A new paper, led by Johnny Ryan, shows that a consumer grade digital camera mounted to a drone can be used to estimate the albedo of ice surfaces with an accuracy of +/- 5%. This is important because albedo measurements are fundamental to predicting melt, but satellite albedo data is limited in its spatial and temporal resolution and ground measurements can only be for small areas. Methods employing UAV technology can therefore bridge the gap between these two scales of measurement. The work demonstrates that this is achievable using a relatively simple workflow and low cost equipment.
The full workflow is detailed in the paper, involving processing, correcting and calibrating raw digital images using a white reference target, and upward and downward shortwave radiation measurements from broadband silicon pyranometers. The method was applied on the SW Greenland Ice Sheet, providing albedo maps over 280 km2 at a ground resolution of 20 cm.
This study shows that albedo mapping from UAVs can provide useful data and as drone technology advances it will likely provide a low cost, convenient method for distinguishing surface contaminants and informing energy balance models.
Our new discussion paper, led by Black and Bloom PDRA Andrew Tedstone, examines in detail why there is a stripe of dark, fast-melting ice on the Greenland Ice Sheet, particularly in the south-west. This ‘dark zone’ is clearly visible in satellite imagery of the Greenland Ice Sheet and is important because darker ice melts faster. It is crucial to understand what causes the ice to be dark there because if it grows or darkens in a warming climate then we can expect the deglaciation of Greenland to accelerate more than is currently predicted. There are two main competing hypotheses that could explain the presence of the dark zone: 1) dust melting out from ancient ice is darkening the ice; 2) algae are growing on the ice sheet and changing its colour.
The paper shows that the dark zone changes its shape, size and duration each year. This appears to be most strongly controlled by the sensible heat flux (air temperature) between June and August, number of days with air temperatures above zero, and timing of the snow-line retreat.
These findings provide some insights into which surface processes are most likely to explain the dynamics of the dark zone. The spatial distribution of the dark ice is best explained by the melting out of dust particles from ancient ice, although these particles are not dark enough to explain the colour change of the dark zone. However, these dusts may be crucial nutrients and substrates for ice algae, suggesting that the dusts control where the dark zone is, and the algae determine how dark it gets. Our other recent TCD paper showed how algae can darken ice and snow; however, there are also meteorological conditions required for algal growth including sufficient sunlight and liquid water. We suggest in the paper that the most likely hypothesis is that dust melts out from ancient ice and stimulates the growth of algae when meteorology allows it. Algae need the dust to grow, and the dust is not dark without the algae.
We are now well into planning 2017 field work so I revisited some archive footage from previous trips. The short clip below provides a good summary of the great diversity of microbial habitats that exist, even within a very small area of ice. These include cryoconite holes, a cryo-pond (the big cryoconite and water filled pool), algal blooms on the ice surface, dispersed cryoconite, streams, cryoconite ‘alluvium’ stranded on the stream banks, weathered ice and the snowpack. The clip also shows how hummocky and non-uniform the ice surface is near the margin of the ice sheet.
To get a better idea of how these habitats are arranged spatially we also flew a small UAV (unmanned aerial vehicle) with a downwards-looking HD camera. The clip below shows some of the footage. The winds were pretty strong and you can actually see the landing gear bow into shot every so often. We’ll have a more sophisticated UAV system in Greenland in 2017 that will collect images at specific wavelengths of light.
Finally, here is a short clip of the 2016 team at the S6 camp enjoying a beautiful full moon over the ice sheet. This site is well into the ‘dark zone’ where impurity loading is very high. We’ll be back there this summer to measure the effect of this on the reflectivity and therefore melt rate of the ice sheet.
Here is a brief field report from our 2016 field season which i also posted on the Arctic Club website (here).
2016 Greenland Field Work Report
Our field work aimed to deepen our understanding of the processes darkening the Greenland Ice Sheet. This is important because the colour of the ice sheet is one of the main drivers of its melt rate because it controls how much sunlight the ice sheet reflects or absorbs. The more sunlight absorbed, the more energy is available for melting ice.
In 2016 a team of researchers from Bristol, Sheffield, Leeds, Potsdam, Aberystwyth and NASA JPL camped on the ice sheet throughout the summer melt season in order to measure and monitor the changing colour of the ice and determine the causes of the darkening. The camp was inhabited in two month-long shifts. The first team comprised Joseph Cook (University of Sheffield), Chris Williamson (University of Bristol), Johan Nilsson (NASA JPL), Ewa Sypianska (Cardiff University), Tom Gribbin (Bristol University), Tris Irvine Fynn (Aberystwyth University) and Jim McQuaid (University of Leeds). Three weeks in, we were joined by Liane Benning, Steffi Lutz and Jenine McCutcheon (all University of Leeds). The team and all the camping and scientific kit was delivered in two flights on an Air Greenland Sikorsky S-61 helicopter.
The camp was built around two large Mountain Hardware “Space Station” tents, one of which was used as a mess tent (with a dining table and chairs, gas hob and food storage) and the other was a laboratory (kitted out with microscopes, spectrometers, filtration units, gas analysers, and all the usual lab consumables). The lab tent was also our power station, with the batteries, inverters and tracking system for our solar array. The long daylight hours and low temperatures helped the solar arrays to perform extremely well and we were able to charge all our scientific equipment, as well as laptops and satellite phones any time without issue. We were even able to run extension cables from the solar array to the mess tent to provide power across the camp! Around these two large tents were our own sleeping tents. Each person had a 3-man tent to provide room for bags and belongings.
A big problem is that the tents can melt the underlying ice, so we pitched on top of layers of white ‘polfelt’ and plyboard that both insulated the floor and provided a flat(ish) surface to walk on. However, this insulation also meant that after a few days the tents rested upon large ice pinnacles so needed to be repitched regularly!
For most of the season the weather was very friendly, with clear skies and very little precipitation – typical of summer on the SW Greenland ice Sheet. However, there was a significant rainfall event early on that washed away the crunchy, weathered ice layer and left a slick, slippery surface that was impossible to walk on without sharp crampons. It is also hard to dry out wet clothes and equipment in cold, overcast conditions. The rain also caused lots of glacier surface sediment (called ‘cryoconite’) to be washed onto the ice surface, instead of being held at the bottom of ‘cryoconite holes’. The combination of washed cryoconite and the loss of the crunchy, white ice made the surface noticeably darker.
We were particularly interested in the role of algae on the colour of the ice, and therefore our microbiology team was hard at work characterising the biology of the ice surface, including identifying the species present, their productivity, abundance and colouration. It seems that algae can bloom very densely and have a severe darkening effect on the ice surface. Coupled with this were detailed measurements of the reflectivity of the surface and the deposition of dark particulates from the atmosphere.
After the first month, the ‘in’ team decamped and was replaced by the project’s head-honcho Martyn Tranter, Alex Anesio, Alex Holland and Andrew Tedstone. Jenine also stayed out there with the second team. By the end of the season, the temperature had dropped significantly – large streams were freezing up completely every evening and remaining frozen until the middle of the day. What were almost 24 hour days at the start of the season became shorter and shorter and the team was treated to spectacular sunrises and sunsets over the ice sheet. In the far distance was a plume of water that, upon close inspection in the helicopter, turned out to be spray from a huge meltwater river crashing round a tight bend. Cryoconite holes grew, coalesced, divided and migrated around the camp.
The field season was successful in terms of the science and the team also reported feeling both awestruck at the scale of the ice sheet and simultaneously surprised by its sensitivity. The growth of microscopic algae and deposition of nanoscale particles of dust and soot influence the rate at which the vast ice sheet melts, and may therefore amplify climate changes and accelerate sea level rise. The challenge now is to quantify these processes and integrate them into future melt predictions.
Cryoconite holes change their shape and size according to environmental conditions. A mechanism for this, driven by nonuniform arrangement of cryoconite granules or receipt of solar radiation, is presented.
Changes in hole shape are accompanied by changes in metabolic processes in microbial communities on the hole floors
Cryoconite systems tend to evolve towards wide, flat floored shapes where cryoconite granules are spread out and able to photosynthesise more. This means cryoconite holes naturally maintain conditions conducive to capturing carbon.
When these equilibrium states are disturbed, the microbes become stressed, send molecular signals to each other and quickly employ metabolic survival strategies.
A possible mechanism for the migration of cryoconite holes away from shade implies biocryomorphic regulation of hole floor conditions for populations of holes.
This paper indicates the potential for combining ice physical, biogeochemical and molecular (in this case metabolomic) analyses in gaining a mechanistic understanding of Earth’s ice as a ‘living landscape’. Another recent paper by Bagshaw et al (Cardiff Cold Climate) examining cryoconite responses to light stress at the other end of the planet is available here.
Thanks to British Society for Geomorphology, Gino Watkins Memorial Fund, Gilchrist Educational Trust, Mount Everest Foundation, Andrew Croft Memorial Fund, Scottish Arctic Club and Gradconsult for supporting this field work. Thanks also to the GRIS15 field team: Ottavia Cavalli, Michael Sweet and Arwyn Edwards.
The team working at the field site, ca. 3 km from the margin of the SW Greenland Ice Sheet, captured using the DJI Phantom Vision 2 + drone.
Despite the mosquitoes, Greenland is a beautiful place. The rocks glisten with flecks of pyrite, the lake waters are beautifully clear, the rivers are turbid with glacial flour and as the season progresses the green land is becoming freckled with blooms of cotton flowers. We have seen Arctic foxes and reindeer. The ice is spectacular, changing colour throughout each day as the melt rate waxes and wanes. Melt pools grow and shrink, cryoconite holes deepen and shallow, supraglacial streams swell and shrink and migrate across the ice surface. The colours are whites and blues to greys and greens. It is a magical, beautiful place and we are very lucky to be working here. Today’s field work went well. We are ahead of schedule on our science goals and the data is looking good. No sign of the weather changing at the moment either, so we are putting our heads together to come up with more ideas to extend the science programme and make the very most of our time here. When we arrived back at camp to find fellow glacier researchers Marek Stibal, Karen Cameron, Jakub Zarsky and Tyler Kohler (collectively @CryoEco) at camp. It was good to catch up and find out a little about their field season over at Leverett Glacier.
Today was another productive day in relatively good weather. Another solid day’s worth of data was recorded by all members of the team. Everything ran pretty much according to plan. I had a look over the data so far and am hopeful of some good results, but it will require some deep analysis once back in the UK. I have been sleeping badly since we got here, largely due to the midnight sun and tonight was especially bad. I walked down to the river and read my book in the early hours and it felt like midday.
My initial science objectives were met today! The weather has been extremely kind to us thus far and our productivity has been higher than expected. I plan to continue to make further measurements and expand the dataset, whilst also establishing some associated extension experiments. Today was hard going though. The katabatic winds were right back up to full strength and it was bitterly cold at the site, especially once my hands had been in a few cryoconite holes! We are all starting to feel tired after a long stretch of continuous field work, but the end of the first observation period is in sight and everyone’s primary science objectives should be in the bag in the next couple of days.
Another hard day weather-wise. It is really the wind that makes things difficult and slows us down. It’s also hard work to stabilise the drone in the wind, and I doubt we will have much useful imagery from these very windy days. Thankfully, there have been enough calm days to ensure sufficient data capture, and more importantly, we haven’t lost or broken the drone! Again, I decanted samples into falcon tubes to process back at camp, and the mosquitoes made it very unpleasant. Still, it got done and as a team our minimum science aims have now been met. This is quite a weight off our minds, since data collected from here on in is largely bonus and if the weather or logistics turned against us from tomorrow onwards, we can still be assured of returning home with some science achievements and data to work up in the autumn.
We finally took a bit of a rest day today, and gained a new recruit to our camp. Leo Nathan is an MSc student at Aberystwyth University who is working under the supervision of Prof. Alun Hubbard. Leo is flying fixed-wing UAVs over long transects to generate Digital Elevation Model data of several of the rapidly melting glaciers in this region. We visited his original camp, up near Point 660, where he has been building and launching the drones. It was all very impressive stuff, and Leo was very knowledgeable and happy to talk about the project, and made a welcome addition to the team.
Today was a final day of measurements at the original field site and was relatively routine. Leo cooked dinner tonight and it was a damn fine spaghetti bolognese (although our resident Italian may disagree)!
Today we pulled our equipment out ready to change field site. This meant dismantling the loggers we had set up, collecting in pieces of equipment and markers, and generally leaving the place as pristine as we found it. This took the morning and we were off the ice just after 1pm. We had some lunch and then went to another nearby glacier to scope out possible access points for obtaining some basal ice samples. On the way we encountered a family of six musk oxen, including two very small calves. Mike and I took a walk over to another nearby glacier and watched the calving ice for a while before dinner. The sun is starting to get lower in the sky at night now, and this evening was especially beautiful down at the river. I sat there and read until it was late and eventually too cold to be out of a tent.
Today was Otti’s final day in Greenland with us. To make it a good one, we took a trip to Russell Glacier, where we watched the glacier calve. This site has changed dramatically since my last visit in 2014, having undergone some major calving and slumping. If there is some out there, I’d love to see some time lapse imagery of this piece of ice. We had some lunch and did some reconnaissance for a future research idea before walking out. Back at camp, we had a good sort out of our field kit, rearranged the tents and packed up gear that Otti would take back to the UK. We also organised the equipment that the remaining team members would need for the rest of the trip and nailed down some further research plans for the final leg of the trip. I stupidly fell asleep out in the open and woke up having been feasted upon by mosquitoes – my face looks like a sheet of bubble wrap!
Today was not a good day. We awoke as usual and ate breakfast, then piled into the truck to drive Otti to town in time for her flight. About 12 km from Kangerlussuaq we were involved in a collision with another vehicle and had to evacuate to KISS. Thankfully nobody was hurt, but there was damage to both vehicles. A police report was filed and the rest of the day was spent trying to contact relevant insurance agencies and our university contacts.
Today we necessarily stayed in KISS to try to sort out the vehicle issues. While we wait, the last of pour funds are evaporating in accommodation costs, plus food etc and we are without a vehicle to get to a field site to extend our science! We also have the additional problem that our camp is still established at the ice margin… Late in the evening two cancellations were made for tomorrow’s flight out of Kangerlussuaq, so Arwyn and I snapped them up. With Otti already home safe and sound, and Mike’s flights only two days away anyway, this was seen as the most prudent damage limitation option. An extremely kind offer of a lift out to decamp by a University of Essex research group meant we could quickly get our kit packed up in time to bail tomorrow.
It is with heavy heart and light wallet that we leave Greenland today. However, we managed to achieve our primary science aims before disaster struck, and everyone is leaving injury free. So overall, although we are a few days early retreating from Greenland, we have the data we need to produce our manuscripts as planned and have loads of images and footage for outreach and analysis. We have met some great folks and seen an incredible part of the planet, and should produce some good publications as a result. However, two secondary objectives that were scheduled for the last few days were not met: depth sampling in a crevasse and bulk sampling of cryoconite. Things could have been a whole lot worse and we are now looking forward to getting stuck into analysing and writing up our findings!
Another huge thank you to our funders British Society for Geomorphology, Gino Watkins Memorial Fund, Gilchrist Educational Trust, Mount Everest Foundation, Andrew Croft Memorial Fund, Scottish Arctic Club and Gradconsult for supporting this field work.
I also thank Professor Alun Hubbard, Leo Nathan, Johnny Ryan and the team from the University of Essex for their company and/or collaboration.
Finally, my thanks go out to the GRIS15 team: Ottavia Cavalli, Michael Sweet and Arwyn Edwards.