Sea ice regulates greenhouse gases on land

February 19, 2013 - 06:13

Atmospheric levels of CO2 and methane above land are mainly determined by sea ice melting to water.

Sea ice is white and it reflects sunlight. Seawater is dark and it absorbs sunlight. In line with the sea ice melting away, the sea will absorb more energy, which accelerates the warming of the sea and the atmosphere. This speeds up global warming. (Photo: Colourbox)

Global warming causes the sea ice to shrink, and the melting plays a much greater part in the ability of continents and oceans to absorb and release greenhouse gases than previously thought.

So concludes a Nordic research group after having reviewed the relevant scientific literature.

”The key message from science is that the current disappearance of the sea ice will play a major part in the exchange of greenhouse gases in the Arctic region. The melting not only affects the sea’s ability to absorb and release greenhouse gases – it also plays a surprisingly great part in this exchange on land,” says Lise Lotte Sørensen, a senior researcher at Aarhus University’s Arctic Research Centre.

Sea and land are not separated

Sørensen and her colleagues have spent years on studying the exchange of greenhouse gases between the atmosphere, the sea ice and the sea beneath. In recent years, they have also taken an interest in what research groups focusing on the land areas have found.

This curiosity prompted them to review the scientific literature to see to the extent of the interplay between these areas.

”It isn’t until now that we have sufficient information to start integrating our research. The world is not divided; it’s connected. It’s not as if the sea air stops like a wall once you reach land,” says Sørensen.

Science has shown that the melting of the sea ice starts to accelerate once the process is underway. As the ice disappears, the underlying dark sea becomes exposed. The sea absorbs far more of the sun’s energy and thus heats up more rapidly, which then also affects the ice.

The interaction not fully understood
The melting not only affects the sea’s ability to absorb and release greenhouse gases – it also plays a surprisingly great part in this exchange on land.
Lise Lotte Sørensen

As long as there is sea ice, it has a cooling effect on the surrounding areas, just like when you drop an ice cube into a glass of water. But the moment this ice has melted away, the water soon becomes warmer and starts warming up the atmosphere above.

When the warm air drifts in over the land, it will make changes to the interaction between the internal exchange of greenhouse gases that takes place between the atmosphere and land.

The exact functions and changes of this interaction remain a mystery to scientists – it is surprisingly poorly described in the literature, says Sørensen. But there’s no doubt that this interaction plays a major role in the Arctic climate.

Atmosphere and sea linked by channels of ice

Although not much is known about the interaction between land and sea, scientists are starting to understand which mechanisms control the processes at sea.

By studying sea ice in the wild and in an ice tank at the University of Manitoba in Canada, Sørensen and her colleagues found that there is an exchange of greenhouse gases between land and the atmosphere even when there is sea ice. When the ice temperature exceeds minus five degrees Celsius, channels start to emerge in the ice. These channels act as a link between the sea and the atmosphere.

The heated ice is not as passive as previously thought. It houses a great deal of chemical processes that cause the ice to release its own greenhouse gas contents, which then rain down into the sea. This transport of greenhouse gases may potentially have a great impact on the climate.

“We now need to focus on this increased importance of the sea ice, and we need to carry out more studies of sea ice. Nobody has so far been aware that the sea ice has such a great impact on the climate and the exchange of greenhouse gases in the entire Arctic region,” says the researcher.

We now need to focus on this increased importance of the sea ice, and we need to carry out more studies of sea ice. Nobody has so far been aware that the sea ice has such a great impact on the climate and the exchange of greenhouse gases in the entire Arctic region
Lise Lotte Sørensen

We need to know more about the processes and we must be able to describe them in models in order to make more accurate predictions of what effects an increased warming of the Arctic region has on CO2 and methane.

“We have no model predictions of what this will entail, so we hope it will be possible to make such models in the long term.”

A sketch for future research

The Nordic researchers’ review article does not present any ground-breaking new findings. It does, however, for the first time highlight what we know at this point. And that’s valuable because it paves the way for future research in the field.

In the coming years, Sørensen and her colleagues will continue to study the processes affecting the exchange of CO2 and methane, along with the warming of the Arctic.

The plan is that over the next three years, the research group will be doing field studies in the Nuup Kangerlua fjord in southwestern Greenland, at the Young Sound and Zackenberg in northeastern Greenland, at the North Pole and at Station North, where Aarhus University is currently constructing a new hi-tech research station.

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Read the Danish version of this article at videnskab.dk

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Translated by
Dann Vinther