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Summer at the sea ice factory

Far up north in the arctic ice 100 scientists and students are involved in a joint field investigation into how the interactions between snow, ice, sea and atmosphere in the Arctic impact the climate of the Earth.

In the sea outside the research station Daneborg at the fjord Young Sound, a large ‘ice factory’ is found. Here, the sea water freezes to ice. But time and time again heavy winds blow the ice away and expose the sea, allowing yet more sea ice to be formed. Such an area is called a polynya. Polynya is Russian for ’pool’. Photo: Peter Bondo Christensen
Gases – including carbon dioxide - are squeezed out when the ice is formed and dissolve in the highly salty water that flows from the ice. This means that when the ice melts in spring, the water is highly undersaturated with carbon dioxide. The sea will therefore absorb large quantities of carbon dioxide, and the formation of sea ice consequently acts as an important carbon pump. The photo shows Nicolas-Xavier Geilfus, Arctic Research Centre, Aarhus University, and Karrie Warner, University of Manitoba, measuring the absorption of carbon dioxide by meltwater pools on top of the sea ice. Photo: Peter Bondo Christensen
Siiri Wickström, University of Helsinki, and Tim Papakyriakou, University of Manitoba, have set up a monitoring station on the sea ice, allowing them to measure the amount of carbon dioxide absorbed and released by the sea ice. Photo: Peter Bondo Christensen
Every 10 km along the 100 km long fjord the scientists drill a hole in the ice and lower a so-called CTD-probe down the water column to the bottom of the sea. The probe measures temperature, salinity and a number of different salts and calculates the amount of carbon transported towards the sea bottom. Here, Søren Rysgaard, Arctic Research Centre, Aarhus University, and Sergev Kirillov and David Babb from University of Manitoba, Center for Earth Observation Sciences, Canada, lower the probe down through the sea ice. Photo: Igor Dmitrenko
The only means of transport in the melting sea ice is by snowboat or iceboat that can sail in water and drive on the ice. Carl Isaksen from the Greenland Institute of Natural Resources is a true master in handling the iceboat. Photo: Peter Bondo Christensen

Since March, the research stations Zackenberg and Daneborg in north-east Greenland have been densely populated by scientists. Until mid-October the research stations serve as bases for intensive studies that particularly attract ice enthusiasts.

Daneborg is situated by the Young Sound fjord, and at the fjord’s opening to the sea a large ‘ice factory’ is found. Here, sea water freezes to ice. But again and again heavy winds blow the ice away and expose the sea, allowing yet more sea ice to be formed.

Such an area is called a polynya. Polynya is Russian for ’pool’. Here, the scientists investigate how sea ice and snow impact the formation of deep water – the heavy, cold and saline water which sinks towards the sea bottom and which produces the great thermohaline circulation that drives the Gulf Stream. Presently, the scientists have special focus on how the sea, sea ice, atmosphere and snow exchange gases, particularly the greenhouse gas carbon dioxide.

Physical pump

The sea ice factory functions as a large carbon oxide pump that draws carbon from the atmosphere and pumps it far down into the deep sea.

The scientists now know that the sea ice is not a dense, tightly fitting lid encapsulating the sea, but is a dynamic part of our climate system.

When the sea ice is formed and melts again, a series of complex processes act as a physical pump, and this pump may have decisive importance for the global carbon cycle.

Briefly explained, all salts and gases are squeezed out of the ice when the sea ice freezes. The gases – including carbon dioxide – are dissolved into the highly saline brine that flows in channels to the lower side of the sea ice. From here, the heavy, saline water slides towards the bottom of the sea and is transported away with the cold sea current, which flows southward and is the actual pump behind the large global oceanic currents.

Thus, when the ice melts during the short arctic summer, the upper layers of the sea water are highly undersaturated with carbon dioxide, and the water therefore removes large amounts of carbon dioxide from the atmosphere.

A preliminary estimate by the scientists is that the physical pump removes between 66 and 199 million tons carbon per year, an amount up to four times as high as Denmark’s total CO2 emission.

New knowledge for use in new models

Many sub-projects are undertaken with focus on various subjects ranging from small ice algae and bacteria in the sea ice over the structure and characteristics of the ice to meteorological measurements of wind conditions in the atmosphere and above the sea ice.

And even in the cold winter, sweat and hard work go behind the figures in the scientists’ Excel sheets. All the way out the 100 km long fjord, water samples are taken and analysed. For every 2-3 km the snow has to be removed, a hole drilled through the ice, which is several metres thick, and the equipment carefully lowered to the bottom of the fjord and up again; and then the scientists move to the next sampling point.

On land, other scientists travel along the coast and investigate, among other things, the density of the snow and its stratification, while another team erects small towers filled with meteorological devices measuring the tiny differences in the air’s concentration of carbon.

The scientists expect the ice to break up in mid-July after which they will continue their measurements both in the open sea and when the new ice is formed at the end of September.

The great effort is coordinated by the Arctic Science Partnership, a collaboration between Denmark, Greenland and Canada. Scientists from a number of different countries are members of the Partnership, and the Danish participants count several researchers with different scientific backgrounds from the Arctic Research Centre at Aarhus University.

The many sub-studies will generate data including data on the effect of ice and snow on the global carbon turnover, knowledge of which has not yet been incorporated into the global models predicting the impact of global warming on the world’s climate and the ecosystems in the Arctic.

Further information:

Senior scientist Lise Lotte Sørensen, Arctic Research Centre, Aarhus University, tel. +45 8715 6417 or +45 3018 3119, e-mail: lls@dmu.dk

Postdoc Nicolas-Xavier Geilfus, Arctic Research Centre, Aarhus University, tel.: +45 8715 6417, e-mail: geilfus@biology.au.dk

Professor Søren Rysgaard, Arctic Research Centre, Aarhus University, and University of Manitoba, Canada, e-mail: rysgaard@science.au.dk