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Subglacial Access and Fast Ice Research Experiment (SAFIRE)

Subglacial Access and Fast Ice Research Experiment (SAFIRE)

The Greenland ice sheet contains 3 million cubic kilometres of ice and has been losing mass at an accelerating rate since 1990 (1). Due to increased surface melting (2) and discharge of ice into the ocean (3), and with more precipitation falling as rain (4), there is a net loss of ice, which has intensified from -50 km3/year per year in 1990s to -200 km3/year in the 2000s to -300 km3/year since 2010 (2, 3, 5). Today, the Greenland ice sheet is raising sea level by 1 mm per year (2), which makes it the most significant contributor in the global Cryosphere.

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Cumulative ice mass loss and sea level equivalent (SLE) due to surface melting and discharge of ice (From Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change Climate Change, 2013)

Fast flowing glaciers

Glaciers terminating in fjords and coastal seas drain 88% of the Greenland Ice Sheet. These glaciers amongst the fastest in the world and they are responsible for up to two-thirds of the ice sheet's contribution to sea level rise (6). Understanding the processes that drive the fast flow of these glaciers is crucial because a growing body of scientific evidence points to a strong, but spatially varied, and often complex response to changes in the ocean as well as the atmosphere. So far, no observations have ever been made from beneath a marine-terminating glacier in Greenland, a potential and likely cause of significant error in current predictions of future sea levels. The SAFIRE project addresses this problem by gaining access to the basal zone and bed of Store Gletscher, a major outlet glacier in West Greenland.

"With no previous observation ever made in a subglacial environment of this type of glacier, this project breaks new ground."

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Flow of the Greenland Ice Sheet. Dashed line and 'Store' show catchment of glacier studied in the SAFIRE project (background image showing MEaSUREs velocity data was produced by NASA)

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The 5-km-wide front of Store Glacier in West Greenland. The glacier terminus extends to a depth of 500 m and flows at a rate of 20 m per day (photo by Poul Christoffersen)

The SAFIRE project

The rationale of this project is to investigate mechanical and hydrological conditions at the bed of a large marine-terminating glacier in Greenland in order to understand the sensitive response of these glaciers to changes in environmental stimuli, whether atmospheric or oceanographic. Underpinning the rationale further is the fact that very little is known about subglacial environments in Greenland. It is commonly assumed that all glaciers in Greenland slide over hard and impermeable bedrock, but this is simply a practical assumption based on lack of better constraints. The fast glacier flow could also be a result of lubrication of weak sediment at the bed. This project will resolve this fundamental unknown by drilling to the bed of Store Glacier in West Greenland. With instruments deployed at the bed and within boreholes, the team of investigators will fully resolve the basal control on fast glacier flow in Greenland.

The SAFIRE project has two specific goals. The first is to identify and characterise the mechanical and hydrological conditions at the base of a large outlet glacier in Greenland, using instruments installed in boreholes drilled to the bed. With no previous observation ever made in a subglacial environment of this type of glacier, this project breaks new ground. The chosen glacier is Store Gletscher (meaning 'Big Glacier' in Danish and henceforth referred to as 'Store'), which drains 35,000 km2 and flows at a rate of 20 m per day where it reaches the sea.

The second goal of SAFIRE is to determine the role of basal processes in governing ice flow and iceberg calving. To achieve this goal the investigators will use data acquired from instruments deployed in boreholes and on the glacier's surface as a means to constrain numerical ice-flow models.

The SAFIRE project is a joint project between the University of Cambridge and Aberystwyth University in Wales.

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Scientists onboard 'Gambo' measure salinity and temperature of seawater near the front of Store Glacier (photo by Alun Hubbard)

Research outcomes

Since 2014, the SAFIRE project has been monitoring the dynamics of iceberg calving while also measuring ice flow and properties at the bed.

Subglacial access drilling and borehole investigations

In 2014, the SAFIRE team drilled four boreholes to the bed of Store Glacier with a hot-water drill. The boreholes were more than 600 m deep and all four connected instantly with a basal water system when the drill stem reached the bed. The team is now monitoring changes in water pressure, turbidity and electrical conductivity from sensors installed at the bed in a region where ice flows at a rate of 3 m per day at the surface. The team has shown that deep boreholes can be drilled on crevassed and fast flowing glaciers.

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Hot-water drilling on Store Glacier in July 2014. (Photo by Poul Christoffersen)

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3D diagram of Store Glacier (above) showing ice flow and bed and location where boreholes were drilled in 2014. Photograph (below) shows cable with sensors installed in 600+ m borehole. (Photo by Poul Christoffersen)

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In 2014, the team also inserted cables with thermistors and tilt cells into the boreholes. These sensors inform temperature and deformation of ice.

Surface geophysics

On the surface, the team is recording ice flow with a network of GPS while simultaneously recording atmospheric conditions with an automatic weather station provided by Prof. Jason Box, a collaborator at the Geological Survey of Denmark and Greenland. The team also carried out a seismic survey with help and hardware from Coen Hofstede, a collaborator at the Alfred Wegener Institute. The team is also trialing the use of autonomous phase-sensitive radio-echo sounding (ApRES) as tool to monitor basal melting and ice deformation in high temporal (hourly) resolution.

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Sam Doyle and Tun Jan "TJ" Young setting up ApRES imaging radar on Store Glacier in May 2014. (Photo by Poul Christoffersen)

Glacier surveillance with UAV

In 2014, a second field camp was set up near the calving front of Store Glacier. From early May to late July, team members consisting mainly of PhD students carried out a detailed surveillance programme using unmanned aerial vehicles (UAVs). With 100,000+ images acquired sequentially in 60+ missions, the team has recorded the calving mechanism with data in unprecedented temporal resolution and detail.

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(Above and below) Johnny Ryan and Nick Toberg (PhD students supported by SAFIRE) launch UAV. The team spent three months surveying the calving front of Store in 2014 (Photos by Nick Toberg).

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Image mosaic of Store Glacier from UAV survey on 16 May 2014:

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Close up of Store Glacier from UAV survey on 16 May 2014:

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Numerical modelling

To determine the role of basal processes in governing ice flow and iceberg calving the SAFIRE team uses numerical ice-flow models constrained by data acquired by satellites, UAVs, surface geophysics, automatic weather station data and sensors deployed in boreholes.

The first set of results from numerical modelling was produced from a 2D model of ice flow along the centreline of Store Glacier. This model showed that seasonal variability in ice-front position and calving rate are primarily governed by the support provided by icebergs, bergy bits and sea ice, which forms a rigid melange in front of the glacier in winter months (7). Undercutting of the ice-front by melting of ice in contact with sea water - a potentially powerful mechanism (8) - plays a secondary role in our simulations because the flux of ice into the ocean is extremely high. Our UAV surveys show that Store Glacier puts 33 million cubic metres of ice is put into the ocean every day (9).

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Vertical profiles of Store Glacier from 2D simulation with Elmer/ICE. The profiles show advance of the terminus and formation of a floating tongue in winter when the front is buttressed by rigid proglacial mélange. Dashed lines show extent of downward propagation of surface crevasses and upward propagation of basal crevasses. See (7) for details.

The SAFIRE team is now developing 3D models of Store Glacier using the Community Ice Sheet Model (CISM) and Elmer/ICE.

Animation

3D finite element grid of Store Gletscher used by Joe Todd (PhD student supported by SAFIRE)

The team

Poul Christoffersen Poul Christoffersen (Principal Investigator, Cambridge): Glaciologist researching the dynamics of fast flowing glaciers in Greenland and Antarctica. His responsibilities in the SAFIRE project include logistical planning, field data acquisition, and overall management of the project.
index14.jpg Bryn Hubbard (Co-Principal Investigator, Aberystwyth): Glaciologist investigating subglacial drainage and ice motion via hot-water borehole access. His responsibility in the SAFIRE project includes hot-water drilling, optical tele-viewing and borehole sensor development.
Marion Bougamont Marion Bougamont (Co-Investigator, Cambridge): Glaciologist who specializes in numerical modeling of glaciers and ice sheets. Her responsibility in this project is to develop a 3D model of Store Glacier constrained by field data. The model will help the team to understand processes of the basal environment. See (10) for an example of her modeling work.
index16.jpg Alun Hubbard (Co-Investigator, Aberystwyth): Glaciologist whose research focuses on the dynamic sensitivity of the Greenland ice sheet. His responsibility in this project is to acquire data with UAVs and time-lapse cameras overlooking Store Glacier, set up GPS networks and conduct geophysical surveys.
doyle.jpg Samuel Doyle (Postdoctoral Researcher, Aberystwyth): Glaciologist researching glacier dynamics and flow of the Greenland Ice Sheet using GPS networks and surface geophysics. In this project he is developing borehole sensors for the study of the basal environment of Store Glacier. See (4, 11) for examples of his recent work.
Joe Todd Joe Todd (PhD student, Cambridge): Joe is using the Elmer/ICE finite element model to investigate calving dynamics and flow of Store Glacier in 2D and 3D. See (7, 9) for examples of his PhD research.
young.jpg Tun Jan "TJ" Young (PhD student): TJ is investigating ice deformation and the basal thermal regime of Store Glacier, using phase-sensitive radar systems deployed in attended and unattended (autonomous) modes.
ryan.jpg Johnny Ryan (PhD student, Aberystwyth): Johnny is developing UAV technology for glacial investigations and is specifically investigating the calving mechanism at Store Glacier. See (9) for an example of his PhD research.
Nick Toberg Nick Toberg (PhD student, Cambridge): Nick is investigating proglacial ice mélange, a seasonally rigid mixture of icebergs, bergy bits and sea ice, which provide stability for tidewater glaciers such as Store Glacier. In this project, he uses images obtained from repeat surveys of Store Glacier with UAVs.

Collaborating partners

References

  1. IPCC, Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. T.F. Stocker et al., Eds., (Cambridge University Press, Cambridge, UK, and New York, USA, 2013), pp. 1535.
  2. E. M. Enderlin et al., Geophysical Research Letters 41, 866 (2014).
  3. E. Rignot, P. Kanagaratnam, Science 311, 986 (2006).
  4. S. H. Doyle, A. Hubbard, R. S. W. van de Wal, e. al., Nature Geoscience 8, 647 (2015).
  5. A. Shepherd et al., Science 338, 1183 (2012).
  6. M. van den Broeke et al., Science 326, 984 (2009).
  7. J. Todd, P. Christoffersen, Cryosphere 8, 2353 (2014).
  8. M. O'Leary, P. Christoffersen, Cryosphere 7, 119 (2013).
  9. J. C. Ryan et al., Cryosphere 9, 1 (2015).
  10. M. Bougamont et al., Nature Communications 5, (2014).
  11. S. H. Doyle et al., Geophysical Research Letters 41, 899 (2014).