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Ice sheet microbes and melt

Greenland contains the largest continuous mass of ice in the northern hemisphere; an area over 2 million km2. The frequency of Greenland surface melting has increased, likely as a result of human-induced climate warming, with the melt-area covering almost the entire ice sheet surface in 2012 (Ngheim et al. 2012; Box et al, 2013; Tedesco et al. 2013).

Ablation zone extent on the Greenland ice sheet: July 8 (left) and July 12 (right). On July 8, ~40% of the ice sheet was melting. Four days later, ~97% of the ice sheet surface had thawed.  Credit: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory

Ablation zone extent on the Greenland ice sheet: July 8 (left) and July 12 (right). On July 8, ~40% of the ice sheet was melting. Four days later, ~97% of the ice sheet surface had thawed. Credit: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory

Although its fair to say that higher temperatures mean more melt, the response of earth’s glaciers and ice sheets to climate warming is complex, also depending upon a range of feedbacks (e.g. Box et al, 2012). For example, when ice melts, liquid water runs over its surface, sometimes collecting in pools and lakes. Liquid water is a more effective absorber of sunlight than snow or ice, so the overall reflectivity (also called albedo, Greek for ‘whiteness’) of the ice decreases. The result is faster ice melt. Melting promotes more melting.

Box et al’s (2012) image of albedo anomaly in summer 2012. Darker blue means greater darkening compared to average albedo.

Box et al’s (2012)
image of albedo anomaly in summer 2012. Darker blue means greater darkening compared to average albedo.

Not only melt water that reduces  Greenland ice sheet albedo. A variety of aerosol ‘impurities’ further reduce surface albedo. These include black carbon (BC) derived from incomplete combustion of fossil fuels, other industrial activity, biomass burning, and wildfire. Black carbon can be transported across the hemisphere through the atmosphere and deposited on ice, and currently the impacts remain uncertain (Hodson, 2014). Dark Snow field science is examining this question in detail based on 2013 field measurements and planned measurements for June-August, 2014.

Black Carbon - produced during the incomplete combustion of fossil fuels

Black Carbon – produced during the incomplete combustion of fossil fuels (photo, wikimedia commons)

The presence of microbes on the ice surface also alter albedo and can therefore influence melt rates (Yallop et al, 2012). They do so by growing and adding dark biomass to the ice, causing mineral fragments to aggregate and resist removal (flushing) by melt water, and by producing dark humic substances and pigments. There may even be a relationship between microbial activity and BC. Yet, it is not yet known whether microbes metabolise BC and reduce its impact, or cause it to “stick” to the ice surface and prevent its removal by flushing (Hodson, 2014).

Many microbes on the Greenland ice sheet inhabit ‘cryoconite’ holes; cylindrical tubes ‘drilled’ into the bright ice surface ice by dark cryoconite debris. The debris is a loose bonding of minerals encased in microbial biomass (e.g. Gribbon, 1979; Cook et al, 2010). Cryoconite holes on the Greenland ice sheet likely provide favourable conditions for photosynthesis by: 1.) maintaining light intensities that are high but not harmful because ultraviolet radiation is not transmitted by water; 2.) providing nutrients in melt water flowing in through the hole walls; and 3.) providing relatively long term (years) storage of microbes. This also promotes proliferation of bacteria and “grazers” that feed upon other microbes. These factors make cryoconite holes active and biodiverse ice sheet habitats (Hodson et al, 2008).

Cryoconite holes – generally considered to be the most biodiverse microbial habitats on glacier surfaces

Cryoconite holes – generally considered to be the most biodiverse microbial habitats on glacier surfaces (photo, J. Cook)

Despite being the most studied biological entity on the surface of the Greenland ice sheet, cryoconite holes remain poorly understood in terms of their biological community dynamics, thermodynamics, evolution and impact on albedo. Further, the characteristics of the holes themselves, and the microbes inhabiting them, have been shown to vary depending upon location on the ice sheet (Stibal et al, 2012), and these spatial patterns probably also evolve over time. Edwards et al (2014) recently found microbial communities to be extremely dynamic in response to environmental change, while Irvine-Fynn and Edwards (2014) showed that hydrological and glaciological processes might also influence microbial activity. Cryoconite holes will provide research foci for some members of the field team in summer 2014. For further information on cryoconite, see: herehere; and here.

JCook_Mugshot-2

Dr Joseph Cook is a Lecturer in Earth and Environmental Sciences at the University of Derby (UK) who is particularly interested in researching the links between biological and physical processes on glaciers and ice sheets. He completed his PhD at the University of Sheffield (UK) in 2012 and has undertaken several Arctic field seasons. He is also an avid rock climber and mountaineer and maintains a cryosphere-focussed website (http://tothepoles.wordpress.com).

 

References:

Box, J.E., Fettweis, X., Stroeve, J.C., Tedesco, M., Hall, D.K., Steffen, K. 2012. Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers. The Cryosphere, 6, 821-839. open access.

Box, J.E., Cappelen, J., Chen, C., Decker, D., Fettweis, X., Mote, T., Tedesco, M., van de Wal, R.S.W., Wahr, J. 2013. Greenland ice sheet. Arctic Report Card. http://www.arctic.noaa.gov/reportcard/greenland_ice_sheet.html

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

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

Gribbon, P.W. 1979. Cryoconite holes on Sermikaysak, West Greenland. Journal of Glaciology, 22: 177-181

Hodson, A., Anesio, A.M., Tranter, M., Fountain, A., Osborn, M., Priscu, J., Laybourn-Parry, J., Sattler, B. 2008. Glacial Ecosystems. Ecological monographs, 78 (1): 41-67

Hodson, A. 2014. Understanding the dynamics of black carbon and associated contaminants in glacial systems.WIREs Water 2014, 1:141–149. doi: 10.1002/wat2.1016

Irvine-Fynn, T.D.L., and A, Edwards. 2014. A frozen asset: The potential of flow cytometry in constraining the glacial biome. Cytometry Part A 85 (1), 3-7

Nghiem, S. V., D. K. Hall, T. L. Mote, M. Tedesco, M. R. Albert, K. Keegan, C. A. Shuman, N. E. DiGirolamo, and G. Neumann (2012), The extreme melt across the Greenland ice sheet in 2012, Geophys. Res. Lett., 39, L20502, doi:10.1029/2012GL053611.

Stibal, M., Telling, J., Cook, J., Mak, K.M., Hodson, A., Anesio, A.M. 2012. Environmental controls on microbial abundance on the Greenland ice sheet: a multivariate analysis approach. Microbial Ecology, 63: 74-84.

Tedesco, M., X. Fettweis, T. Mote, J. Wahr, P. Alexander, J.E. Box, B. and Wouters. 2013. Evidence and analysis of 2012 Greenland records from spaceborne observations, a regional climate model and reanalysis data, The Cryosphere, 7, 615-630, doi:10.5194/tc-7-615-2013.

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

 

About the author Joseph Cook

Dr Joseph Cook is a PDRA on the Black and Bloom project at the University of Sheffield who is particularly interested in researching the links between biological and physical processes on glaciers and ice sheets, and modelling albedo. He completed his PhD at the University of Sheffield (UK) in 2012 and has undertaken several Arctic field seasons. He is also an avid rock climber and mountaineer and maintains a cryosphere-focussed website.

All posts by Joseph Cook →

4 Comments

  1. Matthew Benecke April 25, 2014 at 2:13 pm

    Hello my name is Matthew Benecke and I’m currently enrolled in a climate change class at Kennesaw State University in Georgia (United States). At this moment I am currently working on project regarding the melting of the Ice Caps in Greenland. Since I have discovered Dr. Box’s report on the matter I have become very intrigued and ambitious in the study and examination of this issue. My question for you and your team is 1. Do you have any charts or video explanation of the dark snow which I could upload to a power point and show to my class? 2. Is there any internships or career opportunities within this field of study. My degree is Geography and an advanced certificate in Geographic Information Science (G.I.S). My project is due this coming Monday and I understand that you are all busy, but get back to me before then I would be very grateful. Also I wish you success in your research and continue to do a great job.
    With Regards,
    Matthew Benecke

    Reply

    1. Hi Matthew,

      thanks for your reply, it’s great to hear that people are interested in this research. I suggest you browse the rest of the Dark Snow blog as well as visiting my site http://tothepoles.wordpress.com for further information, images and videos. Regarding internships, I do not know of any current opportunities in this specific field, but keep your eyes peeled as you never know when something might come up.

      Best wishes and good luck with your assignment.

      Joseph Cook

      Reply

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