Melting of the Fimbul Ice Shelf: How much and how?

The Fimbul Ice Shelf is an ice shelf located in Dronning Maud Land, Antarctica. In November 2009 an expedition is headed for Antarctica to study the mass balance of the Fimbul Ice Shelf and also the melting and circulation in the ocean underneath the floating ice. The interactions between the ocean and the ice in Antarctica are important processes for the understanding of the global climate. However, these processes are not understood well enough for their inclusion in the climate models used to predict the climate in the near future. The research we are planning in this project is therefore of great international interest.

Map of Antarctica

Figure 1: The map of Antarctica with the floating ice shelves marked with light blue. The Fimbul Ice Shelf is marked by a red frame. Map: Norwegian Polar Institute

Antarctica consists of a several kilometer thick ice sheet. The ice moves towards the ocean as a viscous fluid. As it reaches the ocean it spreads out as a floating glacier which we call an ice shelf. 10% of Antarctica consists of ice shelves, and is therefore floating on the ocean. The map shows the floating ice shelves in light blue. The Fimbul Ice Shelf is an ice shelf at the coast of Dronning Maud Land. It’s position is marked by a red frame on the map. In figure 2 you can see a satellite picture of the Fimbul Ice Shelf.

The Fimbul Ice Shelf seen from a satellite

Figure 2: The Fimbul Ice Shelf seen from a satellite. The light areas show the ice floating on the ocean (ice shelves). The grounding line divides floating and grounded ice. Jutulstraumen, the large ice stream, can easily be seen and we can also see islands where the ice is grounded. These islands are called ice rises. The blue stars show the locations where we plan to drill holes in the ice. Instruments will be deployed through the holes in order to measure in the ocean underneath. The red circles show the positions where we will estimate the melting underneath from glaciological observations on the ice. Photo: Jezek and RAMP Product Team, 2002

Research goals

Cut of ice masses and ocean along the coast of Dronning Maud Land

Figure 3. A cut through the ice sheet, the ice shelf and the ocean along the coast of Dronning Maud Land. The colours represent the temperatures and are based on real data from the ocean. Figure: Ole Anders Nøst

The first goal of the project is to answer the following question:

Do the ice masses on the Fimbul ice Shelf decrease or increase?

To answer this we have to look at the sources and sinks of the ice and compare them. Sources of ice are snow accumulation and the ice streams transporting ice from the ice sheet to the ice shelf. Jutulstraumen which is the largest ice stream in Dronning Maud Land spreads out on the Fimbul Ice Shelf as you can easily see on the satellite picture above. The Fimbul Ice Shelf looses ice by calving at the ice front and by melting towards the ocean underneath.

Melting of ice requires heat and the melting underneath the Fimbul Ice Shelf is driven by ocean currents transporting the heat in under the ice.

The second goal is:

Understanding how the ocean transports heat in under the Fimbul Ice Shelf

Theoretical models of the ocean circulation in front of and under the Fimbul Ice Shelf are already made. There are disagreements, however, on the amount of melting that is predicted by these models. The clue is the warm deep water existing outside the continental shelf, as shown in figure 3. The costal current is an obstacle between the warm deep water and the ice shelf. This is why the melting is considerably less than it would have been if the warm water was in direct contact with the ice. 

Work on the ice

To do measurements in the ocean underneath the Fimbul ice shelf is a great challenge. The ice is several hundred meters thick and we will drill through the ice with hot water. We are going to deploy instruments through the hot water drilled access holes for measuring temperature, salinity and velocity in the ocean currents. We plan to drill three holes. The positions of the bore holes are shown on the satellite picture of the Fimbul ice shelf. They have been chosen according to the topography of the sea bed underneath. The structure of the sea bed was found during the last expedition to the Fimbul ice shelf in 2001. The echoes from small explosions on the surface of the ice were registered. In that way we found both the thickness of the ice and the depth of the seabed.

We are also observing in the ocean in front of the Fimbul ice shelf by means of elephant seals equipped with instruments glued on to their heads. These instruments measure salinity and temperature of the ocean and the data are being transferred to us via satellite. The seals have provided us with very valuable data helping us to understand the oceanographic processes in front of the Fimbul Ice Shelf.

In addition to the oceanographic work, we will also do a lot of work on top of the ice. Ice thickness and melting can be measured directly with radar. By setting up stakes we can measure the ice velocity. GPS are being mounted on the stakes telling us how fast they move. By drilling and collecting ice cores and studying the annual layers, we can see how much snow is accumulating. Comparison of all this different information tells us whether the ice mass of the Fimbul ice shelf increases or decreases. These measurements, leading to estimates of the amount of melting on the underside of the ice, will mainly be done at six stations spread out on the Fimbul ice shelf as shown on the satellite picture above.

The field work on the Fimbul ice shelf will be carried out dring two seasons. The first season is from 1. November 2010 to 10. January 2011. It is important to know the weather on the Fimbul ice shelf during this period and therefore, a weather station will be placed during the first field season. This will give us weather data via satellite continuously from the Fimbul ice shelf.

FIS- ttb and other research in Antarctica

Ice shelves are the link between the large Antarctic ice sheet and the ocean. The ice shelves are important both for the dynamics of the Antarctic ice sheet and for the ocean. Ice shelves has a damming effect on the flow of ice from the inland ice sheet, and the melting of the ice shelves inputs fresh water to the ocean which play an important role to understand the ocean currents.

Fimbul Ice Shelf – top to bottom is a small, but important part of the big international research activity going on in Antarctica. Earlier the main part of the research on ice shelves were concentrated on the large Filchner-Ronne and Ross ice shelves (marked Ronne Ice Shelf and Ross Ice Shelf on the map of Antarctica). At the end of the 90s the Larsen ice shelf on the Antarctic Peninsula, and earlier this year The Wilkins Ice Shelf in West Antarctica, collapsed. Theoretical calculations show that the ice shelves along Dronning Maud Land (the Fimbul Ice Shelf is one of these) in fact are melting quite as much as the big ice shelves Filchner-Ronne and Ross. This has in all led to much greater interest in the smaller ice shelves. Research on ice shelves and the interaction between the Antarctic ice sheet and the ocean is a subject of interest to many climate researchers. We know for the time being not enough to include these processes in the climate models, but the great interest for this research will make this possible in the very near future.