In collaboration with Rolex Awards for Enterprise, Proudfoot Media and I have produced a documentary film explaining the latest research into the surprising hidden biology shaping Earth’s ice. The story is told by young UK Arctic scientists with contributions from guests including astronaut Chris Hadfield and biologist Jim Al-Khalili. We went to great lengths to make this a visually striking film that we hope is a pleasure to watch and communicates the otherwordly beauty and incredible complexity of the Arctic glacial landscape. We aim to educate, entertain and inspire others into exploring and protecting this most sensitive part of our planet in their own ways.
We think the film is equally suited to the general public as school and university students, and we are delighted to make this a free-to-all teaching resource. Please watch, share and use!
I recently published an article in French pop-sci magazine La Recherche about the wondrous microbial ecosystems on glaciers and ice sheets (here for French speakers). For those English speakers who do not subscribe to la Recherche, here is a translation.
Also, I strongly recommend the excellent translator who worked on this article with me – contact me if you need translation services and I can link you up.
The microbes accelerating glacier melting
Our planet is getting warmer and losing its ice. Mountain glaciers are disappearing and the great Greenland and Antarctic ice sheets are shrinking. These masses of ice are giant coolers for the planet and they reflect energy from the Sun back out into space, meaning the smaller they become, the more the planet warms. Surprisingly, the process of melting the vast glaciers and ice sheets is accelerated by microscopic life.
Glacier and ice sheet melting depends upon more than just temperature. Most of the energy driving melt comes from sunlight that hits the ice surface. Dirtier, darker ice absorbs more solar energy than clean, bright ice meaning more energy is available to drive melting. On the Greenland Ice Sheet in particular, the ice becomes very dark in the summer, with large areas reflecting just 20-30% of the sunlight hitting them. This is not a new phenomenon – in fact it was noticed by explorers during the great polar expeditions of the late 1800s. Intrigued, they examined samples of ice under their microscopes. The dark colour of the ice was not simply due to dust as they expected – astonishingly, the ice was stained by life (Nordenskjold, 1875). The ice surface is a patchwork of greys, reds and purples coloured by the collective effect of countless microscopic organisms, with potential knock-on effects for Earth’s climate (Uetake et al., 2010; Takeuchi et al., 2006; Yallop et al., 2012; Cook et al., 2017).
Microbes on Ice
When explorer Adolf E Nordenskjold arrived on the Greenland Ice Sheet in 1870 he immediately noticed the dark grey-purple colour of the ice. His colleague, a biologist called Berggren, examined the ice under the microscope and discovered a rich variety of microbial life. The importance of their discovery was clear to them – this life darkens the ice and increases its melt rate. Nordenskjold even suggested that the microbial life was the “greatest enemy of the mass of ice” and an accelerator of deglaciation at the global scale (Nordenskjold, 1875)!
Until recently, Nordenskjold’s observations of life on ice have remained obscure footnotes in the history of Polar exploration; however, as climate science has become increasingly urgent in the twenty-first century, Nordenskjold’s work has gained new significance. Contemporary scientists have confirmed the presence of a microbial ecosystem growing on the surface of the Greenland Ice Sheet and elsewhere and are now attempting to quantify their ice-darkening effect. Although it is an extreme environment where temperatures are low and nutrients scarce, there is abundant sunlight and liquid water to support photosynthesis, meaning microalgae can grow on the ice surface (Uetake et al., 2010; Yallop et al., 2012). The days are long in the Arctic in summer, with the sun staying above the horizon for twenty-four hours per day for part of the season, exposing the algae to intense and prolonged solar energy. This powers photosynthesis but over time the exposure stresses the ice algae, causing them to produce biological sunscreen molecules to protect their delicate photosynthetic machinery. These ‘carotenoids’ colour their cells very dark purple and enhance the biological darkening of the ice surface.
At the same time, the ice surface is peppered with holes that are often cylindrical but can have complex and irregular shapes (Cook et al., 2015). These holes range from centimeters to meters in diameter and depth and contain mixtures of biological and nonbiological material bundled up into small balls that sit on the hole floors. Nordenskjold first noticed these holes on the Greenland Ice Sheet and named them ‘cryoconite holes’, from the Greek for ‘holes with frozen dust’. These holes are the most biodiverse microbial habitat on Earth’s ice. They form when dust and debris becomes tangled up by long, thread-like cyanobacteria. The cyanobacteria are photosynthetic and as they grow they exude polymers that act as biological glues, binding the bundles of material together into stable granules. This biological bundling and binding of material creates a microhabitat for other microbes, especially those that can feed on molecules produced by the photosynthesizing cyanobacteria. As the granules grow they become heavier, meaning they settle on the ice surface. The biological material makes them especially dark, so the ice underneath melts quickly, causing holes to form in the ice surface with the granules sitting on the hole floor. The holes provide protection from the weather and intense sunlight and also prevent the microbes from being washed away. The cyanobacteria therefore sculpt the ice surface and engineer a comfortable, stable habitat where diverse microbial life can thrive in this extreme environment.
Cryoconite holes are more than icy buckets that hold microbial life. They are more like microbial mini-cities on ice, with each connected to many others by meltwater flowing between ice crystals just under the ice surface. Cryoconite microbes engage in engineering and construction, production, consumption, competition, predation, growth, reproduction, death, decay, immigration and emigration. There is both import and export of nutrients, waste and other biological material. At the same time, the hole itself changes its shape and size in response to changing environmental conditions with the emergent effect of maintaining the light intensity at the hole floor, promoting photosynthesis (Cook et al., 2010). Algal blooms and cryoconite are crucial components of the wider Arctic ecosystem, acting as stores of carbon (which they draw down from the atmosphere and fix into organic molecules), nutrients and biomass which can all be delivered to soils, rivers and oceans as glaciers melt (Stibal et al., 2012). Truly, these are widely interconnected complex adaptive systems created biologically on Earth’s ice.
The Cutting Edge of Life on Ice
While life on ice has been known for many years, most of the literature on the subject has been produced during the twenty-first century. Modern molecular biological techniques have enabled scientists to catalogue the species present in cryoconite and algal blooms, and modern instruments can measure their darkening effect. However, there are several major gaps in our understanding of life on ice. To quantify their effect on ice darkening worldwide, we need a reliable method to map icy microbes at the scale of entire ice sheets. From a biological perspective, we know which organisms live in algal blooms and cryoconite so we must now concentrate on determining how they function and what ecosystem services they might provide that could impact human society.
To estimate the total coverage of life on ice, we must detect it without actually being present to take samples. It is relatively easy to take samples and analyse them in a laboratory to tell if life is present, but doing the same from the air is a different problem. In addition to biological darkening, soots and mineral dusts colour the ice. Also, as the ice melts the crystals change shape and melt water can fill the spaces between them, which in itself changes the way the ice absorbs and reflects solar energy. Disentangling the biological signal from these other darkening processes has proven to be challenging.
However, because the darkening of ice by living cells is due to biological molecules that absorb light at specific wavelengths, we may be able to use the spectrum of reflected light to identify them. Chlorophyll, for example, absorbs red and blue light much more effectively than it absorbs green light (which is why we see leaves as green). For other biological molecules, the peak absorption will be at slightly different wavelengths, and non-biological materials will have their own absorption patterns too. However, while identifying ‘signature spectra’ is simple when only one material is present, it is much more difficult when several species with different light absorbing properties are mixed with non-biological materials. All of the light absorbers can be scattered unevenly and mixed vertically within the volume of ice which can itself be a complex aggregate of variously sized ice crystals and liquid water. The reflected light is a tangle of signals that can be hard to unpick.
At our laboratory at the University of Sheffield, we are working on a purpose-built drone which will fly back and forth over a patch of the Greenland Ice Sheet taking images at specific wavelengths of light. By analysing these images we hope to be able to produce a map of life on ice. Using the drone means we can follow the flight on foot and take ground samples to examine in the laboratory, enabling us to link the drone images to actual concentrations of different light absorbers on the ground. The wavelengths imaged by the drone match up with those measured by several Earth observation satellites, meaning that achieving life-detection using a drone should then enable the same from space.
As well as knowing where the life is, we also need a deeper understanding of how it functions. Recognition of ice surfaces as microbial habitats came at the same time as an explosion in accessible and affordable techniques in field molecular microbial ecology, meaning several groups have used high-throughput sequencing of marker-genes to identify the particular microbes present within cryoconite communities (e.g. Cameron et al., 2012; Edwards et al., 2014; Stibal et al., 2014, 2015). Environmental genomic techniques have also been used to investigate the total genetic composition of cryoconite communities (Edwards et al., 2013). To date, these have been snapshot studies, but in the very near future great insights into the functioning of cryoconite microbes will come from rapid metagenomic, metabolomic and metatranscriptomic studies. It has been suggested that ice surface microbes might be good targets for bioprospecting. Since they are able to thrive in conditions of low temperature, high light and low nutrients, they may well utilize survival strategies that we can exploit, either by extracting novel genes and biomolecules, or by observing and gaining ecological knowledge. Cryoconite has been suggested to be a potential source of antifreeze proteins, novel antibiotics and cold-active enzymes. The shape, illumination conditions and flushing with flowing meltwater make cryoconite holes natural analogs to industrial bioreactors which are commonly used to synthesise valuable biomolecules (Cook et al., 2015).
Deep insights will come from combining the expertise of microbial ecologists with glaciologists and physicists who, together, will link processes operating at the molecular level with changes in ice surface colour and patterns of melt, which suggests insights into the ecology of ice surfaces might one day be obtainable from the sky or from space. While this is some way off, great insights could be gained from a shift towards a holistic understanding of the ice surface as a ‘living landscape’.
We are working hard to achieve remote detection of life on ice for the purposes of mapping biological ice darkening from satellites and improving our ability to predict future ice melt. However, there is another potential outcome from this work… what if instead of looking down from space at our own planet, we turn the sensors around and start looking out?
The Greenland Ice Sheet is, in many ways, a good place for developing life detection technologies that can be applied to the search for life on other icy planets and moons. Take, for example, Europa. A recently funded NASA project will examine this icy moon of Jupiter for signs of life because of its potentially habitable icy shell and subsurface ocean. On Europa, the icy surface is sunlit and seeded with possibly mineral-rich snow that forms when liquid water in its subsurface oceans escapes via huge geysers (Hand et al., 2017). There is therefore a potentially dusty ice surface illuminated by sunlight that could support photosynthesis, just like the Greenland Ice Sheet (although the solar energy flux and temperature is lower on Europa and photosynthesis is highly unlikely). Any life detection technology that works on the Greenland Ice Sheet will have to overcome the challenges of ice optics, interference by mineral dusts and uncertain biological pigment composition, which would also be the main challenges for remote detection of life on the surface of other icy planets and moons. The frontiers of glacier biology on Earth may therefore intersect with the cutting edge search for extraterrestrial life.
While many people think of Arctic and Antarctic ice as lifeless places, there is in fact abundant microbial activity on Earth’s glaciers and ice sheets. But more surprising is the huge impacts of these tiny organisms. By changing the colour of the ice surface, microbes are potentially enhancing the rate at which glaciers and ice sheets are shrinking, but we cannot yet build them into our climate models. The research priority now is mapping these ecosystems from space because this will enable us to estimate their impact on ice melt worldwide and improve our melt forecasts. The same technologies that will enable us to detect life on Earth may eventually be useful tools for searching for icy life elsewhere in the universe. There is also much to be learned about way these microbes function that can educate us about the limits of life in extreme environments. The true sharp edge of glacier biology research involves understanding how these microbes are able to sense, survive and drive environmental change. The study of life on Earth’s ice is deeply interdisciplinary and ultimately it requires us to recognize – as Nordenskjold did – the intricate bridges joining the very big and the very small.
Cameron K, Hodson A J, Osborn M (2012) Carbon and nitrogen biogeochemical cycling potentials of supraglacial cryoconite communities. Polar Biology, 35: 1375-1393
Cook J, Hodson A, Telling J, Anesio A, Irvine-Fynn T, Bellas C (2010) The mass-area relationship within cryoconite holes and its implications for primary production. Annals of Glaciology, 51 (56): 106-110
Cook, J.M., Edwards, A., Irvine-Fynn, T.D.I., Takeuchi, N. 2015. Cryoconite: Dark biological secret of the Cryosphere. Progress in Physical Geography, 40 (1): 66 -111, doi: 10.1177/0309133315616574Cook et al., 2017
Edwards A, Pachebat J A, Swain M, Hegarty M, Hodson A, Irvine-Fynn T D L, Rassner S M, Sattler B (2013) A metagenomic snapshot of taxonomic and functional diversity in an alpine glacier cryoconite ecosystem. Environmental Research Letters, 8 (035003): 11pp
Edwards A, Mur L, Girdwood S, Anesio A, Stibal M, Rassner S, Hell K, Pachebat J, Post B, Bussell J, Cameron S, Griffith G, Hodson A (2014) Coupled cryoconite ecosystem structure-function relationships are revealed by comparing bacterial communities in Alpine and Arctic glaciers. FEMS Microbial Ecology, 89 (2): 222-237
Hand, K.P., Murray, A.E., Garvin, J.B., Brinckerhoff, W.B., Christner, B.C., Edgett, K.S., Ehlmann, B.L., German, C.R., Hayes, A.G., Hoehler, T.M., Horst, S.M., Lunine, J.I., Nealson, H.H., Paranicas, C., Schmidt, B.E., Smith, D.E., Rhoden, A.R., Russell, M.J., Templeton, A.S., Willis, P.A., Yingst, R.A., Phillips, C.B., Cable, M.L., Craft, K.L., Hofmann, A.E., Nordheim, T.A., Pappalardo, R.P., and the Project Engineering Team (2017). NASA, Report of the Europa Lander Science Definition team. Posted Feb 2017. https://solarsystem.nasa.gov/docs/Europa_Lander_SDT_Report_2016.pdf
Stibal M, Sabacka M, Zarsky J (2012a) Biological processes on glacier and ice sheet surfaces. Nature 1554 Geoscience, 5: 771-774
Stibal M, Schostag M, Cameron K A, Hansen L H, Chandler D M, Wadham J L, Jacobsen C S (2014) Different 1558 bulk and active microbial communities in cryoconite from the margin and interior of the Greenland ice 1559 sheet. Environmental Microbiology Reports, DOI: 10.1111/1758-2229.12246
Stibal, M., Schostag, M., Cameron, K. A., Hansen, L. H., Chandler, D. M., Wadham, J. L. and Jacobsen, C. S. (2015), Different bulk and active bacterial communities in cryoconite from the margin and interior of the Greenland ice sheet. Environmental Microbiology Reports, 7: 293–300. doi:10.1111/1758-2229.12246
Takeuchi, N., Dial, R., Kohshima, S., Segawa, T., Uetake, J., 2006. Spatial distribution and abundance of red snow algae on 35 the Harding Icefield, Alaska derived from a satellite image. Geophysical Research Letters, 33, L21502, doi:10.1029/2006GL027819
Uetake, J., Naganuma, T., Hebsgaard, M. B., and Kanda, H. 2010. Communities of algae and cyanobacteria on glaciers in west Greenland. Polar Sci. 4, 71–80. doi: 10.1016/j.polar.2010.03.002
Yallop, M.L., Anesio, A.J., Perkins, R.G., Cook, J., Telling, J., Fagan, D., MacFarlane, J., Stibal, M., Barker, G., Bellas, C., 25 Hodson, A., Tranter, M., Wadham, J., Roberts, N.W. 2012. Photophysiology and albedo-changing potential of the ice-algal community on the surface of the Greenland ice sheet, ISME Journal, 6: 2302 – 2313
In 2017 I slept in various ice-camps in Greenland in spring, summer and autumn. Living on ice requires some specialist techniques different to camping on dry land, and they vary depending on the season. In summer, the main problem is the melting surface. A tent pitched directly on the ice surface will descend into a wet ditch because of the heat generated by a person inside. To counter this, tents are pitched on sheets of ply with reflective insulating sheets underneath. These slow the ablation under the tents and provide a flat surface to sleep on; however, they often work too well and leave the tents wobbling on raised platforms after a few days.
The most important thing is securing the tent to the ice surface, because it can get very windy on the ice sheet. The ice surface can descend several centimetres per day, meaning short stakes or pins will melt out very fast. For that reason long bamboo or plastic poles are drilled up to 1 metre into the ice at an oblique angle under the tent, providing points to secure the tents to. This is especially important for geodesic dome tents, where tension is required roughly evenly across the poles for the tent to keep its shape. In 2017 the combination of strong winds and very fast surface lowering meant the large mess tent quickly became raised above the surrounding ice and, despite our best repitching efforts, the poles floated freely above the ice. With no ground to push against, the poles became structureless and weak and eventually collapsed.
In winter, a stronger and more permanent solution can be achieved using Abalykov threads. These are loops of tape or rope frozen into the ice itself. There is no surface melting in autumn/winter and the surface does not have a weak weathered layer. The strong, cold surface ice is perfect for drilling obliquely with short ice screws so that two drill-holes meet 10-15cm below the ice surface an create a tunnel from the surface and back. A pipe-cleaner can then be used to drag rope or tape through the hole and tie the tent down. the hole can then be packed with snow or water which will quickly refreeze around the rope and form a super strong tie-point to secure the tent. Using a snow shovel to cover the tent’s snow-skirt with snow helps prevent wind and snow from getting between the flysheet and the inner, keeping it cosy inside and helping to keep the tent a bit better streamlined against the wind.
This Youtube clip posted by Glenmore Lodge (Scotland) explains how to make an Abalykov thread for ice-climbing – it’s the same for securing tents in an ice camp.
The Abalykov threads stood up to extremely strong winds in Greenland in September/October. The poles and fabric seemed more at risk of failure than the threads!
Summer 2017 seriously challenged the idea that summer in SW Greenland has a reliably stable, clear, dry meteorology. Our field work was characterized by unpredictable swings between weather extremes from blizzards dropping 1ft of snow in an evening to bright sunshine and low wind, to rain and tens of centimeters of surface lowering in a few hours. Most of this was inconsequential and actually scientifically very interesting since we experienced what would normally be a year’s worth of surface change in a few weeks. However, we did have to deal with a particularly vicious couple of days of unexpected storm… Here are the notes from my field diary…
Wind steadily increased through afternoon with frequent periods of heavy rain. No real work got done b/c too windy for drones and spectrometer needs to stay dry. As dinner time approached winds continued to strengthen. Tedstone cooked a killer dahl while Stefan and I redrilled the stakes holding down all the tents and added extra guy lines to the mess on the windward side. Side of mess pushing in towards middle of mess during dinner. The fabric was looking a bit delicate and the flex in the tent wall was knocking things off the cooking table – boxes and stove etc gradually moved into the middle of the tent over about an hour as we ate. Downloaded data from AWS – winds averaging 48 kmph with much stronger gusts. Getting a little concerned about the longevity of the mess.
By 2300 the mess was pressing in and becoming quite concave during stronger gusts. Avoided going outside because of rain, but some tent maintenance was now essential. Intense surface lowering around the ply under the mess has caused poles to float in space – tent not so geodesic now! To try to counter this, poles on opposite sides of the tent were tied together with accessory cord to try to maintain dome shape. Outside tent, tags were tied up to the fly sheet to try to stop poles coming out. Predict chance of mess tent survival 40%, so all contents packed down into Zarges boxes and/or tied down, gas disconnected from stove, electrics and batteries dry-bagged and stored. Essentials moved to personal tents or stashed in dry bags for moving later.
Tedstone went to bed, but almost immediately came back with ‘bad feeling’… Bang on. On cue, a strong gust ripped the tent fabric on the windward side, which was now bending inwards to touch the plyboard floor in the centre of the tent. Now no chance of maintaining tent shape. We evacuated the tent, thankfully the rain had died down, and watched the tent collapse inwards. Seeing poles bending and breaking, we pulled as many as possible out of their tags to allow them to flop safely downwards rather than pinging dangerously as they or the fabric snapped under tension. Zarges boxes pulled onto the edges of the fabric to stop tent flying away entirely.
Now early morning and personal tents also looking in poor condition, with surface lowering causing stakes to bob uselessly in shallow drill holes and strong winds bending the tents out of shape. No sign of storm passing – front after front lining up on horizon and winds only getting stronger. Tom and Stefan looking very cold, so sent to their tents to get warm. Buddy system established: in event of any problems with personal tents, warmth etc Tom would get into my tent and vice versa, and the same for Andrew and Stefan. Tedstone and I extracted the drill and flights from the wrecked mess and redrilled holes to stake down all of the personal tents. Agreed that if one personal tent goes down, we call in search and rescue. Rationale was that once a personal tent goes, the others will follow and we then have no shelter. With no sign of storm abating the risk of exposure and hypothermia was not justifiable. However, both know chances of heli getting here soon are slim. No panic yet – personal tents standing up OK and everyone dry and warm. At 0120, Tedstone and I went to our personal tents with agreement to reconvene and check all tents again in 2 hours, and also call back to the UK for up to date forecast.
0330 Reconvened with Tedstone – tents looking ok but storm still raging. Called Martyn (project PI) on satellite phone to ask for urgent weather forecast. Text response indicated clear weather after this storm, but could be a further 6-8 hours. Still satisfied with safety of personal tents, so 0430 back to tent to sleep with agreement to meet at 0730.
0730 Reconvene with Tedstone. Storm still strong and still looks heavy all the way to horizon. Back to tents to sit it out. Tried to snooze.
1000 Fetch stove and emergency dehy food from wrecked mess tent and cooked in porch of my personal tent. Tedstone delivered very odd breakfasts to very hungry researchers in their tents. Personal tents now looking ropey, so agreed to sit out until next break in rain, then repitch. 4 hours until next break in weather. By this time calmer weather was on the way. Cooked a second dehy meal for team and waited another 2 hours. Rain stopped and wind calmed through day. Once manageable, wrecked mess was packed down and entire camp rebuilt. No science done today!
The BBC Science team joined us for our first twenty-four hours on the ice this year, documented our work on algal darkening of the Greenland Ice Sheet. This started in the dusty town of Kangerlussuaq, where I took David Shukman, Kate Stephens and Jonathon Sumberg out to Russell Glacier. There, while I flew the drone to get aerial shots for the news broadcasts, the team did their ‘to camera’ pieces and filmed the melt pouring off out out of the glacier’s calving front. Here’s one of the short UAV clips showing the dramatic front of Russell.
The next morning it was onto the ice. We worked as quickly as possible to get a camp established, including the mess tent, personal tents, equipment cage and toilet. The BBC team filmed their on location pieces and Andrew and I flew the various UAVs and set up the science kit to demonstrate the measurements we’d be taking after the film team were gone. We all gave our interviews which were used for the 6 O’clock and 10 O’clock Evening News, the Morning News, Radio 4 and BBC On Demand. I also recorded a more light-hearted interview about living on the ice sheet which is linked to in the online news article.
The next morning the team packed up and shipped out back to dry land, leaving four of us (me, Andrew Tedstone, Stefan Hofer and Tom Gribbin) on the ice to start making our measurements of surface reflectance and algal growth. The picture below shows our camp from the air, looking roughly west.
One of our team, Tom Gribbin, also made this short film about the season using his GoPro camera.
I’m very pleased to report our new paper is now in open discussion in The Cryosphere. The paper presents a new model for predicting the spectral bioalbedo of snow and ice, which confirms that ice algae on ice surfaces can change its colour and by doing so enhance its melt rate (“bioalbedo”). We also used the model to critique the techniques used to measure bioalbedo in the field. The model is based on the SNow ICe and Atmosphere Radiative model (SNICAR), but adapted to interface with a mixing model for pigments in algal cells. We refer to the coupled models as BioSNICAR.
The model uses Mie theory to work out the optical properties of individual algal cells with refractive indices calculated using a pigment mixing model. The user can decide how much of each pigment the cell contains, the cell size, the biomass concentration in each of n vertical layers, the snow/ice optical properties, angle and spectral distribution of incoming sunlight and the mass concentration, optical properties and distribution of inorganic impurities including mineral dusts and black carbon (soot). From this information, the model predicts the albedo of the surface for each wavelength in the solar spectrum. This can then be used to inform an energy balance model to see how much melt results from changes to any of the input values, including growth or pigmentation of algae.
The model shows that smaller cells with photoprotective pigments have the greatest albedo-reducing effect. The model experiments suggest that in most cases algal cells have a greater albedo-reducing effect than mineral dusts (depending upon optical properties) but less than soot.
As well as making predictions about albedo change, the modelling is useful for designing field experiments, as it can quantify the error resulting from certain practises, such as using devices with limited wavelength ranges, or neglecting to characterise the vertical distribution of cells. I’ll cover this in some further posts. The most important thing is metadata collection, since standardising this enables the measurement conditions to be as transparent as possible and encourages complementarity between different projects. Importantly, following a protocol for albedo measurements and collecting sufficient metadata will make it easier to couple ground measurements to satellite data. We outline two key procedures: hemispheric albedo measurement, and hemispherical-conical reflectance factor measurement. To accompany the discussion in our paper, we’ve produced some metadata collection sheets that might be useful to other researchers making albedo measurements in the field (download here: metadata sheets) and made our code and data available in an open repository.