ice to the atmosphere. Frost flowers on newly formed sea ice were important in promoting ice-air CO2 gas flux, causing a CO2 loss to the atmosphere of 140-800 μmol kg--1 d-1 melted frost flowers (7-40 mmol m-2 d–1).