Petermann Glacier, NW Greenland
At latitude 81°N is Petermann Glacier, a 15 km-wide floating ice tongue draining the north-western sector of the ice sheet. Satellite imagery from between 2002-2009 showed the terminus of the glacier advancing towards the ocean, along with the development of several large lateral rifts. In anticipation of a major detachment event, scientists including Alun Hubbard, Jason Box and Richard Bates (with the help of the Greenpeace ship Arctic Sunrise) travelled to the glacier in 2009 in order to carry out a suite of multi-disciplinary observations.
In August 2010 a 275 squared km ice "island" broke free from the glacier - the largest single area loss observed for Greenland, and effectively retreated the glacier front by 15 km in one event.
Alun Hubbard made a return trip to Petermann in the summer of 2011 to observe the changes taken place and also collect data from the many instruments left there during the previous two years. Details of the trip can be found on Jason Box's blog, while specific details of the data collected can be read below.
The video, left, produced by Greenpeace sets the scene in 2009 and gives an overview of Alun, Jason & Richard's work to instrument the potential breakup of Petermann Glacier's floating ice shelf. [14.3mb; 2m04s]
With joint support from the US National Science Foundation and the UK NERC, during late July, 2011, a helicopter charter brought Alun Hubbard into and out of far northwest Greenland. Jason Box stayed behind to attend urgent family matters. The purpose of the "Peter-mission" was to gather data from time lapse cameras and GPS set up July-August 2009 with the assistance of Greenpeace. The sensors were set in anticipation of a large ice area detachment that occurred by 5 August, 2010.
The helicopter charter's last standard airport leg flew from Qaanaaq, Greenland, the northernmost non-military permanent settlement in the world, to Petermann. The round trip would have been impossible without support from SV Gambo setting a fuel dump further north. The helicopter trip spanned 5 days (24 - 29 July, 2011). Fly time was ~10 hours in total roundtrip from Qaanaaq.
Alun Hubbard: "Although I knew what to expect in terms of ice loss from satellite imagery, I was still completely unprepared for the gob-smacking scale of the breakup, which rendered me speechless." ... "What the breakup means in terms of inland ice acceleration and draw-down of the ice sheet remains to be seen, but will be revealed by the GPS data recovered, which we are now processing at Aberystwyth."
in terms of GPS:
- - Recovery and redeployment of high precision (Trimble NetRS or 5700) 'geodetic' GPS stations. Four of six of these sites were located, data downloaded, and re-deployed with new batteries.
- - Recovery of data from the Trimble NetRS GPS base station. Stored on site, here on land, were data records from 3 telemetric rover GPS, two of three which had failed.
- - Failed to locate the 3 masts that held the (small) stand-alone single-frequency GPS from Institute for Marine and Atmospheric research, Utrecht University, Utrecht, The Netherlands.
- - Recovery of temperature, precipitation rate, and humidity record from the cliff 900 m above sea level at the position of 2 of the time lapse cameras.
- - Completed a photographic record of changes of before and after the breakup.
Six high-precision, 'geodetic' GPS stations were deployed on the glacier in 2009. At each site GPS antennas were mounted on poles drilled into the ice at a height of 1-2 m above the surface.
During a return expedition in 2011, Alun Hubbard was able to locate and download data from four of the sites. Larger-than-expected melt rates of ~5 m in 2 years meant the GPS masts had fallen, making them much harder to find.
Alun Hubbard: "Petermish was a success but it was hard-won and pretty stressful for both of us. We were severely limited by time, fuel and were very isolated. There is no rescue up in the far north of Greenland - no backup; one screw up with the flying, a mechanical or the logistics and we'd have been up merde creek. At one point we were siphoning the last drops of fuel out of jerry cans into the EC120 to get us back to our depot. The whole thing was expected to take less than 30 hrs but, in fact, the mission took treble this time as equipment masts had fallen and were hard to locate due to the enhanced melt since installation in 2009. Whilst Tore - the pilot - slept to replenish his flight duty hours - I'd be out on foot searching for fallen equipment. With 24 hour sunlight - you can go non-stop for days but I was pretty baked by the end."
Preliminary data analysis suggests that the horizontal flow velocities of the Petermann Glacier are modulated by the fortnightly spring-neap tide cycle. The 2010 break-up event itself occurred during a neap tide on a warm day preceded by two days of lower temperatures and a strong WSW wind. GPS data is currently being processed by Sam Doyle and Hilmar Gudmundsson
[ABOVE] GPS positions along the Petermann Glacier.
[RIGHT] GPS and tide records show that the forward velocity of Petermann Glacier is greatest when the tide is lowest.
In August 2010 a 275 squared km ice "island" broke free from the glacier - the largest single area loss observed for Greenland, and effectively retreated the glacier front by 15 km in one event. The breakup was tracked by MODIS satellite imagery, and can be observed in the animation below left (at ~50s).
During 2011, sea ice in Nares Strait persisted until relatively late into the summer. Its rapid breakup is captured by the animation above right.
Andrew Fitzpatrick, Centre for Glaciology, Aberystwyth University, UK
The Petermann Glacier Ice-shelf comprises two major flow units - the main central trunk and a smaller subsidiary unit fed by outlet glaciers that flank the eastern side of the valley (Light green, Figure 1). The shear zone between these units is easily identifiable from satellite imagery due to the different surface features visible. The eastern unit is heavily deformed, indicated by the distortions to the debris stripes and meltwater ponds that highlight the chaotic surface relief. Consequently this flow unit is susceptible to break-up, leaving the eastern flank of the main Petermann shelf unprotected and vulnerable to fracturing and open rifts developing.
The shelf is characterised by several persistent meltwater channels aligned sub-parallel to the flow direction. The foremost 30 km of the shelf is undergoing rapid ablation with many lakes and channels visible but too small to map. Meltwater lakes dominate the western flank and tend to be elongate due to the relief being distorted be shear deformation along the valley side. Small-scale crevassing also dominated along much of the glacier's length, with larger crevasses further south. Although the position of the grounding line is not obvious, this area of heavy crevassing is a likely candidate.
Henry Patton and Sam Doyle, Centre for Glaciology, Aberystwyth University, UK