New AGU paper: Microbes change the colour and chemistry of Antarctic snow

In recent decades there has been a significant increase in snow melt on the Antarctic Peninsula and therefore more ‘wet snow’ containing liquid water. This wet snow is a microbial habitat In our new paper, we show that distance from the sea controls microbial abundance and diversity. Near the coast, rock debris and marine fauna fertilize the snow with nutrients allowing striking algal blooms of red and green to develop, which alter the absorption of visible light in the snowpack. This happens to a lesser extent further inland where there is less fertilization.

hod_bgfig2
Figure showing the location of the field sites on the Antarctic Peninsula at two scales (A/B), plus close up views of the red snow algal patches (C/D).

A particularly interesting finding is that the absorption of visible light by carotenoid pigments has greatest influence at the surface of the snow pack whereas chlorophyll is most influential beneath the surface. Higher concentrations of dissolved inorganic carbon and carbon dioxde were measured in interstitial air near the coast compared to inland and a close association was found between chlorophyll and dissolved organic carbon. These observations suggest in situ production of carbon that can support more diverse microbial life, including species originating in nearby terrestrial and marine habitats.

hod_bgfig
Reflected light from clean snow, snow with green algae and snow with red algae.

 

These observations will help to predict microbial processes including carbon exchange between snow, atmosphere, ocean and soils occurring in the fastest-warming part of the Antarctic, where snowmelt has already doubled since the mid-twentieth century and is expected to double again by 2050.

 

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New Scientist’s “Icy Oases” Article: The full interviews!

New scientist recently published an article introducing cryoconite holes as oases for microbial life on ice surfaces. As ‘new scientists’ working on cryoconite, colleagues Arwyn Edwards (Aberystwyth University), Karen Cameron (GEUS / Dark Snow Project) and I (University of Derby) were interviewed by science writer Nick Kennedy. Of course only a few sound-bites made it into the final article, so here I present mine and Arwyn’s answers to Nick’s questions – in full – to provide further detail for intrigued readers. 

NK = Nick Kennedy, AE = Arwyn Edwards, KC = Karen Cameron, JC = Joseph Cook

video credit: J Cook, H Davies (LEI – University of Derby). With thanks to Arwyn Edwards, Tris Irvine – Fynn, Dark Snow Project, Gino Watkins Memorial Fund, Andrew Croft Memorial Fund, Scottish Arctic Club and Royal Society.

NK: What is the most fascinating creature in cryoconite holes for scientific purposes? What about just because of peculiarity/oddness? Presumably there’s several unusual adaptations that enable them to survive there.

JC: There are several species of particular interest inhabiting the cryoconite holes. Firstly I’d propose the Cyanobacteria that are apparently ubiquitous in cryoconite worldwide – not because they are unique to cryoconite (far from it!) but because of their vital role as ecosystem engineers. These microbes are filamentous, allowing them to capture and entangle mineral and organic matter to form coherent granules. They are the dominant primary producers that provide food for several trophic levels of biota and as a by-product of their activity they form stable microhabitats that enable diverse microbial communities to develop.

In terms of peculiarity, it has to be Tardigrades. These are commonly referred to as “water bears” and usually represent the highest predators in cryoconite communities (although midges and some insects have been identified on some mountain glaciers). They are incredibly hardy creatures that can remain active in deep ocean, high mountain and deep englacial environments and have even survived periods in the vacuum of space!

AE: My Biology students at Aberystwyth University love tardigrades. It’s hard not to as they have a certain anthropomorphic appeal. However, I find rotifers, which are also present in cryoconite to be the most intriguing. We know they have been asexual for an estimated 80 million years, and believe that must make radical rearrangements to their chromosomes to survive. Not even tardigrades go to the extent of rearranging their genomes to survive.

Scanning electron microscope image of a live “water bear”. Ph from "Eye of Science"
Scanning electron microscope image of a live “water bear”. Photo: Nicole Ottawa & Oliver Meckes / Eye of Science / Science Source Images

NK: Do we have a lot to learn from these highly adapted species?

AE: I would like to think so. DNA sequencing tells us there are hundreds to thousands of species of microscopic life in cryoconite, biodiversity levels comparable to soils even, and we know that that the total community’s metabolic rate (technically its rate of carbon production) equals that of some Mediterranean soils. But all of this is happening in a temperature range between 0.1°C and 1°C in the active growing season, which would be thermodynamically very unfavourable relative to, say, those Mediterranean soils. We therefore assume that the organisms in cryoconite have lots of adaptations to these extreme conditions. But, to date – we don’t know what these adaptations are.

The beautiful cryoconite at S6, Greenland ice sheet
The beautiful cryoconite at S6, Greenland ice sheet

NK: Are cryoconite holes contributing to glacial melt? Is that influenced by the organisms that live in them?

JC: This is a very interesting question, without a simple answer! The key issue is the reflectivity, or “albedo” of the cryoconite. Because cryoconite is dark (i.e. it has low albedo), it efficiently absorbs solar radiation and transfers that energy to the underlying ice, accelerating it’s melt rate. It is precisely this process that leads to cryoconite hole formation. However, when cryoconite holes form, they fill with melt water and hide the dark granules beneath a layer of reflective water, reducing their albedo-lowering effect on the ice surface. While cryoconite definitely does have an albedo lowering effect, and cryoconite holes do darken the glacier relative to clean ice, dusts and algae that remain upon the ice surface between cryoconite holes have the greatest darkening effect (see Yallop et al, 2012) and the evolution of both cryoconite granules and cryoconite holes can lead to complex patterns of melt.

The organisms that live in cryoconite granules strongly control their albedo. Inert mineral dusts are darker than clean ice but they have much lower albedo when they are encased in organic matter in cryoconite granules (see Takeuchi et al, 2001, 2002, 2010; Tedesco et al, 2013). This organic matter includes cyanobacterial biomass that entangles dusts, soot and organic matter along with biological “cements” that glue the organic and inorganic materials together into coherent granules. In addition, heterotrophic bacteria feed upon organic matter and produce dark, sticky humic substances and some microbes produce dark pigments to protect themselves from intense sunlight. All of these processes darken the granules and enhance their ability to absorb solar energy and locally accelerate glacier melt rates.

What is most fascinating (to me) is that the formation of these dark granules is ultimately a biological process, and the result is the formation of cryoconite holes that can change their shape to maintain favourable light intensities on the hole floors and therefore promote photosynthesis (see Cook et al, 2010). This allows cryoconite to support diverse and remarkably active microbial communities in an otherwise hostile environment – a great example of ecosystem engineering (see Jones et al, 1994) that arises from locally accelerated melting of ice.

AE: The answer here is a clear yes. We have known for about fifteen years that microbially-formed pigments in cryoconite darken it and that this is a significant contributor to glacial surface melt, both on valley glaciers, and thanks to more recent work, the Greenland ice sheet. Vast swathes of the Greenland ice sheet are covered in cryoconite – even visible in satellite imagery – and so we have strong evidence that the biological darkening of ice is an important feedback in melting. Unfortunately, climate models assume that all impurities on the ice surface are black carbon, and thus do not capture the effect of biology, or its consequences stemming from the impurities being alive and growing…

Greenland ice sheet melt in action: observing surface runoff in a stunning supraglacial stream (ph. Sara Penrhyn-Jones)
Greenland ice sheet melt in action: J Cook observing surface runoff in a stunning supraglacial stream (ph. Sara Penrhyn-Jones)

NK: If there’s life hiding in such tiny dust particles on an otherwise inhospitable land, could we see something similar on other planets?

JC: It is possible, and there are several research groups that look specifically at the astrobiology of other icy places in the solar system. Antarctic ice is commonly cited as a Martian analog because it is the coldest, driest place we can currently access. The cryoconite holes in Antarctica are different from elsewhere – because the temperatures are so low they are completely entombed in ice, melting small pockets of liquid water under the surface thanks to a solid-state greenhouse effect. This effectively isolates them from chemical exchanges with other environments and promotes the development of rather extreme hydrochemical conditions (see Tranter et al, 2004). These holes in particular might be good analogs for potential habitats elsewhere in the solar system.

AE: Potentially, yes. Cryoconite holes are self-stabilizing systems. Their albedo-reducing effect is strong until they melt to a depth which has the same melting rate as the ice surface. Meanwhile, the microbe-dust aggregates tend to rearrange themselves laterally to become a single layer thick. The net result is an microbially-mediated system which sits at its optimum depth for photosynthesis (not too deep to have too little sunlight, not too near the surface to be irradiated by UV), and “ensures” that as much of its surface area as possible is exposed to promote photosynthesis. As such, it presents an elegant example of how life can promote conditions to sustain itself, even in otherwise hostile environments.

NK: Could these organisms be life’s stowaways that might soon populate other areas covered in ice (do these occur on the polar caps, too)? Would they change the local flora and fauna thanks to hitching ride in these dust bits?

JC: Cryoconite holes exist on almost all ablating ice surfaces – they are a near-ubiquitous feature of melting ice. This includes ice sheets and glaciers in the Arctic, Antarctic and smaller valley glaciers at lower latitudes (e.g. Alps, Himalaya, Tien Shan, Andes). It has recently been recognised that they are not isolated habitats, but are actually part of a dynamic glacier-wide aquatic ecosystem comprising microbes and nutrients flowing through porous ice near the glacier surface (see Irvine-Fynn et al 2013; Edwards et al, 2014). The cryoconite holes can be thought of as sites of favourable conditions for photosynthesis and therefore enhanced microbial activity and biodiversity within this spatially expansive aquatic ecosystem. These habitats migrate, divide and coalesce throughout a melt season, while the microbes within them change their community structures and biogeochemistry in response to changing environmental conditions. Their role as ecological entities is therefore complex and there are certainly fluxes of cells both into cryoconite holes from other environments and also out of cryoconite holes to other environments. Given that glaciers are receding and the planet will deglaciate ever-more rapidly in a warming climate, the microbes inhabiting cryoconite holes will increasingly be delivered to newly exposed land, glacier fed streams, lakes and the oceans, with currently unknown impacts upon the ecology of those environments. Glacial sources contribute significantly to the flux of organic carbon from the land to the ocean (see Hood et al, 2009), but the role of cryoconite microbes in the storage, release and transformation of that carbon is still unknown.

Millions of cryoconite holes occupy melting ice surfaces on the Greenland Ice sheet
Millions of cryoconite holes occupy melting ice surfaces on the Greenland Ice sheet

NK: Do cryoconite holes affect carbon dioxide levels?

JC: Microbes in cryoconite holes are remarkably active, especially considering they exist in conditions of low nutrients and low temperatures. Some studies have suggested that they cycle carbon at rates comparable to Mediterranean soils (see Anesio et al, 2009). Major differences in carbon budgets exist in different geographic regions. As a general rule cryoconite holes on low gradient, slow moving, stable ice in the interior zones of large glaciers and ice sheets seem to be carbon sinks, whereas cryoconite holes on steep, fast moving, dynamic ice on valley glaciers and at the edges of ice sheets are more likely to be carbon sources (see Stibal et al, 2012). Stability seems to favour net carbon drawdown from the atmosphere. Whether these fluxes are of significance to large scale atmospheric carbon concentrations is still to be firmly established. Several estimates of cryoconite carbon fluxes have been made (see Anesio et al, 2009; Hodson et al, 2010; Cook et al, 2012) but they were based upon linear extrapolations of very limited empirical data and do not take into consideration any bio-glaciological feedbacks or changes in microbial activity over time. Given that there are billions of cryoconite holes covering the melting parts of glaciers and ice sheets worldwide, and the rates of carbon cycling within them are surprisingly high, it is possible that these features affect atmospheric carbon concentrations, but this remains uncertain.

AE: Cryoconite holes are important as ice-cold hot-spots of carbon sequestration on glacier surfaces. We have no clear idea about their contributions to the global carbon cycle in quantitative terms beyond early, limited datasets which based their assumptions on linear extrapolations. What we do know though is that these are organic-carbon hot-spots in carbon limited environments: both the glaciers themselves, and downstream environments like coastal seas and glacier forefields, so the cryoconite carbon cycle can have strong regional influences. Finally, much of the organic carbon present is “dark”, as proto-soil pigments formed by microbial decomposition or microbial pigments. The impact of this dark carbon on ice melt is important (as mentioned above).

transfers of organic carbon and viable cells occur between cryoconite covered glaciers and other nearby environments including proglacial streams and newly deglaciated land.
transfers of organic carbon and viable cells occur between cryoconite covered glaciers and other nearby environments including proglacial streams and newly deglaciated land.

NK: How will this change with climatic change?

AE: We know that cryoconite microbial aggregates are an intermediate to mature stage of colonization of glacier surface, a process which starts with microbial (often algal) growth on snow and bare ice. There is the notion that the microbial feedback to ice-melt from cryoconite represents a biological pre-conditioning of a glacier to its death by the accumulation of microbial biomass which can then establish itself in nearby habitats (forefields and coastal seas, as above). We therefore expect glacial systems to be increasingly biological as they decay thanks to climatic change.

NK: Might there be a host of species in cryoconite holes that may never be classified or seen?

AE: I’m an optimist, so I would never say never. However, there is an element of truth to this, but that which is true for many if not most natural environments as far as microscopic biodiversity is concerned. It is only through the rapid developments in high-throughput DNA sequencing technology that we are aware that glaciers have any biodiversity at all. At first glance, glaciers are not the Amazon. But we know now that there are more microbes in the top metre or so of glacial ice than in rainforest soils. As glacial ice holds 70% of Earth’s surface water, they are its major freshwater ecosystems. But of the 198,000 or so glaciers on earth, we only have DNA data published from 20-30 of these sites.  Moreover, our ability to sequence the DNA of all life-forms present is technically limited. We can reliably detect the hundred or thousand most dominant, but rare organisms are easily missed.

Personally, although we have some interesting discoveries about eukaryotes, I am most puzzled about the Archaea associated with cryoconites. We often think of Archaea as the experts at surviving extreme environments, and we know that methanogenic Archaea are prevalent beneath glaciers. But it is very difficult to detect Archaea in cryoconite, and we have only a few reliable reports. Either they are generally absent, or the Archaea there are too different to be detected by our DNA sequencing experiments for some reason.

NK: In what ways are the anabiotic qualities of organisms found in cryoconite holes interesting to biotechnological science?

AE: Dormancy (=anabiosis) is an interesting phenomenon from an applied perspective. Some of the adaptations concerned with becoming dormant are relevant for protecting freeze-sensitive materials such as drugs or vaccines, for example the production of “cryoprotectant” molecules, and as far as microbes are concerned, there are common dormancy and revival mechanisms between some of the bacteria in cryoconite and medically-important pathogens which are latent in human hosts for many years, such as tuberculosis.

JC: Adaptations related to anabiosis might make cryoconite important for bioprospecting and biotechnology; however, this has not really been explored in depth. It seems reasonable to suggest that organisms that utilise anabiosis to thrive in hostile conditions of low temperature and low nutrient concentrations might have adaptations that could be exploited by biotechnologists. For example, harvesting anti-freeze proteins could potentially be useful for cryo-preservation.

Many thanks to New Scientist, Nick Kennedy, Arwyn Edwards and Karen Cameron

Water Bears on Ice: Guest blog by Jesamine Bartlett

Huge thanks to Jesamine Bartlett – a recent MSc graduate from the University of Sheffield who has been working on Tardigrade research – for providing this introduction to the weird world of water bears…

Scanning electron microscope image of a live “water bear”. Ph from "Eye of Science"
Scanning electron microscope image of a live “water bear”. Ph from “Eye of Science”

Whether or not you like microbiology, bugs, or even science, no one can deny the frankly awesome nature of the Tardigrade. Even the tabloid press are fans!  Tardigrades are small, inconspicuous invertebrates that live quietly in almost every habitat we know of. If there is water, there will be probably be active Tardigrades. Even where there isn’t water they have a remarkable ability to enter a hibernation state that allows them to survive freezing and drying out. They have been found at both poles, 20,000ft up mountains in the Himalaya to 14,000ft deep on the ocean floor (Everitt, 1981; DeSmet & Van Rompu, 1994; Ramazzotti & Maucci, 1983; Renaud-Mornant, 1982 ). They are as close as residents in your back garden and as far out as visitors to outer space! More on that later…

Known as moss piglets or water bears because of their clawed legs (called lobopods) and lumbering bear-like gait, the Tardigrade is a tiny creature that measures on average 500µm when adult. They are small enough that you can’t see them with the naked eye, but large enough that you can easily extract them from moss and view them with a good hand lens or simple microscope. Similarly to many invertebrates with a hard outer cuticle, they grow by moulting. This process is known as “ecdysis” and is the same process as spiders shedding their skin. Often Tardigrades take advantage of this discarded hard outer shell by laying vulnerable eggs inside them for protection.  Tardigrades reproduce sexually, with females either laying the eggs in the moult with the male fertilizing them afterwards, or through internal fertilization and eggs lain afterwards. Tardigrades can also reproduce via “parthenogenesis” – a hermaphroditic “female” fertilizing her own eggs internally. Tardigrades are generally omnivorous, eating plant cells, algae and also other microscopic invertebrates such as rotifers or even other Tardigrades. Having a flexible diet that relies on no single food source helps water bears to exist in such disparate places across the globe. Because of their ability to survive pretty much anywhere, Tardigrades are one of comparatively few multicellular animals to earn the status “extremophile”, a label that is usually attributed to bacteria and archaea that can happily live in extreme environments such as deep sea hydrothermal vents, or trapped deep in glacial ice with little or no oxygen. Since extremophiles live in such rare and inhospitable conditions, they can tell us about the ranges of conditions where life is possible.

Live Tardigrades extracted from Arctic cryoconite – Credit - Jesamine Bartlett
Live Tardigrades extracted from Arctic cryoconite – Credit – Jesamine Bartlett

Tardi 2

Over the last few decades, the extreme habitats at Earth’s poles have attracted increasing research attention. Complex life has now been identified on, in and beneath Arctic, Antarctic and mountain ice (Wharton et al, 1981; Kohshima 1984; Hodson et al, 2008). Recently, fish were even discovered living beneath lake ice in Antarctica (see also Brent et al 2014), illustrating the potential for previously undiscovered complex life on Earth. At the poles, Tardigrades inhabit deglaciated terrain, and the surfaces of glaciers and ice sheets. Living in and under ice is extreme in the highest degree, with low nutrients, low light, low temperatures and high pressures. But it is comparatively stable to that of the surface; Frequent and drastic environmental fluctuations including periodic freezing and thawing, glacier hydrology, meteorology and intense irradiance challenge incumbent microbes, some of which develop specific physiological adaptations that allow them to survive. In order to survive extremely low temperatures (for example on ice surfaces during winter beneath a seasonal snowpack). Tardigrades enter a state of “cryptobiosis”, slowing their metabolisms to ~0.01% of normal and losing up to 99% of their total moisture. This cold, dry hibernation state is known as their “tun” state. The cessation of metabolism to such levels would kill most animals, but Tardigrades can amazingly reverse this state, blurring the line between living and dead. In the presence of liquid water, such as a spring thaw, Tardigrades can awaken, rehydrate and reanimate themselves. While in the tun state, a Tardigrade can survive for years in adverse environments, and after 10 years most can fully reanimate and continue their life cycle as if they had only just stopped to have a nap. The record for reanimation is 120 years in tun state – although the Tardigrade in question didn’t survive very long after awakening. As a tun, Tardigrades are light, dry capsules of their former selves, capable of being transported about by wind, animals and perhaps even asteroids, which to some extent revived the Panspermia hypothesis – that life on Earth was brought here by a ‘hitchhiking’ organism (Jönsson et al, 2008; Pasini, 2014).

Scanning electron microscope image of a Tardigrade in its dehydrated “tun” form.  Ph. credit - Eye of Science
Scanning electron microscope image of a Tardigrade in its dehydrated “tun” form. Ph. credit – Eye of Science

The ability to survive in the extreme cold, even close to absolute zero in some experiments, has led to Tardigrades being studied for their viability in space. In 2007, the European Space Agency (ESA) sent live Tardigrades and unhatched eggs into the vacuum of space beyond the International Space Station, where they orbited the Earth for 12 days, fully exposed to the full spectra of solar radiation. They called the programme “Tardigrades in Space”, or TARDIS for short to the acclaim of many a Dr Who fan!  The eggs hatched unharmed and 68% of the adult Tardigrades reanimated with no apparent ill effects. In preparation for a potential launch to Mars in the coming decade through the ExoMars programme, the ESA are currently recreating Martian environments to test the Tardigrades under. So you can be assured that they will continue to be a key to exploring the possibilities of extra-terrestrial life in the future.

One of the keys to a Tardigrade’s ability to reanimate from a tun state and survive such extreme habitats seems to be their ability to turn glucose sugar into trehalose sugar (Teramoto et al 2008). Trehalose is a disaccharide cellular sugar found throughout the natural world that helps prevent molecular desiccation (the process of cell deformation and rupture from drying and/or freezing). Trehalose stores water in a “gel phase” that can form a supportive cast around cell walls and organelles, preventing them from distorting and also reduces the amount of un-bonded water available for freezing.  Converting blood sugars into trehalose is not unique to Tardigrades. Bees switch between glucose, trehalose and sucrose depending on their metabolic rates (Blatt & Roces, 2001). Trehalose does not fully explain the resilience of Tardigrades, however. It is still unclear how they withstand drastic fluctuations in solar radiation, pressure or temperature and survive to produce healthy offspring. Understanding these processes might help scientists find ways of better preserving living tissues, whether that is human eggs for fertilization, organ transplant, maybe even one day full human suspended animation!

The physiology of Tardigrades therefore make them extremely interesting invertebrates, but they are also significance players in many ecosystems, in particular the truncated food webs at the poles. And it is in cryoconite holes that Tardigrades are able to thrive on ice. These habitats provide favourable conditions for primary production by forming quasi-stable holes in the ice surface (Cook et al, 2010). Cryoconite holes collect allochthonous organic carbon (Telling et al, 2010), receive nutrients and cells from in-flowing meltwater (Irvine-Fynn and Edwards, 2013) and prevent the redistribution of debris for long enough for a multi-trophic ecosystems to develop (Hodson et al, 2008). And where there is an active ecosystem, carbon is cycled. The carbon potential of glaciers and ice sheets has been estimated to be equivalent to terrestrial soil systems (Anesio et al, 2009), and the cryoconite ecosystem could potentially be a large contributor to that (Cook et al, 2012). My work has begun to explore the role of Tardigrades in the cryoconite hole’s carbon cycle, a process they contribute to by oxidizing carbon stored in organic molecules within the cryoconite micro-habitat by grazing on algae and cyanobacteria. And recent data suggests that they could be a significant component in Svalbard cryoconite, particularly during the autumn months when they potentially contribute to cryoconite holes turning from a carbon sink to a carbon source with the onset of seasonal snowfall.

Although small and innocuous, Tardigrades might play a huge role in developing our understanding of the limits and origins of life. Where they exist, their role in biogeochemical cycling and microbial ecology needs to be better understood, especially in truncated glacial food webs where their top-down controls upon community ecology might be important.

To summarise, I think we should all pay homage to the space-venturing, ice-surviving, reanimating microscopic “hoover-bag”: The water-bear, the moss-piglet, the Tardigrade!
J Bartlett

 

References:

Anesio, A., Hodson, A., Fritz, A., Psenner, R. & Sattler, B. (2009). High microbial activity on glaciers: importance to the global carbon cycle. Global Change Biology. 15: 955–960.

Blatt, J., & Roces,F. (2001). Haemolymph sugar levels in foraging honeybees (Apis Mellifera carnica): Dependence on metabolic rate and in vivo measurement of maximal rates of trehalose synthesis. Journal of Exp. Bio. 204: 2709–2716.

Cook, J., Hodson, A., Telling, J., Anesio, A., & Bellas, C. (2010). The mass – area relationship within cryoconite holes and its implications for primary production. Journal of Glaciology. 51: 106–110.

Cook, J., Hodson, A., et al. (2012). An improved estimate of microbially mediated carbon fluxes from the Greenland ice sheet. Journal of Glaciology. 58:1098-1108.

De Smet, W., & Van Rompu, E. (1994). Rotifera and Tardigrada from some cryoconite holes on a Spitsbergen (Svalbard) glacier. Belg J Zool. 124: 27–37.

Everitt, D. (1981). An ecological study of an Antarctic freshwater pool with particular reference to Tardigrada and Rotifera. Hydrobiologia. 83: 225-237.

Hodson, A., Anesio, A., Tranter, M., Fountain, A., Osborn, M., Priscu, J., Laybourn-Parry, J., & Sattler, B. (2008). Glacial ecosystems, Ecological Monographs. 78: 41–67.

Irvine-Fynn, T.D.L., Edwards, A., Newton, S., Langford, H., Rassner, S., Telling, J., Anesio, A., Hodson, A.J. (2013). Microbial cell budgets of an Arctic glacier surface quantified using flow cytometry. Environmental Microbiology. 14: 2998 – 3012.

Jönsson, K. I., Rabbow, E., Schill, R. O., Harms-Ringdahl, M. & Rettberg, P. (2008). Tardigrades survive exposure to space in low Earth orbit. Curr. Biol. 18: 729-731.

Kohshima, S., (1984) A novel, cold tolerant insect found in a Himalayan glacier. Nature. 310: 225-227.

Nelson, D.R. (2001). Current status of the Tardigrada: evolution and ecology. Integrative and comparative biology. 42: 652–9.

Pasini, D., & Price, M. (2014) Panspermia survival scenarios for organisms that survice typical hypervelocity solar system impact events. European Planetary Science Congress 2014, EPSC Abstracts, Vol. 9, id. EPSC2014-68.

Brent, C., Priscu, J et al. (2014) A microbial ecosystem beneath the West Antarctic ice sheet. Nature 512:310–313.

Ramazzotti, G., & Maucci, W., (1983). Il Phylum Tardigrada. III edizione riveduta e aggiornata. Mem. Ist. Ital. Idrobiol, 411-1012 [NB: English translation is available from Dr. Clark Beasley, Biology Dept., McMurry University, Abilene, TX, USA 79697].

Renaud-Mornant, J. (1982). Species diversity in marine Tardigrada. In D. R. Nelson (ed.), Proceedings of the third international symposium on the Tardigrada, August 3–6, 1980, Johnson City, Tennessee, pp. 149–177. East Tennessee State University Press, Johnson City.

Telling, J., Anesio, A. M., Hawkings, J., Tranter, M., Wadham, J. L., Hodson, A. J., & Yallop, M. L. (2010). Measuring rates of gross photosynthesis and net community production in cryoconite holes : a comparison of field methods. Annals of Glaciology. 51:153–162.

Teramoto, N., Sachinvala, N., Shibata, M. (2008). Trehalose and trehalose-based polymers for environmentally benign, biocompatible and bioactive materials. Molecules. 13:1773-816.

Wharton, R.A., Vinyard, W.C., Parker, B.C., Simmons, G.M., Seaburg, K.G. (1981) Algae in cryoconite holes on Canada glacier in southern Victoria Land, Antarctica. Phycologia. 20: 208-211

Geophysical Surveys on Glaciers

Yesterday, I took a group of enthusiastic third year geologists and environmental scientists to the British Geological Survey in Keyworth for a tour of the facilities and discussion/demonstration of their geophysical equipment. The BGS staff did a fantastic job of entertaining and educating us all – thanks BGS! – and this post primarily provides back-up notes and further information about the geophysical surveying techniques we saw – with a cryosphere twist!

Why Use Geophysics?

If we want to find out what is underground, we must either dig down and look, or use geophysics to gather data that we can interpret. Geophysical surveys measure the properties of the earth’s subsurface, allowing us to visualise structures we can’t access or see directly. This is usually achieved by taking measurements at or above the Earth’s surface, eliminating the need to drill or dig. Theses methods are therefore referred to as “non-intrusive”. Non-intrusive surveying is usually far cheaper, far quicker and much less disruptive than intrusive methods such as borehole drilling and digging pits. Non-intrusive geophysical surveys may also be able to resolve structures and stratigraphies that are inaccessible by intrusive means, and cover a wider area in much greater resolution. The disadvantages of geophysical surveys include the need for very sensitive, specialist equipment and expertise in data analysis and interpretation, and the lack of physical samples for physico-chemical analysis.

What are the Main Geophysical Methods?

GPR

Ground penetrating radar uses the reflection of electromagnetic radiation to build an image of a material’s subsurface. A high-frequency radio wave is emitted from the device which travels downwards until it meets a boundary between materials of different density. Here, the wave is reflected and detected by a sensor at the surface. By using  differently calibrated antenna, the device can be used to image to a wide range of depths and has been used to identify buried objects, rock and ice stratigraphies. The equipment usually comes mounted onto a lawnmower-like frame that can be wheeled across surfaces at a brisk walking pace and a lot of data can be gathered in a relatively small time, but this depends on the nature of the terrain – heavily crevassed glacier ice might be more challenging!

GPR data showing subsurface objects (wiki commons)

Gravimeter

Everything has a gravitational attraction to everything else. The closer things are and the denser they are, the stronger the gravitational force exerted. This concept is exploited by gravity surveys to identify subsurface density variations. Gravity surveys measure minute shifts in Earth’s gravity due to the density of the subsurface. It does so using a weight on the end of a horizontal bar. This bar is suspended by a spring. The extension in the spring varies in different locations despite the weight remaining constant, as a result of changes in the gravitational force acting on it. This is measured by the number of turns of a sensitively calibrated wheel on the device required to return the weight to a standard starting position. This device is extremely sensitive and provides only relative measurements. It requires frequent recalibration against standards. These standards are found at known locations on Earth and require visitation with the device. There also several corrections that need to be made, including for the “free air” effect. This is produced by the decrease in gravitational pull as the distance from the centre of the earth increases. Next, the “Bouger correction” must be applied to account for the density of material raising the gravimeter above sea level. Both corrections act to reduce gravimeter readings to sea level, or in other words to account for the changes in gravity resulting from topography. Furthermore, there are variations in the centrifugal force generated by Earth’s rotation depending upon latitude. Therefore, a latitudinal correction must also be applied. The earth’s tides and instrument drift also need to be considered. Temperature would also have an effect, but most gravimeters come in temperature controlled housings. The remainder of the variance in gravity measurements is assumed to be due to subsurface density variations.

Further information can be found here: http://www.ga.gov.au/image_cache/GA2236.pdf

and here:

BGS data showing gravity anomalies overlain on a contour map (BGS)

Seismic Surveys:

Seismic reflection is a commonly used method of determining subsurface density variations. It is conceptually simple – a seismic “shot” is created which sends elastic waves through the surface layers and also down through the subsurface mass until it reaches an interface between materials of different densities. Here, some of the wave energy is reflected back up towards the surface where it is recorded using a “geophone”. If the distance between the shot point and the geophones is known, the depth to the density boundary can be calculated from the time between shot and detection. However, this requires knowledge of the velocity of the seismic waves in the local medium, its variation with depth and the expected wave refraction. The result of seismic surveying is a “seismogram” – a record of seismic activity represented as a horizontal line with deviations in the vertical dimension representing seismicity (greater deviations = stronger seismic waves).

The type of shot used in seismic surveys depends upon the density of the medium being tested and the depth/resolution desired by the survey. Shots can range from tapping the surface with a hammer, heavy strikes with sledge-hammers onto high density rubber discs, mechanical impacts and dynamite blasts. The distance between the shot point and the geophones can also be manipulated depending upon the data requirements of the survey.

Seismic data is conceptually simple but can be tricky to interpret. Reflected waves have to be separated from direct compressional waves that travel horizontally along the surface, and also from background noise. This could be footfall, traffic noise, seismic noise from industry, mining, wildlife, geological activity and that produced by the seismic operators themselves.

See the video here for a deeper explanation:

The principle if seismic reflection (wiki commons)

Geophysics in the Cryosphere

Geophysical methods have long been extremely useful to glaciologists because Earth’s ice cover is thick, slow moving, and the subsurface is inaccessible. Understanding the structures inside and underneath ice masses can provide great insights into how they behave now, how they have behaved in the past and how they will behave in the future. It is through geophysical methods that we know how thick the Antarctic and Greenland ice sheets are, what the topography is like underneath them, where water is routed, the role of internal deformation, the location of subglacial lakes and the extent of isostatic rebound throughout the cryosphere. A particularly interesting book that details extensive geophysical surveying on the Greenland ice sheet in the mid 1900’s is “Venture to the Arctic”, edited by R.A. Hamilton. More recently, geophysical survey techniques have been adapted to image the calving fronts of ice shelves and marine-terminating glaciers in Greenland – see the BBC’s Operation Iceberg! The links and videos below provide just a few examples of geophysical applications in the cryosphere… and of course check NSIDC and NASA Earth Observatory for more information and stunning images!

Venture to the Arctic, edited by R.A. Hamilton - a classic, accessible read that recounts a tough two years of geophysical surveying in Greenland.
Venture to the Arctic, edited by R.A. Hamilton – a classic, accessible read that recounts a tough two years of geophysical surveying in Greenland.
Geophysical surveys of Greenland from satellites are used to determine melt rates, flow velocities, mass balance etc (image: NASA JPL)

Video: CBBC “Blow Your Mind”: Imaging calving glaciers

Video: Subglacial ice sculptures

Video: Vintage Seismic Reflection

GEUS “Airborne high resolution geophysics in Greenland

Bell et al 2014 Deformation, warming and softening of Greenland’s ice by refreezing meltwater

Enderlin et al (2014) Improved mass budget for Greenland ice sheet 

Ferraro and Swift (1995)  Measuring geophysical parameters of the Greenland ice sheet

Maurer and Hauck (2007): Geophysical imaging of alpine rock glaciers

Navarro (2014): Ice volume estimates from GPR

Palmer et al (2013): Greenland lakes detected by radar

Shean and Marchant (2010): Seismic and GPR surveys of Mullins Glacier

A Cryoconite Bibliography

Below is a bibliography of cryoconite literature that may help those looking for material in this field. I will endeavour to regularly update this with omissions and new work! If you are a cryoconite researcher/enthusiast and you notice anything I’ve missed, please let me know so I can make this as complete as possible!

Cryoconite - seemingly inocuous but the focus of much research!
Cryoconite – the focus of much research!

CRYOCONITE BIBLIOGRAPHY

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Living the High Life… in the aeolian biome

At the top of the highest mountains – where air is thin, solar irradiance intense, meteorology unpredictable, temperatures low and food scarce – spiders live on snow. The same spiders that are found in much more favourable conditions at sea level around the world. With no specific adaptations and no obvious lower trophic levels to feed on, the presence of these spiders seems to oppose ecological sense. This puzzled twentieth century ecologist Lawrence Swan until he realised… there is biology in the sky!

This species of salticid spider was found on snow slopes on Everest (ph. Wikimedia Commons)
This species of salticid spider was found on snow slopes on Everest (ph. Wikimedia Commons)

Swan (1992) proposed the existence of an “aeolian biome” that transports both flora and fauna around the globe in atmospheric suspension, depositing them in a wide range of environments. Once deposited, fauna either tolerates local conditions and survives, or dies due to exposure or competition. In ecology, a species that is tolerant to a wide range of conditions and can survive many environments is described as “cosmopolitan” whereas one with very specific adaptations to a particular habitat is known as “endemic”. The spiders were simply widely cosmopolitan and able to survive in the extreme conditions on high mountain tops, feeding upon smaller organisms also delivered by wind.

Swan (1992) also suggested an aeolian origin for the microbes inhabiting cryoconite holes on ice at the poles. Later, researchers such as Sattler et al (2001) and Pearce et al (2009) realised that not only are microbes transported in the atmosphere, they are active there too. This is important for understanding microbial ecology on glacier surfaces since many of the stresses experienced by microbes in the atmosphere reflect those of glacier surfaces, e.g. low temperatures, intense irradiance, dessication and freeze-thaw cycles. This suggests communities might be shaped to some extent before they are deposited. A viable aeolian community of cryo-tolerants is therefore established to be deposited on ice surfaces. Sattler et al (2001) showed that some cryo-tolerants even exploit super-cooled water droplets in the atmosphere. Certain bacteria with specific surface proteins have been found to initiate ice crystal formation in supercooled water in the atmosphere by acting as nuclei, as demonstrated in the video below…

Bacteria has recently been found thriving at 33,000 feet in the upper atmosphere, leading to suggestions of a “bubble of bacteria” surrounding the earth that could contribute significantly to global nutrient cycling and provide condensation nuclei for cloud  and snow formation (DeLeon-Rodriguez et al, 2013; Bauer et al, 2003), thereby playing a role in snow accumulation and ultimately glacier formation. Some have conjectured their potential as climate regulators (Morris et al, 2011). Climate regulation by microbes on ice surfaces is an area of current research; however the pre-depositional selection of microbes in the aeolian biome, and the potential for climate regulation in the “bacterial bubble” suggest global-scale climate mediation by microbes across all the earth subsystems.

The aeolian biome could extend as far as the upper layers of earth's atmosphere (ph. Wiki commons)
The aeolian biome could extend as far as the upper layers of earth’s atmosphere (ph. Wiki commons)

Even within specific biomes, community structures are probably highly dynamic, responding to local environmental stresses over very short timescales, as has recently been shown on glacier surfaces by Edwards et al (2014) using combined FTIR-spectroscopy and metabolite profiling. Clearly, the microbial ecology of ice surfaces is very complex, dependent not only upon ice surface conditions but also pre-depositional history and this is likely the case in other biomes too.

 

Refs:

Bauer, H.H. GieblR. HitzenbergerA. Kasper-GieblG. ReischlF. Zibuschka, and H. Puxbaum(2003), Airborne bacteria as cloud condensation nucleiJ. Geophys. Res.108, 4658, doi:10.1029/2003JD003545D21.

DeLeon-Rodriguez, N., Lathem, T.L., Rodriguez, L.M., Barazesh, J.M., Andersond, B.E., Beyersdorf, A.J., Ziembad, L.D., Bergin, M., Nenes, A., Konstantinos, T.K. 2013. Microbiome of the upper troposphere: species composition and prevalence, effects of tropical storms, and atmospheric implications. PNAS, 110 (7): 2575-2580

Edwards, A., Mur, L. A.J., Girdwood, S. E., Anesio, A. M., Stibal, M., Rassner, S. M.E., Hell, K., Pachebat, J. A., Post, B., Bussell, J. S., Cameron, S. J.S., Griffith, G. W., Hodson, A. J. and Sattler, B. (2014), Coupled cryoconite ecosystem structure–function relationships are revealed by comparing bacterial communities in alpine and Arctic glaciers. FEMS Microbiology Ecology. doi: 10.1111/1574-6941.12283

Morris, C. E., Sands, D. C., Bardin, M., Jaenicke, R., Vogel, B., Leyronas, C., Ariya, P. A., and Psenner, R.: Microbiology and atmospheric processes: research challenges concerning the impact of airborne micro-organisms on the atmosphere and climate, Biogeosciences, 8, 17-25, doi:10.5194/bg-8-17-2011, 2011.

Pearce, D.A., Bridge, P.D., Hughes, K.A., Sattler, B., Psenner, R., Russell, N.J. 2009. Microorganisms in the atmosphere over Antarctica. FEMS Microbiology Ecology, 69 (2): 143-157

Sattler, B., Puxbaum, H., Psenner, R. 2001. Bacterial growth in supercooled cloud droplets. Geophysical Research Letters, 28: 239-242

Swan, L. 1992. The aeolian biome. Bioscience, 42 (4): 262-270

Nutrient Cycling on Glaciers 2: Carbon

Carbon cycling on glaciers has received a lot of attention over the past decade because it impacts glacier albedo and therefore melt rates, as well as regional atmospheric carbon concentrations.

Atmospheric carbon concentrations and glacier retreat are known to be tightly coupled at a wide range of spatial and temporal scales. This article will concentrate upon relatively fast cycling through supraglacial microbial communities rather than tackling permafrost or millennial – geologic timescales. Following the structure of the N-cycling article, the fundamentals of global carbon cycling will be introduced, providing a background for  exploring supraglacial carbon cycling afterwards.

The Carbon Cycle

Carbon is an absolutely crucial element fundamentally underpinning life on earth. It is the backbone of organic molecules from which life is composed; it is a primary constituent of the food we eat and the ground we inhabit.

Carbon continuously cycles between all components of the earth system, from the global scale over geologic time to the microscopic scale over fractions of seconds; between the hydrosphere, atmosphere, biosphere, cryosphere, lithosphere and anthrosphere. At the individual micro-organism scale, heterotrophs metabolise organic carbon to provide energy and release inorganic carbon into the atmosphere, while autotrophs use atmospheric carbon to synthesise organic molecules.

The constant flux of carbon molecules between various stores in the earth system is known as the carbon cycle. Human activities in contemporary times have disturbed the carbon budget – adding atmospheric carbon faster than the earth can absorb it into it’s other stores, and consequently temperatures have risen.

U.S. DOE. 2008. Carbon Cycling and Biosequestration: Report from the March 2008 Workshop, DOE/SC-108, U.S. Department of Energy Office of Science. (p. 2-3)
U.S. DOE. 2008. Carbon Cycling and Biosequestration: Report from the March 2008 Workshop, DOE/SC-108, U.S. Department of Energy Office of Science. (p. 2-3)

The diagram above shows the major components of the global carbon cycle. These components can be broadly split into two superimposed cycles: the slow C cycle and the fast C cycle:

Slow C Cycle:

The slow C cycle involves the incorporation of carbon into rocks. Atmospheric carbon reacts with water vapour to form carbonic acid, which reacts with silicate rocks to form bicarbonate ions. These ions find their way to the ocean via groundwater and rivers. In the ocean, carbon from bicarbonate ions is incorporated into the shells of marine organisms. When the organisms die, their shells collect on the seabed and are eventually compacted into carbonate rocks. Over geologic time, these are subducted into the mantle and released back into the atmosphere as CO2 via out-gassing during volcanic eruptions.

Fast C Cycle:

Superimposed upon the slow carbon cycle are much more rapid fluxes comprising the fast C cycle. These processes take days to decades and involve the transfer of carbon between the ocean, atmosphere, soils and organisms. Plants and phytoplankton absorb atmospheric CO2 and convert it – in the presence if sunlight – into sugars via a process called photosynthesis. This is called ‘fixing’, as atmospheric carbon is converted into larger molecules that have various uses within the biosphere. The first is as an energy source for the plants which fixed the atmospheric carbon in the first place (autotrophs). Secondly, they provide an energy source for organisms that eat the autotrophs (heterotrophs). Thirdly, plants die and decay. Finally, plants can be combusted by fire. Each of these four processes returns fixed carbon back into the atmosphere as carbon dioxide.

Carbon Cycling on Glaciers:

On glacier surfaces, carbon cycling is dominated by biotic processes. Although the supraglacial environment appears lifeless, it actually provides numerous habitats for microbial life – in particular algal blooms on the surface of the ice and small cylindrical depressions known as cryoconite holes (Yallop et al, 2012). Cryoconite holes are particularly active and biodiverse microbial habitats in which carbon is both fixed and respired (Hodson et al, 2010). Stibal et al (2012) described glacier surfaces as “factories that sequester organic carbon from the atmosphere and recycle recalcitrant organic carbon from various sources into more labile carbon substrates”, indicating that these highly active environments cycle carbon both produced in situ, predominantly via photosynthesis (aka autocthonous OC), and also carbon delivered from other sources (allochthonous OC).

Simplified schematic of glacier surface C fluxes
Simplified schematic of glacier surface C fluxes

Atmospheric carbon is predominantly fixed by photoautotrophic microbes inhabiting glacier surfaces – mostly cyanobacteria and other algae. These organisms absorb carbon dioxide and fix it into sugars. In surface algal blooms these sugars are mostly used for microbial processes within the algae such as growth – adding biomass to the ice surface (Yallop et al, 2012). In cryoconite holes they are also used as a primary source of energy for higher organisms. When heterotrophic microbes feed upon primary producers some of the carbon which was used to build algal biomass is respired and released back into the atmosphere as CO2.

NEP

Net ecosystem productivity (NEP) describes the balance between autotrophy (fixing of CO2 into sugars) and heterotrophy (metabolism of sugars back into atmospheric CO2). This has been a particular focus for glacier microbiologists because not only does NEP determine whether a community represents a carbon sink or a carbon source (e.g. Stibal et al, 2008; Hodson et al, 2010; Cook et al, 2012), but also determines whether there is an overall increase in the amount of dark organic material on a glacier surface. The darker the surface, the more heat it absorbs and the faster it melts. Therefore, supraglacial carbon cycling might play a crucial role in the rate at which a glacier melts. Furthermore, autotrophic activity results in the production of dark humic material, photoprotective pigments and EPS (extracellular polymeris substances) (Langford et al, 2010) which actually give biomass a darker colour as well as just increasing its volume.

Allochthonous and Autochthonous Carbon

Microbes on glacier surfaces utilise carbon synthesised by autotrophs in situ (autochthonous), and also carbon deposited on the glacier from elsewhere (allochthonous). Autocthonous organic carbon is produced on ice surfaces as cellular biomass or cell exudates. Allochthonous organic carbon is deposited by wind – fragments of flora delivered from nearby deglaciated regions. Also black carbon from soot and anthropogenic pollutants are deposited from distant sources. Autochthonous and both types of allochthonous organic carbon provide energy for bacteria. The fraction of the total organic carbon originating from each of the above sources varies spatially and temporally, and has been the focus of much research (e.g. Stibal et al, 2008). It seems that the interiors of large ice sheets and glaciers are generally characterised by abundant autochthonous organic carbon providing substrate for community respiration – suggesting they represent carbon sinks – whereas ice sheet margins and small glaciers are likely dominated by local allochthonous carbon and act as net carbon sources (Stibal et al, 2012; Telling et al, 2012).

Export

Carbon fixed on glacier surfaces can also be redistributed. This is usually by entrainment into supraglacial streams or transport in solution through the low density ice that makes up the weathering crust (top ~2m of ice surface) (Irvine-Fynn and Edwards, 2013). Whole cells and organic carbon molecules dissolved in water (DOC) are transferred between habitats within the supraglacial zone and other glacial environments, as well as being redistributed to extra-glacial regions. This is likely to be important for seeding other environments (Wilhelm et al, 2013), such as proglacial streams, glacier fed lakes and the subglacial zone, as well as providing nutrients and energy sources for downstream ecosystems, and has recently been appreciated as an important factor in determining downstream biodiversity and community structure.

More information

For a bit more detail, see the article I wrote here and follow the references therein!

REF:

Cook, J.M., Hodson, A.J., Anesio, A.M., Hanna, E., Yallop, M., Stibal, M., Telling, J., Huybrechts, P. 2012. An improved estimate of microbially mediated carbon fluxes from the Greenland Ice Sheet. Journal of Glaciology, 58 (212)

Hodson, A., et al. 2010. A glacier respires: quantifying the istribution and and respiration CO2 flux of cryoconite across an entire Arctic supraglacial ecosystem. Journal of Geophysical Research, 112: G04S36

Irvine-Fynn, T. D. L. and Edwards, A. (2013), A frozen asset: The potential of flow cytometry in constraining the glacial biome. Cytometry. doi: 10.1002/cyto.a.22411

Langford, H., Hodson, A.J., Banwart, S., Boggild, C. 2010. The microstructure and biogeochemistry of Arctic cryoconite granules. Annals of Glaciology, 51 (56): 87-94

Stibal, M., Tranter, M., Benning, L., Rehak, J. 2008. Microbial primary production on glacier surfaces is insignificant in comparison with allochthonous organic carbon input. Environmental Microbiology, 10: 2172-2178

Stibal, M., Sabacka, M., Zarsky, J. 2012. Biological processes on glacier and ice sheet surfaces. Nature Geoscience,  5: 771-774

Telling, J. et al. 2012. Controls on the autochthonous production and respiration of organic matter in cryoconite holes on High Arctic glaciers. Journal of Geophysical Research, 117, G01017

Wilhelm, L., Singer, G.A., Fasching, C., Battin, T.J., Besemer, K. 2013. Microbial biodiversity in glacier-fed streams. ISME Journal, 7: 1651 – 1660

Yallop, M.L., Anesio, A.J., Perkins, R.G., Cook, J., Telling, J., Fagan, D., MacFarlane, J., Stibal, M., Barker, G., Bellas, C., 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