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SPRI Review 2008: Polar Physical Science

Polar Physical Science

Iceberg calving flux and mass balance of Austfonna, Nordaustlandet, Svalbard

Satellite radar interferometry, 60 MHz airborne ice-penetrating radar data, and visible-band satellite imagery were used to calculate the velocity structure, ice thickness, and changing ice-marginal extent of Austfonna (8,120 km2 and 2,500 km3), the largest ice cap in the Eurasian Arctic. Ice-cap motion is less than about 10 m yr-1, except where faster-flowing curvilinear features with velocities of several tens to over 200 m yr-1 occur. Most drainage basins of Austfonna have undergone icemarginal retreat over the past few decades at an average of a few tens of metres per year. Integrating margin change around the whole ice cap gives a total area loss of about 10 km2 yr-1. Iceberg flux from the marine margins of Austfonna is about 2.5 km3 yr-1, about 45% of the total calving flux from the whole Svalbard archipelago. When mass loss by iceberg production is taken into account, the total mass balance of Austfonna is negative, by between about 2.5 and 4.5 km3 yr-1. This iceberg flux represents about 33% of total annual mass loss from Austfonna, with the remainder through surface ablation. Iceberg flux should be included in calculations of the total mass balance of the many large Arctic ice caps, including those located in the Russian and Canadian Arctic that end in tidewater. The neglect of this term has led to underestimates of mass loss from these ice caps and, thus, to underestimates of the contribution of Arctic ice caps to global sea-level rise.

Julian Dowdeswell and Toby Benham

A crevassed glacier reaches fjord waters in East Greenland
Image as described adjacent

Hydrology of the Greenland Ice Sheet

The Greenland Ice Sheet has recently been losing mass at an accelerating rate due to both increased surface melting and more rapid flow of outlet glaciers. There is growing interest in the possible links between these two processes, with evidence suggesting that higher melt rates may deliver more water to the bed, elevating subglacial water pressures and promoting basal slip. We are currently developing a semidistributed hydrology model that is capable of predicting melt rates across the ice sheet surface, routing this water across the surface (through unsaturated and saturated snow and firn, and across bare ice) to supraglacial lakes and moulins which then eventually deliver the water to the bed of the ice sheet. Subglacial water flow is currently modelled in terms of flow through a dendritic network of channels, which enlarge and contract in response to the discharge and pressure of water flowing through them. We are currently developing the model for the Paakitsoq / Swiss Camp region of West Greenland where we have good surface and bed topography data to set boundary conditions, meteorological data to drive the model, and proglacial stream discharge data to test the model. A key area of model development includes the role of ice fracturing and the delivery of large volumes of surface lake water to the bed. Preliminary results suggest that stable channels can exist beneath the lower portion of the ice sheet (up to ~6 km from the margin) where meltwater delivery is high and ice is relatively thin. Subglacial channels are unstable further from the margin due to low channel melt rates and high closure rates (due to thicker ice) suggesting flow here is via a distributed drainage system. Knowledge of the stability or otherwise of the subglacial drainage system, and the water pressure within it, is a key factor in understanding the possible mechanisms which might explain the acceleration of parts of the Greenland Ice Sheet. The work is being undertaken together with our former Masters student, Sylvan Long, current PhD student, Alison Banwell, and Dr Andreas Ahlstrøm (Geological Survey of Denmark and Greenland).

Ian Willis and Neil Arnold

Investigating basal conditions and flow dynamics on Vestfonna Ice Cap, Svalbard

The body of scientific evidence for significant anthropogenic impacts on the global climate is growing and public concern underscores a need for better assessments of contemporary environmental changes in regions such as the Arctic. Although the vast majority of ice on Earth is stored in Greenland and Antarctica, maritime ice caps and alpine mountain glaciers are expected to dominate the cryospheric contribution to 21th century sea-level rise. Arctic ice caps are an important component of global change, especially as Arctic temperatures are increasing at almost twice the global average. A new project led by the SPRI and funded by the Natural Environment Research Council focuses on Vestfonna Ice Cap, which is located in remote northeast part of Svalbard. This Arctic ice cap is of particular interest because its northern ice margin terminates on land while the southern margin contains a series of tidewater outlet glaciers, comparable to those draining the Greenland Ice Sheet. We are conducting glaciological investigations with the aim to determine how ice flow responds to atmospheric and oceanic forcings. The project includes the collection of radio-echo sounding data in a traverse across the ice cap and in two designated study areas, one on the land-terminating northern ice margin and one on a southern tidewater glacier. The radar data provide a means to measure ice thickness and examine the nature of the bed (e.g. the distribution of melting and freezing and the presence of lubricating water). In 2008, we installed five GPSs on Frazerbreen, a fast-flowing tidewater glacier, and two GPSs on the land terminating northern ice margin. Outputs from the GPS equipment, which will monitor changes in surface position over one year period, will be integrated with radar data and outputs from automatic weather stations. The fieldwork is coordinated through the Kinnvika International Polar Year Consortium.

Poul Christoffersen and Julian Dowdeswell

Understanding contemporary change in the West Antarctic Ice Sheet

Satellite investigations have revealed a spatially complex pattern of contemporary change in the West Antarctic Ice Sheet. The ice streams that discharge into the Amundsen Embayment are thinning and accelerating, but the ice streams feeding the Ross Ice Shelf are slowing down and some have even ceased to flow fast. The Scott Polar Research Institute is part of a collaborative project that aims to determine the cause and magnitude of contemporary change in the West Antarctic Ice Sheet by development of a higherorder numerical ice-flow model. The model will have accurate predictive capabilities for simulation of the 21st century when coupled to an Earth-system model. The study will make use of a wide range of observations including satellite imaging, airborne surveys and ground-based field campaigns. This latter aspect of the project is facilitated by links to a range of project partners and to close collaboration with the US National Science Foundation's programmes on West Antarctica; in particular, the Amundsen Sea Embayment Plan coordinated through the International Polar Year. The project will take place over a three-year period. It links expertise in subglacial processes and ice-stream dynamics (SPRI), largescale numerical modelling (Bristol University) and data assimilation techniques (Durham University). The project is funded by the Natural Environment Research Council.

Poul Christoffersen and Marion Bougamont

CryoSat-2

SPRI staff continued to participate in international campaigns to validate data collected by a new radar altimeter (SIRAL) to be carried by the CryoSat-2 satellite. In Spring 2008 a twoperson team from SPRI completed a traverse across the North West sector of the Greenland Ice Sheet, ending at the Danish "NEEM" drilling camp. Measurements of snow density profiles were made using an automated neutron profiling system and will be compared with data from the airborne ASIRAS radar altimeter which was flown along the traverse by scientists from the Danish National Space Centre.

These measurements have extended the CryoSat-2 pre-launch validation studies to an area of low accumulation where thick layers of hoar crystals form within the firn. The observations help to explain why the correlation coefficient of height change versus power change in the ENVISAT altimeter data is high in this part of the dry snow zone on Greenland. This was the last of the prelaunch activities, as CryoSat-2 is due to be launched at the end of 2009. Postlaunch field studies are planned for 2010 onwards.

Liz Morris

A major submarine fan in the Bellingshausen Sea, West Antarctica

A 330-km length of the little known continental shelf edge and slope of the Bellingshausen Sea, West Antarctica, has been investigated using multibeam swath-bathymetric and sub-bottom profiler evidence. When full-glacial ice advanced across the shelf to reach the shelf break about 20,000 years ago, it was partitioned into fast- and slow-flowing elements, with an ice stream filling the trough. This had important consequences for the nature and rate of sediment delivery to the adjacent continental slope. Off Belgica Trough, the upper continental slope has convex-outward contours indicating a major sedimentary depocentre. Acoustic profiles and cores from the depocentre show a series of glacigenic debris flows. The depocentre is interpreted as a trough-mouth fan, built largely by debris delivered from the ice stream. The main morphological features on the Bellingshausen Sea slope are gully systems and channels, which are found mainly on the fan surface. The largest channel is over 60 km long, about a kilometre wide and 10 to 15 m deep. The channels provide pathways for sediment by-passing of the upper slope and transfer to the continental rise and beyond by turbidity currents. Gullies on the Bellingshausen Sea margin cut through debris flows on the slope. Assuming the debris flows are linked mainly to downslope transport of diamictic debris when ice was at the shelf edge under full-glacial conditions, then those gullies cut into them formed during deglaciation. Belgica Fan is about 25,000 km2 in area. It is the largest depocentre identified to date on the continental margin of the West Antarctic Ice Sheet, fed by an interior ice-sheet basin of approximately 200,000 km2. This work is collaborative with R.D. Larter and C.-D. Hillenbrand of the British Antarctic Survey.

Julian Dowdeswell, Riko Noormets, Jeff Evans

Circumpolar treeline research by the IPY core project PPS Arctic

2008 has been a year of intense activity by the international research consortium 'PPS Arctic', which is jointly coordinated by the Norwegian Institute for Nature Research and SPRI. A key question is: Are trees invading the Arctic? The 'expected' answer is 'yes', but this is based on rather simple models that relate the position of the treeline to the local climate. The idea is that it is too cold for trees to exist north of the present-day treeline, so a warming climate ought to produce a northward advance of the trees. However, nature responds in a complex manner to environmental changes – where temperature, precipitation, snow distribution, wind, soil conditions, tundra and forest fires, insect outbreaks, browsing, melting permafrost and land use all interact – and the existing models are almost certainly too simplistic. Until now, there has also been very little hard evidence for an advance of the treeline. The few studies that have been carried out represent a small fraction of the huge area covered by the transition zone between the boreal forest and the tundra. The work of PPS Arctic is integrated by three questions:

  • Is the Arctic treeline zone moving; and if so, in what direction and where?
  • What controls the position and structure of the Arctic treeline zone?
  • What are the ecological and social consequences of changes in the position of the zone?

We see examples of advancing, retreating and stationary treeline zones across our study sites, but the advancing zones are dominant. These questions are addressed both from a scientific perspective and through interaction with stakeholders and the general public. The perspective is circumpolar, and the project group consists of over 110 researchers and graduate students, studying sites in Alaska, Canada, Norway, Sweden and Russia. We are using fieldwork ecological and socio-economic methods, airborne and satellite remote sensing, and historical data from aerial photography. We have been actively collecting data from more than 30 sites around the Arctic since 2007, and data collection will continue into 2009. During 2008, SPRI scientists participated directly in data collection activities across the Kola Peninsula, Russia. Project planning meetings took place in St John's, Newfoundland, Vancouver and Helsinki. The project website is http://ppsarctic.nina.no.

Gareth Rees