Filchner Ice Shelf System, Antarctica

The prime aim of the project is to determine how a large sector of Antarctica will respond in a warmer world.  The sector to be studied, which spans one fifth of Antarctica, is the Filchner Ice Shelf and its five tributary ice streams.  Projections will be made, for the middle of this century, of the amount of global sea-level rise from this sector. To achieve this aim the following three objectives need to be met:

Objective 1

Determine the dynamics of the coupled Filchner Ice Shelf and its tributary ice streams with the present southern Weddell Sea atmospheric and continental shelf oceanographic regimes.  This will entail the capture of new observations and data required to understand and numerically describe the present system.

Objective 2

Determine how the oceanographic regime would respond to the likely future change in atmospheric forcing and how a modified sub-ice shelf circulation would change the pattern and intensity of basal melting.  Then, determine the reduction in buttressing offered by the ice shelf when thinned and finally, quantify the response of the ice sheet through the five tributary ice-streams.

Objective 3

Use what was learned to evaluate the processes within the next generation of Hadley Centre predictive earth-system models.

Project deliverables:

1. New datasets from the Filchner region, and validated simulations of the present-day system and its variability

Determine the geometry of the model domain (ice-bed elevation, ice thickness and sub-ice shelf bathymetry) in several key areas that lack data coverage. Collect datasets designed to supply a physical understanding of Filchner Ice Shelf, its tributary ice streams and the sub-ice shelf ocean, in the present atmospheric and oceanographic regime. Numerical simulation of the complete system will demonstrate the various interconnected physical processes and importantly, their sensitivities to a change in climatic forcing.

2. Reliable projections on how the Filchner region will contribute to sea-level rise over the 21st century

3. An assessment of the uncertainties in the projections, and a broadening of the study to encompass all of Antarctica

Key to the attainment of the project is the success of a carefully designed field campaign that will collect data both to improve the way the models work, and also to validate their results. There is an urgent need to get and use the field observations. However, a substantial legacy of the project will be the observational datasets: long after the end of this five-year project the precious, hard-won data will be referred to time and time again.

Field research includes:

Oceanographic observations through hot water drilled access holes

The cavity beneath an ice shelf is probably the least observed part of the World Ocean, as a result, models of the sub-ice shelf circulation lack an observational basis for validation.  A hot-water drill will make three access holes through the Northern Filcher Ice Shelf and obtain oceanographic (CTD) profiles from the underlying water column.  Deployed instrumented moorings in the water column at each site will obtain long-term records of water properties, including currents, temperature and salinity.  Currents will be measured at 3 depths, and temperature and salinity at 7 depths.  In addition, a thermistor cable will be frozen into the ice shelf at one of the sites to obtain time series of temperatures at 24 depths, with ~0.03°C accuracy in temperature.  To drill through approximately 650 metres of ice shelf and gain access to the ocean below a hot water drill, pumping 90l of water per minute at around 90 °C is used.  The resultant 0.5 MW of heating power makes a 30 cm diameter access hole through the ice. Whilst the hole is open (unfrozen) water samples will be taken at discrete heights in the water column Sediment cores from the ocean floor are planned to be recovered.

Bathymetry beneath Filchner Ice Shelf

The fieldwork has three components:

1. Conventional spot depths for bathymetry at 104 locations
2. The revisit of 13 pRES sites established by in 15/16
3. A focused, high resolution seismic-study of the geomorphology of the ocean bed forms

To define the model domain refinement a two-person team will carry out seismics surveys to measure the bathymetry beneath Filchner Ice Shelf in regions where it is presently poorly known. A particular focus will be in the vicinity of ice stream grounding lines where, along the centre-line of the extension of the ice stream into the ice shelf, a spatial resolution on the order of one or two ice thicknesses will be sought. Using a power auger to install the explosive charge, with 24 Georods and a Geometrics Geode datalogger, we anticipate approximately 104 sites will be occupied during the season. An estimated traverse distance of 2,500 km is anticipated.  The spot measurements of water depths and bed elevation will provide a dramatic and vital improvement to the available bathymetric coverage. The repeated pRES measurements will provide an average melt-rate of the ice shelf.

Ground radar measurements(pRES and snow accumulation)

In the 2015/16 season 14 phase-sensitive radars (ApRES) were established at carefully selected locations on both the Ronne and Filchner ice shelves.  The ApRES instruments yield time series of ice shelf thickness change at precisions of ~1 mm, so that over a 10-day period a precision in derived melt rate of a few cm per annum is determined. The aim is not to quantify the total melt rate of the ice shelf, but to use its variability to improve the performance of the ocean models. By adjusting otherwise poorly constrained model parameters to obtain the best match between modelled and observed variability. The system is a low-power, light weight instrument developed in a collaboration between BAS and UCL. It is a 200-400 MHz FMCW radar, with a 1-second chirp, run by controller: housed within its characteristic yellow box the radar and a 100 AH battery is buried in a shallow hole.  The radar’s transmit aerial and receive aerial are spaced 5 meters each side of the yellow box and are also buried. Each system will record for a nominal 12 months and has the ability to process and send, via satellite link, melt-rate data.

Static GPS on Recovery Ice Stream

The two person party will work along an area of the Filchner Ice Shelf between the grounding-line of Support Force Ice Stream and the southern drill sites using a pRES instrument to provide an average melt rate for the area. During the previous season (15/16) a total of 132 pRES sites were established.  Each site is required to be reoccupied and the change in ice thickness recorded.  Then by accounting for any spreading of the ice shelf the average melt rate can be determined. A high frequency radar will also be used in profile mode, this wideband system will provide intricate detail of the spatial variation in accumulation and strain by tracking the internal reflection horizons. The distanced to be travelled is estimated to be 1,000 km. In addition the team will service an automatic weather station (AWS) and in the latter part of the season joint forces with Sledge Victor to support the high resolution seismics.