Arctic sea ice plays an important role in removing CO2 from the atmosphere


The 16th PhD student has been honored the PhD degree at the Greenland Institute of Natural Resources’. Scientist Dorte Haubjerg Søgaard from the Climate Research Centre at the Greenland Institute of Natural Resources recently defended her thesis entitled ”Biological activity and calcium carbonate dynamics in Greenland sea ice – implication for the inorganic carbon cycle” at the University of Southern Denmark.

Dorte Haubjerg Søgaard, in cooperation with a number of scientists from Greenland, Denmark, Great Britain, Finland, Germany, Belgium and the US, demonstrated in her thesis that the sea ice plays an important role in removing CO2 from the atmosphere to the bottom of the ocean. In other words, the atmosphere’s content of greenhouse gasses is expected to increase and climate changes caused by greenhouse gasses is therefore also expected to increase if the ice disappears in the future.

”If our results are representative for similar areas, the sea ice plays a larger part than previously expected and this new knowledge should be taken into account in the global CO2 budgets in the future”, says Dorte Haubjerg Søgaard.

Dorte Haubjerg Søgaard’s PhD  project was initiated in 2010, where the sea ice in a number of fiords surrounding Nuuk and Young Sound in Northeast Greenland was examined. Dorte wanted to characterize the processes in sea ice that helps removing CO2 from the atmosphere.

It was only recently discovered by scientists that sea ice influences the global CO2 budget. “It has been known for many years that the World´s oceans are able to absorb enormous amounts of CO2. But it was assumed that this was not true for sea ice covered seas, because sea ice was considered impermeable . However, this is not true, since new research shows that the Arctic sea ice absorbs large amounts of CO2 from the atmosphere and removes it to the bottom of the ocean,” Dorte Haubjerg Søgaard explains.

Furthermore, it was established that within the sea ice there are two ongoing processes directly influencing the exchange of greenhouse gasses between sea and atmosphere:  precipitation of calcium carbonate (CaCO3) and the activity of microorganisms. 

First crystals of calcium carbonate are formed in sea ice in winter. During this formation CO2 splits off and is dissolved in a heavy cold brine, which gets squeezed out of the ice and sinks into the deeper parts of the ocean. Calcium carbonate cannot move as freely as CO2 and therefore it stays in the sea ice. In summer, when the sea ice melts, calcium carbonate dissolves, and CO2 is needed for this process. Thus, CO2 gets drawn from the atmosphere into the ocean - and therefore CO2 gets removed from the atmosphere", explains Dorte Haubjerg Søgaard. 

The PhD project revealed that the relative contribution of the formation of calcium carbonate crystals to the CO2 uptake was much more significant than the biological processes, which are primarily driven by sea ice algae and bacteria. 

Another important discovery is that every winter flower-like ice formations are formed on the surface of newly formed sea ice. They are called frost flowers. Dorte Haubjerg Søgaard has discovered that these frost flowers hold extremely high concentrations of calcium carbonate, which can have a further significant impact on the potential CO2 uptake in the Arctic. 

Therefore, there are still a lot of important future research questions in terms of understanding the influence of the sea–ice–driven CO2 pump and the role of Greenland coastal waters in relation to the global carbon cycle, and it is needed urgently since climate change threatens to take these frozen high latitude environments from us.

Download the thesis here.



For further information, please contact:
Dorte Haubjerg Søgaard         Telephone +299 321200 or 

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Researcher Dorte Haubjerg Søgård in action in the field during her Ph.D project Photo: GN.

Frost flowers, growing on the sea ice. The Ph.D project revealed, that the frost flowers are not just for garnish. Photo: GN