Biological activity and calcium carbonate dynamics in Greenland sea ice – Implication for the inorganic carbon cycle. Technical Report No. 92

The contribution of sea-ice-covered regions to the global 
air-sea CO2 exchange was, until recently, assumed to be 
insignifi cant primarily because sea ice was considered impermeable. The discovery of a sea ice CO2 pump and the 
recognition that extensive and productive microbial communities exist within sea ice, however, has changed this 
general perception. Therefore, an improved understanding 
of the current role of sea ice in the overall carbon budget is 
needed. The main focus of this PhD study was: 1) to investigate the factors that control the spatial and temporal distribution of calcium carbonate and other important biogeochemical parameters in Greenland sea ice, 2) to discuss the 
potential interactions between these parameters, and 3) to 
assess how these parameters aff ect the sea ice CO2 system. 
Here, I report measurements of calcium carbonate dynamics, biological activity, total alkalinity (TA), total inorganic 
carbon (TCO2) and other biogeochemical parameters from 
sea ice in Greenland. First, I look at the dynamics of these parameters at temporal and spatial scales in Subarctic sea ice 
and, secondly look at the dynamics of these parameters in 
High Arctic winter sea ice on a more patchy level. Altogether, 
my results indicate that the TCO2 depletion of the Subarctic and High Arctic sea ice is mainly controlled by physical 
export through brine drainage and CaCO3 precipitation/
dissolution – a conclusion that, therefore, strengthens the 
concept of the sea-ice-driven carbon pump in high latitude 
waters. Furthermore, the diff erent studies combined revealed that the relative contribution of primary production 
to TCO2 depletion is minor compared to the contribution of 
calcium carbonate precipitation. However, the biological 
contribution to the TCO2 depletion might be much higher 
in areas with high primary production. Consequently, the 
evaluation of the sea ice sink described in this thesis may 
not be representative of the Arctic as a whole since the uptake of CO2 by biological activity seems to be much lower in 
Greenland sea ice compared to other regions. Extensive investigations are, however, still needed to elucidate local and 
regional variation in biological activity in sea ice in Greenland and in other Arctic regions. 
The highest concentrations of calcium carbonate ever reported in natural sea ice was measured in approximately 
5-month-old High Arctic land-fast sea ice, followed by high 
concentrations in newly formed High Arctic polynya sea ice; 
whereas the lowest concentrations observed during our 
studies were in Subarctic land-fast sea ice. Variations in sea 
ice properties such as temperature, salinity, pH, ice texture 
and freshwater input are likely responsible for some of the 
diff erences found in calcium carbonate concentrations between sites. 
Consequently, the diff erent studies revealed large variations in calcium carbonate concentration and other biogeochemical parameters at diff erent temporal and spatial 
scales, emphasising the importance of full-season studies 
covering the meter-hundred meter spatial scale in order to 
make reliable carbon budgets. 
This PhD thesis also presents a survey of the infl uence of 
biological processes and glacier runoff on the pCO2 dynamics in Subarctic coastal waters. The study revealed that the 
Subarctic Godthåbsfj ord system in SW Greenland can be 
considered as a strong sink of CO2 and that the CO2 uptake 
is highly regulated by biological processes and by mixing 
glacial meltwater and coastal waters. Moreover, the CO2
uptake is strongest nearest to the outlet from the Greenland Ice Sheet. If our estimates are representative of similar 
Subarctic fj ord system in Greenland, then the coastal areas 
of Greenland constitutes a larger sink than anticipated and 
this knowledge should be included in future global carbon 
budgets.